The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released Aug. 9, 2011.

IPM guidelines for beet armyworm in lettuce

By John Palumbo, UA Research Scientist and Extension Specialist

The beet armyworm, Spodoptera exigua, is a major pest of leafy vegetables grown in the Desert Southwest. Typically, beet armyworm populations infest newly planted fields soon after plants emerge in early September and can remain heavy through early November under favorable weather conditions.

Fortunately for local pest control advisers (PCAs), several insecticide alternatives are available that provide excellent residual activity on this pest. Many products have different modes of action (MOA) that can be alternated throughout the growing season. The rapid development of resistance by beet armyworm to insecticide compounds should not readily occur.

However, if an insecticide compound, or products with the same MOA, are used repeatedly for beet armyworm control in the same field, the risk of resistance increases significantly.

This is particularly important with the Diamide group of insecticides (IRAC group 28) because the products can be applied as foliar sprays and soil injections, and because there are currently six Diamide products labeled in leafy vegetables with the same MOA (Coragen, Durivo, Voliam Xpress, Voliam Flexi, Synapse and Vetica).

Applying these Diamide products to the soil at planting, and applying them as foliar sprays in the same field, can expose multiple generations of beet armyworm to the same MOA. That is not a good way to use these products to remain effective for more than a couple of years.

Since the Diamides, as well as the other products currently available (Radiant, Proclaim, Intrepid, Avaunt), are critical to effective management of beet armyworm and other Leps in leafy vegetables, PCAs should consciously avoid the overuse of these compounds.

The most effective way to delay the onset of resistance by beet armyworm in leafy vegetables is to consider the recommendations provided in the guidelines recently prepared entitled Insecticide Resistance Management Guidelines for Beet Armyworm in Lettuce.

Contact Palumbo: (928) 928-782-3836 or jpalumbo@ag.arizona.edu.

Plant disease resistance

Plant disease resistance

By Mike Matheron, UA Extension Plant Pathologist

Plants can be resistant to many potential pathogens, but just how is this resistance accomplished? One method is the use of physical defense.

Just as our skin provides a physical barrier preventing movement of microbes into the body, the cuticle or surface covering on plants serves the same function. Many plant pathogens must adhere to the plant surface for a given time to penetrate into the plant and cause infection.

This ability to colonize plants may be disrupted by the amount of wax present and the quality of the cuticle that covers plants. Waxes prevent the formation of a film of water on plants which is essential for the deposition and growth of bacterial and fungal pathogens on plants.

Abundant plant hairs can perform a similar water repellency function. Cuticle thickness and toughness of epidermal cell walls play an important role in the resistance of plants to several pathogens.

This form of disease resistance can be circumvented by wounds. Many pathogenic bacteria and fungi enter plants only through stomata or other natural openings. The structure and size of the openings can greatly affect the ability of some pathogens to invade plants. These physical plant attributes, that are present before exposure to potential plant pathogens, play an important role in the plant’s ability to resist many diseases.

Without the presence of these physical barriers, plants in general would be susceptible to infection by many more plant pathogens than they are now.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.

Vegetable herbicide formulations

Vegetable herbicide formulations

By Barry Tickes, UA Area Agriculture Agent

While there have been few new herbicides developed for vegetables over the past 20 years, new formulations of old products have slowly become available. Some of the new formulations have been developed after active ingredients came off patent as a means of differentiating and improving new products.

Five of the most notable vegetable herbicides with new formulations are Kerb, Dacthal, Prowl, Goal, and Select. For the first time since Kerb 50W was registered in 1964, the product will be available as a liquid suspension concentrate. This formulation contains 3.3 pounds of Pronamide per gallon. 1.25 pints to 2.5 pints is equivalent to 1.0 to 2.0 pounds of the old 50W. Otherwise the label is the same.

Dacthal (DCPA) was first registered as a 75WP (wettable powder) in 1958. A flowable formulation was first sold about 10 years ago. The flowable contains 6 pounds of the active ingredient per gallon and 1.0 pint of the 6F is equivalent to 1.0 pound of the old 75WP which is still available.

Prowl was first registered in 1975 as an emulsifiable concentrate. A water-based encapsulated formulation (H2O) was developed and registered about seven years ago.

The active ingredient, Pendimethalin, of the H2O formulation is encapsulated in a polymer coating that swells and ruptures when diluted with water. It requires much more agitation to stay in suspension than the EC formulation. The original formulation contains 3.3 lbs. of active ingredient per gallon while the H2O formulation is a little more concentrated and contains 3.8 pounds per gallon.

Goal was first registered in 1979 as an emulsifiable concentrate. A water-based flowable formulation, GoalTender, was registered about five years ago.

This newer formulation has increased crop safety and less potential “lift-off” from codistillation with water. The older 2XL formulation contained two pounds per gallon of the active ingredient pronamide while the newer formulation contains four pounds per gallon and requires half the rate of the 2XL.

Select was first registered in 1991 as an emulsifiable concentrate. It was registered at the same time in California as Prism. Select contained two pounds per gallon of the active ingredient clethodim and required half of the rate of Prism which contained one pound per gallon. Several other formulations became available when this product came off of patent that contained one to two pounds active ingredient per gallon.

Select Max was registered about five years ago. This product contains one pound per gallon of active ingredient and does not require the addition of a crop oil concentrate adjuvant required with the other formulation.

Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu.

Question of the week

Weed science: how do plant growth regulators kill weeds?

A). Contact

B). Systemic Activity.

C). Ask Barry: video