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

Insecticide usage in head lettuce

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

Results from the recent Lettuce Insect Losses Workshop reveal interesting trends in insecticide usage on Arizona head lettuce. Data was summarized from pest control advisers and grower surveys completed over the last six years.

When compared by the class of chemistry using the Insecticide Resistance Action Committee (IRAC) mode of action classification system, pyrethroids have consistently been the most commonly used insecticide class by far. Over the past few years the usage has declined only slightly.

In contrast, the next most commonly used class, spinosyns (Radiant and Success) was used on about half as many acres in 2010 and down significantly since 2005.

This is likely due in part to the recent registration of the diamides (Coragen, Voliam Xpress) which were treated on significant acreage in 2009 and 2010. Due to regulatory issues, Ketoenol usage (Movento) was down significantly in 2010 (~ 3 fold reduction) and was compensated by a large increase in neonicotinoid usage.

Overall organophosphate/carbamate/endosulfan usage has steadily decreased in the last few years due to regulatory issues and the availability of the new reduced-risk products.

To view the insecticide usage data for 2005-2010, click on this link: http://cals.arizona.edu/crops/vegetables/advisories/docs/LettuceInsecticideUsageData2010.pdf.

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

Melon powdery mildew

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

Heavy infections of powdery mildew have been reported in some melon fields in the Yuma Valley. This should be a warning to all melon growers in the area.

Spores of Podosphaera xanthii, the fungal pathogen that causes powdery mildew, germinate at temperatures ranging from 72-88 F. Once germination has occurred, the fungus grows on the plant and can begin to produce spores four days later, continuing to do so until the plant tissue dies.

This short generation time can lead to a rapid increase in disease when the plant canopy is well developed and the melon fruit is developing. Also, remember that by the time powdery mildew is seen in the field that many more emerging but invisible infections are already present.

Successful management of powdery mildew involves the initiation of a fungicide application program before or at the very latest at the very first appearance of powdery mildew.

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

Weed identification

By Barry Tickes, UA area agriculture agent, YAC, Yuma

It is important to accurately identify weeds when deciding upon a control strategy.

Most people use common names to identify weeds. Common names are any names that people have come up with to describe a particular weed. They sometimes invent their own names or apply the same name to different weeds. The use of common names often causes confusion.

There are exact names, however, for each particular species, which are established and governed by strict international botanic law. Although there are less than 100 weeds common in Arizona, hundreds more are potential problems.

“An Illustrated Guide to Arizona Weeds” lists 172 species while “Weeds of California and Other Western States” lists 750.

The illustrated guide can be accessed online at www.uapress.arizona.edu/onlinebks/weeds/titlweed.htm.

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