Cucurbit crops grown in Oklahoma include watermelon, cantaloupe, squash, pumpkin, and cucumber. All are warm season crops and produce well in many areas of the state. Cucurbits are sensitive to chilling injury and frost damage. Grown on nearly 19,000 acres, these crops generate an estimated $14 million annually in farm income to Oklahoma producers (Table 4). Production is scattered across the area, with acreage concentrations located in the south-central and southwestern regions of the state.
Watermelon is a warm, long-season crop, with production acreage concentrated in the central and south-central areas of Oklahoma. Watermelon can be grown in most areas of the state. A producer must produce good yields of high quality melons to earn a profit. This can only be attained with careful management of the crop.
Cantaloupes are the most important type of muskmelon grown in Oklahoma. Other
types of muskmelons grown in the state include honeydew, casaba, and crenshaw.
These other types are becoming more popular and could increase in importance.
Cantaloupe and other muskmelons adapt better to the drier, southwestern areas
of the state where foliage diseases are less apt to occur. Although hot, dry
weather is favorable for cantaloupes, they can be grown successfully in most
areas if diseases are managed. Cantaloupes are not as well adapted as water
melons to extremely hot summer weather.
Squash, pumpkin, and cucumber can be grown throughout the state. Low humidity is best for production due to the lower incidence of both foliar and fruit disease in drier areas. Producers grow squash in Oklahoma for both the fresh and processing market. High labor requirements for harvesting and difficulty in controlling virus diseases limits squash production within the state. Light, sandy loam soils are best for early production. High temperatures may cause light green fruit color and bitterness in many cucumber varieties, so producers should consider this when selecting which variety to produce.
Expected yields vary considerably for different cucurbit crops, but with good management and ideal conditions, yields given in Table 5 may be achieved. Yield estimates assume that producers are using irrigation and other management practices that work together to provide for the most profitable production of cucurbits.
Table 4. Estimated acreage and value of vine crops in Oklahoma 2000-2001*
When using a low-intensity management strategy, commercial growers should over-seed relatively inexpensive varieties and plan to tolerate moderate levels of damage to seedlings
and young plants prior to thinning stands. Individual seeds and plants have relatively low value due to the low cost of the seed and of production. Low to moderate levels of pest infestation and damage can be tolerated, and pests should be treated only when numbers increase to the upper thresholds of tolerance.
When using high-intensity management strategies, commercial growers typically purchase expensive seed or transplants and plant them into well-cultivated fields with abundant nutrients and irrigation systems installed. Individual seeds and plants have a relatively high value due to the invested value in the seed, nutrients, cultivation, mulch, and irrigation. Thus each plant has a high value for protection and economic thresholds for pest abundance are low.
Manage pests by avoiding them altogether. Planting the same type of crop in the same field year after year can allow build-up in that field of insects, nematodes, and diseases. Weeds can become a problem because the same herbicides, labeled for that crop, are used repeatedly. Breaking the cycle by planting alternative crops on a rotating 3- or 4-year cycle can reduce pest numbers. Examples of non-cucurbit crops grown in rotations are grasses, such as wheat, sorghum, and oats, or legumes, such as peas or alfalfa.
Field sanitation complements crop rotation in breaking the cycle of pest infestation. Many insects, such as squash bug, overwinter in crop debris. Diseased plant parts, including foliage, roots, and fruit, can provide the source of disease, such as Alternaria leaf spot, for next year's crop, even if the cucurbit crop is in an adjacent field. Destroy plant residue after harvest to reduce this source of pest problems. In addition, diseased fruits should not be put back into the field and left on the soil surface. Shredding and disking crop debris after harvest will eliminate many pests.
Keeping equipment clean plays a key role in sanitation. Many diseases can be carried from an infested field into a clean field in the soil and crop debris carried on equipment or workers' shoes. Equipment should be washed before moving it to the next field and before storing it at the end of the season. Finally, keep storage facilities and packing areas free of culled fruit and crop debris, and thoroughly clean these areas before the next field season.
Selecting the proper growing site is one of the most important decisions to make in cucurbit production. Choosing the field carefully prevents many crop and pest problems. This decision cannot be made in hindsight, and while some remedial steps can lessen the impact of planting in a poor site, advanced planning can save money in the long run.
Most cucurbits grow best on sandy loam, sand, or silt loam soils with a pH of 6.5 to 7. Growth on acidic or poorly drained soils often results in increased incidence of diseases such as Fusarium wilt and fruit rots.
Consult management records for past problems in the desired field, such as weedy areas, low spots, areas of significant soil compaction, disease, or soil insects. If this field will be used, then correct these problems in advance with tillage, targeted herbicide applications, or soil insecticides before planting. In addition, test the soil for nutrient and pH composition before planting. Correct nutrient deficiencies and pH problems before or at planting.
Table 5. Potential yields of cucurbit crops
Taking a soil sample accurately determines fertility requirements. A minimum of 20 cores/40 acres, taken to a 6-inch depth is suggested. With smaller fields, a minimum of 10 cores per field is necessary. These cores should be collected in a plastic bucket (never use a galvanized bucket) and mixed thoroughly by hand. The soil sample bag should be filled with the mixture. Soil sample bags and sampling tools are available at local Cooperative Extension Service office. For further information, see OSU Fact Sheet F-2207.
Farm testing provides an excellent way for producers to have a first hand look at new products and methods and to fine-tune them to their operations. Many producers would be more than happy to have university people involved, but there are not enough resources to allow for university involvement in each research project that needs to be carried out. Therefore, producers should learn the basics of on-farm testing so they can perform their own testing.
Most research and extension specialists would agree that the following points will help a producer learn the basics about on-farm testing.
1. Keep it simple. People have a tendency to want all questions answered and problems solved with one giant test, but do not be tempted to do this. Often the results of too many treatments in a test will just cause confusion.
2. Decide on what treatments to include. Whether it's 5 new varieties of watermelon or one new wetting agent for sprays, sit and think about the end result and pick reasonable treatments.
3. Always include a check. Compare the old way and the new treatment. As an example: If testing new varieties of watermelon, include "Old Reliable" that has been used for 20 years as a check to compare with the "new and improved" varieties. This provides proof to see if they are actually better or not.
4. Replicate and randomize: the two R's of field testing. Replicating
simply put means to repeat the treatments several times. Most research people
will repeat their treatments at least three times, preferably four or five times
to reduce the effect of differences
within the field. Those differences could include such things as different soil
types, watering differences, dogs and kids stepping on the plants, pivot irrigation
tire tracks, etc. Randomize by randomly picking where different treatments will
be placed in the field. This helps reduce the effect of differences within the
field.
5. Make a plot map and label the plots. Before setting foot in the field, be sure to make a plot map to follow (Table 6). After organizing the plots in the field according the plot map, label the plots with some type of marker (i.e., plot stakes or something easy to see). This is important, because like an old field researcher once found out, not knowing which treatment is in which plot, he'll never know which one worked best.
6. Keep good records of results. Date and record what happens in the field test. It will be difficult to remember in six months what happened. This could be particularly critical when planning the next season's crop and needing to utilize some of the new discoveries.
Table 6. Plot map example
Cucurbit crops perform best when the soil pH is between 6.5 and 7.0. If the soil test indicates a more acidic soil (< 6.5), lime should be applied at the recommended rate to neutralize soil acidity. Lime requires several months to fully offset soil acidity and should be applied several months prior to planting time. Applying lime later is better than making no application at all (when no advanced application could be made).
Cantaloupe is particularly sensitive to acid soils. Soils that are more acid than pH 6.0 cause the "acid yellowing" disorder, which may produce weak plants with yellowish leaves that do not set or properly mature the fruit. The management of diseases section describes this disorder in more depth. Most fertilizers, particularly those containing ammonium or urea nitrogen, will offset the benefits of lime. If heavy applications of these fertilizers are made, frequent applications of lime may be needed to maintain the desired soil pH. Test the soil on a regular basis.
Phosphorus (P) and potassium (K) can be applied pre-plant, either broadcast or banded, or the application can be divided with part being broadcast while the remainder banded. Rates for phosphorus and potassium vary from crop to crop and recommended amounts are given in Table 7. In soils with medium or high levels of P and K, broadcasting all of the fertilizer is an acceptable practice. Broadcasting can be done prior to plowing or disking, and the fertilizer can be incorporated into the soil during normal field preparation.
When soils are acidic or contain low levels of phosphorus, banding may be
preferable to broadcasting. Banding lessens the chance that phosphorus will
be "tied up" by the soil and made unavailable to the plant. Banding
in or near the row provides abundant fertilizer to the young plant with a limited
root system. Also, when planting a crop with wide row spacing, banding in or
near the row will make the fertilizer
available to the crop plant in the row instead of being available to weeds
in the row middles.
Some growers band fertilizer by opening a 6-inch-deep furrow or trench with a lister (a double-moldboard plow), applying the fertilizer in the trench, and then filling the trench and forming a raised seedbed above the trench with a pair of listers or a disk bedder.
Fertilizers may also be placed in a band 3 inches beside and 3 inches below the seed. Placing the band close to the seeds can result in the fertilizer salts damaging seedling roots.
If phosphorus and potassium are applied in a band, pre-plant nitrogen may be combined with the phosphorus and potassium. The combined amount of nitrogen and K2O should not exceed 100 pounds/acre. If amounts greater than 100 pounds are banded near the plant roots, salt injury can occur. When combined nitrogen and K2 O exceeds 100 pounds, the amount above 100 should be broadcast and incorporated into the soil to avoid seedling injury.
If plants are to be transplanted instead of direct seeded, a starter solution high in phosphorus should be applied at a rate of 1/2 pint of solution per plants. This will be beneficial if soil phosphorus is very low or if plants are seeded early in the year when the soil is cool. Three pounds of soluble 15-30-15 in 50 gallons of water can be used in making starter solution. The starter fertilizer is in addition to the fertilizer applied to the soil.
Nitrogen can leach from the soil after a heavy rain or excessive irrigation. Soil tested in the fall may contain a nitrogen level that will not be present the following spring. Also, nitrogen applied early in the season may be leached from the soil before the crop can use it. Nitrogen leaching is particularly true in deep, sandy soils. Growers should closely observe their crops for indications of nitrogen deficiency after heavy rains have occurred. Slow growth, sparse foliage, and light green or yellow older leaves generally indicate nitrogen deficiency. Additional applications of N may need to be made if the plant is nitrogen deficient. However, too much nitrogen can cause excessive foliage development, poor fruit set, and can be leached into the water table as a pollutant. Therefore, additional N should not be applied unless the need has been established.
With each cucurbit crop, apply 50 pounds of nitrogen/acre pre-plant if nitrate levels are near zero at 0-6 inch soil depth. Otherwise, deduct surface nitrate level from the recommended nitrogen. As previously mentioned, N can be applied in the band along with P and K, as long as the combined amount of N and K2O applied in a band does not exceed 100 pounds/acre.
Extra N will be needed with each crop in addition to the total 50 pounds/acre pre-plant. With watermelon, sidedress with an additional 40 to 60 pounds of nitrogen/acre 3 weeks after plants have emerged. Cantaloupe and cucumber require a sidedress with an additional 50 to 60 pounds nitrogen/acre when young plants are about to "tip-over" and run. With squash and pumpkin, sidedress with an additional 30 to 40 pounds of nitrogen/acre 3 weeks after plants have emerged. For extended harvest of summer squash or cucumber, an additional 25 pounds of nitrogen/acre may be needed to keep plants growing vigorously.
With all crops and nutrients, the amount of fertilizer applied may need to be adjusted to obtain maximum yields under different management systems. Plant spacing will affect the number of plants per acre, and closely spaced plants will require more fertilizer per acre than will widely spaced plants. Also, the expected yield and level of management will affect the level of fertilizers needed.
Properly tilling the soil several days prior to planting will allow the soil time to settle and provide for improved seedbed moisture and firmness. In addition to plowing and disking, sub-soiling beneath the row promotes deeper rooting in soils having a compacted layer.
Vine crops are usually grown on the flat. Under ideal conditions, there is no advantage in bedding a well-drained sandy soil. On low, tighter bottom ground, bedding can be beneficial. If a soil is not well drained, bedding will promote soil warming and thus increase early growth of vine crops.
Black plastic mulch and drip irrigation has become increasingly popular with cucurbit producers. There are several reasons to use black plastic mulch and drip irrigation including increased earliness, weed control, water conservation, and cleaner fruit at harvest. Plastic mulch and drip irrigation have been adopted primarily by cantaloupe and honeydew producers because of higher yields from these technologies.
Some watermelon producers have utilized plastic mulch to warm soils in the spring to provide for crop earliness, but most mid- to late-season watermelons are currently grown on bare soil. This technology has also been used to a lesser extent to produce early season crops of fresh market squash and cucumbers. Plastic mulches are available in different colors and each type possesses different attributes (Table 8).
Black mulches and Green Infrared Transmittable (IRT) mulches control weeds and reduce herbicide use by cutting off light to the soil surface. Without a source of light, few weeds will sprout or grow. Some weeds, particularly yellow and purple nutsedge, are not controlled by plastic mulch. They will puncture and grow through plastic. This creates problems from weed competition and makes plastic removal at the end of the season very difficult. Therefore, producers with these problem weeds should consider utilizing other fields or use an effective herbicide for controlling them.
Reflective mulches can deter aphids from landing in, feeding on, and transmitting viruses to susceptible cucurbit varieties.
Table 7. The following amounts of P2O5 and K2O
are recommended based on OSU soil test results
Table 8. Plastic mulch types and properties
When producers are considering the use of drip irrigation and plastic mulch, they need to be aware of both the potential benefits and costs of utilizing this technology. The obvious costs include the mulch and drip tape, but additional costs also include installation, additional machinery, labor, and removal and disposal costs for the mulch and drip tape following the growing season. Producers should understand that it takes a high level of management for drip and plastic mulch production, and it will take time to learn, so initial work with these technologies should be kept on a small scale and increase as experience is gained. For more information on mulches contact the American Society for Plasticulture at www.plasticulture.org.
Wind stress slows plant development, increasing the days to harvest. Windbreaks are an effective method to reduce wind exposure and to hasten plant development. Windbreaks still standing during flowering improve fruit set by reducing water loss at this critical time.
Windbreaks should be planted well in advance of the cucurbit crop, so that sufficient height and width of the windbreak exists to retard the wind speed. Windbreaks are needed most when cucurbits are young and tender. A wind break planted at the same time as the crop will be of little or no use for slowing the wind during the establishment period when the crop is most vulnerable to wind damage.
Fall-planted wheat or rye is a commonly used windbreak. Spring-planted windbreaks usually do not have enough growing time to reach a sufficient height.
Many different windbreak widths and spacing have been used. A narrow windbreak strip can be left standing every 25 to 50 feet for wind protection. Crop row spacing and the number of rows planted in one tractor-pass are used to determine windbreak patterns. Future drive rows for harvest are an ideal place to establish a windbreak. Plants used in the windbreaks can be killed mechanically or with an appropriate herbicide before vines enter the windbreak area.
Selecting the best cultivar (variety) of a crop is one of the most important decisions made by a producer.
In addition to market acceptability, a variety must yield well, be adapted to the production area, and have the highest level of needed pest resistance available. Another factor to consider when selecting varieties is that diversity in the number of varieties used will provide some protection from pests and adverse conditions.
Seed companies are very diligent in releasing new varieties that have improved disease resistance and fruit qualities. There are many sources of cultivar information available from seed companies and most of these were utilized to develop the crop variety tables in this guide. We hope the reader understands that this information is generally correct but should be taken as an estimate, not as the absolute, particularly when considering days to harvest, fruit size, etc. Producers would be wise to study the Oklahoma State annual "Vegetable Trial Report," which contains variety trial results for several vegetable crops and other pertinent research reports. The trial report is available from Oklahoma State University by contacting the department of horticulture at 405.744.5404.
Watermelons can be genetically classified as diploid open pollinated, diploid hybrid, and triploid hybrid types. Triploids are commonly referred to as seedless watermelon. A triploid hybrid is a cross between a common diploid variety and a tetraploid line. Triploids occasionally contain a few seeds. Triploids can be produced anywhere conventional watermelons are grown, although seed and establishment costs for them are considerably higher than seeded types.
Light-green and gray-green watermelons are less subject to sunburn injury than dark green and striped varieties. Resistance to races of Fusarium wilt and Anthracnose disease are an important varietal characteristic to consider. Most varieties have varying levels of resistance to one or more races of Fusarium wilt and or Anthracnose. It is important to note that black diamond, Texas giant, Florida giant, and tendergold watermelon varieties are not disease resistant. None of the watermelon varieties are resistant to all races of Fusarium or Anthracnose, therefore these diseases can occur even though a cultivar is commonly referred to as being resistant. No cultivar is known to have insect or nematode resistance.
Brief descriptions of several varieties grouped as diploid open pollinated, diploid hybrid, and triploid are listed in Table 9.
The shipping market prefers a smaller, heavily netted, broadly oval or round, and slightly ribbed type of variety. Short-distance shipping, local markets, and roadside stands desire the larger, more deeply ribbed, and lightly netted varieties. Varieties vary greatly in disease resistance. Disease resistance should be considered, particularly resistance to powdery mildew. Resistance to Fusarium wilt is also very important. Otherwise, Fusarium cannot be controlled unless fumigation is practiced. Listed in Table 10 are varieties and brief descriptions of the various types of muskmelons that have performed well in Oklahoma. No varieties have shown insect or nematode resistance.
Both summer and winter types of squash are grown in Oklahoma. Summer squash are marketed when soft and immature. Winter squash are marketed when the skins are hard and the seeds mature. Hybrids with increased vigor and high yields are recommended. Processors will require specific varieties for their use. Table 11 lists varieties that have some level of disease resistance. Disease resistance is very important, particularly to the virus diseases of squash.
No pumpkin variety claims resistance to major diseases, but several do have resistance to powdery mildew. Table 12 lists varieties that have some level of disease resistance. Most varieties will require 100120 days to mature and have vine type plants.
Cucumber varieties producing all female flowers (gynoecious types) produce fruit earlier and have more concentrated production than monoecious types. Many cucumber varieties have resistance to several important diseases, including Anthracnose, downy mildew, and powdery mildew. Table 13 lists disease resistance varieties. No varieties have shown insect resistance. Each cultivar listed has uniform green fruit color required in the market place.
Winter melons are not as well adapted to Oklahoma growing conditions as cantaloupes. Except for some honeydew varieties, winter melons are susceptible to most melon diseases, but some varieties do have resistance to powdery mildew and Fusarium wilt. Winter melon production should only be attempted with a careful foliar disease management program. Without a protective spray program against disease, complete crop loss can result. Winter melon varieties are given in Table 14.
Vine crops will not reach their full production potential if subjected to moisture stress. About 8 to 10 inches of water from rain or irrigation on a deep, sandy soil will produce a good crop of watermelons, pumpkins, or winter squash. Growers with limited irrigation capabilities can often increase yields substantially with 1 or 2 irrigations.
Moisture stress is most harmful before seedling emergence, at early bloom, and the last 10 days before harvest. Inadequate moisture at planting will result in poor and uneven emergence. Moisture shortage at bloom reduces fruit set and increases the number of misshapen fruit. Moisture stress close to harvest can bring on rapid vine decline and reduce fruit size.
When producers irrigate, they should apply 1 to 2 inches of water. Irrigation of watermelons should be limited as they approach ripening. Excessive moisture at this time can promote white-heart, hollow-heart, lower sugar content, and cause fruit bursting.
Because root systems are not as deep as watermelon, cantaloupes, cucumbers, and summer squash will need moderate amounts of water more frequently. Apply adequate moisture while plants are growing rapidly and fruits are sizing. Moisture stress during fruit set of summer squash and cucumbers can seriously reduce marketable fruit yield. Heavy irrigation or rainfall just before or during cantaloupe harvest will cause reduced sugar content, stem-end cracking, and fruit rot.
Irrigating vine crops in the late afternoon or at night can increase the risk of foliage disease. This risk primarily happens in the spring, fall, and during periods of cool or cloudy weather. During hot, dry spells in the summer, nighttime irrigation often does not pose a high disease threat.
Avoid sprinkler irrigation during flowering when bees are most active, usually between 7 and 11 A.M. Overhead irrigation during this time may reduce bee activity and result in reduced fruit set, misshapen fruit, and/or small fruit.
Most cucurbits in Oklahoma are grown with overhead irrigation, but drip irrigation is used on some fields. Furrow irrigation is rarely used on cucurbit crops in the state.
Overhead irrigation is widely used in Oklahoma, especially in areas with less uniform terrain. It is also used to reduce irrigation labor. Systems can be designed for high- or low-pressure water application based on the type of nozzle used. Center-pivot, wheel-move, and hand-move systems use sprinklers to deliver water to the crop. Center pivots have the lowest labor requirement, but have the highest capital cost. OSU Fact Sheet F-1207, "Managing Center-Pivot Irrigation Systems," provides a more detailed look at center-pivots. Hand-moveable aluminum pipe requires the highest labor input, while having the lowest capital cost for a sprinkler system.
Drip irrigation improves water use efficiency and uniformity of water applications. Drip irrigation is being used on more melon acres in the United States, although its use is still minimal in Oklahoma. The most common drip irrigation system for cucurbit use is drip-tape. Drip-tape is a long, thin, plastic tape with minute holes usually spaced at distances of 12, 18, or 24 inches.
Water is pumped through the inside of the drip-tape, seeping out in small droplets. Water pressures for drip-tapes are usually in the range of 8 to 12 pounds per square inch. To prevent plugging, drip systems require excellent water filtration, occasional additions of chlorine to control algae, and/or acid to prevent mineral accumulation.
Drip systems have a high initial cost. However, increased crop yield, improved fruit quality, and superior water application efficiency are making drip irrigation systems more attractive to cucurbit growers.
Table 9. Cultivar characteristics and disease reactions of some watermelon
varieties grown in Oklahoma (R=resistant, subscript denotes race, S=susceptible)
Table 10. Cultivar characteristics and disease reactions of some cantaloupe varieties
grown in Oklahoma (R=resistant, subscript denotes race, S=susceptible)
Table 11. Cultivar characteristics and disease reactions of some squash varieties
grown in Oklahoma (R=resistant, S=susceptible)
Table 12. Cultivar characteristics and disease reaction of some pumpkin
varieties grown in Oklahoma
Table 13. Cultivar characteristics and disease reactions of some cucumber
varieties grown in Oklahoma (R=resistant, S=susceptible)
Table 14. Cultivar characteristics and disease reactions of some winter melon
varieties grown in Oklahoma (R=resistant, subscript denotes race, S=susceptible)
