Potato leafhoppers are small bright green insects which migrate annually from the gulf coast to Kentucky on wind currents and can cause significant injury to alfalfa if left unmanaged. They do not normally impact the first cutting of established alfalfa stands; Infestations in later cuttings can stunt growth and reduce yields. The most common symptom of leafhopper damage is yellowing of the leaves, commonly referred to as “hopper burn.” Although nutrient deficiencies can also cause yellowing of the leaves, damage from leafhoppers can be distinguished by a characteristic inverted yellow “V” at leaf tip.
Scouting and Economic Thresholds
Determining leafhopper populations requires the use of a sweep net with a 16-inch opening and a 3-foot handle. Sampling is accomplished by quickly walking through the stand as 10 sweeps are collected in a back and form motion that grazes the top of the alfalfa canopy. Adult and nymph leafhoppers should be immediately counted. Sampling should be conducted in three to five areas of the field and then averaged. In general, if the number of leafhoppers collected in 10 sweeps equals the height of the alfalfa plant in inches, the economic threshold has been reached. For stands that are under high levels of stress, the economic threshold levels are lower. Conversely, stands that are vigorously growing and under lower levels of stress possess higher economic thresholds. If potato leafhopper resistant cultivars were used, economic thresholds are three times higher than those outlined in Table 1.
|Table 1. Economic thresholds for the control of potato leafhopper in non-potato leafhopper resistant alfalfa.|
|Alfalfa Height||Alfalfa Stress Level|
|inches||number of potato leafhoppers per 10 sweeps|
Adapted from R.B. Hammond, A. Michel, J.B. Eisley, and M. Sulc. 2014. Potato Leafhopper on Alfalfa. ENT-133, Ohio State University Extension, Columbus.
Insecticides for the Control of Potato Leafhopper
If the alfalfa stand is 7 to 10 days from harvest, treatment is NOT recommended. Following harvest, regrowth should be closely monitored for reinfestation. Insecticide recommendations on Table 2.
|Table 2. Insecticide recommendations potato leafhopper control in alfalfa.|
|Potato leafhopper Insecticides||Harvest or Graze Interval (days) and REI (hours)|
|Carbaryl ‐ Sevin 80 S, etc. Sevin 4F, etc.||May temporarily bleach tender foliage. 7 / (12 hrs)|
|Methomyl ‐ Lannate SP||7 / (48 hrs)|
|Chlorpyrifos ‐ Lorsban 4E, Chlorpyrifos 4E||Some temporary yellowing may occur. 1 pt ‐ 14 d/ (24); more than 1 pt ‐ 21d|
|Dimethoate ‐ Dimethoate 400, Dimethoate 2.67, Dimate 4 EC,||10 / (2 days)|
|Phosmet ‐ Imidan 70 W||7 / (5 days)|
|b‐Cyfluthrin ‐ Baythroid XL||7/ (12 hrs)|
|g‐Cyhalothrin ‐ Bolton, Declare, Proaxis 0.5 EC||Apply only to planted pure stands. 1 day forage, 7 day harvest (24 hrs)|
|l‐Cyhalothrin ‐ Warrior II||1 d ‐ forage, 7d – hay / (24 hrs)|
|z‐Cypermethrin ‐ Mustang Maxx||3 / (12 hrs)|
|Permethrin ‐ Ambush, Pounce 25 WP, etc.||Do not apply to intentionally mixed stands of grasses or legumes (more than 4 fl oz/a ‐ 14 d) / (12 hrs)|
|Pyrethrins ‐ PyGanic||0 / (12 hrs)|
|Idoxicarb ‐ Steward 1.25 SC||7 / (12 hrs)|
|Azadirachtin (26) ‐ Aza‐Direct, etc.||0 days (4 hrs)|
|Chlorpyrifos + l‐cyhalothrin ‐ Cobalt EC||7 / (24 hrs)|
|z‐cypermethrin + chlorpyrifos ‐Stallion||7/ (24 hrs)|
|I-Cyhalpthrin + Chlorantraniliprole – Besiege||1-forage, 7-hay / (24 hrs)|
|Always follow label recommendations.
Adapted from L. Townsend. 2017. INSECTICIDE RECOMMENDATIONS FOR ALFALFA, CLOVER, AND PASTURES – 2017. ENT-17, University of Kentucky Extension, Lexington. (http://pest.ca.uky.edu/EXT/Recs/ENT17-Alfalfa.pdf) For a more information on the management of insects in alfalfa, contact your local extension office or visit https://entomology.ca.uky.edu/fieldcrop. Potato Leafhoppers (https://entomology.ca.uky.edu/ef115)
~Chris Teutsch, Raul Villanueva, UK Princeton Research and Education Center