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March 2nd 2014 Vegetable IPM Updates
Insect Management
Weed Science
Some Videos to Check Out
Insect Management:

Whitefly Management on Fall Produce

Now that produce planting/transplanting is well underway, one of the first pests you’re likely to encounter is adult whiteflies. Given the high numbers found on spring melons and cotton this summer, one would also expect whiteflies to be heavy on fall produce crops. Surprisingly though, adult numbers have been lighter than expected on fall melons. For instance here at the Yuma Ag Center, whitefly populations in our experimental plots based on vacuum samples taken this week are lower than what we’ve encountered the past few years (see graph below). However, this appears to be site-specific as I’ve observed melon fields in the Wellton/Roll area with very high numbers this past week. This makes sense; whitefly population abundance can be influenced to a large extent by the crop landscape throughout Yuma. Crops planted near or adjacent to cotton and alfalfa are clearly more heavily infested than fields isolated away from these crops. In addition, our monsoon conditions often play a role where humidity and rainfall can influence population abundance. Nonetheless, you can bet heavy whitefly numbers will eventually show up in one of your fields. It is important that PCAs pay particular attention to early whitefly control on their newly planted produce crops. Prolonged feeding by heavy numbers of adults on seedling lettuce/cole crop plants can cause stunted plant growth. If you observe honeydew on leaves in the absence of nymphs then there are way too many adults on the seedling plants. There are likely too many eggs being laid as well. With the loss of endosulfan, growers have few options for effective residual control of adults, but good knockdown can be achieved on lettuce and cole crops with combinations of pyrethroids tank-mixed with Orthene, Lannate, Lorsban, Venom, Scorpion, or Sequoia. In addition, Exirel (the foliar formulations of Cyazypyr) was recently labeled for use on produce crops and can provide excellent adult control. Sometimes it can be difficult to determine whether a product is working 3-4 days following application when adult whiteflies are continuously moving into you field from outside sources. To assess adult control under heavy migrations, try monitoring young leaves for the presence of light-colored eggs (newly laid) using a hand lens. Absence of newly laid eggs can be an indication that adults are not actively feeding on leaves or are dying before they can lay eggs. Furthermore, allowing adults to remain unchecked on small plants generally results in the development of large nymph populations that can cause significant growth/yield reductions in all produce crops. It is strongly recommended that growers apply a soil insecticide on lettuce and cole crops throughout September and early October. Local research has shown that imidacloprid applied at 0.25 lbs AI/ac at planting provides less residual control of nymphs today than it did 10 years ago. However, given the current economics of imidacloprid, cost-effective whitefly control can still be achieved by using higher rates of imidacloprid (0.38 lbs. AI/ac) to extend residual control (e.g., Alias 2F-24 oz; Wrangler 4F-12 oz; Admire Pro- 10.5 oz). Verimark, the soil formulation of Cyazypyr, applied at 13.5 oz/ac can provide excellent control of nymphs when applied at planting similar to the neonicotinoids to lettuce and cole crops. Once plants get larger, products like Movento, Exirel, Venom, Scorpion, Assail, Knack and Courier/Vetica can provide effective control of nymphs. For more information on whitefly biology, management and insecticide alternatives see these reports: Whitefly Management in Fall Produce- 2014 and Insect Management on Desert Vegetables and Melons: Whitefly.
Remember, When in Doubt . . . . . “Call Barry Tickes”

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Plant Derived Chemicals as Disease Control Tools

Chemicals are indispensible tools in the continuing effort to minimize crop losses due to plant diseases. Various active ingredients within fungicides are especially useful for managing diseases caused by many fungal plant pathogens. Although often not recognized, various substances formed by plants and present before infection can enable plants to defend themselves against potential plant pathogens. The level of defense against potential plant pathogens can range from various levels of resistance up to outright immunity. A variety of chemical substances are present on the surfaces of plant parts such as leaves, stems, fruit, seeds and roots. Chemicals with antimicrobial properties include phenolic compounds, tannins and fatty-acid like materials. Experiments have shown that some of these compounds have an inhibitory action on certain plant pathogens. As an example, toxic exudates on leaves of a specific variety of sugar beet are present at a sufficient concentration to inhibit spore germination of certain fungal pathogens. Another compound in certain types of tomato plants was shown to impart resistance to powdery mildew by inhibiting spore germination. Additionally, proteins and enzymes on plant surfaces can inactivate pathogen enzymes that are essential for disease development. These preformed compounds, together with various types of structural plant disease defenses, often drive what we recognize as resistance to diseases in plants. Even if these plant derived chemical and structural disease defense systems are not sufficient to totally prevent disease, they along with disease management tools applied by growers contribute to the overall level of disease suppression obtained on a particular crop

Plant Disease Defenses
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Weed Science:

Adjuvants with Lettuce Herbicides

Adjuvant is a broad term for anything that is added to a herbicide that helps with performance or handling. Adjuvants can be added by the manufacturer for a variety of purposes such as improving solubility, shelf life, handling, compatibility, stability and other characteristics. Most people, however, think of an adjuvant as those products that they add to the spray tank. The most common type of adjuvants are surfactants or surface-active agents that are used to improve spreading and/or absorption of the applied solution. There are many other uses for adjuvants. These include deposition agents, drift control agents, anti foam agents, buffering agents, compatibility agents, water conditioners, tank cleaners and others. Rarely are adjuvants used with soil applied herbicides. There has been interest, however, in using adjuvants with two of the soil applied herbicides used in lettuce to improve weed control. The intent is to use an adjuvant to either increase the movement of Prefar down into the soil or to reduce the movement of Kerb too far into the soil.

Prefar (bensulide) is normally applied to the soil surface and incorporated with water. It adheres very strongly to the surface and can be difficult to move down to the germinating weed seed in many fine textured soils. Some growers and pest control advisers have used non-ionic surfactants, crop oil concentrates or other specialty adjuvants to improve movement into the soil and have reported improved weed control. Results of our trials have not demonstrated this however, and we have no reason to recommend these products.

Kerb (pronamide), on the other hand, does not adhere strongly to the soil and can often be leached below germinating weed seeds by irrigation water before they germinate. Adjuvants that are used to increase the adsorption of products to foliage and soil have been tested with Kerb to reduce leaching. Results of our trials have again not demonstrated any benefit to adding adjuvants to Kerb.
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To contact Barry Tickes go to:

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Check Out These Videos!

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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