Alfalfa aphid (Macrosiphum creelii)
Blue alfalfa aphid (Acyrthosiphon kondoi)
Pea aphid (Acyrthosiphon pisum)
Spotted alfalfa aphid (Therioaphis maculata)
Pest description and crop damage Aphids are common on legumes. Aphids can frequently cause problems when their natural enemies are eliminated by sprays targeting alfalfa weevil. Border harvesting or strip cutting can help preserve natural enemies for aphids and other pests. Aphids feed by sucking juices from leaves, stems, and pods. Large populations reduce plant vigor. Aphids secrete honeydew that can promote a black sooty mold and decrease photosynthesis. Aphids may also transmit viruses to alfalfa, including Alfalfa mosaic virus and others. The pea aphid is "large" and can be green or red. The spotted alfalfa aphid is small and pale yellow or grayish, with conspicuous dark spots on the abdomen. It often is on the lower plant and can seriously damage some varieties. Correct species identification is important for optimal control. Damage thresholds are lower for blue alfalfa aphid than for pea aphid. The following guide provides easy to use diagnostics for key pest aphid species:
Contact your local extension office for assistance with identification. For additional information, see: https://www.agronomy.org/files/publications/alfalfa-management-guide.pdf
Sampling and thresholds
Treat for pea aphid when:
- The population approaches 100 per sweep and plants are less than 1 ft high. Blue alfalfa aphid may cause damage at levels lower than 100 aphids per sweep.
- The field is about 2 weeks or more from cutting or is under water stress, as evidenced by wilting plants.
- Predators and parasites are not controlling the aphids.
Treat for spotted alfalfa aphid when:
- Aphids average 10 or more per stem, and honeydew is noticeable. Seedling stands are most susceptible and can be damaged seriously even by relatively few aphids.
Several species of predatory bugs and parasitic wasps occur in alfalfa and can maintain aphid populations below damaging levels. Insecticides often destroy such beneficial insects, leading to severe outbreaks of aphids and other pests. A field guide of important natural enemies of aphids and other pests is available at: http://ipmnet.org/Pocket_Guide_of_Natural_Enemies.pdf. Information on which pesticides are most compatible with natural enemies can be found at: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74140.html#TABLE4 or by contacting your local extension office.
Certain commercial cultivars have resistance to aphids. Consult seed company representatives or your local extension office for recommendations. Information is also available from the National Alfalfa and Forage Alliance (http://www.alfalfa.org/).
Most of the following insecticides are hazardous to bees and should not be used if bees are foraging in the alfalfa.
- azadirachtin (Aza-Direct, Neemix 4.5)-See specific labels for rates. PHI 0 days. REI 4 hr. Aza-direct and Neemix 4.5 are OMRI-listed for organic use.
- Beauveria bassiana GHA (Mycotrol ESO) at 0.5 to 2 qt/100 gal. PHI 0 days. REI 4 hr. OMRI-listed for organic use.
- chlorantraniliprole/lambda-cyhalothrin (Besiege) at 0.059 to 0.088 lb ai/a. PHI 1 day for forage and 7 days for hay. REI 24 hr. Minimum of 5 days between applications. Do not exceed 0.12 lb ai of products containing lambda-cyhalothrin or 0.2 lb ai of chlorantraniliprole-containing foliar products per acre per growing season. Refer to product labels for application limits if products containing gamma-cyhalothrin and products containing lambda-cyhalothrin are to be used in the same season. Can be used on alfalfa grown for seed, but make applications when bees are not foraging by applying during the early morning or during the evening hours. Be aware of bee hazard resulting from a cool evening and/or morning dew. Remove in seed crops, remove bee shelters during and for 2-3 days following application. Do not apply directly to bee shelters. (Groups 28 and 3A)
- chlorpyrifos (numerous products) at 0.5 to 1 lb ai/a. PHI grazing or cutting is 7 days at 0.25 lb ai/a; 14 days at 0.5 lb ai/a; 21 days at rates greater than 0.5 lb ai/a. REI 24 hr. Do not apply any chlorpyrifos products more than four times per season or more than once per cutting. Do not reapply within 10 days of the first application. Certain products can be chemigated by sprinkler irrigation. Highly toxic to bees exposed to direct treatment and should not be applied when bees are foraging in the treated area. Minor phytotoxicity is possible on new growth. (Group 1B)
- chlorpyrifos/gamma cyhalothrin (Cobalt) at 0.26 to 0.52 lb ai/a. PHI 14 days. REI 1 day. Do not apply Cobalt nor any other product containing chlorpyrifos more than once per cutting nor more than 4 times per season. Refer to product labels for application limits if products containing gamma-cyhalothrin and products containing lambda-cyhalothrin are to be used in the same season. Highly toxic to bees when exposed to direct treatment. Do not apply if nearby bees are clustered outside of hives and bees are foraging in an area to be treated. (Groups 1B and 3A)
- Chromobacterium subtsugae (Grandevo) at 0.6 to 0.9 lb ai/a per 100 gal. PHI 0 days. REI 4 hr.
- dimethoate (numerous products) at 0.25 to 0.5 lb ai/a. PHI 10 days for grazing or cutting. REI 48 hrs. Do not apply during bloom. Do not exceed one application per cutting. Do not exceed 0.5 lb ai/a per season. Higlhy toxic to bees. Restrict application to the period after dark when bees are inside the hive or in the early morning before the bees are foraging in the ﬁelds. (Group 1B)
- flupyradifurone (Sivanto 200) at 0.09 to 0.137 lb ai/a. PHI 7 days forage, silage, cutting for hay. REI 4 hr. Retreatment interval 10 days. Do not exceed 0.365 lb ai/a per season.
- gamma-cyhalothrin (Declare) at 0.01 to 0.015 lb ai/a. PHI 1 day for forage harvest or 7 days for hay harvest. REI 24 hr. Do not exceed 0.015 lb ai/a per cutting or 0.06 lb ai/a per season. Refer to product labels application limits if products containing gamma-cyhalothrin and products containing lambda-cyhalothrin are to be used in the same season. (Group 3A)
- lambda-cyhalothrin (Warrior II) at 0.02 to 0.03 lb ai/a. PHI 1 day for forage harvest or 7 days for hay harvest. REI 24 hr. Apply only to pure stands. Do not apply when bees are actively foraging. Do not exceed 0.03 lb ai/a per cutting or 0.12 lb ai/a per season. Refer to product labels application limits if products containing gamma-cyhalothrin and products containing lambda-cyhalothrin are to be used in the same season. (Group 3A)
- malathion (numerous products) at 1 to 1.25 lb ai/a. PHI 0 days. REI 12 hr. Not effective below 65°F. Retreatment interval 14 days. (Group 1B)
- methomyl (Lannate LV; numerous other products) at 0.45 to 0.9 lb ai/a. PHI 7 days for grazing or cutting. REI 48 hr. Do not exceed 2 applications per cutting, or 10 applications or 3.6 lb ai/a per season. (Group 1A)
- permethrin (numerous products) at 0.05 to 0.2 lb ai/a. PHI 0 days at 0.1 lb ai/a or less, 14 days at more than 0.1 lb ai/a. REI 12 hr. Do not exceed 0.2 lb ai/a per cutting. Retreatment interval 30 days. (Group 3A)
- sodium borate (Prev-Am Ultra) at 50 fl oz/100 gal. PHI 1 day. REI 4 hr. Retreatment interval 7 days.
- thiamethoxam (Cruiser 5FS / 5FS Alfalfa - seed treatment) at 0.001 milligrams per seed. Will protect young alfalfa seedlings from damage caused by aphids for the first cut only. (Group 4A)
- zeta-cypermethrin at 0.028 to 0.05 lb ai/a (Mustang), or at 0.014 to 0.025 lb ai/a (Mustang Maxx). PHI 3 days for cutting or grazing, 7 days for harvesting seed. REI 12 hr. Retreatment interval 7 days. Do not use more than 0.1 lb ai/a per cutting or more than 0.3 lb ai/a per season (Mustang) or 0.05 lb ai/a per cutting or 0.15 lb ai/a per season (Mustang Maxx). These products are highly toxic to bees exposed to direct treatment or residues on blooming crops or weeds. Do not apply this product or allow it to drift to blooming crops if bees are visiting the treatment area. (Group 3A)