Insecticide Usage in Head Lettuce, 2011-12

Our annual Lettuce Crop Losses Workshop was recently held in April and the results of the surveys reveal some interesting trends in insecticide usage on desert head lettuce. In general, the most commonly used insecticides in fall and spring lettuce correspond directly to the key pests that typically occur during these growing periods. When compared by class of chemistry using the IRAC mode of action classification system, the pyrethroids, applied both as foliar sprays and chemigations, were by far the most commonly used insecticide class (Tables 1, 2 and 3). This makes sense because they are one of the few inexpensive, broad spectrum insecticides still available for effective control of beetles, crickets and plant bugs. Nonetheless, over the past few years pyrethroid usage has been steadily declining, as has usage of organophospahates, and carbamates where Lannate and Orthene continue to be the primary compounds used in desert lettuce. The spinosyns remain the second most commonly used class of insecticides, where greater than 90% of the lettuce acreage was treated with Radiant and Success in 2011-2012. Their activity against both lepidopterous larvae and thrips make them a good fit in desert lettuce. The third most commonly used class of chemistry in fall and spring lettuce are the neonicotinoids driven primarily by at-plant, soil uses for sucking insects. Estimates this season showed that PCAs used generic imidacloprid and Admire Pro on a larger percentage of acres this season compared to last year. Estimates of Diamide usage (Coragen, Voliam Xpress, Vetica) showed that PCAs applied more of this chemistry in 2011-2012 than the previous season, and estimates further suggest that growers are slowly beginning to incorporate at-planting, soil uses of Coragen into their programs. Ketoenol usage (Movento) on fall lettuce was down compared to 2010, but usage as an aphicide on spring lettuce remains about the same. From an IPM perspective, the industry has made great strides in minimizing environmental impacts in lettuce production by continuing to incorporate the newer insecticides into their insect management programs. And for the second season in a row, PCAs treated a greater percentage of their acreage with selective, reduced-risk products than with the broadly toxic, older chemistries (pyrethroids, organophosphates, carbamates). To view a summary of the estimated insecticide usage by chemical class, as well as the 15 most commonly used insecticides on head lettuce during the past two growing season, go to Insecticide Use in Arizona Head Lettuce.

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Remember: When in Doubt-Scout.

To contact John Palumbo go to: jpalumbo@ag.arizona.edu

Fusarium Wilt on Melons

Fusarium wilt can occur in Yuma area melon fields and has already been detected in a melon planting this season. Symptoms of Fusarium wilt on melons are similar to Fusarium wilt diseases on other plants and include initial yellowing and wilting on one side of the plant or on one runner, followed by runner collapse. Internal discoloration of the xylem tissue at the base of the plant can occur as well. As the disease progresses, other runners will show symptoms and collapse, eventually leading to plant death. Fusarium wilt on cantaloupes and on watermelons is each caused by a specific form of the fungal pathogen Fusarium oxysporum. For cantaloupes and other melons classified as Cucumis melo, the relevant pathogen is Fusarium oxysporum f. sp. melonis; whereas the pathogen for watermelon (Citrullus lanatus) is Fusarium oxysporum f. sp. niveum. In general, Fusarium wilt severity increases when plants are stressed due to temperature extremes, heavy fruit loads, or other plant growth stress factors. The use of resistant cultivars is a useful disease management tool; however, the performance of a resistant cultivar can be affected by the inoculum level of the pathogen in soil. According to published articles, rotation out of melons for from three to 10 years, depending on the report, will significantly reduce but not eliminate the inoculum load of the pathogen in soil. There are numerous different forms of the Fusarium wilt pathogen, and each form has the capability of initiating disease on one or at most a few closely related types of plants. No worries about planting melons in a former lettuce field known to have had Fusarium wilt. The Fusarium wilt pathogen of lettuce Fusarium oxysporum f. sp. lactucae will not cause disease on melons.

To contact Mike Matheron go to: matheron@ag.arizona.edu.

How and Where To Drop Off Samples for Weed Identification and Herbicide Injury Evaluation:

It is difficult to solve a problem without first identifying what is causing it. We recognize that helping people to identify problems is an important part of our jobs and we spend much of our time collecting and analyzing samples. Most of the samples that we receive are for either weed identification or herbicide injury evaluation.

Although there are probably less than 50 common weeds in this region, there are hundreds more that occasionally turn up. We have been identifying weeds for many years but there are few weeks that we don’t see one that we are not sure about. Even the common ones can look significantly different when they are growing in different areas under different conditions. Weeds growing in the irrigated desert can have characteristics that complicate their identification. Annual weeds are normally classified as those that live during the summer or winter and then die. This distinction is often inaccurate in the low deserts of Arizona when weeds that are normally classified as summer annual weeds survive into the winter months under mild winter temperatures and frequent irrigations. It is not uncommon for some summer annual weeds to live for two years as biennials or even longer as weak perennials. Similarly, winter annual weeds can sometimes survive through the summer where they are shaded by a crop and receive frequent irrigations. One of the best resources for identifying weeds is by Joe DiTomaso that is two volumes, 900 pages, contains more than 750 species and is only $80. Click on the next link for more information on Weeds of California and Other Western States.

We also receive many herbicide injury samples and these can be even more difficult to accurately identify. There are more than 100 different active ingredients contained in herbicides used in this region. None of these produces crop symptoms that can’t also be produced by many other factors such as diseases, insects or other pests, nutritional problems, environmental stresses etc. Sometimes symptoms, patterns in the field or herbicide use history make diagnosis easy although often the only conclusive method to identify the problem is chemical analysis. This can be costly and time consuming but we send many samples to laboratories every year.

Processing weed identification and herbicide injury samples are an important part of our responsibilities. You can download the sample ID form or fill it out at the Agriculture Center when you drop samples off. Please let either Barry Tickes or Marco Peña know that you are bringing samples by and we will arrange to receive them. We are currently working on locating a refrigerator for sample drop off when no one is around to receive them.

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To contact Barry Tickes go to: btickes@ag.arizona.edu.

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.