Asparagus Aphid: Brachycorynella asparagi
The asparagus aphid was brought over from Europe as recently as 1969. It is primarily a pest in the arid Northwest, but can occasionally be a minor problem in the Northeast as well. It will infest cultivated, wild, and ornamental asparagus. These are small, oval, green to gray aphids that may be covered in a waxy secretion. The cornicles (tail pipe-like projections) are small and inconspicuous.
Life Cycle: Males and female adults are produced in September and October and will mate and lay eggs on the lower portion of the ferns. Eggs hatch in the spring, go through 4 nymphal instars and then develop into stem mothers: capable of producing up to 55 live female nymphs within 20 days. The nymphs mature in 8-10 days and begin to produce the next generation of female nymphs soon after. In the spring, some adult females have wings and will disperse to new hosts.
Damage: Aphid feeding causes a shortening of the internodes and a rosetting or brush-like appearance of the foliage, especially near the tips of the lower branches. High aphid populations will reduce plant vigor and yield or kill seedlings. A combination of infestations and cold winters can kill even full size crowns within two years.
Monitoring: Watch for abnormal plant growth on the lower portion of the fern.
Cultural, Biological and Chemical Management: A combination of removing dead ferns during the fall or winter, and spring tillage will usually control this pest. There are many natural enemies that help keep the aphid populations in check during the season including; lady beetles, lacewings, predatory midges, flower fly larvae, the Braconid wasp Diaeretiella rapea, and parasitic fungi. Treating the ferns twice, about 10 days apart, with a systemic insecticide (i.e. dimethoate) will also provide effective control.
Pea Aphid: Acyrthosiphon pisum
The pea aphid has a worldwide distribution. It is light-green with unusually long legs and cornicles (tail pipe-like projections). It is the primary aphid that attacks peas, and is also a pest of fava beans, and lentils.
Life Cycle: This aphid overwinters as an egg on alfalfa, vetch, and clover, where the population will reproduce and build up in the spring. They will move to peas after the plants emerge in the spring. Live females nymphs (no egg stage necessary) are produced throughout most of the year. Females take 12 days to mature and produce up to 150 nymphs. There are between 13-20 generations per year. Adults may or may not have wings, but will produce winged individuals and disperse if conditions become crowded or plants become desiccated. Sexual forms will occur in the fall and eggs will be laid after mating. Populations tend to be lower after cold, snowless winters or springs with persistent wet weather.
Damage: Infestations during the bloom and early pod stages will reduce yield and crop quality by removing plant sap, impairing pod appearance, reducing seed fill and by the presence of aphid honey-dew. Plants with high populations also have a reduced ability to fix nitrogen. Pea aphids can transmit many different viruses, even to crops that they rarely feed on, such as cucurbits.
Monitoring: Start monitoring when plants begin to flower. Action threshold include, 1-2 aphids per leaf, 2-3 aphids per stem tip or 9-13 per sweep, if a sweep net is being used.
Cultural, Biological and Chemical Management: Harvest or spray nearby alfalfa, vetch or clover before winged adults are formed in the spring. Varieties differ in their susceptibility to pea aphid damage. Plant varieties less prone to high infestations and damage. There are many natural enemies (lady beetles, lacewings, flower fly larvae, predatory midges, Braconid wasps) that help reduce aphid numbers, but they may not provide adequate control. Fungi will control high aphid populations during warm, humid or wet weather. A single systemic insecticide application (i.e. dimethoate) will control this pest. There are also many other products registered for use on pea aphids (see New England Vegetable Management Guide).
Corn leaf aphid: Rhopalosiphum maidis
Corn leaf aphids occurs world-wide, but do not overwinter in extreme northern states or Canada, where they may be brought in on prevailing winds. In Connecticut, they may not survive cold, snow-less winters. This aphid is blueish-green or black, with black legs. Host plants include many common grass weeds (barnyardgrass, crabgrass and foxtail) and most cereal crops (corn, barley, rye, oats, wheat, sorgham and millet).
Life Cycle: Corn leaf aphids overwinter as females on the host plant, particularly barely. No males or egg stages occur. Females produce live young which mature in as little as 6 days. There are up to 9 generation per year in Northern states.
Damage: Corn leaf aphids first colonize whorl leaves and the immature tassel. Populations may become numerous enough to interfere with pollen shed and to stunt plants. Maize dwarf mosaic virus may be spread by the corn leaf aphid, though the most important vector for this disease is the green peach aphid. The presence of high aphid populations or honey dew on corn ears can render the ears unmarketable. Honey dew on ears has been reported to increase the number of corn earworm moths attracted to the plants. Ample rainfall and soil moisture during the silk stage of development can reduce or eliminate damage.
Monitoring: Start monitoring for aphid colonies while scouting pre-tassel stage corn for European corn borer or fall armyworms in late July or August. Pre-tassel stage sprays may be needed in dry seasons, particularly on varieties with yellow tassels, when 50% of the plants are infested.
Cultural, Biological and Chemical Management: Sweet corn planting that are seeded before 10 June are not bothered by corn leaf aphids. Varieties with purple or green tassels seem to be less susceptible to aphid build-up than those with yellow tassels. There are many natural enemies (lady beetles, lacewings, flower fly larvae, predatory midges, pirate bugs, Braconid wasps) that help reduce aphid numbers, but they may not provide adequate control, especially in dry seasons after warm winters. Providing adequate irrigation during the silk stage can reduce or eliminate aphid damage. Growers that use selective insecticides (i.e. B.t products or spinosad) for most early and mid-season sprays seem to have fewer problems with corn leaf aphids than those choosing broad-spectrum material like synthetic pyrethroids. Also, if selective material are used routinely, and aphid problems do occur, a single application of a material (i.e. Warrior) that normally would only suppress the population, can produce complete control. See the New England Vegetable Management Guide for a list of registered products that are effective on this pest.
Potato leafhopper: Empoasca fabae
Potato leafhopper (PLH) is thought to be native species. It overwinters on legumes in the Gulf states and disperses to northern states on wind currents annually. It usually arrives in Connecticut in June. Preferred hosts include: alfalfa, beans, soybeans, potatoes, and to a lesser extent, eggplant, celery, cucumber, Jerusalem artichokes, squash, sweet potato and rhubarb. Potato leafhopper adults are about 1/8 inch long, light-green and wedge-shaped, while nymphs are bright, almost neon-green.
Life Cycle: Adult PLH arrive in June and can usually be found first in alfalfa or beans. They move to potatoes as the plants mature and contain more sugar. If high populations arrive, they may infest all hosts simultaneously. Adults may continue to migrate in from the South for a month or two. There are 5 nymphal instars and development from egg to adult takes 20-35 days. Females may lay up to 300 eggs. Generally, 2-3 generations occur each season in Connecticut during June and July. Prior to 1997, damaging populations only occurred in Connecticut every few years, but they have reached treatment thresholds every year since.
Damage: Potato leafhoppers inject a toxin into the foliage while feeding which causes a symptom know as "hopperburn." Leaf tips and margins first turn yellow or bronze, curl upward and then begin to die. Potatoes, beans and seedling eggplants can be killed outright by high numbers of PLH. Yields can be reduced in many years. On eggplant, symptoms of Verticillium wilt can resemble hopperburn, except that the edges of the leaves droop down instead of curling up. Drought can compound the damage.
Monitoring and thresholds: Leafhoppers can be monitored by counting adults and nymphs on leaves or with a sweep net. Treat seedling beans if more than 2 adult leafhoppers are found per foot of row. Between the third trifoliate leaf and bud stage the bean threshold is 5 adult leafhoppers per foot of row. Adults move fast and will streak past you if you disturb the foliage while inspecting the plants. Treat eggplant if you find 1-1.5 adults or large nymphs per leaf. Treat potatoes if 5 adults or 15 large larvae are found on 50 leaves.
Management: Natural enemies include general predators such as lady beetles, lacewings, ants spiders and Nabid bugs, but they will not provide adequate control of leafhoppers. Provide adequate moisture through timely irrigation. Row covers can prevent leafhoppers from feeding on crops. To minimize spraying, choose insecticides with a long residual period of effectiveness such as systemic materials, if available. See the New England Vegetable Management Guide for a list of registered products on each crop.
T. Jude Boucher, University of Connecticut, Cooperative Extension System
January 2005
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