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

EPA to cancel endosulfan in vegetables, melons

By John Palumbo, Research Scientist and Extension Specialist, UA Yuma Agricultural Center (YAC), Yuma, Ariz.

The Environmental Protection Agency (EPA) has announced plans to end all uses of endosulfan in the United States.

EPA believes endosulfan, an organochlorine first registered in the 1950s, poses unacceptable risks to agricultural workers and wildlife. The agency is currently working out details with the manufacturer to voluntarily phase out endosulfan use over the next several years while considering growers' needs.

Details on EPA’s proposed actions are available at: www.epa.gov/pesticides/reregistration/endosulfan/endosulfan-cancl-fs.html.

This action could ultimately have a significant effect on Arizona vegetable and melon growers because of the cost-effective insect control benefits provided by the timely use of endosulfan.

Endosulfan has a particular niche in local vegetable IPM programs because of its broad spectrum, quick knockdown contact activity against the adult life stage of several insect species including whiteflies, aphids, thrips, flea beetles, bagrada bugs, and other minor pests.

Although many new reduced-risk alternatives (i.e., Radiant, Movento) have become available over the past several years, most of the active ingredients have very narrow activity against specific insect species (Leps or aphids/whiteflies) and life stages (immatures).

Products including the pyrethoids, neonicotinoids, Lannate, Vydate, MSR, and Orthene will be likely alternatives to replace current endosulfan uses in vegetables and melons.

Endosulfan will be particularly missed in the desert on fall melons, where to date endosulfan combinations have provided the adult whitefly control necessary to reduce cucurbit yellow stunting disorder virus infection.

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

Summer pre-plant soil flooding for lettuce drop management

By Mike Matheron, UA Extension Plant Pathologist, YAC, Yuma

The two fungi that cause lettuce drop, Sclerotinia minor and Sclerotinia sclerotiorum, carry over in fields between lettuce crops as structures called sclerotia. These “seeds” of the fungal pathogens remain dormant in the soil until germination in cool moist soil and infect lettuce plants.

Many of the sclerotia decay naturally over time. More than enough can remain in a field after one or more years to cause lettuce drop when the crop is planted. If virtually all sclerotia in a field could be rapidly destroyed, then this field would no longer be a source of the lettuce drop pathogens.

This is where summer pre-plant soil flooding comes in. Past research trials conducted at the UA YAC demonstrated that a three-week period of flooding in the summer completely destroyed all sclerotia of S. minor and S. sclerotiorum present in soil.

Some growers in the Yuma area have used this procedure to successfully control lettuce drop in fields chronically affected by this disease. For more information on this topic, read the complete research paper published in Plant Disease, Vol. 89, Number 1, 2004.

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

Herbicide resistance

By Barry Tickes, UA Area Agriculture Agent, YAC, Yuma

Arizona is one of only four states in which no cases of herbicide resistance have been confirmed. All of the surrounding states, including California’s Imperial Valley, have confirmed cases of herbicide resistance which is a source of growing concern.

Weeds inherit characteristics that determine how they will likely respond to herbicides. When a weed species is treated and not controlled and never has been, we say that it is tolerant to that particular herbicide.

On the other hand, when a weed species is controlled by a herbicide we say that it is susceptible to that herbicide. It is when weed species change from susceptible to tolerant that we say that they may have developed resistance to the herbicide.

The resistance of littleseed canarygrass to some of the ACCase Inhibitor herbicides, including Poast, Select, Fusilade, and generics of these, has been confirmed in the Imperial Valley. Poor control of Canarygrass and Rabbitsfootgrass from Poast has been reported in a few fields in the Yuma area in recent years, although resistance has not been confirmed. We hope to evaluate this further next season.

Weed populations may look uniform but in fact are very diverse on a genetic level. Resistance to a particular herbicide occurs when there are naturally occurring variants of weed species that are tolerant.

Two important principles include:

1 - Tolerant variants are not caused by the herbicide but occur naturally; and

2 - Individual weeds do not change to become resistant, rather the weed population changes to become resistant over time.

If the same herbicide is used continuously for a prolonged period of time, the susceptible biotypes will die out while the resistant biotypes will survive and reproduce, passing on the resistance to the next generation.

More information on the current state of herbicide resistance can be found online: www.weedscience.org/In.asp.

Contact Tickes: (928) 782-3836 or btickes@ag.arizona.edu.