UNIVERSITY OF MISSOURI
Cotton Insect Management Guide - 2005

Phase I (Planting to Pre-bloom)

• Avoid using pyrethroid insecticides when possible, and limit the use of organophosphates (ex. Curacron).
• Avoid automatic insecticide applications.
• Maintain beneficial insect populations that help suppress aphid and bollworm/tobacco budworm infestations.
• Strive for >80% first position fruit retention.

Phase II (Post-bloom to end-of-season)

• Scout fields once and preferably twice a week when pest populations are peaking.
• Bollworm/tobacco budworm treatments should be targeted at the egg and small larval (<1/4-inch in length) stages. Selection of insecticides should be based on the species composition of the bollworm/tobacco budworm complex. Agricultural consultants and producers can utilize pheromone trap data, moth flushing counts, etc. to determine the species complex.
• A minimum of two applications four to five days apart may be necessary for satisfactory control of moderate to heavy budworm infestations.
• Evaluate potential reasons (ex. population level and age structure, application timing, environmental conditions, and levels of insecticide resistance) in the event of a control failure with tobacco budworms. Avoid consecutive applications of insecticides from the same chemical class.

These insecticide management guidelines were partially adapted from those drafted by entomologists in Arkansas, Louisiana, Mississippi, and Tennessee.

Insect Control Termination:
Once cotton is at the "cutout" stage, the crop becomes less attractive to many late-season pests. Insecticide applications often can be discontinued when a majority of the harvestable bolls are past the economic loss stage caused by insects (ex. cotton bollworms, tobacco budworms). But, aphid, European corn borer, fall armyworm, and whitefly infestations may still pose a threat late in the season. European corn borers and fall armyworms can damage relatively mature bolls, and aphids plus whiteflies produce honeydew that can lower the lint quality and crop prices if not controlled.

An effective decision-making guide to determine when insecticide termination can occur is using heat unit accumulation to measure boll maturity. Current research suggests that the accumulation of 350-450 heat units (DD60s) from the "cutout" stage [Nodes Above White Flower (NAWF) = 5] is enough time for yield-producing bolls to mature beyond the stage that cotton bollworm and tobacco budworm feeding damage could cause economic losses. This generally corresponds to a calendar date of around August the 10th. Bolls should be protected for approximately 21 days.

Bacillus thuringiensis (Bt) Cotton Guidelines:
1) Current Bt-transgenic varieties are recommended for areas with a high risk for tobacco budworm and cotton bollworm infestations.

2) Do not trigger insecticide treatments for tobacco budworm and cotton bollworm infestations based on egg counts because larvae must first ingest a toxic dose of the Bt toxin.

3) Monitor fields weekly and examine blooms and under bloom tags of Bollgard I and II varieties for larvae feeding on developing bolls. Flower pollen has a lower expression of the Bt toxins in the Bollgard I and II technologies. Thus, larvae feeding on flowers are less likely to die and may damage developing bolls beneath bloom tags. With the WideStrike technology, newer leaf tissue (ex. terminal) may have a lower expression of the Bt toxins than older tissue; therefore, more terminal damage may be observed with the WideStrike versus Bollgard technologies.

4) For 2005 there are three approved refuge options for planting Bt cotton.

Option 1:
With the 20% acreage refuge all Bollgard fields must lie within 1-mile of the refuge area, and this refuge area cannot be treated with foliar Bt sprays for control of tobacco budworms or cotton bollworms. Foliar insecticide treatments are recommended when 4 or more surviving larvae (¼-inch or greater in length) per 100 plants and/or 2% boll damage is present.

Option 2:
With the 5% refuge option, do not control tobacco budworms or cotton bollworms in these areas with any product specially targeted at these insects. This unsprayed refuge must be at least 150 feet wide. All Bollgard fields must lie within ½-mile of this unsprayed refuge option.

Option 3:
A third option is a non-Bt embedded 5% refuge. The refuge area can be embedded within a larger field or field unit (1-mile by 1-mile), and can be treated with any insecticide used to treat the Bollgard fields within the same 24-hour period. It also can serve as a community refuge area provided the distance and other requirements are met. Whether you chose the 5% or 20% refuge option, you should still control all non-caterpillar pests.

Second Generation Bt Cotton:
Bollgard II and WideStrike cotton each are a combination of two Cry toxins that provide a wider range of control of other caterpillar (ex. armyworms, cotton bollworm, loopers) pests than that obtained with the original Bollgard I cotton technology. Research indicates that both Bollgard II and WideStrike cotton probably will not require insecticide applications for caterpillar infestations except at high population levels. New thresholds and scouting procedures are still being developed at this time for second generation Bt cotton technologies; therefore, you should consider using thresholds originally developed for Bollgard I cotton unless otherwise advised. Do not expect control of cutworm infestations, nor do these new Bt cotton technologies control aphids, plant bugs, stink bugs, and other non-caterpillar pests. Refuge requirements for Bollgard II and WideStrike will remain the same as those recommended for Bollgard I cotton.

Insecticide Use:
Once-a-week scouting is usually sufficient to determine insecticide use; however, in areas with high insect pressure or rapidly increasing populations (ex. plant bugs), twice-a-week scouting may be required. Economic thresholds (ET), the pest density when treatment is needed to prevent pest populations from reaching economically damaging levels, have been established for most cotton pest species. Total fruit loss, nodes incurring loss, and the status of fruit positions on each node should be considered when utilizing an ET. Apply insecticides only when needed to preserve beneficial insect populations and prevent secondary pest outbreaks.

Precautions: : All insecticides are poisons and should be handled with caution. Carefully follow manufacturer label directions before you buy, mix, apply, store, or dispose of any insecticide. Protective clothing and proper safety precautions are needed when applying an insecticide. Growers, scouts, and farm laborers should communicate about when, where, and what insecticide was applied. Reentry periods vary by product, and scouts should not enter fields until the reentry interval has expired. Reentry and preharvest intervals for some insecticides are listed in Table 1. Do not apply long residual or highly toxic insecticides immediately adjacent to or over fish-bearing waters. An insecticide-free zone (50-100 feet) should be in place between the treated crop and bodies of open water.

Table 1. Reentry and preharvest intervals for selected insecticides used in cotton. This list does not include all insecticides labeled for cotton. Reentry and preharvest intervals for insecticides not listed can be found on the insecticide label.

Plant Bugs / Cotton Fleahoppers: There are two plant bug species (clouded and tarnished plant bug) plus cotton fleahoppers commonly found in Missouri. Plant bugs cause injury by extracting plant juices, and these plants will abort damaged squares and small bolls. Cotton fleahopper damage also can cause plants to develop spindly branches. The most severe injury from these insects occurs during the first four weeks of the fruiting season. Environmental conditions that lead to carbohydrate stress also cause square shedding; therefore, be sure insects are causing this fruit shed before applying insecticides. Scouting efforts should be intensified for plant bugs and other pests if square retention drops below 80% at first position sites before bloom. Examine border vegetation to determine the extent of plant bug populations in an area. Fields treated for plant bugs should be closely monitored until harvest for subsequent aphid and/or bollworm infestations. Damage Symptoms: square shed; deformed and brownish-colored blooms; young bolls stunted with reddish-brown specks, bolls eventually turn yellow and fall off the plant.