Foliar disease control demonstrations for watermelon: Distant presentation of field trials

Authors: SHREFLER, JAMES - OSU, LANE, OK; DAMICONE, JOHN - OSU, STILLWATER, OK; Bruton, Benny

Submitted to: Interamerican Society of Tropical Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2006
Publication Date: 9/1/2006
Citation: Shrefler, J.W., Damicone, J., Bruton, B.D. 2006. Foliar disease control demonstrations for watermelon: Distant presentation of field trials. Interamerican Society of Tropical Horticulture Proceedings. 50:54-58.

Interpretive Summary: Foliar disease management is a challenge for watermelon producers in the south central portion of the United States. There are four foliar diseases that can be probablematic, but tend to occur under somewhat different environmental conditions. Gummy stem blight generally occurs following multiple rain events over an extended time. Anthracnose tends to be worse once the plants have developed substantial canopy coinciding with multiple rain events. Downy mildew moves up from the southern production areas each year in about July and August and tends to be more severe under cooler conditions. In contrast, powdery mildew tends to be more severe in August and September under humid conditions but does not require rain events. Depending on the stage of plant development and the environmental conditions, one or more of the aforementioned diseases may be present at the same time. Since fungicide applications can expensive, we wanted to compare the effectiveness of weekly spray applications versus a weather-based model. The study involved two broad-spectrum fungicide treatments consisting of a mixture of Mancozeb and Thiophanate-methyl or Chhlorothalonil. In 2004, downy mildew was the predominant foliar disease encountered. There was no difference between application method (weekly vs weather-based model) and both fungicide treatments performed equally well until very late-season. Using a weekly spray, six fungicide applications were made vs three when using the weather-base model. In 2005, gummy stem blight was the predominant foliar disease encountered. Again, there was no difference between application method and both fungicide treatments performed equally well throughout the entire season. Using a weekly spray, seven fungicide applications were made vs four when using the weather-base model. In conclusion, the weather-based model reduced fungicide application by nearly 50% without sacrificing disease control efficacy.

Technical Abstract: Foliar diseases are a serious concern of watermelon producers. In Oklahoma, for instance, several distinct foliar fungal diseases can result in complete crop loss when conditions are conducive to disease development. Proper fungicide use can reduce or prevent losses to these diseases. An education problem exists in that many growers do not apply fungicides at the proper time. Fungicides are most effective when applied prior to disease infection. However, growers often do not apply fungicides until after disease symptoms appear. In order to address this education need and to verify fungicide use recommendations, field demonstrations were established at Lane, Oklahoma in 2004 and 2005 using two fungicide treatments and two methods of applications timing. Fungicide treatments were a either a mixture of Mancozeb (Dithane 75DF) and Thiophanate-methyl (Topsin 70WP) or Chlorothalonil (Bravo Weatherstick). Fungicide application timing decisions were determined by one of two methods. One method was a weather-based model that was developed in Oklahoma for anthracnose and the other was a weekly application schedule. All fungicide treatments were initiated with an application that was made when the crop began to flower. To make the trial accessible to all interested growers, real-time presentation of crop and disease development, along with discussion of the decision making process, was provided over the Internet at www.lane-ag.org. The presentation will discuss the affects of the treatments on foliar disease control in watermelon and the methodology used for delivering the online presentation.