The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released April 3, 2013.

Insecticide modes of action

By John Palumbo, UA research scientist and Extension specialist

With the 2012-2013 produce season winding down, the melon season is getting started. Now is a good time to review the insecticide chemistries commonly used on desert crops to control insect pests.

Sustaining insecticide efficacy to annually provide pest control advisers and growers with cost effective crop protection requires a conscious effort to prevent insecticide resistance.

Over the past 20 years, the agrichemical industry has developed and brought to the market an unprecedented number of new chemistries which are highly effective, selective, and safer than chemical predecessors. These include the neonicotinoids, spinosyns, tetramic acid derivatives, and diamides.

However, the development of new chemistries has slowed a bit. Older chemistries are continually phased out of the marketplace. Endosulfan was lost last summer.

It is imperative to sustain the efficacy of newer integrated pest management (IPM) tools currently available which makes insecticide resistance management (IRM) more important than ever.

The most fundamental approach to IRM is to minimize the selection of resistance to any one type of insecticide.

Historically, alternating or rotating compounds with different modes of action has provided sustainable and effective IRM in this desert cropping system.

The Insecticide Resistance Action Committee (IRAC), a coordinated crop protection industry group, was formed to develop guidelines to delay or prevent resistance.

Using their most recent IRAC MoA Brochure, the UA created a table which provides Insecticide Modes of Action on Desert Produce and Melon Crops. It also provides general information on the route of activity and pest spectrum for each chemistry.

These classification lists provide an additional set of guidelines for the selection of insecticides for use in desert IPM programs.

Click link to listen to John.

“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or

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Powdery mildew

By Mike Matheron, UA Extension Plant Pathologist

Spring is a time of transition for agriculture in the Desert Southwest. The cool season crop harvest is wrapping up. Spring and summer crops are planted and grown.

This is also powdery mildew season.

Powdery mildew can develop on commercial crops, including late-season lettuce, wheat, melons, and landscape plants. It is not too early to consider management options for powdery mildew on melons.

The disease generally is favored by dry weather conditions, moderate temperatures, reduced light intensity, fertile soil, and succulent plant growth. The overall risk of powdery mildew increases as more of these factors are established in a melon field. Dry weather conditions and fertile soil are givens in desert melon production fields.

Spores of the melon powdery mildew pathogen, Podosphaera xanthii, can germinate to initiate disease at temperatures ranging from 72-88 degrees Fahrenheit, and optimally at about 82 degrees F.

These moderate temperatures, plus reduced light intensity and succulent plant growth, become increasingly prevalent as melon plantings grow rapidly during April and May.

Another factor to consider when determining powdery mildew risk is the inherent susceptibility of the melon cultivar grown. Varieties known to be susceptible to powdery mildew require the implementation of a rigorous disease management program involving applications of fungicides with differing modes of action throughout the high disease risk period.

On the other hand, melon varieties with moderate to high levels of genetic resistance to the pathogen require less fungicide inputs.

To achieve maximum levels of disease control, powdery mildew fungicide application programs must be initiated before the visible detection of the fungus. Less than optimal but good levels of disease control can also be achieved by waiting to begin fungicide applications until no later than the very first sign of disease in the field.

These initial infection sites are often on the underside of leaves. Frequent and comprehensive examination of the melon planting is required.

Click link to listen to Mike's Update.

Contact Matheron: (928) 726-6856 or

Weed control in fall vegetables begins now

By Barry Tickes, UA area agriculture agent

It can be a challenge to selectively control weeds in vegetables with the limited number of herbicides currently registered on specialty crops. Producers have the next 5-6 months to control the bank of weed seeds which can be a problem after fall vegetables are planted.

This involves keeping weeds in the current crop from producing seed and extends through the summer crop or fallow period.

Much of the wheat and cotton in the field now will be followed by vegetables. There are more herbicides registered for use in cotton than for any other crop grown in Arizona.

With proper management, weeds should not be a problem.

The herbicides available for use in wheat and barley are more limited, although tools exist to control most common weeds in these crops. Nonetheless, we get calls about this time of year on what can be done now to control weeds that should have been treated earlier.

At this point, it is usually necessary to wait until wheat is maturing before applying preharvest treatments to desiccate weeds which are green, contain too much moisture, and reduce grain quality.

There are herbicides registered for preharvest use after the grain is in the hard dough stage and contains less than 30-percent moisture. These include systemic herbicides, including glyphosate and some PGRs; and contact herbicides, including Aim, ET, Gramoxone, bromoxynil, and others.

Not all of these products are registered in this area so labels should be checked.

Fallowed periods before vegetable planting offer an excellent opportunity to control weeds which cannot be selectively controlled after the crop is planted. Depending on the length of time the field will be fallow, almost every weed can be controlled. Even difficult perennial weeds, including nutsedge, can be controlled at this time.

The Eptam-fallow technique is an example of an effective and affordable treatment if 40-60 days are available. Non-chemical treatments, including flooding and solarization, are effective in weed and disease control.

At the very least, weeds can be germinated and disked to reduce the seed bank prior to planting.

Click link to listen to Barry.

Contact Tickes: (928) 580-9902 or

Future meetings

Lettuce insect, disease, and weed loss workshop - April 17, 12:00 -2:30 p.m., Yuma Agricultural Center, 6425 W. 8th Street, Yuma, Ariz. Click link to see the Agenda.

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