Aphids are a serious pest of many crops including peas. Aphids have piercing-sucking mouthparts which extract plant juices from leaves, stems, blossoms, and pods; inject toxins into the plants; and serve as vectors of viral diseases.
Pea aphids (PA) are comparatively large (3/16 inch long), bright green aphids, with long cornicles (paired "tails" near the end of the body). They over-winter as eggs, which are glued on fallen stems and leaves of alfalfa in the fall. After hatching in the early spring, the nymphs feed on alfalfa. Nymphs closely resemble adults although they are smaller and lack wings. Both adults and nymphs are found together on plants and both have piercing sucking mouthparts. After one or two generations, winged forms are produced that move to other crops. Asexual reproduction continues through the summer. Later, males are produced, and sexual reproduction results in over-wintering eggs. Dry, cool conditions (55 to 60° F.) favor the development of dense populations.
Aphids may damage peas directly through sucking plant juices resulting in stunted, less vigorous plants that produce fewer and smaller seeds. Heavy populations or prolonged feeding by pea aphid may cause severe stunting, yellowing, wilting and ultimately death of the plants.
Aphids are known to vector pea enation mosaic, pea streak, pea seedborne mosaic, alfalfa mosaic, bean yellow mosaic and pea leaf roll. Only pea leaf roll virus is persistent, indicating that once it is acquired by the aphid it may transmit the virus throughout its lifetime. The other viruses are non-persistent and carried on aphid mouthparts from infected to non-infected plants. The importance of aphid-vectored viral diseases varies with environmental factors that influence viral infection and outbreaks.
Conditions that increase the risk of pea aphid outbreaks include:
1. Abundant regrowth of perennial host plants (alfalfa) in the fall
2. Late killing fall frost, allows for abundant production of overwintering forms
3. Mild January and February temperatures
4. Spring conditions that favor aphids but not natural enemies
5. Stresses on perennial host plants (alfalfa) in spring resulting in early movement of aphids to peas and lentils.
6. Pea aphids migrate to pea and lentils fields from nearby alfalfa fields and may be of particular concern after nearby fields of alfalfa hay are cut.
Monitor using a standard, 15-inch diameter sweep net when fields are beginning to bloom through pod set. If there are 30-40 aphids per sweep present and few if any natural enemies are present, insecticide treatment is justified. However, if natural enemies are present, resample in 2 days. If numbers are the same or decreased, treatment may not be needed. Continue sampling until you have determined whether the population is increasing, decreasing or stabilized. If the population increases, treat the field promptly.
Pea aphids have many natural enemies but populations of general predators such as ladybird beetles, lacewings, nabids and syrphid fly larvae and parasitic wasps are the most effective. Parasitic wasps can be determined by the presence of aphid "mummies", swollen, tan-to-copper aphid skins that are the result of parasitism.
Research by Dr. Bill Synder at WSU has indicated that the impact of parasitism and general predation is additive, with the generalist predators having an immediate negative effect on aphid populations but allowing aphid populations to increase in time. He found that parasitoids have a small initial impact but cause aphid populations to eventually decline.
When both parasitic wasps and generalist predators were present, pea aphid dynamics reflected the impact of both generalists and specialists – pea aphid population growth was depressed early, and pea aphid densities strongly declined later. Overall, the density independent impact of generalists and the density dependent impact of specialists were complimentary, so that biocontrol was most effective when both classes of natural enemy were present. The impacts of generalists and specialists were additive despite a high rate of predation among aphid and natural enemy populations, because predators did not alter percent parasitism by the parasitic wasp, A. ervi.
Peas are a cool season crop and should be planted as early as possible. Early planting allows plants to become well established before aphids move from alfalfa into lentil fields. Younger plants are more susceptible to aphid feeding damage and impact of virus infection is apt to be more severe.
Varieties resistant to pea leaf roll, pea seedborne mosaic and other common viruses are available and are the best way to manage viral diseases. Use of virus-free seed is essential for pea seedborne mosaic control. Because it may take 2-4 weeks for disease symptoms to develop, by the time the virus is recognized, there is no recommended action. Control of aphids is not effective for managing viral diseases.
Product List for Pea Aphid:
Insecticide |
Lbs Active Ingredient per Acre (Fl oz. or oz. product) |
Preharvest Interval, remarks |
|
Asana XL R,1 |
5.8 – 9.6 oz |
21 days. Do not apply more than 38.7 oz per season. Do not feed or graze livestock on treated material. |
|
Dimethoate (several formulations) 1 |
1/2 - 1 pt (400) 0.75 – 1.5 pt (267) 1/2 - 1 pt (4E) |
0 PHI. Do not feed treated vines. Do not make more than 1 application per season. Highly toxic to bees. |
|
Di-Syston R, 1 |
1 – 2 pts |
60 days, Do not apply more than once per season. Do not feed vines or hay. |
|
LannateR,3 |
0.5 -1 lb (SP) 3pts (LV) |
14 days to harvest, graze or hay. 48 hr REI. Do not apply more than 4.5 lbs ai /season. Do not make more than applications per crop. Do not apply when bees are foraging. |
|
Malathion3 |
1.5 – 2 pts (5EC, 57) 1.5 pt (8EC)
|
1 day. 12 REI. Do not feed or graze treated foliage. |
|
Methyl parathion 4ER |
1-3 pt |
15 days for 1 pt/A or less. 21 days for more than 1 pt. Do not apply if crop or weeds are in bloom. |
|
R Restricted Use Pesticide 1 Labeled for chemigation 224c labels may be available, check with State Dept of Agriculture 3Several formulations |
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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 regulation, 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. |
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Categories: Dry Peas, Insects, Pea Aphid
Date: 04/29/2006