Carrots XXVIII – 1

Leafhoppers/Aster Yellows

Whitney S. Cranshaw and Michael J. Brewer

leafhopper adult.

Identification (and life cycle/seasonal history)

Several leafhoppers, primarily aster leafhopper, transmit aster yellow disease. Leafhoppers do not overwinter well in our region. When occasional late season damage and disease transmission occurs, it is the result of northerly migrations of adults into our region, and the generation that is produced from this migration. During heavy flights of infected leafhoppers, disease transmission can be high. Eggs are laid in stems. Both immatures and adults suck plantsap from leaves and stems. They are generally small (less than five millimeters (¹/₄ inch) in length. The wings are held arched over the back.

Plant Response and Damage

Leafhopper immatures and adults suck the sap from their host plants. During feeding, infected insects, principally aster leafhopper, can transmit aster yellows disease. Transmission of this disease to carrot results in hairy roots and leaves that are bunchy and miscolored. Infection typically occurs in late July through August.

Cultural Control

As a supplement to other control strategies, removing weed hosts along field edges can reduce the number of leafhoppers in the area. Also, carrot cultivars vary in their susceptibility to the disease.

Biological Control

Winter mortality is a principal mortality factor of leafhoppers in our region.

Chemical Control

Leafhopper control can reduce the incidence of aster yellows. During heavy flights of infective leafhoppers, repeat applications at short intervals may be needed. Insecticidal coverage can be terminated two weeks prior to harvest since symptoms of the disease require 10 to 14 days to develop on carrots.

Product list for leafhoppers:
Insecticide	Product per acre	Preharvest Interval, remarks
Lannate 90S^RLannate L^R	0.5-1 lb 2-4 Pt	(1 day) Carbamate insecticide (methomyl). 48 hour reentry interval proposed. Not registered for chemigation.
Asana XL^R	5.8-9.6 fl oz	(7 days) Proposed 24 hour reentry interval. Has given superior control of aster yellows in University trials. Pyrethroid insecticide (esfenvalerate). Ground application only. Some rotation restrictions with root crops.
Baythroid 2^R,1	1.6-2.8 fl oz	0 days. Pyrethroid insecticide. Maximum 5 applications per season, with minimum 7 day intervals between treatments.
Thiodan 50W, Thiodan 3EC ^1,2	1 - 2 lb	7 days.  Do not use tops for food or feed.  One application per year.
^RRestricted use pesticide. ^1Labeled for chemigation  ^2Generic active ingredient, several formulations.
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

Categories: Carrot, Leafhoppers, Aster yellows, Insects

Date: 08/19/2002