Area-wide Incidence of Whiteflies and CYSDV

Growers are beginning to prepare local fields for fall melons, and with that comes the threat of cucurbit yellow stunting disorder virus (CYSDV). The virus was first identified in desert melons in the fall of 2006 where widespread infection on cantaloupes, honeydews and other melons cost growers a significant portion of their crops. USDA statistics suggest that fall melon yields in Arizona have declined considerably compared to years before the virus was introduced into the state. Without question, yields and quality in desert melon crops have suffered as a result of CYSDV infection. Additionally, melon pest management has been effected by CYSDV as insecticide usage on fall melons has increased significantly since 2006. Over the past six years we have been studying the virus and trying to understand its epidemiology and impact on fall melon production. In addition, we continue to develop new information on control of the vector of CYSDV (Bemisia whitefly adults). Whitefly numbers this spring and summer have been relatively light and the incidence of CYSDV on spring melons was relatively low. However, how this translates into virus incidence this fall is anybody’s guess. Given the aggressive management programs that PCAs and growers are now using, it will be interesting to see how CYSDV impacts melon production this fall. Our research to date suggests that fall melons produced near cotton or near areas where melons were produced the previous spring are at a high risk of infection. When possible, growers should attempt to isolate fall plantings as far away as possible from these sources of whiteflies and CYSDV. Growers forced to plant fall melons near these crops should be vigilant in minimizing adult whitefly infestation levels during pre-bloom growth stages. To view a summary of our research that details our findings visit our report on the Area-wide Incidence of Whiteflies and CYSDV in Yuma County, 2007-2012.

Remember: “ When in Doubt…… Scout”

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To contact John Palumbo go to: jpalumbo@ag.arizona.edu

Further Comments on Summer Preplant Soil Flooding as a Management Tool for Sclerotinia Lettuce Drop

As stated last time, research studies revealed that a 3-week period of field flooding during the hot summer months of July and August proved to be an effective cultural means of controlling Sclerotinia lettuce drop in future lettuce plantings, as this procedure destroyed all sclerotia of Sclerotinia minor and S. sclerotiorum in soil. During 2011 and 2012, over 4,200 and 3,600 acres, respectively, were subjected to preplant soil flooding in the Yuma Valley. However, some negative effects of this practice have been noted in certain circumstances. One concern is the rising of the ground water table, particularly in areas already affected by high ground water. Also, in certain areas in the Yuma Valley, damage to the open drainage system has occurred as a result of erosion of the sides of earthen drains. These concerns have led to the initiation of additional field research at the Yuma Agricultural Center to further define the method of water delivery and the duration of soil wetness required to destroy sclerotia of Sclerotinia minor and S. sclerotiorum. The goal of this research is to achieve destruction of the Sclerotinia lettuce pathogens in soil with the least amount of water possible. The research trial this summer will tell us if this is possible. Although summer soil flooding may not be appropriate for all ground planted to lettuce, this cultural practice can be an effective component of an integrated management program for lettuce drop.

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To contact Mike Matheron go to: matheron@ag.arizona.edu.

Herbicides for Ground Preparation in Lettuce

Because there are so few selective herbicides registered for use in lettuce, it is necessary to kill as many weeds as possible prior to planting. Fumigants, flooding and solarization will kill weed seeds but it will be necessary to germinate them first for most herbicides to be effective. Almost any herbicide can be used preplant that is registered for “fallow” conditions as long as the preplant and preharvest intervals are observed. The following table summarizes the most commonly used herbicides for ground preparation in lettuce.

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To contact Barry Tickes go to:btickes@ag.arizona.edu.

The Vegetable IPM Updates Archive page provides links to updates from previous weeks.

The Vegetable IPM Video Archive page contains a collection of educational videos from current research work in vegetable crops by University of Arizona Researchers.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.