The cotton aphid, Aphis gossypii Glover, has developed into a serious problem over much of the cotton acreage in West Texas. The Cotton Aphid Task Force was formed in September, 1991 to aid in the coordination of research and education efforts. The following management suggestions are a product of this continuing collaboration between Texas Agricultural Experiment Station and Texas Agricultural Extension Service scientists. These suggestions incorporate current knowledge of aphid biology and ecology, cultural management practices and insecticide resistance management.
 

Season-long Management of Cotton Aphids

At-Planting Considerations

Aphid numbers tend to be lower on varieties with the smooth-leaf characteristic. Pubescent varieties develop higher aphid numbers than glabrous varieties. However, most commonly planted commercial varieties are pubescent with relatively little difference between them.
 

Aphid numbers in cotton can be lower following crops that leave a high level of residue. Aphid numbers are generally higher in clean-till or conventional-till production systems than in fields where cotton is planted into wheat or sorghum residue. Light reflectance from the residue slows aphid reproduction.
 

Planting dates influence aphid abundance. Aphid numbers during August are higher in late June-planted cotton than cotton planted either in April or May in the West Texas production region. Suggested planting dates for each region follow:
 

High Plains: April 25 - May 20

Rolling Plains: May 15 - June 7. These dates also optimize boll weevil management.

Trans-Pecos: April 25 - May 25
 

Where practical, land preparation no later than April will allow producers to have fields ready for planting during the preferred planting period.
 

Plant to assure an adequate and uniform stand. Cotton aphid numbers are generally higher in fields with skippy stands and in cotton planted in a skip-row pattern. Producers should use high quality seed and plant only enough seed to achieve a uniform stand of 2-4 plants per foot of row (30 and 40 inch rows) for dryland and irrigated production.
 

Avoid excessive nitrogen levels by fertilizing based on a soil test. Fertilizing based on soil tests and realistic yield goals will avoid cotton with high nitrogen levels. Aphid numbers are higher on plants with higher nitrogen levels. Additionally, aphids on plants with high nitrogen levels are less susceptible to aphicides.
 

Early Season

Aphids  in pre-blooming cotton, from emergence to first bloom, rarely develop to economically damaging levels. These aphids are an important food source for natural enemies such as lady beetles and parasites. Insecticide treatments for aphids in pre-blooming cotton should be avoided if possible.
 

Insecticide Selection. Insecticide selection for early season pests (thrips, cotton fleahoppers, overwintered boll weevils) can reduce aphid populations, but these insecticides vary in their impact on natural enemies. Repeated use of the same insecticide chemistry can reduce aphid response to similar insecticides later in the season.
 

Natural Enemies. Predators and parasites can reduce aphid populations to non-economically damaging levels. Conservation of natural enemies throughout the season will usually maintain aphid populations at low levels.
 

Mid-Season

Delay insecticide control of aphids until infestations exceed 50 aphids/leaf, from early bloom to first open boll. Most aphid infestations develop to their highest levels after mid-August, often declining to low levels soon after this peak. When populations approach 50/leaf, scouting efforts should be intensified. Aphid populations at 50/leaf may rapidly increase, level off or decline. Infestations exceeding 50/leaf for more than 3 weeks or 100/leaf for more than 2 weeks have resulted in yield decreases.
 

Adherence to these thresholds provides an opportunity for parasites and predaceous insects, such as lady beetles, to control the aphid populations without the use of insecticides. When maturing grain sorghum or corn fields are nearby, natural enemies often move into cotton where aphid populations are increasing. These natural enemies can reduce aphid numbers within two weeks.
 

Aphid populations often increase rapidly after a field has been treated with pyrethroid insecticides. These fields may require earlier and more frequent treatment compared to fields which have not been treated with a pyrethroid.
 

Postpone the use of pyrethroid insecticides as late into the season as possible. Aphid infestation levels often increase following pyrethroid applications during August. Prior to boll set, alternative insecticides for bollworms/tobacco budworms such as Bacillus thuringiensis products, Curacron®, Lannate®, Larvin® and Tracer® should be used where necessary. When a pyrethroid is used and cotton aphid numbers exceed 50/leaf and are rapidly increasing, add a full recommended rate of an effective aphicide. Full aphicide rates are necessary for extended residual control.
 

Maximize insecticide coverage. Cotton aphid infestations develop on the undersides of leaves throughout the plant canopy. Thorough top-to-bottom coverage through increased spray volume is very important. The use of drops on ground application equipment is recommended. A minimum of 10 gallons total spray volume/acre for ground equipment and 5 gallons/acre by air is suggested. Some aphicides may not perform well if delivered to the crop using oil as the carrier.
 

Late Season

Avoid sticky cotton  once bolls open. Low infestation levels of cotton aphids can excrete sufficient honeydew to contaminate the lint of open bolls and create significant and costly problems at the textile mill. Mills are reluctant to buy contaminated lint. Factors that increase late season aphid populations include late irrigations (after August 25), warm fall temperatures, plant regrowth, ULV malathion applications for boll weevil control, pyrethroid applications in late August-early September and Prep®, when used alone in early September.
 

In the Rolling Plains, planting date can be used to reduce the probability of lint contamination by aphid honeydew. An average of 3% of the bolls will be open by late August in cotton planted between May 15 and June 7, whereas cotton planted in late April-early May can average 36% open bolls in late August. Early planted fields are very susceptible to honeydew contamination of lint during September.
 

After bolls open, treatment should be considered even when aphid numbers are low (California threshold is 10-15 per 5^th mainstem node leaf). Once lint has been contaminated very little can be done to alleviate the problem. Available research data indicate that rainfall of at least 1/4 inch can reduce honeydew deposits. Overhead sprinklers delivering 1/4 inch or more of water can achieve the same results. However, if aphids remain on the plants after a rain or irrigation, the lint remains susceptible to further contamination.
 

Fields should be harvested in a timely manner to prevent late season aphids from contaminating lint.
 

Consult your local Extension entomologist or agent for the latest list of effective insecticides. Resistance to insecticides has varied considerably from community to community and even between adjacent fields. There can also be considerable seasonal variation in aphid susceptibility to aphicides. Insecticides and insecticide combinations are continually being evaluated during the growing season.