In this issue

Welcome to the 2002 Vegetable IPM Newsletter!

New Publications for 2002

Potato or Aster Leafhopper?

Weed Identification

Herbicide Application Checklist

Irrigation Scheduling "Software" Available

Potato or Aster Leafhopper?

Bill Hutchison, Dept. of Entomology, University of Minnesota, St. Paul, Minn.

Up until May 22nd much of our spring weather has been dominated by high pressure systems bringing cool (cold) air from the north and northwest. Dominant high-pressure systems have delayed much of the insect migrations from the southern and gulf-coast states that we typically see in the spring. However, about 2½ weeks ago, we did have some warm weather from the south, which was likely responsible for an increase in Aster Leafhopper (ALH), Macrosteles quadrilineatus, commonly found now in alfalfa throughout southern Minnesota, and likely to be in carrot fields with young plants emerging. To date, the only Potato Leafhopper (PLH), Empoasca fabae, was a recent catch on May 21st by MDA personnel in Filmore County (SE Minn.). Two primary reasons we may receive more ALH or PLH in any given migration event is that each leafhopper has different overwintering sites across the southern and southeastern U.S., and different southerly winds patterns may originate in overwintering regions that favor one species over the other.

Correct identification is critical. For both vegetable and alfalfa growers, it is critical to distinguish the two species. Aster leafhopper can readily be distinguished from PLH by the 6 black spots across the head, between the compound eyes; ALH is also dark or olive green in color (see photo). In contrast, PLH has mostly white eyes, with white markings between the eyes, and is bright green in color (see photo).

Aster leafhopper adult

Potato leafhopper nymphs (left) and adult (right) (Michigan State University)

Vegetable Crops. Aster leafhopper is a primary pest of carrot, celery, lettuce, and occasionally potato, because it vectors a phytoplasma known as aster yellows. In carrot, excessive damage includes the adventitious root hair growth, and a bitter taste (see photo). In lettuce and other crops, leaf tissue turns yellow or is discolored. Insecticidal control is required to minimize adult infestations and keep diseased plants to a minimum. In most years, only 3-5% of the early-season adults will carry the phytoplasma, but this is usually enough to vector the aster yellows disease and cause considerable damage.

ALH Action Thresholds for Vegetable Crops. ALH Action Thresholds for Vegetable Crops. The most common way to monitor ALH is with a standard 15" diam. sweep net; nylon mesh nets, however, are much better than cloth. The following thresholds have been developed with the following assumptions in mind. It takes about 3 weeks for the aster yellows organism to "incubate," before the leafhopper can effectively transmit the disease to plants. Also, some crops are more susceptible than others. Although we cannot always know the exact percentage of adults that are infective at any given time, pervious experience suggests that a reasonable assumption is 2.5-5% of the leafhoppers are vectoring the disease. Treatment thresholds are summarized in the following table.

Carrots infected with aster yellows

Alfalfa. Aster leafhopper is not a concern in alfalfa, and fields should NOT be treated when this is the primary species present. Specifically, very little if any Minnesota alfalfa will need to be treated, during the first (current) crop for PLH. Alfalfa will also be approaching harvest before economic insect damage will occur. It will be best for growers to watch the regrowth of the 2nd crop for potential damage from PLH, weevil larvae and/or cutworms.

For more information on each leafhopper, please consult the following fact sheets, located at the VegEdge Web site, at:

Potato Leafhopper
Aster Leafhopper

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Cindy Tong, Department of Horticulture, University of Minnesota, ctong@extension.umn.edu
Production Editor: Suzanne Wold, Research Assistant, University of Minnesota, woldx018@tc.umn.edu

Disclaimer
Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer

Last Revised May 30, 2002.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer.©2002 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.