Corn, sweet-Aphid


Bean aphid (Aphis fabae)
Green peach aphid (Myzus persicae)
Potato aphid (Macrosyphum euphorbiae)

Pest description and crop damage The green peach aphid is slender, dark green to yellow, and has no waxy bloom. Green peach aphid infestations may result in wilting. The potato aphid has both a pink and green form. It is a larger aphid. High potato aphid populations can distort leaves and stems, stunt plants, and cause necrotic spots on leaves. These aphids also secrete a large amount of honeydew that promotes development of sooty mold on foliage and fruit. The bean aphid is dark olive green to black with light-color legs. It is usually more of an early year pest.

Aphids may become very abundant on leaves, tassels, and ear-silk, especially in eastern Oregon. Aphids damage plants by sucking plant sap, which causes heavily infested leaves to curl and stunts plants; excreting honeydew, which causes sticky, shiny leaves to turn black because of a sooty-mold fungus growth; and spreading plant diseases such as alfalfa mosaic, tomato yellow top, and zucchini yellow mosaic (a large number of viruses are spread by aphids).

There is some evidence that severe infestation of ear-silk reduces tip fill, but this needs further evaluation. In fresh market corn, the most serious problem caused by aphids is contamination of the harvested ears.

Biology and life history


Pest Monitoring A specific action threshold for aphid control in sweet corn has not been established in Oregon. The need for aphid control depends on whether the corn is being grown for processing or fresh market. There is very little tolerance for aphid contamination or honeydew in the corn silk of fresh market sweet corn. Although aphid populations can be dramatic, treatments for aphids in commercial sweet corn for processing are rare.

If aphids become numerous, increase frequency of sampling. Begin controlling significant aphid infestations in fresh market corn prior to silking. Aphids often are concentrated in hot spots or near the field margin. Infestations frequently are localized, with heavily infested leaves curled downward. Note the presence of any hot spots, but avoid sampling only those areas. Also, be sure to look for evidence of biological control; i.e., the presence of predators, parasites (aphid mummies), and disease. Aphid flights are most common during periods of moderate temperatures (60° to 80°F). Monitor fields particularly closely during April and May.

Management-biological control

Many parasites and predators attack aphids. Early year aphids have many natural enemies that frequently bring them under control later in the year. Among the more common predators are lady beetles and their larvae, lacewing larvae, and syrphid fly larvae. Populations of green peach aphids are reduced in winter by a parasitic fungus, Entomophthora aphidis.

Monitor the proportion of aphid mummies relative to unparasitized aphids and the numbers of predators such as lady beetles. If the proportion of mummies is increasing, or predators appear to be gaining control, and aphid populations are not yet damaging, avoid sprays that will disrupt these natural enemies if the crop is not in a susceptible stage. Most materials available for aphid control are highly disruptive of natural enemy populations.

Sweet corn for processing can tolerate higher levels of aphid pressure before treatment is required, because the husks and eartips are removed in the processing plant. In most cases, natural enemies provide adequate control of aphids in processing sweet corn.

Management-cultural control

Destroy aphid-infested crops growing next to maturing sweet corn plantings immediately after harvest to prevent dispersal. Destroying weed hosts late in the year may help destroy overwintering populations. Aphid populations tend to be higher in crops that are fertilized liberally with nitrogen. Irrigation and rain depress aphid populations.

Home gardeners can often get effective control by washing aphids with a strong stream of water.

Management-chemical control: HOME USE

  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • Beauvaria bassiana-OMRI-listed for organic use.
  • bifenthrin
  • carbaryl
  • cyfluthrin
  • cyhalothrin
  • deltamethrin
  • efenvalerate
  • gamma-cyhalothrin
  • insecticidal soap-Some formulations are OMRI-listed for organic use.
  • kaolin-When applied as a spray to leaves, stems, and fruit, it acts as a repellant to some insect pests. Some formulations are OMRI-listed for organic use.
  • lambda-cyhalothrin
  • malathion
  • permethrin
  • plant-derived essential oils (rosemary, peppermint etc.)-Some formulations are OMRI-listed for organic use.
  • pyrethrins (often combined with other ingredients)-Some formulations are OMRI-listed for organic use.
  • spinosad-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin

Management-chemical control: COMMERCIAL USE

  • acetamprid (Assail 30SG) at 0.04 to 0.054 lb ai/a. PHI 1 day. REI 12 hr. Limit 4 treatments per year. Retreatment interval 7 days. Do not exceed a total of 0.21 lb ai/a per growing season.
  • alpha-cypermethrin (Fastac EC) at 0.018 to 0.025 lb ai/a. PHI 3 days. REI 12 hr. Retreatment interval 3 days. Do not exceed 0.075 lb ai/a per season.
  • azadirachtin-See label for application rates. Some formulations are OMRI-listed for organic use.
  • Beauveria bassiana (Mycotrol O) at 0.25 to 1 quart/a. PHI 0 days. REI 4 hr. Some formulations are OMRI-listed for organic use.
  • chlorantraniliprole/lambda-cyhalothrin (Besiege) at 0.06 to 0.1 lb ai/a. PHI 1 day. REI 24 hr. Retreatment interval 1 day. Do not exceed 0.48 lb ai of lambda-cyhalothrin or 0.2 lb ai of chlorantraniliprole per acre per growing season. Suppression only.
  • chlorpyrifos (Lorsban 4E) at 0.5 to 1 lb ai/a. PHI 21 days. REI 24 hr. Postemergence broadcast or sprinkler application. Limit 3 treatments of any chlorpyrifos product. Retreatment interval 10 days. Do not exceed 3 lb ai/a per season. Consult label for application details. Toxic to fish.
  • Chromobacterium subtsugae (Grandevo) at 0.6 to 0.9 lb ai/a per 100 gal. PHI 0 days. REI 4 hr. OMRI-listed for organic production
  • deltamethrin (Delta Gold) at 0.018 to 0.028 lb ai/a. PHI 1 day. REI 12 hr. Do not exceed 0.45 lb ai/a per year.
  • esfenvalerate (Asana XL) at 0.03 to 0.05 lb ai/a. PHI 1 day. REI 12 hr. Do not exceed 0.5 lb ai/a per year.
  • gamma-cyhalothrin (Declare) at 0.01 to 0.015 lb/a. PHI 1 day. REI 24 hr. Do not graze. Do not exceed 0.24 lb ai/a per season.
  • Isaria fumosorosea (PFR-97 20% WDG)-Most effective when application is initiated just before or at the first signs that target pests are present. OMRI-listed for organic use.
  • lambda-cyhalothrin (Warrior II) at 0.02 to 0.03 lb ai/a. PHI 1 day. REI 24 hr. Do not exceed 0.48 lb ai/a per year. Retreatment interval 4 days. Do not harvest for feed or graze livestock for 21 days.
  • lambda-cyhalothrin+tebuconazole (Crossover) at 0.14 to 0.16 lb ai/a. PHI 21 days for ears & forage; 49 days for fodder. Do not exceed 0.48 lb ai/a tebuconazole or 0.12 lb ai/a lambda-cyhalothrin.
  • malathion (Drexel Malathion 5EC) at 1.0 lb ai/a. PHI 5 days. REI 12 hr. Retreatment interval 5 days. Limit 2 treatments per year.
  • methomyl (Lannate SP) at 0.23 to 0.45 lb ai/a. PHI 0 days for ears, 3 days for forage, and 21 days for stover. REI 48 hr. Do not exceed 6.3 lb ai/a per season.
  • mineral oil-OMRI-listed for organic use.
  • oxydemeton methyl (MSR Spray Concentrate) at 0.375 to 0.5 lb ai. PHI 26 days. REI 13 days. Retreatment interval 7 days. Do not exceed two applications per year.
  • permethrin (Ambush 25WP, Pounce 25WP) at 0.1 to 0.2 lb ai/a. PHI 1 day for ears. REI 12 hr. Do not exceed 1.2 lb/a per season.
  • potassium laurate (insecticidal soap)-OMRI-listed for organic use.
  • zeta-cypermethrin (Mustang) at 0.034 to 0.05 lb ai/a. PHI 7 days for grain, stover & forage. REI 12 hr. Do not exceed 0.2 lb ai/a per season.