Mid to Late Season Insect Control in Cotton

KEY POINTS

  • Several insect pests are of importance to watch for near or after first bloom.
  • Late-season insects can be difficult to control due to dense crop canopies and poor insect control can reduce yield potential, even late in the season.
  • There are different control measures available and depending on the insect complex, a tank mix of insecticides may be necessary.

Causes

Cotton plants can be damaged by a wide range of insect pests throughout the growing season. Symptoms include curled leaves, chlorosis, misshapen flowers, aborted squares and bolls, and damaged bolls, including stained lint. It is imperative for cotton to be scouted regularly and thoroughly. Inadequate scouting can lead to increased insect populations and decreased yield potential.

Management

Weed control. Removing weeds from the field helps limit available plant material that can harbor insects.

Insecticide application. Insect pressure varies by year and by field; therefore, insecticide application should be based on scouting observations, and not by a pre-determined schedule. Apply during the most susceptible stage of insect development and be mindful of preventing resistance.

Plant growth regulator (PGR) application. Controlling plant height with PGRs can help prevent rank growth that can reduce insecticide coverage and extend the time for ground application before an aerial application would be necessary.

Scouting. Effective cotton insect control relies on frequent and thorough scouting. Fields should be scouted every 4 to 5 days with enough time spent in the field to accurately assess insect populations and stages. The objective is to avoid unnecessary insecticide applications and time applications correctly. Allot time for additional field checks to account for possible increased insect pressure.

Beneficial agents. Lady beetles, spiders, minute spider bugs, parasitic wasps, and insect fungal diseases help control inspect pests. It is important to identify these beneficials correctly in the field and what they help control to help prevent unnecessary insecticide application.

Economic thresholds. Economic thresholds are the point at which insect density requires action to prevent economic loss. It is important to apply insecticides based on scouting and threshold levels to reduce costs and loss of beneficial insects. Thresholds can vary for several reasons including insect species, crop development stage, yield potential, treatment cost, market price, secondary pests, and other considerations. Use local thresholds recommended by state extension specialists along with on-farm considerations.

When late-season insect economic threshold levels are met, first consider what cotton technology the crop contains. Fields that are planted with technology that manages certain insect pests may still require insecticide application in fields with heavy insect pressure. Be sure insect pests are at threshold prior to treatment. Insect control should be terminated at 350-400 DD60s after “cutout” or at 5 nodes above white flower (NAWF). Cotton fields do not need treatment beyond this stage as the crop is less attractive to insect pests and the bolls can tolerate more damage without reducing cotton yield potential.

Identification

 spidermite

 

Figure 1. Spider mite leaf damage.

 

Spider Mites.
Infestations appear first in field border and occur more often with hot and dry conditions. Spider mites infest the underside of leaves to feed on plant sap, causing leaf surfaces to discolor (Figure 1). Severe infestations can defoliate cotton plants and cause small bolls to shed. Insecticide application can cause an increase in spider mite damage if beneficials are killed. Miticide application can help reduce damage and should begin when spider mites begin to cause noticeable leaf damage, or when 40-50% of plants are affected. 
spidermite

Figure 2. Tarnished plant bug adult.

Plant Bugs.
Plant bugs, including tarnished plant bugs (Figure 2) and cotton leafhoppers, cause puncture wounds on both cotton squares and small developing cotton bolls. Multiple generations may overlap in one growing season. The presence of nymphs after first bloom indicates reproduction is occurring. Dirty blooms and darkened anthers are signs of plant bug feeding. Contact your state Extension office for local economic threshold levels and treatment recommendations.
spidermite

Figure 3. Brown stink bug adult.

Stink Bugs.
There are several species of stink bugs that can reduce cotton yield potential. Stink bugs pierce small bolls and suck the sap from seeds. Internal boll damage includes stained lint or callous growths inside the boll. Feeding can allow entry of boll rots. Damaged bolls may either open early or become hardlocked and not open. Insecticides are specific to different stink bug species. If stink bug populations reach local economic thresholds, organophosphate insecticides can help provide control of southern green and brown stink bugs. Pyrethroid insecticides may help control southern green stinkbugs.
spidermite 

Figure 4. Aphid infestation present on the underside of a cotton leaf.

Aphids and Whiteflies.
These insects suck sap from plants causing stunting and leaf curling. Sticky “honeydew” is deposited on leaves and can reduce cotton fiber quality. Most economically damaging infestations develop during bloom. Treatment should be considered when areas of high aphid populations cause heavy honeydew accumulation without signs of diseased aphids. Do not apply an insecticide if there are dead aphids present, as natural control agents are working to manage populations.
spidermite 

Figure 5. Cotton bollworm. Peggy Greb, USDA Agricultural Research Service, Bugwood.org.

Bollworms and Tobacco Budworms.
These worms are similar in morphology, feed on the same plant structures, and are often found together in a field. Tobacco budworms are known to be resistant to multiple insecticides. In corn-growing regions, bollworm moths will typically deposit eggs in cotton fields after emergence in nearby cornfields. Eggs are deposited on upper leaves and hatch after three days. Eggs and larvae may be found anywhere on the plant, especially on blooms (Figure 5) or young bolls. Frequent scouting is recommended. Treatment may be necessary in situations of high pressure. Please refer to local Extension recommendations.
spidermite

Figure 6. Fall armyworm.

Fall Armyworm.
An inverted “Y” mark on the larvae head can be used to identify this pest (Figure 6). Problems may occur late in the season. Fall armyworm moths may lay eggs on the underside of leaves and larvae may be found feeding on younger growth, bloom tissue or pollen. The larvae will eventually feed on cotton bolls. Depending on local recommendations, the economic threshold for fall armyworms may be met when 10 larvae are found per 100 plants. It is best to time insecticide application to coincide with egg hatch or larval emergence.