Aster leafhopper in celery and carrot

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

A few aster leafhoppers have been caught recently in celery and carrot fields in Michigan. At this point, the numbers are very low and they are not likely to cause problems. Aster leafhoppers spread the disease aster yellows. The risk to a particular crop depends on the inherent susceptibility of the crop, the percentage of leafhoppers that carry the disease, and the number of leafhoppers present. To assess risk and determine whether an insecticide treatment is warranted, all three factors must be known.

The inherent susceptibility of a crop to aster yellows is fixed and is reflected by the aster yellows index; the lower the number, the more susceptible the crop. The aster yellows index for celery is 35, for lettuce it is 25 and for susceptible varieties of carrots it is 50. The number of aster leafhoppers can be assessed easily by taking sweep net samples. The last factor – the proportion of leafhoppers carrying the aster yellows disease – can now be determined with molecular laboratory tests. Diagnostic Services will be testing aster leafhoppers for infection with aster yellows again this year. Grant funds will be used to support limited testing of leafhoppers in a couple carrot and celery locations over the season. Results, including percent infectivity and suggested treatment threshold will be provided to growers and will be published in the Vegetable CAT Alert.

In addition, Diagnostic Services will test leafhoppers submitted by individual growers or crop consultants. The test requires a minimum of 45 leafhoppers. The cost ranges from $25 to $35 depending on the number of leafhoppers submitted (the more leafhoppers, the more reliable are the results). Vegetable Entomology will provide growers with results (percent infectivity) and suggested thresholds (the number of leafhoppers per 100 sweeps) and which insecticide application is warranted.

If you are interested in submitting aster leafhoppers for aster yellows infectivity testing, please collect at least 45 leafhoppers and place them in a plastic bag. The leafhoppers do not have to be kept alive. The sample can be delivered to Diagnostic Services or it can be mailed. If mailing a sample, please place the bag in a small, hard container such as a plastic dish used for food or a small cardboard box, and mail to: Diagnostic Services, 101 CIPS, Michigan State University, E. Lansing, MI. 48824-1311. Please include the following information with your sample: Date collected, crop collected from, name and contact information of person submitting the sample.

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