Table 15. Weeds commonly found in Oklahoma cucurbits and suggested management (refer to pages 46-47 for weed photos)
Use only fresh, high quality, vigorous seed that has been treated with an approved seed-treatment fungicide.
Watermelon
Watermelon planting begins in late March in southern Oklahoma and mid-April in northern areas. Seed will not germinate at soil temperatures below 60°F, and the most rapid germination occurs at 80-95°F. Seedless watermelon varieties have comparatively weak seeds; because of this and high seed cost, they are normally transplanted. Planting should be delayed until soil temperature at seed depth reaches above 70°F. Soil temperatures can be estimated using a soil thermometer or are available at 111 sites statewide through the Oklahoma Mesonet system. County Extension offices have instant and free access to Mesonet.
Research suggests that over-watering creates germination problems with triploid watermelons. The planting medium should be moist but not overly wet. If water can be squeezed from the planting medium, it is too wet.
Plant seed of open-pollinated varieties at 1 to 2 pounds per acre at a depth of 1/2 to 11/2 inches, with deeper planting in sandy or dry soils. The cost of watermelon seeds varies greatly, depending upon the type of plant being grown. Open-pollinated seeds average about 0.2 cents per seed, hybrid diploids average about 3.5 cents per seed, and triploids average about 18 cents per seed. Therefore, reduced seeding rates of hybrid varieties are used to reduce costs. Planters and planter plates can be modified to plant single seeds at desired in-row plant spacing. With this technique, 1 pound of seed can plant several acres with a good chance of achieving an acceptable stand. Extreme weather conditions, including frosts and heavy rains during the spring, may necessitate replanting.
The type and size of available equipment, the availability of irrigation water, and the availability of land determines plant spacing. Typical in-row plant spacing ranges from 1 plant every 4 to 6 feet in the row on irrigated land, to 1 plant every 6 to 10 feet on dry land. Typical row spacing varies from 6 to 18 feet apart. High yields in tons per acre are being reported with spacing as close as 9 to 18 square feet per plant. Cultural practices involving soil fertility, plant diseases, and insect control may need to be adjusted according to the plant spacing. Growers should adjust their plant spacing to obtain the best size, quality, and quantity of melons for their market.
Oklahoma growers market an average of 1 melon per plant. Very few growers market more than 2 melons per plant. Thus, higher numbers of plants per acre will usually result in more marketable fruits per acre.
Some growers seed in twin rows 36 inches apart. This allows young plants to vine together and provides some additional protection from wind damage.
Cantaloupe
Plant cantaloupe seed 1/2 to 11/2 inches deep. Use deeper planting on sandy and drier soils. Planting begins in late March in southern Oklahoma and mid-April in northern areas. Seed will not germinate at soil temperatures below 60°F, and the most rapid germination occurs at 90°F.
Plant cantaloupe seed at the rate of 11/2 to 2 pounds per acre in single rows 6 to 8 feet apart, or in twin rows 3 feet apart on 9 to 15 foot centers. After plants are well established, thin to 12 to 15 inches between plants in the seeded row. If irrigation is not going to be used to supplement rainfall, thin to 24 to 30 inches in the row.
Squash and Pumpkin
Bush-type squash and pumpkin are usually seeded in single rows at the rate of 2 to 3 pounds per acre. Vine-type squash and pumpkin require 1 to 2 pounds of seed per acre. Row spacing vary from 3 to 6 feet for bush-type varieties and 6 to 15 feet for vine-type squash and pumpkin varieties. In-row plant spacing will vary from 1 to 3 feet for bush types and 3 to 5 feet for vine types. Plant seeds at a depth of 1/2 to 1 inch. Thin seedlings to desired in-row spacing when plants have 3 or 4 leaves.
Squash and pumpkin seed will not germinate at soil temperatures below 60°F, and the most rapid germination occurs at 90°F, so delay planting until after the date of the last spring frost. Larger pumpkins grown for Halloween should be planted in mid-to-late June for harvesting and marketing in October.
Cucumber
Cucumbers are usually seeded in single rows at 1 to 2 pounds per acre at a depth of 1/2 to 1 inch. Row spacing varies from 3 to 6 feet. Final plant spacing should be 9 to 12 inches in the row on irrigated land and 15 to 18 inches on dry land.
Plants should be thinned before the 4-leaf stage if the stand is too thick.
Cucumber seed will not germinate at soil temperatures below 60°F, and the
most rapid germination occurs at 95°F, so delay planting until after the
date of the last spring frost. Seedlings are very sensitive to chilling injury.
They will be stunted, and leaves will become brittle and turn white under cold
growing conditions.
All vine crops can be transplanted in bare soil or through plastic mulch. Cucumbers, pumpkins, and squash are rarely transplanted, while transplanting of cantaloupe and watermelon has increased substantially in the past few years. Though transplanting is becoming more common, watermelons are not well suited to this practice. The fact remains that watermelon roots systems are easily damaged and do not recover quickly when broken or bruised. Take care to ensure that the roots are not damaged during the transplanting operation. Containers should be selected so transplants can be planted with minimal root disturbance. Transplanted watermelon plants have a shallower and more restricted root system than direct seeded watermelon plants. The use of transplants increases the cost per plant and labor costs per acre. The grower must have an increased yield or price or a reduced per-acre seed cost to offset these increased costs,.
Consult OSU Fact Sheet F-6020, "Growing Vegetable Transplants," to find out how to grow transplants. In many cases, it is cheaper to purchase plants than to grow them. If purchased, transplants should be obtained from a reliable greenhouse grower. Plants should be inspected upon delivery for disease and insects. Yellowed or flowering plants should be rejected. Seedlings must not have more than 4 leaves at planting.
Vine crops have been grown in containers from 1 to 3 inches in width. Large 3-inch containerized plants need to be hand-planted. Many growers have gone to 1.5-inch containers to allow as much root area as possible, while creating a transplant that can still be mechanically planted.
Transplants may need to be hardened-off before transplanting under certain conditions. If necessary, limit the amount of water or lower the temperature, but fertilizer should not be withheld. If weather conditions are good at the time of transplanting, do not harden the plants. Overly hardened or stressed plants may never fully recover and will rarely meet the growth rate of the plants that were never stressed or hardened. Hardening may be required if environmental conditions at the time of planting are overly cold, hot, windy, or dry. If plants are purchased, transplanting should be done as soon as possible following arrival of the plants.
The use of a starter solution at transplanting will speed plant establishment. Starter fertilizers are water-soluble and contain a high rate of phosphorus, which stimulates root development. Plants should be irrigated immediately after planting to remove air pockets around the roots. Newly transplanted fields need to be monitored closely for adequate soil moisture in the seedling root-balls.
When producers prune fruit, they should begin as soon as defective melons are noted. Remove misshapen and blossom-end-rot fruit to promote additional fruit set and better size of remaining melons. If a market demands larger melons, remove all but 1 or 2 well-shaped melons from each plant. To avoid disease spread, do not prune melons when vines are wet. Care should be taken to avoid bending the vines, as bent vines will break easily.
Proper harvesting of cucumbers, summer squash, and cantaloupe usually eliminates any need for fruit pruning. Defective fruit are cut from the plant along with good fruit and then left in the field or culled before packing. Be sure to disk under the culled fruit to limit disease problems during the next growing season. Winter squash and pumpkins rarely have cull fruit removed, because removal of defective fruit is not cost effective.
Management of weed pests begins prior to planting, cultivation, or the application of herbicides. It begins in the planning stage with proper site selection including weed surveys of potential sites and a review of production goals and technologies available for the control of weeds in a given crop.
Weeds interfere with cucurbit production by competing for light, nutrients, and water, thus reducing the yield and quality of the crop. Weeds can further complicate production by providing habitat for insect and disease pests, and may also provide cover for vertebrate pests that damage maturing fruit. In situations where weeds are not controlled, serious yield losses may occur because of reduced water availability to the crop and from difficulty in harvesting the crop.
Control practices are site specific and dependent upon what weeds are present. Table 15 lists weeds common to Oklahoma production fields. Consult the County Extension office for assistance in weed identification. Weed control practices include cultural, mechanical, and chemical control measures.
Cultural controls for weeds include proper field selection, crop selection, crop rotational schedules, mulching, mechanical control, and drip irrigation. Avoid fields known to have weed problems or those infested with difficult-to-control weeds. Crop selection is important because cucurbits vary in the speed of development with fast growing cucurbits, such as watermelon, shading the soil earlier to reduce weed growth. Crop rotation can be used to rotate to other crops whose culture can reduce weed species not easily controlled in cucurbits. Black and IRT plastic mulches can reduce the need for other weed control measures by shading the soil surface and preventing weed seed germination. This works except for controlling nutsedge, since nutsedge can easily penetrate plastic mulches. When using plastic mulch, weed control may be needed at plant holes and between plastic strips. Drip irrigation may reduce weed infestation by limiting soil moisture to the area of the crop row. However, this benefit may be eliminated by untimely rainfall.
Mechanical controls include cultivation, hoeing, and hand pulling. Close cultivation and hand hoeing are usually performed before plants vine or begin setting fruit. Cultivation should never be so deep or close to the plant that roots or vines are pruned. Root pruning slows plant and fruit development, reduces yield, and may lead to blossom end rot in watermelon. Roots normally extend past the area covered by vines and are often very shallow. Cultivation of row middles with aggressive implements, such as disk harrows, must be done with care to minimize root injury. Root depth can be determined by sifting through soil at different distances from the plants prior to cultivation. Hoeing removes weeds that survive cultivation, and may be especially important for difficult-to-control weeds. Hand pulling, in some instances, may be a practical means of removing large weeds and nutsedge, but is a costly practice.
Chemical control plays a valuable role in overall weed control strategy. There are few herbicides approved for use with cucurbits. Those approved for weed control in cucurbits are given in Publication E-832 "Oklahoma Extension Agents' Handbook of Insect, Plant Disease, and Weed Control." The Oklahoma Cooperative Extension Service Current Report CR-6008 also provides information on vegetable herbicides. A listing of materials that were labeled for use at press time can be seen in Appendix 2. Generally, no single herbicide will be effective on the entire spectrum of weeds found in a crop. For some weeds commonly found in Oklahoma, none of the herbicides approved for cucurbits are effective.
Therefore, weed control in cucurbits usually requires a combination of cultural, mechanical, and chemical practices.
Planting method often dictates which chemical control methods may be used. Be certain to read and follow herbicide label instructions closely as time and methods of application can have serious effects upon the effectiveness and crop safety aspects of these materials.
Insects serve a critical role in cucurbit crop production by pollinating flowers so the fruit develops correctly to a marketable size and shape. However, there are species of insects that can cause reductions in fruit production when abundant. These pest insects and mites must be controlled. In addition, there are beneficial insects and mites that feed on pest insects and mites and limit pest populations.
Table 15. Weeds commonly found in Oklahoma cucurbits and suggested management
(refer to pages 46-47 for weed photos)
Cucurbit crops are primarily pollinated by insects and various species of bees. The pollinating insects can and should be managed to provide effective and efficient pollination.
Effective pollination results in increased yield, earliness, and quality of
crops with the
exception of some cucumber varieties. Male flowers, separate from female flowers,
produce pollen and insects (especially bees) are essential to production by
spreading the pollen. Wind does not effectively move cucurbit pollen. Therefore,
pollinating insects are essential for carrying the pollen between flowers.
Factors Affecting Pollination
The following factors affect management of domesticated honey bees that are moved into production fields in hives. These factors affect other bees as well.
Weather: Cloud cover, temperatures below 60°F, and wind speeds above 15 mph reduce honey bee activity. When these weather conditions occur and persist during flowering and fruit set periods, additional bee hives may be required for adequate pollination.
Competing bloom: Honey bee hives should be located around or in fields as soon as the first fruit-producing flowers appear (see section on monitoring plant growth and scouting for insects). A delay in introduction of bees may result in a delay in peak fruit production and reduce the crown set of fruit. Flowers on melon crops tend to be less attractive to bees than cotton and alfalfa flowers. When cotton or alfalfa grows adjacent to melons, a large percentage of bees will work cotton and alfalfa flowers at the expense of the melons. Crops that attract bees away from the target crop during the blooming period should not be planted nearby (a half-mile buffer is desirable). Similarly, many weed species are very attractive to bees and can draw bees away from the target crop. If weeds in bloom are present in or around the field, they should be destroyed before the crop begins to bloom.
Flowers: Cucurbit crop flowers are open for one day. Bees are most active in mid-morning during the summer months. They generally collect pollen during the morning and may continue activity in the afternoon but focus on collecting nectar. Male flowers appear before female flowers, produce pollen, and then fall from the plants. Female flowers that are not pollinated fall off the plant and do not produce fruit. Plants should be monitored after flowering to determine number and location of fruit set on plants.
Placement of hives: beehives should be placed in clusters around the perimeter of the field. Hives close to the field will have bees that more readily work flowers on the plants closest to the hives. Placing hives in clusters results in competition among the bees from hives and acts to push the bees further into and throughout the field.
Pesticides and irrigation: Pesticides (especially insecticides) can kill wild and domesticated bees. Therefore, pesticide applications to control insects, diseases, and weeds should be completed prior to the critical time of the crop flowering and fruit set. If a pesticide application must be made during the flowering stage, apply the pesticide late in the evening so that flowers are not open and bees are less likely to be active in the field. Overhead irrigation may decrease pollination because the flowers fill up with water and are less attractive to bees. Overhead irrigation should be avoided during peak pollination periods.
The Importance of Wild Bee Pollinators
By far, domesticated honey bees (Apis mellifera) are the most effective insects for pollinating crops. However, for crops grown in Oklahoma, wild bees can be extremely important as pollinators. Wild colonies of honey bees appear to be important, but populations have declined in recent years due to introduced parasitic mites that have destroyed honey bee populations. Other bee species are present in the state and may contribute significantly to crop pollination. The more common types of wild bees include bumble bees, alkali bees, leafcutter bees, and carpenter bees. Many wild bees are ground nesting and some are solitary, not living in colonies as do honey bees. The major limitation of using wild bees in pollination of crops is the inability to manipulate them to focus on the target crop. In addition, the abundance of wild bees varies greatly by location and from year to year and thus they are less dependable. Honey bee colonies can be used to supplement wild bee activity.
Monitoring Pollination
During flowering, pollinating bee populations should be monitored by observing 100 individual flowers between 8 A.M. and 10 A.M. Note whether a bee is present in the flower. Because crops differ in the way pollination occurs and thus their pollination requirements, a separate discussion of the major cucurbit crops follows.
Watermelon 0.25 to 2 hives per acre: Because of their flower structure, watermelons are dependent on bees for pollination. Nearly all varieties of watermelon have separate male (staminate) and female (pistillate) flowers. Watermelon pollen tends to be sticky, requiring bees to move the pollen from one flower to another. The source of the pollen, be it from a male flower on the same or a different plant, is not important for effective pollination to occur.
Watermelons have a very distinct flowering pattern. Male flowers appear first, followed by female flowers 7 to 10 days later. Female flowers are open for only one day and must be pollinated on that day, or they will abort and drop off. The ratio of male-to-female flowers ranges from 4-to-1 up to 20-to-1, depending on the variety and growing conditions. Flowers open shortly after sunrise and may remain open into the afternoon. Flowers do not reopen after closing, whether or not pollination has occurred.
Each seed forms from the union of the contents of a single pollen grain and a single ovule. Successful fruit production requires the transfer of about 500 to 1,000 of the large, sticky pollen grains from a male flower to the stigma of a female flower. Although seedless watermelon does not require pollination for production of seed, it has been shown that the proper development of marketable fruit depends upon pollen stimulation of the female flower stigma. If the female flower receives an inadequate amount of pollen, the resulting melon will be lopsided or smaller on one end. For elongate varieties, a poorly pollinated melon will be smaller on the stem end of the fruit and will not contain seeds inside on the stem end. Such watermelons are usually considered culls. In addition, watermelons that are poorly pollinated are usually undersized and presence of these cull melons may inhibit the setting of additional fruit for several weeks.
Adequate numbers of honey bees must be available at the right time to provide sufficient pollination. A premium price is paid for early production, so it is best to get bees to the field within a week after the appearance of male flowers. Bees should remain in the field for approximately 1 month to ensure fruit set. In most cases, leaving bees in the field for more than a month does not substantially improve the yield but only increases the risk of pesticide contamination of the beehives.
Research indicates that about 8 bee visits per flower are necessary to obtain proper fruit set and development. In order to get this level of activity, 1 honey bee colony per acre should be adequate. However, this depends on the abundance of wild bees. For dry land watermelon production, which utilizes a relatively low plant population, 1 strong hive for every 2 to 4 acres ensures good fruit set. Irrigated watermelons may require a slightly higher bee population and growers should place 1-2 hives per acre. Field surveys, in which the numbers of bees and flowers are counted along a diagonal in the field during mid-morning, are probably the best means to determine if an adequate number of bees are present. In general, a minimum of 1 bee per 100 flowers is needed to get good fruit set.
Muskmelons 1 to 2 hives per acre: Cantaloupe and honeydew melons are depend on bee pollination for good production. Nearly all information available on muskmelons comes from studies on cantaloupe. Flower structure of cantaloupes differs somewhat from watermelons, in that the "female" flowers are actually hermaphroditic (contain both male and female parts). In practice, these flowers are incapable of self-pollination, and thus pollen must be transferred from the male flowers to the "female" flowers. If no pollen is transferred to these hermaphroditic flowers, flowers shed without setting fruit. In cantaloupe, melon size is strongly related to the number of seeds present in the fruit; the more seeds, the larger the fruit. At least 1 pollen grain is required for each seed that is produced; therefore as bee activity is increased, seed production and fruit size is improved. In general, cantaloupe with fewer than 400 seeds per fruit fail to size properly and are considered culls. Increased bee activity also improves the likelihood of early fruit set (known as crown set). Crown set fruit are normally larger and higher in sugars, commanding greater market prices.
The honey bee stocking rate for muskmelons is higher than that of watermelon. In general, 1 hive per acre is needed to get good fruit set and obtain large size melons. During a midmorning survey, 1 bee per 10 "female" flowers is the minimum level of activity to maximize production. Previous research has demonstrated the economic benefit of using up to 2 hives per acre.
Cucumbers 1 hive per acre: The pollination requirements for cucumber do not differ substantially from those of muskmelon. If cucumber fruit are inadequately pollinated, deformed fruit usually result and may appear as "crooks" or "nubbins." In addition, if cucumbers are to be machine harvested (for pickle processing), good pollination maximizes uniform production. Research indicates a honey bee stocking rate of 1 good hive per acre, but this may vary depending on variety and end use of the cucumbers (pickles or fresh-market).
Squash and Pumpkin 1 to 3 hives per acre: Squash and pumpkin have similar pollination needs because of the similar flower structure. Male and female flowers are separate; therefore movement of pollen to female flowers by insects is essential for a fruit to be produced. Like cantaloupe, fruit size and seed set of squash and pumpkin are strongly related to bee activity. Flowers are open for one day and with squash, are usually open only in the morning. Because squash and pumpkin flowers are large, honey bees are not as efficient in pollinating them as larger, wild bees. In particular, bumble bees serve as excellent pollinators where their populations are sufficient. However, honey bees serve as the only means to increase bee activity levels where wild bee activity is inadequate. A minimum of 1 hive per acre is normally necessary although yield increases have been noted with up to 3 hives per acre.
Recommendations for managing insect and mite pests vary depending upon the type of production. Differences in tolerance levels for pests and damage will exist for large commercial watermelon growers producing open-pollinated watermelon without irrigation, in contrast to growers that transplant seedless watermelon plants into plastic mulch with drip irrigation. Thus, we offer a few general recommendations based on production level and additional specific recommendations for each pest listed in Appendix 3.
Several insect and mite species reduce plant growth and productivity when their numbers are abundant and at a time when the plants are susceptible to damage. These insect and mite populations must be monitored using common scouting techniques to determine species occurrence and population abundance. When the populations become too numerous, then the insects and mites must be controlled. Managing pest insect and mite populations has been shown to be most successful when producers follow IPM strategies.
1. Monitor crop growth and insect and mite pest abundance
Monitoring or scouting for insect and mite pests should be conducted in conjunction with a weekly monitoring of the fields for pollinating bees, weeds, diseases, and plant growth. Record the numbers of insects or mites per plant or leaf and average the numbers after completing the scouting of the field. Compare these numbers from week to week and among fields to determine whether pests are increasing in abundance or are greater problems in specific fields.
Early in the production season, when plants have fewer than 5 leaves or prior to vining, samples may consist of 50 plants per field. As the plants increase in size, sampling should focus on individual leaves and 100 leaves per field should be examined. Both small and large plants and old and young leaves should be included in samples each week. Scout the field by starting in a corner of the field and taking the first sample, then walk a pre-determined number of steps across the field before taking the next sample. Walking across the field in an X or Z pattern usually provides a representative idea of what is in the field. Take care to include edge as well as middle areas of the field. A hand lens or good-quality magnifying glass is a useful aid to see small pests such as aphids, thrips, or spider mites.
Germinating, seedling, and vining stage plants - Check fields twice per week by examining 50 plants per field when plants are small (up to 5 leaves).
Vining stage to harvest
As plants get larger, change the sampling plan to 100 leaves per field. Take care to check the undersides of leaves, the preferred site for aphids, worms, and other insects, but also check the base of plants where squash bugs are likely to be found.
Flowering stage
In addition to checking for pests, observe 100 flowers and record number of flowers with active bees to determine whether sufficient pollinators are present (see section on pollination).
Monitoring plant growth and fruit set
The weekly or biweekly scouting program for each field should include scouting for and recording plant growth and fruit set (see section on cultural practices).
Evaluating yield and harvest dates
After fruit is set, monitor the growth of the fruit during the weekly pest scouting to better project harvest dates.
2. Identify insect and mite pests
Use this reference manual or one indicated in the reference section to assist
in identifying insects and mites found feeding on plants. When a question arises
as to identification, collect the insect and/or plant part with the insect and
the plant damage and place in a plastic bag, seal the bag, and place in a cool
location. Take the sample
to the county Cooperative Extension Service office for assistance in identification.
3. Decisions to take management actions
Use this manual to assist in determining whether to spend resources managing a pest. The main issue is whether the cost of the management action will result in returns greater than the cost of the control. For example, low population numbers of mites that are not increasing in number from week to week will not significantly reduce yield especially if present late in the growing season close to harvest. Therefore, the cost of application of a miticide to control the mites may simply add to the cost of production and not result in a net return to the producer.
4. Taking action
When deciding to control pests, choose the most cost effective method. Application of insecticides or acaricides is the most commonly chosen and most effective method for controlling pest populations when they are so numerous as to affect plant growth. Consult the Oklahoma Cooperative Extension Service for recommendations for pesticide applications for specific pest problems or see Appendix 3. Make applications as directed to ensure best control.
5. Evaluating controls
Within one week of applying a control measure, monitor the field to determine whether the pest population has been reduced to a level as desired. Compare the number of insects or mites per plant or leaf as recorded prior to application of the control measure with the number of insects or mites present 3 to 7 days after application of the control measure.
Generally, plants that are weakened by poor growing conditions are more susceptible to insect pest damage and may be more attractive to pests than healthy, vigorously growing plants. Cultural methods greatly influence the extent of pest problems by 1) the selection of a good site for production, 2) the proper fertilization and irrigation, 3) the use of varieties that are less susceptible to pest attack, 4) the proper arrangement of crop plantings, 5) the consideration of crop planting dates, 6) the use of effective weed management practices in and around the cucurbit field, and 7) the timely destruction of crop residue from previous cucurbit plantings.
Beneficial insects and mites, diseases, and other animals feed on and kill many pest insects and mites. Many of these beneficial insects and mites occur naturally in fields. Application of broad spectrum insecticides, fungicides, and herbicides can kill many of the beneficial insects and mites and thus pesticides should only be applied if the beneficials are unable to maintain the desired level of pest control.
Many cucurbit crops have been developed to be resistant to diseases but currently there are no recommended varieties with significant resistance to insect and mite pests. However, aphids are carriers of viruses that cause devastating diseases, which cannot be controlled with pesticides. Research has shown that controlling the aphids is not effective in preventing these viral diseases. Therefore, plant virus-resistant varieties instead of trying to control aphids. These viruses and the resistant varieties are described in Tables 9-14.
Applying effective insecticides or
to control insects and mites provides a cost effective method of managing pest populations. A Cooperative Extension Service educator can make specific recommendations. Guidelines for safe and effective pesticide application are found in the last chapter of this manual.
Insects living in the soil become significant pests when planting a crop into a field with high organic matter, especially in a newly broken pasture. Soil-inhabiting insects feed on seeds, seedlings, and roots of plants and destroy large areas of newly planted crops. Treating these pests is not routinely required; rather, the decision to treat a field before planting should be made on the basis of field cropping history and the potential of the field to have pest problems. If crops are planted in an area that was previously pasture or had a significant weed problem, apply a pre-plant insecticide to control soil insect pests. A soil insecticide works best when lightly incorporated (with a heavy chain or light cultivator) into the soil before planting. Keep the insecticide in the upper 6 inches of soil.
Seed or Root Maggots
Adults resemble small houseflies and lay eggs in the soil in early spring when soil temperatures are below 70F. Eggs hatch into larvae (maggots) (Figure 1) and feed on seeds, germinating seeds, and developing seedlings. They are primarily a problem in soils with high organic matter; therefore, if a cover crop precedes a cucurbit crop, especially if planted in cool weather, then preventative measures should be taken.
Threshold No treatment threshold has been developed based on scientific research. High value crops such as irrigated seedless watermelon should be treated with a soil-applied insecticide prior to planting.
Control Plow cover crops into the soil 3 to 4 weeks prior to planting and plant after soil warms to 70F. Apply a pre-plant application of insecticide, such as carborfuran, when planting early in cool soil, and in high organic matter. (Appendix 3).
Wireworms
The wireworm adults are called click beetles and are harmless to most crops. However, the larvae are called wireworms; these are brown yellow in color, cylindrical in shape, and grow to 1-1.5 inches long (Figure 2). These larvae feed on seeds, germinating seeds, and plant roots, and when abundant, they can destroy large areas of new plantings. Monitor wireworms by placing 5 bait stations in each field 3 weeks prior to planting: dig 6-inch-deep holes and place wheat or rye seed in the bottom. Cover the hole with soil and mark with a flag. After 2 weeks, uncover the seed and check for wireworms.
Threshold One wireworm per bait station (see preceding for bait station monitoring).
Control Plant seeds after soil warms to 70F and/or apply a recommended soil insecticide to the soil prior to planting. (Appendix 3).
Grubs
Adult grubs are called May or June beetles/bugs. Their offspring are white to off-white, with a tan head capsule, and generally wrap their bodies into a 'C' shape form (Figure 3). Adults lay eggs in the soil, the eggs hatch, and the larvae feed on plant roots. When abundent, they can destroy a large area of young plants.
Threshold No threshold has been developed based on scientific research. High value crops such as irrigated seedless watermelon should be treated with a soil-applied insecticide prior to planting.
Control Plow or cultivate fields with abundant organic matter 3 weeks prior to planting and then again at planting, or allow field to lay fallow and without vegetation for several months prior to planting. Apply a recommended soil insecticide at planting. (Appendix 3).
Cucumber Beetles
The spotted cucumber beetle (Figure 5) is about 1/4 -inch long, yellow to greenish-yellow with 12 black spots on its back and a black head. Larvae are yellowish white with a brown head and a brown patch on top of the last body segment (Figure 4). They are approximately 1/2 -inch long when fully grown. The larvae typically feed on plant roots; however, they may also feed on the rind of melons, especially cantaloupe, and can be found under the fruit where it touches the soil.
The striped cucumber beetle is pale yellow to orange-yellow with a black head (Figure 5). Its wings have 3 black stripes running their entire length. There are punctures or stripling on the wings also, so that it appears as if a small punch were used to make a row of dents on the wing covers. Larvae are about 1/3 -inch long when fully grown and feed on roots. The larvae are white, with brownish ends and slender bodies (Figure 4).
The spotted and striped cucumber beetles are among the first insects to attack cucurbit crops as the plants germinate and emerge. They feed on the cotyledons and stems of seedling plants. Their chewing may result in loss of cotyledons, which weakens seedlings. Often they eat the growing point from the young plant and thus kill the plant. Also, they will chew into or half way through the stem, weakening it so that it may break off during a strong wind. Other than immediate stand loss, the greatest damage from cucumber beetle feeding is through their ability to transmit bacterial wilt. This disease does not occur regularly in Oklahoma, though when present, it can cause severe yield losses. The insect's body carries the bacterium which transmits to the plant as the beetles feed. Controlling the beetle will limit the occurrence of the disease. Beetle feeding can reduce watermelon stands. The next section, management of diseases, provides more information on bacterial wilt.
Threshold: Control of cucumber beetles is critical within 2 weeks of plant emergence from the soil. In general, if 4 to 5 beetles are found in sampling 50 plants, an insecticide should be applied. Controls are generally not needed on watermelon plantings after the plants begin to flower and fruit unless beetles are very abundant (1 per leaf). However, cantaloupe, cucumber, squash, and pumpkin varieties may be susceptible to bacterial wilt; the adult beetles must be controlled even at low numbers throughout the season so that they do not transmit the bacteria that cause the disease.
Control Apply a recommended soil insecticide at planting (Appendix 3). Foliar insecticides should be applied at seedling stage, as a side dress to the soil at vining stage, and/or after fruit set if the treatment threshold is exceeded or when planting varieties susceptible to bacterial wilt.
Squash Bug
Adults emerge in the spring from their over-wintering sites and search and feed on cucurbit host plants. Adults are brownish black to dark ashy black in color and are about 5/8 -inch long (Figure 6). The body is compact and solid, with the wings overlapping on the back 1/3 of the abdomen. After mating, females deposit creamy white eggs in clusters, generally on the underside of the leaves. The eggs turn metallic bronze in color within a few hours (Figure 7). When the young insects (nymphs) hatch, they are pale green. They develop a grayish body color with black legs as they mature. A squash bug passes through 5 nymphal stages, increasing in size, before becoming an adult. The entire life cycle (egg to adult) takes 30-45 days, and there are 3 to 4 generations per year in Oklahoma. As winter approaches, egg laying decreases and the adults move out of the fields looking for places to overwinter. Nymphs present in late fall are killed by freezing temperatures and the remaining adults search for and move to overwintering sites. This overwintering population is the source of the following year infestations of adults that move into spring planted crops.
Both the nymphs and adults feed by inserting their needle-like mouthparts into the plant and sucking nutrients from the plant tissues. Overwintered adults that move into crops in early spring can cause extensive damage by feeding on small plants and seedlings. Their feeding can greatly stress and kill young seedlings. Once plants are larger, they can withstand a low number of squash bugs. Both adults and nymphs prefer feeding on leaves but will feed on all above ground plant parts.
Squash bugs are mobile and move easily among plants within a field or among fields. The insects spend most of their time within the plant canopy, mainly around the stems and on the underside of the leaves. Adults often congregate near the base of the plant and the nymphs congregate on the leaf where they hatched and then migrate to other plant parts. Squash bugs can increase in numbers very rapidly, and when present in large numbers, can cause plant wilting. When there are large numbers of squash bugs and the weather is hot and dry, the stress on plants increases significantly. Damage is noted by the sudden wilting and death of plants. Larger plants generally begin turning yellow and then wilt, just as fruit is set and maturing on the plants.
Good cultural practices can help prevent serious squash bug damage. Healthy, vigorously growing plants, tolerate feeding by squash bugs. Squash lines that exhibit some tolerance to squash bug feeding include butternut, royal acorn, and sweet cheese.
Crop residues must be destroyed after harvest to reduce squash bug problems in later plantings. Following the final harvest, crop residues should be shredded and disked to reduce numbers of squash bugs that can overwinter and invade the next year's crop.
Threshold For high value plantings apply a recommended soil insecticide at planting. For all crops treat with foliar applications of insecticide if live squash bug adults are noted laying eggs on seedling-stage plants. After plants increase in size to the flowering stage, make insecticide applications when there is an average of 1 egg mass per plant.
Control Apply a recommended soil insecticide at planting. Foliar insecticides should be applied at seedling stage, as a side dress to the soil at vining stage, and/or after fruit set if the treatment threshold is exceeded. See Appendix 3 for specific recommendations. Insecticide applications should be timed to kill the maximum number of overwintering adults as they move into the production field. If adults successfully mate and lay eggs in the field, look for hatching of nymphs and time applications to control the majority of the nymphs. It is important to remember that small nymphs are much easier to control than large nymphs or adults. It is critical to achieve good coverage with insecticide sprays including significant penetration of the plant canopy. This usually requires a ground application of the insecticide using a tractor-mounted sprayer rather than using aerial application.
Aphids
There are several species of aphids that can feed on cucurbits, but the main one is the melon aphid (Figure 8). Aphids cause damage by 1) removing nutrients from plants and causing wilting, 2) transmitting virus, and 3) secreting honeydew, which inhibits photosynthesis and contaminates the fruit. Honeydew does not wash off easily and permits the growth of sooty mold on leaves and fruit.
Aphids can cause serious damage to all cucurbit crops, and lower yield even at relatively low populations. Many aphids, including the melon aphid, transmit viruses. Research has shown that the major vectors of cucurbit viruses are species that migrate through the field as they search for proper hosts. Scouts will not generally note the presence of the migrating aphids because they move into the field, land on plants, "taste" the plants by feeding, decide the plant is not a proper host, then leave the plant and often the field. However, that single feeding by a migrating aphid is often enough to transfer a virus. The most common aphid-transmitted viruses on cucurbits grown in Oklahoma are watermelon mosaic viruses, papaya ringspot, and zucchini yellow mosaic. These viruses stunt plant growth and cause considerable yield loss, especially in squash and pumpkin, and occasionally in watermelon. They generally appear in late summer and are worse on late-planted (fall) squash and pumpkin. Refer to the management of diseases section for more information about the viruses, and refer to Tables 9-14 for virus-resistant varieties of cucurbits.
Thresholds - In general, if aphids are present on more than 10% of the leaves, an insecticide should be applied to the crop foliage. If aphid populations are near the threshold level, the presence of insect predators and parasites should be considered in making a spray decision. If the activity of beneficial insects, particularly lady beetles and parasitic wasps, appears to be increasing, sprays should be delayed for a few days to see if biological control will limit aphid populations effectively.
Control - Apply systemic insecticides to the foliage (Appendix 3). Insecticides are rarely effective for preventing virus transmission; however, applications may limit or delay the spread of viruses within a field where the virus disease is present. The use of reflective mulches has been shown to provide significant reductions in virus occurrence. The use of mulches can be a practical, but costly, method for limiting yield losses to viruses, particularly in fall-grown cucurbits that are more likely to experience debilitating virus problems. Producers should plant virus-resistant varieties for late-season production or if virus diseases have been noted in previous years' production. See Tables 9-14 for examples of these varieties.
Thrips
Thrips are tiny elongate insects, usually dark in color (Figure 9). Thrips feed on young plant leaves, scarring the leaf tissue, and may slow plant growth. Damage appears as small pale-yellow blotches or silver streaks on leaves, and may resemble the type of damage caused by blowing sand.
Threshold----A clearly defined threshold has not been established, but if thrip populations exceed 1-2 per plant on plants with less than 3 true leaves, an insecticide application is probably justified.
Control----Foliar application of a recommended insecticide (Appendix 3).
Squash Vine Borer
This moth generally occurs east of Interstate 35 and is most commonly a pest of squash and pumpkin. The moth resembles a large wasp without the stinger. Females deposit eggs near the base of the plant about the time the first planting of squash begins to bloom. A small larva (caterpillar) (Figure 10) emerges and enters the stem of the plant. Larvae feed inside the stem or the main stalk of the plant. The feeding damage will eventually cause the stem or stalk to die, because it destroys the plant tissue that transmits food and water in the plant. When this occurs, runners or branches of a plant begin to wilt or die while the rest of the plant looks healthy. There will be sticky excrement at the entrance hole of the larva. This is generally near the base of the plant and always near the soil surface. The worm will eventually exit the stem and enter the soil to pupate. There is one generation per year in Oklahoma.
Threshold - Squash vine borers are not considered major pests of cucurbit crops.
Control - If borers have been a problem in the past, control can be achieved by using a spray schedule started when the plants begin to bloom and continued once a week until harvest is completed (Appendix 3). Often, if a field has not had problems in the past, there is no need to control squash vine borer.
Melonworm and Pickleworm
These insect pests occur infrequently in Oklahoma. The melonworm larva feeds mainly on the foliage and in the plant terminal bud. They attack most cucurbit crops except watermelon. The melonworm (Figure 12) is green with two white, well-separated slender stripes running the full length of the body on the upper side. The larvae are very active when disturbed and will wiggle violently. The pickleworm larva feeds on the fruit of cantaloupe, cucumber, and squash. The larval stage is green to coppery in color, except for the brown head and a brown area just behind the head, and is about 3/4-inch long. Young larvae are strikingly marked, with nearly 100 black spots evenly scattered over the body (Figure 11). The melonworm feeds on leaves and seldom feeds on fruit.
Pickleworm larvae can cause serious damage to cucumber, squash, and cantaloupe. Pickleworms bore into the stems and terminal buds, especially squash blossoms, early in the season. Later in the season, pickleworms bore into the fruit from the side next to the ground. They push out small masses of green, sawdust-like excrement from their holes in the fruit. After feeding for about 2 weeks, the larva moves out of the fruit to the leaves, where it rolls a leaf around its body and spends 7 to 10 days as a pupa.
Control - These insects are seldom a significant economic problem for producers. If the foliage-feeding melonworm becomes a problem, sprays used for the squash bug can easily control it. The pickleworm is more difficult to control and more damaging because it feeds inside fruit. When the pickleworm becomes a problem, a spray schedule of 5 to 7 day intervals should be followed. Use the same insecticides as used to control squash bugs (Appendix 3). Destroy plant materials from infested fields after harvest to lessen further population build-up and future problems with pickleworm.
Spider Mites
These minute (1/60 -inch long) creatures are not insects but are related to spiders and ticks and have 8 legs. The two-spotted spider mite is the most common (Figure 13). It is red and brown in color with two spots on the back part of its oval body, though the spots cannot be seen without magnification. Mites increase in abundance during hot, dry weather and are found on the underside of the leaves. Mites reproduce very rapidly and can become very numerous in a short period of time. They lay shiny, spherical, straw-colored eggs on the underside of the leaves. These eggs hatch in 3 days. A female lays an average of 100 eggs. Mites can complete a life cycle in 5 days when the temperature is 75°F or above. Mites spin fine silk webbing on the underside of the leaves, which is often easier to see than the mites themselves.
Mites feed by sucking out the contents from individual leaf cells. The feeding of one mite is not damaging, but mites are usually present in huge numbers. When this occurs, their feeding puts tremendous stress on the plant. Damage appears as mottling of the leaf from the many tiny feeding punctures by the mites. This area dies and the leaf turns bronze-colored or dies. Infestations of mites often start near an unpaved road or in patches in the field and spread from these areas. Under hot, dry conditions, mite populations can build to damaging levels within a few days.
To inspect for mites, use a hand lens for positive identification. Be sure the mites are alive and moving. Dead mites will adhere to the leaf and can be mistaken for live mites during inspections. Another method is to place a piece of white paper beneath leaves then rap the leaves with a pencil or finger. Wait about 15 to 30 seconds. If small dots begin to move on the paper, mites are present.
Threshold - Generally, if 10 to 25% of the leaves have mites or mite eggs, then a miticide should be applied. If the weather is hot and dry, thus favoring mite build-up, use the lower threshold.
Control - With the rapid life cycle of mites, control is based on "breaking the cycle" and stopping the build-up before large infestations become established. This requires being mindful of the weather and plant conditions. It also requires field inspection for possible build-ups. Mites often occur in patches within a field or at the edge of the field. Sometimes treatment of localized infestations can be effective, and thus could save money by treating the smaller infested area instead of treating the entire field. Effective control of mites depends on thorough distribution of the miticide to the underside of leaves and leaves within the crop canopy. The miticide must get to the underside of the leaves where the mites are present. Do not expect one application to completely control a mite infestation. Most miticides do not kill the eggs, and those eggs will hatch within 3 days after the spray application. See Appendix 3 for specific miticide recommendations.
A hard drenching rain or overhead irrigation can control a mite infestation, especially if the rain or irrigation is followed by cloudy, cool weather. The water acts to dislodge mites and increased humidity allows the growth of parasitic fungi that kill mites. However, the increased humidity can also encourage the growth of fungi that cause plant disease, different than the fungi that kill the mites. Limit this control option if disease-causing fungi or bacteria have been a problem in this field.