H. R. Willson
J. B. Eisley
The insect pest complex affecting alfalfa includes a variety of insect species of which one or more may become abundant enough to warrant the use of an insecticide treatment. In general, the alfalfa plant can tolerate a significant amount of injury by insect pests before a rescue treatment is economically justified. Most insect pests such as the alfalfa weevil, aphids, plant bugs, and the alfalfa blotch leafminer are maintained at subeconomic levels of activity by biological control agents, but outbreaks do occur. The potato leafhopper periodically causes significant injury to alfalfa, and vigilance is needed to apply timely rescue treatments when necessary. Recent successes in host plant resistance breeding of alfalfa have provided alfalfa varieties that offer a non-chemical management option to management of the potato leafhopper.
This publication provides a general summary of insecticide products registered for control of insect pests on alfalfa. For additional information on the biology and management of specific insect pests of alfalfa, the reader is directed to additional fact sheets in this series.
The insect pest complex on alfalfa includes a variety of species that can be readily found in Ohio alfalfa fields throughout the growing season. The time periods in which selected pest species can be found causing some degree of injury to alfalfa are presented in Table 1.
Table 1. Occurrence of insect pests on Ohio alfalfa. |
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|---|---|---|---|---|---|---|---|
| Alfalfa Growing Season | |||||||
| Insect Pest | Abbriviation | Apr | May | Jun | Jul | Aug | Cutting Most Affected |
| Alfalfaweevil | A W | XX | XXX | XX | 1st | ||
| Meadow spitllebug | MSB | X | XXX | X | 1st | ||
| Tarnished plant bug | PB | X | XXX | XXX | XXX | 2nd & 3rd | |
| Alfalfa plant bug | PB | X | XXX | XXX | XXX | 2nd & 3rd | |
| Alfalfa blotch leafminer | ABL | XXX | XXX | XXX | XX | 2nd & 3rd | |
| Potato leafhopper | PLH | X | XXX | XXX | XXX | 2nd & 3rd | |
| Pea aphid | PA | X | XXX | XXX | XX | 2nd & 3rd | |
| Grasshoppers | GH | XX | XXX | XXX | 3rd & 4th | ||
| Variegated cutworm | CW | X | XX | Spring Seeding | |||
| Insect pests most likely to warrent treatment with insecticide shown in bold print. | |||||||
Comments relevant to the economic occurrence of common insect pests include the following:
Alfalfa weevil: Controlled by introduced parasites in most seasons. Outbreaks occur sporadically when biotic controls fail.
Meadow spittlebug: Regarded as a pest of secondary importance. Tarnished plant bug: Although important in the western United States, rare problem in Ohio.
Alfalfa plant bug: Economic infestations by this plant bug are very rare.
Alfalfa blotch leafminer: Controlled by introduced parasites since mid-80s.
Potato leafhopper: Economic infestations occur every year throughout Ohio. PLH is the most important pest of Ohio alfalfa.
Pea aphids: Economic infestations may occur when insecticide treatments (usually carbaryl) remove natural predators.
Grasshoppers: Outbreaks may occur during very dry seasons. Variegated cutworm: Infestation of new seedings are very rare.
In summary, management of insect pests on Ohio alfalfa should focus on the alfalfa weevil during the 1st cutting and on potato leafhopper during the 2nd and 3rd cuttings. The 4th cutting of alfalfa in Ohio rarely exhibits an economic infestation of PLH.
A number of insecticide products are registered for use on alfalfa. Labels of various products may or may not be registered for both alfalfa weevil and potato leafhopper. A quick reference on products labeled for specific alfalfa pests is presented in Table 2.
Table 2. Insect pests listed on insecticide products registered for alfalfa. |
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|---|---|---|---|---|---|---|---|---|
| Labeled Alfalfa Pests | ||||||||
| Active Ingredient | Product Formulation | AW | MSB | PB | PLH | PA | GH | CW |
| azinphosmethyl | Guthion Solupak | X | X | X | X | |||
| carbaryl | Sevian 80S | X | X | X | X | X | ||
| carbofuran | Furadan 4 F | X | X | X | X | X | ||
| chlorpyrifos | Lorsban 4 E | X | X | X | X | X | X | X |
| cyfluthrin | Baythroid 2 | X | X | X | X | X | X | X |
| dimethoate | Dimethoate 2.67 EC | S | X | X | X | X | ||
| Dimethoate 4 E | S | X | X | X | X | |||
| lambda-cyhalothrin | Warrior T | X | X | X | X | X | X | |
| malathion | Malthion 5 | X | X | X | X | X | ||
| Malthion 57 EC | X | X | X | X | X | |||
| Malthion ULV | X | |||||||
| methomyl | Lannate WSP | X | X | X | X | |||
| Lannate LV | X | X | X | X | ||||
| methoxychlor | Methoxychlor 2 EC | X | X | |||||
| permethrin | Ambush 2 E | X | X | X | X | X | X | |
| Pounce 3.2 EC | X | X | X | X | X | X | ||
| phosmet | Imidan 70 W | X | X | X | X | |||
| Products shown in bold are periodically included in PLH control
trials conducted by OSU entomologists at the OARDC Western Branch Station. Other formulations of dimethoate include Dimate 2.67, Dimate 4 E, Dimethoate 267, and Dimethoate 400. |
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Most insecticide products registered for use on alfalfa provide a choice in the rate of application that may be used in a treatment. It should be noted that the preharvest limitation for products is often dependent on the rate of application.
For additional information the following fact sheets are available from Ohio State University Extension:
Alfalfa Weevil, FC-ENT-32-2000
Potato Leafhopper on Alfalfa, FC-ENT-33-2000
Table 3. Rates and pre-harvest limitions of insecticides registered for use on alfalfa. |
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|---|---|---|---|---|
| Active Ingredient | Formulation | Rate per Acre | Preharvest Limitations | Days |
| azinphosmethyl | Guthion Solupak | 0.5 to 1.0 lb | < 1lb / acre | 14 |
| @ 1lb / acre | 16 | |||
| carbaryl | Sevian 80 S | 1.25 lb | PHL | 7 |
| carbofuran | Furadan 4 F | 1.0 to 2.0 pt | 4F < = 1 pt / acre | 14 |
| 4F > 1 pt / acre | 28 | |||
| chlorpyrifos | Lorsban 4 E | 1.0 to 2.0 pt | @ 0.5 pt / acre | 7 |
| @ 1 pt / acre | 14 | |||
| > 1 pt / acre | 21 | |||
| cyfluthrin | Baythroid 2 | 0.8 to 1.6 fl oz | 7 | |
| dimethoate | Dimethoate 2.67 EC | 0.75 to 1.5 pt | PHL | 10 |
| Dimethoate 4 E | 0.5 to 1.0 pt | |||
| lambda-cyhalothrin | Warrior T | 1.9 to 3.8 fl oz | PHL for forage: | 1 |
| PHL for hay: | 7 | |||
| malathion | Malathion 5 | 1.5 to 2.0 pt | PHL | 5 |
| Malathion 57 EC | 1.5 to 2.25 pt | |||
| Malathion ULV | 16 fl oz | |||
| methomyl | Lannate WSP | 1.0 lb | PHL | 7 |
| Lannate LV | 3.0 pt | |||
| methoxychlor | Methoxychlor 2 EC | 2.0 to 3.0 qt | PHL | 7 |
| permethrin | Ambush 2 E | 6.4 to 12.8 fl oz | 2 E < = 6.4 fl oz | 1 |
| 2 E > 6.4 fl oz | 14 | |||
| Pounce 3.2 EC | 4.0 to 8.0 fl oz | 3.2 EC < = 4 fl oz | 1 | |
| 3.2 EC > 4 fl oz | 14 | |||
| phosmet | Imidan 70 W | 1 to 1.3 lb | PHL | 7 |
| Other formulations of dimethoate include Dimate 2.67, Dimate 4 E, Dimethoate 267, and Dimethoate 400. | ||||
Harold R. Willson, Associate Professor
Department of Entomology, The Ohio State University
1991 Kenny Road, Columbus, OH 43210
Phone: (614) 292-1554
E-mail: willson.1@osu.edu
J. B. Eisley, Research Associate
Department of Entomology, The Ohio State University
1991 Kenny Road, Columbus, OH 43210
Phone: (614) 292-3851
E-mail: eisley.1@osu.edu
R. Mark Sulc, Associate Professor
Department of Horticulture and Crop Science, The Ohio State University
2021 Coffey Road, Columbus, OH 43210
R. B. Hammond, Associate Professor
Department of Entomology, Ohio Agricultural Research and Development Center,
The Ohio State University
1680 Madison, Wooster, OH 44691
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868