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University of Arizona
March 2nd 2014 Vegetable IPM Updates
Insect Management
Weed Science
Insect Management:

Insecticide Usage on Desert Lettuce, 2016

Our annual Lettuce Crop Losses Workshop was held in April and the results of the surveys continue to show 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. Overall, the pyrethroids, applied as foliar sprays and sprinkler chemigations, were the most commonly used insecticide class. No surprise there. Over the past 12 years, pyrethroid usage has remained consistently high. Although the overall use of OP/carbamates continues to decline, Lannate (methomyl) usage was up on spring lettuce this season due to heavy thrips pressure. Along with acephate, these older compounds remain important rotational alternatives for Radiant. The spinosyns remain the second most commonly used class of insecticides, where greater than 95% of the lettuce acreage was treated with Radiant or Success in 2015-16. Their use against both lepidopterous larvae and thrips has remained steady over the past 12 years, averaging over 2 sprays per treated acre. Foliar uses of the Diamides (Coragen, Voliam Xpress, Vetica, Belt) were the third most commonly chemistry used in fall lettuce. Since they were first registered in 2008, PCAs have steadily incorporated this new chemical class into their Lepidopterous larvae management programs. The use of Belt increased significantly this season, whereas foliar uses of Coragen declined. Exirel and Verimark usage was reported for the first time in the fall 2015 on about 5% of the acreage. Use of the tetramic acid chemistry (Movento) on fall lettuce declined in 2015, but increased on spring lettuce (Figure 4) where it is an important tool for aphid management. The usage of imidacloprid on both fall and spring lettuce has increased markedly since 2009 and was used on about 80% of the fall and spring acreage. Foliar neonicotinoid usage decreased last season, whereas Sivanto (butenolide) usage increased slightly. Sequoia (sulfoxamine) usage was down in spring 2016 due to the recent cancellation of the label. Torac usage for thrips management was up significantly the season. Although the broad spectrum, consumer–friendly pyrethroids were by far the predominant chemistry applied to lettuce, for the sixth season in a row, PCAs treated a greater percentage of their acreage with selective, reduced-risk products than with the broadly toxic, OP and Carbamate chemistries. To view a summary of the estimated insecticide usage by chemical class, as well as the 15 most commonly used insecticides on lettuce this past growing season, go to Insecticide Usage on Desert Lettuce, 2015-16.


Name this Insect Pest. - Exposed Bird Dropping Moth

Remember, When in Doubt . . . . . “SCOUT”

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Fusarium Wilt on Melons

One of the diseases that can occur in desert melon production fields is Fusarium wilt. Symptoms on melons are similar to Fusarium wilt diseases on other plants, usually beginning as 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 be present as well. The xylem discoloration is usually light yellow to tan in color, not the dark reddish brown observed on lettuce. As the disease progresses, other runners will show symptoms and collapse, eventually leading to plant death. Fusarium wilt on cantaloupes and on watermelons is caused by two different specific forms 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 high temperature, heavy fruit loads, or other plant growth stress factors. The use of resistant varieties is a useful disease management tool; however, the performance of a resistant variety can be affected by the inoculum level of the pathogen in soil. According to various published research articles, rotation out of melons from three to 10 years can 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. Are you concerned about planting melons in a former lettuce field known to have had Fusarium wilt? Not to worry. The Fusarium wilt pathogen of lettuce (Fusarium oxysporum f. sp. lactucae) will not cause disease on melons.

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Weed Science:

Herbicides Registered For Irrigation Ditch Banks in Arizona

Weeds are a problem year after year even where they have been diligently controlled. A major reason for this is that weed seeds continually move into fields by irrigation water, wind, equipment, contaminated seed and other means. Controlling weeds on irrigation ditch banks can greatly help to reduce weed seed movement into fields. The EPA regards non-crop areas as those that are not dedicated to crop production. Although crops are not normally grown on irrigation ditch banks, these areas should not be managed as non-crop. Several very broad spectrum and long lasting herbicides are registered for non-crop areas which include roadsides, industrial sites, fence rows, around structures, railroads etc.. Irrigation ditch banks should be considered separately because of their proximity to crop fields and irrigation water and the potential for herbicide movement into sensitive areas. It is important to read herbicide labels carefully and only use those products that are specifically allowed for use on ditch banks. Some products are restricted to drainage ditch banks or dry ditches. Some can be used only above the water line and some can only be used for non-irrigation ditch banks. Because most ditches here are used for irrigation, this can be confusing. The definition of a ditch ,however, can include an open trench or natural channel. It can also include ditches that are not in use for long periods of time. Some labels specify how long this non-use period should be. Some herbicides must be leached with standing water in the ditch for a certain period of time. The following table “Herbicides Registered For Irrigation Ditch Banks in Arizona.” Specifies those herbicides that can only be used on drainage ditches or dry ditches and if they have soil residual or foliar activity. It does not include several premixes and there may be some other products available that are not listed.


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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.

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