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Vol. 17, No. 10
Article 4 of 10
May 25, 2007

Potato Leafhopper Numbers High in Some Alfalfa Fields
By Wayne Bailey

Potato leafhoppers are about 1/8-inch in length, wedge shaped and greenish-yellow in color. They are very mobile and quickly move sideways, jump or fly when disturbed. This is a native insect that migrates into Missouri each spring from more southern states and Mexico. The potato leafhopper is often transported into the state by early spring storms that move in a northeast direction. The leafhoppers are thought to fly into the storms and be carried great distances by low level winds which approach 100 mph. After a storm containing hail passes, high numbers of leafhoppers can often be found in their wake. In Missouri, the potato leafhopper adults generally arrive about May 5 of each year. The arriving adults may first feed on several tree species before moving to alfalfa to feed and reproduce. Two to three generations of potato leafhopper are often produced, and economic damage generally occurs on alfalfa following removal of first harvest. Damage is caused when both adult and nymphal (immature) leafhoppers use their piercing-sucking mouthparts to penetrate alfalfa leaflets and stems. They remove plant juices and often cause yellowing of established plants, stunted plant growth and mortality of seedling alfalfa. Both forage quality and quantity are reduced by this pest. This year, potato leafhopper adults were found in alfalfa very early with adults arriving sometime during mid-April. Similarly, Arkansas entomologists are reporting very high numbers of this leafhopper in the state. Elevated numbers of leafhoppers in Missouri and Arkansas along with early arrival in Missouri suggest potato leafhoppers may be a moderate to severe threat to alfalfa this year. Scouting is best accomplished using a 15-inch diameter sweep net. Take 10 pendulum sweeps at five random locations in the field. If the average number of potato leafhopper adult and nymphs per sweep reach or exceed the threshold numbers listed below, treatment is justified. The economic threshold for potato leafhopper in alfalfa depends on the height of the alfalfa and whether the alfalfa is a potato leafhopper resistant variety or a traditional alfalfa variety.

Economic Threshold for Potato Leafhopper in Alfalfa
Alfalfa Stem Length (inches)	Ave # PLH/Sweep (traditional variety)	Ave # PLH/Sweep (PLH Resistant Variety)
<3	0.2	0.6
6	0.5	1.5
8-10	1.0	3.0
12-14	2.0	6.0

Recommended Insecticides for Management for Potato Leafhopper Adult and Nymphs in Alfalfa
Chemical name	Common name	Rate of Formulated Material	Rate of Active Ingredient (a.i.)	Preharvest Interval
Beta-cyfluthrin	*Baythroid XL	0.8 to 1.6 fl oz/acre	0.0065 to 0.0125 a.i./acre	7 days
Dimethoate	Dimethoate	see specific label	0.25 to 0.5 lb a.i./acre	10 days
Carbofuran	*Furadan 4F	1 to 2 pts/acre	0.5 to 1 lb a.i./acre	14 - 28 days
Chlorpyrifos 4E	Lorsban 4E numerous products	1 to 2 pts/acre see specific labels	0.5 to 1 lb a.i./acre see specific labels	7 - 14 days 7 - 14 days
Malathion	numerous products	see specific labels	1 to 1.25 lbs a.i./acre	0 - 7 days
Methyl Parathion	*numerous products	see specific labels	0.5 to 1 lb a.i./acre	15 days
Zeta-cypermethrin	*Mustang Max	2.0 to 2.8 fl oz/acre	0.0125 to 0.0175 lbs a.i./acre	3 days
Permethrin	*numerous products	see specific label	0.1 to 0.2 lbs a.i./acre	7 - 14 days
Gamma-cyhalothrin	*Proaxis	1.92 to 3.2 fl oz/acre	0.0075 to 0.0125 lb a.i./acre	1 day forage 7 day hay
Carbaryl	Sevin 4F	1 qt/acre	1.0 lb a.i./acre	7 days
Carbaryl	Sevin XLR Plus	1 qt/acre	1. lb a.i./acre	7 days
Lambda-cyhalothrin	*Warrior	1.92 to 3.2 fl oz/acre	0.015 to 0.025 lb a.i./acre	1 day forage 7 day hay
Lambda-cyhalothrin	*Numerous products	see specific labels	see specific labels	1 day forage 7 days hay
Read and follow all label direction, precautions, and restrictions. * Designated a restricted use product.

Wayne Bailey
BaileyW@missouri.edu