Alfalfa X-17

Potato Leafhoppers

Michael J. Brewer, Frank B. Peairs & Jay D. Donahue

Potato leafhopper adult.

Identification (and life cycle/seasonal history)

The potato leafhopper occasionally damages alfalfa in our area. They feed on weeds during the early spring, and then adults fly into alfalfa fields where several generations may be completed during the rest of the growing season. Adult leafhoppers are green, wedge shaped insects about 1¦8 inch long. Immature leafhoppers are shaped similarly, but are smaller and do not have fully developed wings. Adult leafhoppers are quite active, usually jumping or flying away when disturbed.

Plant Response and Damage

Leafhoppers feed on plant sap at leaf tips. A toxin is introduced into the plant during feeding, causing small yellowish or purple triangular areas. Heavy infestations may cause leaves to become curled or stunted, and can cause "hopper burn," in which the whole stand is yellowish and stunted. Seedling plants may die under heavy attack by leafhoppers. Leafhoppers are usually more abundant during second and third cuttings, but do not economically damage alfalfa every year.

Management Approaches

Cultural methods

Harvest will kill the egg and small nymphal stages of potato leafhopper, so can be used in place of chemical control if the alfalfa is taller than 12 inches or is approaching bloom. Surviving leafhoppers will often be few enough that populations do not build to economic levels after cutting.

Host plant resistance

Some varieties are moderately resistant to leafhopper feeding, and if acceptable otherwise (in terms of agronomic superiority and disease resistance), can be planted in place of non-resistant varieties.

Biological control

Natural enemies of potato leafhoppers do not suppress leafhopper populations satisfactorily during outbreak years.

Chemical control

Sampling/Surveying/Timing of sampling

Plants should be inspected for signs of leafhopper feeding, looking for chlorosis at the tips of individual leaflets. Newly established stands should be scouted vigorously if leafhoppers are present in older fields. Using a standard (15 inch diameter) sweep net randomly through the field, the following treatment thresholds are recommended.

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Table X-6. Treatment threshold for potato leafhoppers.

Alfalfa height (inches)	Average number of potato leafhoppers per sweep
0-3	0.2
3-6	0.5
6-12	1.0
12 or taller1	1.5
1early harvest should be considered in place of insecticides at these heights, or if bloom is approaching (See Cultural methods, above.)

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Product List for Potato Leafhopper:

Insecticide	Product per Acre (Fl oz. or oz. product)	Preharvest Interval, remarks
Baythroid XLR,1	0.8-1.6	7 days.  Extremely Hazardous to Bees!
carbaryl1,2	See labels	7 days. Most formulations are Extremely Hazardous to Bees! Do not apply to alfalfa in bloom. Sevin XLR+ is safe for bees if applied at <1.5 lbs ai/acre when no bees are in the field.
CobaltR1	7-13	7 days after application of 13 fl oz, 14 days after application of 26 fl oz, 21 days after application of rates above 26 fl oz per acre. Extremely Hazardous to Bees! Do not apply when bees are present.
dimethoate1,2	See labels	10 days (harvest, grazing). Extremely Hazardous to Bees! Do not apply to alfalfa in bloom. 1 application/cutting.
Furadan 4FR	16-32	14-28 days depending on rate. 1 applications/season. Extremely Hazardous to Bees! Do not apply to alfalfa in bloom. Check label for other restrictions.
lambda cyhalothrinR1,2	1.92-3.2	7 days.  Extremely Hazardous to Bees!
malathion2	See labels	0 days.  Hazardous to bees. Apply only during late evening.
Mustang MAXR,1	2.24-4.0	3 days.  Extremely Hazardous to Bees!
permethrinR,1,2	See labels	0 days for rate of 0.1 lb a.i. or less. 14 days for higher rates. No more than 0.2 lb a.i. per cutting.  Extremely hazardous to bees! Do not apply to alfalfa in bloom.
ProaxisR,1	1.92-3.2	7 days.  Extremely Hazardous to Bees!
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: Alfalfa, Insects, Potato Leafhoppers

Date: 5/20/2008