Watermelon Disease Control Demonstration

Lane, Oklahoma

2004

The objective of this project is to demonstrate to the use of fungicides for controlling foliar diseases in watermelon. The demonstration will include two different fungicide treatments and two different methods to decide when to apply the fungicides.

Fungicides:

A mixture of Dithane 75DF applied at 2 lbs. per acre and Topsin 70 WP applied at ½ lb. per acre.
Bravo Weatherstick applied at 1½ pints per acre.

Application Decision Methods:

Apply on a calendar schedule. Since diseases have already been observed in other fields in the area we chose a weekly schedule.
Apply based on the Mesonet Anthracnose Forecaster Model.

For both methods an initial fungicide application was made when plants began to produce male flowers. That day was August 17.

Activity Record
Date	Field Observations and Activities	Fungicide Application
Date	Field Observations and Activities	Calendar	Forecaster
August 15	First Flowers Observed.	Yes	Yes
August 17	Apply Fungicides	Yes	Yes
August 19	Forecaster results – 3 infection hours since last fungicide application (Aug. 17) - no spraying is recommended today	No	No
August 23	Forecaster results – 55 infection hours have occurred since the last fungicide application (Aug. 17) - no spraying is recommended today	No	No
August 23	Disease lesions observed. Diseases include Powdery Mildew and Downy Mildew	No	No
August 24	Time for weekly spray application	Yes	No
August 25	The anthracnose forecaster indicated 83 infection hours since the last spray application. Time to Spray!	No	Yes
August 30	The anthracnose forecaster indicated 41 infection hours since the last spray application. Spraying not advised by the forecaster.	No	No
August 31	Vines are running extensively Weekly treatments were sprayed today. The forecaster indicated 43 infection hours so treatment is not advised.. Disease symptoms are obvious in untreated plots	Yes	No
Sept. 2	The anthracnose forecaster indicated 46 infection hours since the last spray application 0n August 25. Spraying is not advised by the forecaster	Yes	No
Sept. 7	The anthracnose forecaster indicated 91 infection hours since the last spray application on August 25. Time to Spray! Time for the weekly spray application also. 80% crown area defoliation has occurred in the untreated plots. Disease is less severe in all treated plots with 27 to 42 % defoliation.	Yes	Yes
September 14	Weekly fungicide application made today.	Yes	No
September 16	Defoliation has reached 75% in the untreated plots (this is the entire plot, not just the crown area). The most abundant disease appears to be Downy Mildew. All fungicide treatments have provided significant protection of foliage. Bravo fungicide applied weekly has provided greater protection than applications based on the Anthracnose Forecaster.	No	No

For questions or comments contact Jim Shrefler at jshrefler-okstate@lane-ag.org or by phone at 580-889-7343

This information is provided for educational purposes only. When using pesticides, always read and follow label directions. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.