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Vegetable IPM Updates Archive
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How to Interpret Test Results Conducted to Evaluate Herbicide Injury in Lettuce (Oct. 5, 2011)

There are three major herbicides that have been used in the production of lettuce in Arizona for the past 40 years. Kerb, Balan and Prefar are used alone or in combination on almost every acre of lettuce grown in the state. The three are all preemergence herbicides that work by inhibiting root growth in developing seedling weeds. Under some conditions, all three can produce crop injury that ranges from slight stunting and chlorosis to death. Symptoms of crop injury are marginal chlorosis, stunting, irregular development of the coteledon and early true leaves and inhibition of both the primary and lateral roots. Other factors can cause crop injury and produce similar symptoms. These include salt and nutrient toxicity , saturated soils, environmental stress from cold, heat, wind, disease and other factors. Symptoms of herbicide injury are sometimes confused with the symptoms caused by these other sources of injury. The most common diagnostic tool used to evaluate herbicide injury in lettuce is to take soil and or tissue samples from the effected field and have them run by a laboratory. Most laboratories use gas chromatographs (GC) and liquid chromatographs (HPLC) for analysis. Standard extraction and detection methods are costly but accurate and precise. Once results are obtained, however, there have been no guidelines available to interpret what they mean. The method most often used to evaluate if reported levels are toxic has been to compare results from injured and uninjured areas in a field. If levels are significantly different between the two, it can indicate possible herbicide injury. This method is relative, imprecise and sometimes misleading. We conducted a project to establish quantitative guidelines for evaluating herbicide injury in lettuce. To access the project and the results with guidelines click: Herbicide Injury In Lettuce.

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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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