Jul 27, 20222022 Management Guidelines for Whiteflies and CYSDV on Fall Melons
After Bemisia whiteflies invaded the desert in 1991, production of fall melons became very difficult, and acreage declined in many desert growing areas. With the Section 18 registration of Admire 2F in 1993, growers could effectively control whiteflies again and soon began to profitably produce fall melons in Yuma, and central Arizona. Then in 2007, a new challenge emerged for melon growers when Cucurbit Yellows Stunting Disorder Virus (CYSDV) became established throughout the desert Southwest. It’s taken some time, but now economic production of fall melons appears to be back on track in Arizona. Until last season, whitefly populations during the fall have been lighter than normal for several years, and CYSDV incidence on fall melons was consistently below 20% (see graphs below). However, last fall CYSDV infection increased dramatically even though whitefly abundance was relatively light. This occurred due to abandoned watermelons (~200 acres) in the Tacna area that were left untreated all summer. The watermelon acreage was located 1-5 mile southeast (upwind) of several cantaloupe and honeydew fields and had an abundance of whiteflies and heavily infected with CYSDV Although the watermelons had not been irrigated during the summer, heavy monsoon activity in July and August (>3” rain), sustained foliage in the fields and allowed both whitefly adults and CYSDV to build up to unusually high levels. We estimated that the incidence of CYSDV in all the cantaloupe/honeydew fields in the Tacna and Roll areas was greater than 80% at harvest. Melon yields were significantly impacted, and a couple of fields did not harvest. Fields further downwind in Wellton and Dome Valley averaged less than 20% CYSDV infection. These results stress the importance of cultural management of whiteflies. To download the most recent information for whitefly and CYSDV management in fall melons go to: 2022 Guidelines for Whitefly / CYSDV Management on Fall Melons.
The epidemiology of CYSDV is a complex relationship between the virus, the adult whitefly vector and our local melon cropping system. It has been our goal over the past 15 years to understand this pathosystem and develop practical approaches for reducing CYSDV impact on fall melon production. We continue to develop new information on cultural and chemical control tactics for adult whiteflies (see 2022 Guidelines). Our knowledge to date suggests that fall melons produced near cotton, alfalfa or near areas where spring melons were recently produced are at the highest risk of infection. When practical, growers should try to isolate fall melon plantings as far away as possible from these sources of whiteflies and CYSDV. The high infection rates in Tacna/Roll last season are evidence of this. Growers forced to plant fall melons near these crops should be vigilant in minimizing adult whitefly infestation levels with insecticides during pre-bloom growth stages. This can be achieved with at-planting and side-dress applications of soil insecticide (Venom, Scorpion, Sivanto) and well-timed applications of foliar sprays. For Arizona growers, new insecticide labels are available for adult knockdown control. PQZ and Sefina, registered for use on Arizona melons in 2019, are feeding disruptors with a high degree of bee safety. Based on local research, both products will provide excellent adult knockdown and CYSDV suppression when used in a fall management program. Transform (same active ingredient as Sequoia) is also labeled for use on melons and provides another alternative for adult knockdown. Bottom line: cost-effective tools are available but minimizing whitefly abundance in the surrounding crop landscape (e.g., cotton, volunteer melons, abandoned crops) is critical for them to be most effective.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu