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March 2nd 2014 Vegetable IPM Updates
Insect Management
Weed Science
Insect Management:

Whitefly Management on Spring Melons

Whitefly populations are becoming abundant on spring melon crops throughout the region. In addition, there appears to be a higher number of late planted melons this year which can be a magnet for whiteflies later in the spring. As temperatures continue to increase on maturing crops, feeding damage from whitefly nymphs should be a primary concern on all melon types. Honeydew and sooty mold contamination on fruit of cantaloupes, mixed melons and watermelons can significantly reduce quality and marketability. Although whitefly numbers have been low up to now in a number of locations, PCAs should not be complacent in their
monitoring and sampling. With the warmer weather, numbers are likely to increase rapidly in the next few weeks. Our research has shown that to prevent melon yield and quality losses, a foliar insecticide treatment should be applied when on a threshold of 2 adult whiteflies per leaf is exceeded when averaged across an entire melon block. By timing sprays based on the adult threshold, immature populations should just be starting to colonize and applying foliar sprays at this stage in population development has been shown to significantly reduce the chance of yield / quality loss during harvest. This threshold applies for the use of recommended IGRs (Vetica, Courier, Knack, Oberon), and foliar applied neonicotinoids (Assail, Venom, Scorpion). For more information, go to these documents on 1) IPM and Whitefly Management 2) Whitefly Action Thresholds and 3) Whitefly control options Also, be aware of pollinators in or around melon fields. Carefully read labels to determine the products bee safety before applying any pesticide in melon fields, particularly when bees are foraging. Note: Cucurbit Yellow Stunting Disorder Virus (CYSDV) is not generally known to be yield limiting on spring melons. However, research to date suggests that fall melons may be at greater risk of CYSDV infection when planted in areas where CYSDV symptoms were found on late spring melons. Thus when practical, it is advisable to keep whitefly populations low on spring melons. This will also reduce dispersal to cotton other alternative crops and weeds later in June and July.

Remember, When in Doubt . . . . . “SCOUT”

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Gray mold

The disease gray mold can occur on lettuce and onion crops in the desert southwest. Botrytis cinerea, the fungus that causes this disease, produces an easily recognizable grayish fuzzy growth on affected plants when humidity levels are high. Although invisible without magnification, profuse amounts of spores are produced by the gray growth and dispersed in the air. When favorable temperature and humidity levels exist, spores landing on senescent or damaged lettuce or onion tissue will germinate and grow into healthy plant leaf and stem tissue, leading to potential plant collapse and death. This outcome on lettuce is similar to that caused by Sclerotinia minor and S. sclerotiorum, the causal agents of lettuce drop. Botrytis and Sclerotinia are related fungal pathogens; however, the visible mycelial growth of Sclerotinia on plants is white. Fungicides effective against Sclerotinia are usually active against Botrytis as well. As with Sclerotinia, fungicide applications for Botrytis management are beneficial when plants are treated before the appearance of fungal growth and disease symptoms.

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Weed Science:

Adsorption of Glyphosate to Soil Particles

Can soil from fields treated with glyphosate injure crops that it is wind-blown onto? This question comes up every year. The answer is that it is unlikely. Glyphosate binds strongly to soils, especially those that are fine textured. Glyphosate is a systemic herbicide and it must be absorbed into the plant to work. If it is bound to soil it is no longer active. This is still the case if treated soil is deposited onto the foliage. Dirty water that contains soil particles also reduces the activity of glyphosate. We have conducted trials in the greenhouse where we blew treated soil unto foliage and seen no symptoms. This is not the same for all herbicides. Oxyfluorfen (Goal, Galigan), for instance, does not adhere well to soil and it can “lift off” readily from the soil with water and injure crops it comes in contact with.

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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.

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