Cotton Insect Management
Integrated Pest Management
Successful, economical control of cotton insect pests requires using a variety of control methods instead of only one, such as scheduled insecticide use. This is approach to insect control is called integrated pest management, or IPM. Current cotton insect control recommendations are based on the IPM concept.
Insecticides are a key part of cotton IPM, but relying only on insecticides is not possible in Mississippi.
The objective of cotton IPM is to use all available, practical, nonchemical methods of suppressing insect populations; to monitor pest populations closely; and, when scouting indicates that pest populations have exceeded economic thresholds, to integrate insecticides in a way that optimizes crop production and minimizes ecosystem disruption. Because of the number of insect pests that attack cotton and the relatively high unit value of the crop, cotton IPM is quite complex. Management tactics applied against one pest may be favorable or unfavorable to the development of other pests in the system. Also, treatments applied during one part of the season may affect future pest populations or your ability to control those pests at later points during the season or in the following years. An overall cotton IPM program must consider these types of long term effects. They greatly influence the ability of Mississippi growers to maintain economical cotton production.
There are many aspects of IPM that must be used to manage cotton insect pests effectively. These include using resistant varieties, managing for early crop maturity, using various cultural practices, managing for insecticide resistance, using economic thresholds, scouting thoroughly, and applying insecticides in a timely manner when needed.
To produce an early high-yielding crop, follow recommended practices for soil preparation, variety selection, planting dates, use of fungicides and herbicides, and protection from insect and mite damage.
To minimize the impact of pests and pest control costs,
- Scout fields regularly. Make careful counts of insect pest populations.
- Use all available, practical noninsecticidal IPM tools.
- Apply insecticides promptly when needed.
- Use the most cost-efficient insecticide recommended for the target pest. Apply insecticide during the most susceptible stage of development.
- Follow recommended guidelines for practicing insecticide-resistance management.
Before deciding to treat and before choosing the insecticide, consider such factors as the potential to intensify secondary pest problems and insecticide resistance.
Information in this guide is provided for educational and planning purposes only. When using agricultural chemicals, you (the user) are responsible for making sure the intended use complies with current regulations and conforms to the product label. Before applying any insecticide, be sure to get current usage information. Read and follow the product label.
Before using a pesticide, read the label carefully. Follow the directions. Pay attention to all precautions on the pesticide container label. Observe all regulations on worker protection and pesticide record-keeping. Store pesticides in plainly labeled containers safely away from livestock, pets, and children. Store pesticides in an area where they will not contaminate food or feed.
Research indicates most cotton pests are pesticide-resistant. Some pesticides control pests in one area and not another. Excessive use of pesticides will intensify the problem.
Proper scouting is the backbone of an effective cotton insect management program. The goal of any scouting program should be to minimize insecticide use and insect control costs by avoiding unnecessary treatments and by timing required treatments properly. Effective scouting requires spending enough time in the field and taking enough samples to make an accurate decision on whether or not treatment is required. Frequency of scouting is critical. During most of the growing season, scout fields thoroughly every 3 to 4 days. Allow enough time in the scouting schedule to allow more frequent “spot checks” when necessary.
Making insect management decisions based on established treatment thresholds rather than applying treatments based on schedules or presence of pests is a proven method of reducing insect management costs. Effective use of thresholds requires frequent, intensive scouting to get accurate estimates of populations of various pest species that may be present in a field.
The term “treatment threshold” means the pest population level at which treatment must be applied to avoid economic loss that would be greater than the cost of the treatment. thresholds can vary, depending on species of pest present, stage of crop development, yield potential of the crop, cost of the treatment, market price, populations of other pests present, number of beneficial insects, potential for flaring secondary pests, ability to control secondary pests, and other factors. The thresholds recommended in this guide vary according to pest species and stage of crop development, but fixed thresholds cannot fully consider the many other factors that can influence a treatment decision. Although the thresholds recommended in this guide are generally somewhat conservative (quick to treat), factors such as multiple pest species or unusually low fruit retention could indicate a need to reduce thresholds. Factors like high beneficial insect populations, risk of flaring difficult-to-control secondary pests, high treatment costs, or low price potential could indicate a need to use higher thresholds.
Available varieties have different levels of susceptibility to certain insect pests. Consider insect resistance/tolerance when selecting seed varieties. Some key traits and their general effect on certain insects are as follows:
Early Maturity — Early maturing, short-season varieties are more likely to escape attack/damage from late-season infestations of budworms/bollworms, tarnished plant bugs, etc.
Smooth Leaf — Aphid and whitefly populations tend to be reduced on smooth leaf varieties. Budworms/bollworms tend to deposit fewer eggs than on hairy varieties. The smooth leaf trait may somewhat favor plant bugs.
Okra Leaf — Varieties with okra leaf trait allow improved canopy penetration of foliar insecticide treatments. This trait also has been associated with resistance to whiteflies.
Nectariless — Plant bug populations tend to be lower on nectariless varieties. Also, the nectariless trait tends to reduce egg production capacity of most moth species because of reduced nectar availability. Populations of beneficial insects that help suppress bollworms/budworms are also generally lower in nectariless cotton.
High Glanding — Varieties with the high glanding trait have additional gossypol glands, increasing resistance to budworms/bollworms.
Bt-transgenic Varieties — Dual gene transgenic varieties (Bollgard II and Widestrike) provide better suppression of bollworms and other caterpillar pests than Bollgard cotton did.
Cultural practices can affect populations of specific insect pests. Here are effects of some common cultural practices:
Fall stalk Destruction — Destroying stalks as soon as possible after harvest helps reduce populations of overwintered boll weevils dramatically.
Fall tillage — Budworms/bollworms overwinter as pupae 1 to 3 inches deep in the soil. Fall tillage destroys some pupae and disrupts exit tunnels, reducing numbers that emerge from overwintering.
Spring tillage — Destroying weeds and/or cover crops by tillage or herbicide at least 3 weeks before planting minimizes risk of cutworm problems. Tilling in early spring, before April 15, will also destroy many overwintering tobacco budworm and bollworm pupae.
No-till Planting — No-till planting has both negative and positive effects on cotton insect populations. Fields planted no-till are at greater risk for cutworm infestations. They are much more likely to have stand-threatening infestations of occasional early-season seedling pests, such as grasshoppers, false chinch bugs, and a variety of other pests. Scout fields planted no-till very frequently during the first 3 to 4 weeks after emergence. One of the most significant features of no-till production is the establishment of high populations of fire ants. Fire ants will tend and protect certain sucking pests, such as aphids and three-cornered alfalfa hoppers, causing their numbers to be higher in no-till cotton. But fire ants are also very aggressive predators of the eggs, larvae, and pupae of caterpillar pests. The impact of fire ants on caterpillar populations in no-till cotton can be very significant, and it is not unusual for fire ants and other beneficial insects together to suppress caterpillar pests in both Bt and non-Bt fields that are planted no-till. High numbers of snails and negro bugs often occur in no-till fields, but neither of these species has been observed to cause damage to cotton, even when populations are extremely high.
Plant stand Density — Excessive plant stand density can result in delayed fruit initiation and delayed maturity, increasing exposure to late-season insects.
Early Maturity — Early-maturing crops are more likely to escape attack/damage from late-season infestations of tobacco budworms, bollworms, armyworms, loopers, and other pests. Cultural practices such as excessive nitrogen use, late irrigation, or excessive stand density can result in delayed maturity and increased exposure to late-season insects.
Insecticide treatment termination — End insecticide treatments for tobacco budworms, bollworms, and other pests as soon as crop maturity monitoring indicates the crop is reasonably safe from further damage. This step will reduce insecticide use, control costs, and reduce future insecticide resistance.
Border Vegetation Management — Plant bugs can build up on flowering plants growing around field borders. They may move into cotton fields when the flowering plants are destroyed or begin to dry up. Timely mowing of such areas can help reduce available hosts for plant bugs. Mow before cotton is established. Mowing after these weed hosts begin forming flower buds will only force plant bugs into nearby cotton. Wild geranium is an important spring host of tobacco budworms, and controlling it by mowing or displacing it with a non-host plant may help reduce tobacco budworm populations. Caution: do not spray field borders with insecticides. Such use is not labeled and may worsen pesticide resistance.
Mississippi cotton producers are fortunate to have a wide array of naturally occurring biological control agents that play an important role in managing pest populations. Collectively, these biological control agents are the main method of controlling cotton insect pests in Mississippi. Often the full economic value of these biological agents is not recognized or appreciated. Severe outbreaks resulting in high levels of crop loss or unusually high control costs seldom occur unless natural control has been disrupted. Profitable cotton production would not be possible in Mississippi without the help of these biological control agents. These biological agents include predators such as big-eyed bugs, lady beetles, spiders, and minute pirate bugs; parasites such as Cardiochiles, a wasp that parasitizes tobacco budworms; and diseases such as the Neozygites fungal disease, which helps control aphid outbreaks.
To gain the maximum economic benefit from the control provided by these natural control agents, growers need to know which species are beneficial, how to identify these species, which pests they attack, what factors enhance their usefulness, when they are most useful, and when they may not provide effective control.
Predators and Parasites
Predators and parasites can often prevent a pest population from reaching treatable levels, and the control they provide is often cheaper, better, and longer-lasting than that provided by insecticides. Be aware of population levels of naturally occurring predators and parasites and recognize that treatment thresholds can often be increased when predator and population levels are high. Certain cultural practices may favor populations of specific predators. (For example, reduced tillage encourages fire ants.) When insecticide treatment is necessary, choose treatments that have minimal impact on populations of certain beneficial insects but still control the target pest.
Pathogens or Diseases
Most species of insect pests are susceptible to one or more known diseases. In some cases, the impact of the disease is relatively subtle and slows population development. In other cases, the disease is quite dramatic, providing quick, almost total control of a pest population that has neared or exceeded damaging levels. Growers should be especially aware of these latter types of diseases because an outbreak of this type can eliminate the need for any insecticide treatment. Two examples of diseases of this type are the Neozygites fungal disease, which attacks cotton aphid populations, and a similar fungal disease, which attacks loopers.
When feasible, eradication of a pest can be a highly effective IPM tool. Eradication is seldom feasible for native pests, but it is sometimes possible to eradicate nonnative pests, such as the boll weevil. Since it invaded the state in the early 1900s, the boll weevil has been considered to be a “key pest” of cotton. This is because the early-season insecticide treatments that had to be applied to control boll weevils also destroyed beneficial insects and caused a flare-up of “secondary pests,” such as tobacco budworms and cotton aphids. Eradication of the boll weevil eliminates the yield losses and control costs that are directly caused by boll weevils. Eradication also eliminates yield losses and control costs from secondary pest problems that are caused by boll weevil control efforts. Currently, all cotton in Mississippi is considered weevil-free. • Promptly alert eradication personnel of any field detections of live boll weevils or weevil-punctured squares.
In addition to this publication, several other Extension publications on cotton insect biology and management are available at
www.MSUcares.com or from your county Extension agent.
Publication 1614—Pests, Thresholds, and the Cotton Plant
Publication 1640—Cotton Insect ID Guide
Publication 2294—The Boll Weevil in Mississippi: Gone but Not Forgotten
Publication 2108—Insect Scouting and Management in Bt-Transgenic Cotton
Publication 2302—Biology and Control of Thrips on Seedling Cotton
Cotton Insect Situation Newsletters (call 662-325-2085 for information)
MSU Cotton Entomology website: MSUcares.com/insects/cotton
NOTE: The scientific name of the cotton bollworm, formerly Heliothis zea, has been changed to Helicoverpa zea. However, in this guide the use of Heliothis or Heliothis spp. continues to refer to both cotton bollworms and tobacco budworms.
Insecticide Resistance and Resistance Management
Insecticide resistance is the increased tolerance to a particular insecticide by a pest population to the point the insecticide no longer controls effectively. This definition applies to insecticides delivered through transgenic crops as well as to foliar-applied insecticides.
Resistance develops as a result of repeated or continuous exposure of a pest population to a particular insecticide or class of insecticides. Following an insecticide application, the death rate for susceptible insects is considerably higher than the death rate of resistant insects. The numbers of resistant insects increase, and the resistance genes are passed down to the next generation. If the same insecticide or class of insecticide is used against the next generation of pests, the level of resistance increases even more. At first the number of resistant individuals within a population may be really low — 1 in every 10,000 or more — and the pesticide is very effective. However, if you keep using the same insecticide or class of insecticides, the percent of the population made up of resistant insects increases. As a result, that pesticide or pesticide class becomes less efficient, and field failures begin to occur.
High Cost of Resistance: Resistance is costly to cotton producers because it creates the need to increase insecticide rates, shorten treatment intervals, use expensive mixtures of insecticides, or use more costly alternative insecticides to maintain effective control. Reduced control means lower yield, which further reduces profits. Without effective treatment alternatives, outbreaks of resistant pests can result in disastrous levels of crop destruction.
Resistance Management: Insecticide resistance management is a plan of insecticide use that limits exposure of a pest population to a particular class of insecticide chemistry in order to prolong the useful life of that insecticide or class of insecticides. It is important to note that the goal of resistance management is not necessarily to prevent resistance from ever occurring, but to slow the development of resistance.
To be most effective, resistance management must be started before resistance is evident (while the frequency of resistance genes is very low) rather than after resistance is evident in the field (when the frequency of resistance is high). Because most cotton insects can readily move from farm to farm, resistance management efforts are most effective when all producers in a large geographic area practice them.
With foliar insecticides, selection for resistance may occur whenever an insecticide is used, simply because the pests that survive exposure to the treatment are more likely to be resistant. After an insecticide has been applied, the proportion of the pest population that carries genes for resistance to that insecticide is higher. With foliar insecticides, you can delay resistance by not exposing successive generations of pests to insecticides from the same class. Rotating different classes of insecticides against different generations of pests is an effective resistance management tool because insects resistant to one class of chemistry are often susceptible to insecticides from a different class. This provides immediate benefits in terms of improved control and long-term benefits in terms of reduced selection for resistance. The risk of resistance developing to transgenic control methods is especially high because the toxicant is present throughout the life of the plant, and any target pests that attack the crop are subjected to selection for resistance. With transgenic crops, resistance can be delayed by limiting the planting of crops that express a particular insecticide and by planting significant acreage of nontransgenic crops close to the transgenic crops. The objective is to let nonresistant insects from the non-transgenic crops interbreed with any resistant insects that survive in the transgenic crop.
In past years cotton growers have had difficulty effectively managing resistance because of the limited availability of effective alternative control tools. Mississippi growers are now very fortunate to have a wide array of tools available to control many of the most damaging pests. these include boll weevil eradication, transgenic Bt cotton, and an impressive array of highly effective foliar applied insecticides. By effectively using all of these tools and avoiding overuse of any single method of control, Mississippi cotton producers have a greater opportunity than ever before to practice resistance management effectively.
Resistance Management Plan, Caterpillar Pests: Growers can optimize their ability to manage resistance to both Bt cotton and foliar-applied insecticides by observing the following precautions:
1) Continue to support boll weevil eradication maintenance and take advantage of the benefits it offers in managing caterpillar pests. These benefits include increased ability to rely on beneficial insects to suppress populations of caterpillar pests and an overall reduction in the number of foliar insecticide treatments required to control caterpillar pests.
2) Plant the crop in a timely manner (April 15 to May 15 is the optimum planting window). Manage the crop to promote early maturity.
3) Plant fields that historically experience heaviest tobacco budworm infestations to Bt varieties.
4) Scout Bt fields for caterpillar pests and treat promptly with supplemental foliar insecticides if you detect damaging levels of caterpillar pests.
5) When non-Bt fields require treatment for caterpillar pests, rotate use of different classes of foliar insecticides against different generations of pests. Do not use the same insecticide or class of insecticides on successive generations of pests.
6) Stop insecticide applications as soon as the majority of the harvestable crop reaches maturity.
Dual gene Bt Cottons (Bollgard II and Widestrike): Currently, the U.s. environmental Protection Agency does not require the planting of a non-Bt cotton refuge for plantings of Bollgard II and Widestrike.
Resistance Management Plan, tarnished Plant Bugs and Cotton Aphids:
1) When choosing insecticides for use at planting or as foliar sprays for early-season thrips control, avoid using products that will be used later to control cotton aphids.
2) When choosing insecticides for use against aphids or plant bugs, avoid making repeated applications of the same insecticide or insecticides from the same class against following generations of pests.
Responding to Control Failures
Key considerations and responses following suspected insecticide failures:
1) Don’t panic! Do not automatically assume that the presence of live insects following an insecticide application is the result of an insecticide failure.
2) Examine the possible reasons that unsatisfactory control may have occurred. Control decisions should consider a wide range of variables that influence insecticide efficacy and damage potential: species complex, population density and age structure, application
timing, insecticide dosage rate, application methods and carriers, treatment evaluation timing, need for multiple applications, environmental conditions, and levels of insecticide resistance.
3) Under continuous pressure, multiple insecticide applications are required to reduce crop damage. Against high, sustained infestations, multiple close-interval (3 to 5 days) applications of recommended economical treatments are often more effective than applications of expensive mixtures at high rates applied at longer intervals.
4) Selected combinations of insecticides are recommended to manage tobacco budworms at discrete time periods throughout the growing season. Do not use excessive rates of one or more insecticides in these mixtures. Using more than the recommended rate may not improve control.
5) If a field failure is suspected to be due to insecticide resistance, do not reapply the same insecticide. Change to another class of insecticides or use mixtures of insecticides from different classes.
6) Do not apply insecticides to control tobacco budworms beyond the time the major portion of the crop is resistant to insect damage. Protecting fruit that will not be harvested is not cost-effective and further selects for insecticide resistance.
IMPORTANT: The following cotton insect control recommendations include treatment thresholds, insecticides, and suggested rates for specific pests. The recommendations are divided into three distinct sections based on stage of plant development
(Emergence to First Square, First Square to First Bloom, and After First Bloom). Because important pests, thresholds, and control recommendations depend on stage of plant development, be sure you are referring to the proper section when using this guide.
CAUTION: Recommendations of specific insecticides are based on information on the manufacturer’s label and performance in a limited number of efficacy trials. Because levels of insecticide resistance, environmental conditions, and methods of application by growers may vary widely, insecticide performance will not always match the safety and pest control standards indicated by experimental data.
Insecticides are listed alphabetically, not in order of their effectiveness. Effectiveness of a particular insecticide can vary greatly from field to field, depending on previous insecticide use, pest species, levels of resistance, and many other factors. Within a group of insecticides recommended for control of a specific pest, there is often considerable variability in cost, effectiveness against the primary target pest, and secondary pests controlled. When selecting insecticides, growers must consider each of these factors as well as the need to rotate among different insecticide classes for resistance management purposes.
Classes of insecticides: Effective resistance management requires rotation among the various classes of available insecticide chemistry. Often when one insecticide in a class fails because of insecticide resistance, other insecticides in the same class will also be ineffective. Selection of an insecticide from a different class will improve the chances of obtaining control. Growers need to be very aware of the type of insecticide chemistry being used. Classes of insecticides recommended in this guide are identified by the following abbreviations:
Avermectins – (AV)
Biologicals – (B)
Chloro-nicotinyl – (CN)
Carbamate – (C)
Insect Growth Regulators – (IGR)
Organophosphate – (OP)
Organochlorine – (OC)
Oxadiazine – (OX)
Pyrethroid – (P)
Pyridine Carboxamide – (PC)
Tetronic Acid – (TA)
Spinosyns – (SPN)
Terminating Insecticide Applications
In a normal, healthy crop, “cutout” is the point when Node Above White Flower averages 5 (NAWF = 5). In other words, cutout is the point when terminal growth slows to the point that the first position white flower is at the fifth node below the first “unfurled” leaf in the terminal. An unfurled leaf is about the size of a quarter. Sample at least ten plants per site from four representative
sites per field to determine average NAWF. Begin monitoring NAWF at weekly intervals shortly after first bloom.
Shift to twice weekly monitoring as NAWF counts begin to decline toward five. Begin monitoring daily heat unit (DD60s) accumulation on the day the crop reaches NAWF = 5.
Recent research has shown that growth and development in a normal, healthy crop are such that the last population of bolls that will effectively contribute to yield will be represented by those white blooms that are present at cutout (when the crop reaches NAWF = 5). Research has also shown that when these bolls accumulate 350 to 400 heat units (HU), or DD60s, they have a low
probability of sustaining economic damage from tarnished plant bugs (nymphs or adults) or from budworm/bollworm larvae that emerge after this point. erefore, control of tarnished plant bugs and budworms/bollworms can generally be terminated at nAWF = 5 + 350-400 HU (DD60s). Note, however, that threshold populations of larvae hatching before this point in the development
of the crop should be controlled. Also note that this guideline for terminating insecticide treatments applies primarily to bollworms and tobacco budworms and tarnished plant bugs.
Control of stinkbugs can be terminated at nAWF = 5 + 450 HU.
Control of fall armyworms can be terminated at nAWF = 5 + 500-550 HU.
Leaves help bolls mature, so protect the crop from excessive defoliation from pests such as loopers beyond the point of NAWF = 5 + 350 – 400 HUs.
NOTE: This technique for deciding when to end cotton insect control has not been tested under all weather and crop conditions, especially where early stress or insect damage results in poor square set or any other condition that causes late maturity. Growers and consultants must monitor crop maturity and insect populations carefully on a field by field basis and use all available information on crop development and status to decide when to end insecticide treatments. Ask your Extension entomologist or county Extension agent for more about how to use this technique.
Estimating plants/acre, squares/acre, bolls/acre, etc: An acre of land is 43,560 square feet. If the crop is planted on 40-inch row centers, there are about 13,070 linear row feet on an acre. If crop is planted on 38-inch row centers, there are about 13,760 linear row feet on an acre. The following technique for estimating numbers of plants (and others) per acre involves making total counts on about 1/1,000 of an acre. Choose four 40-inch lengths of row from four different locations in the field. Count all plants, etc., on these 40-inch units. Add together the individual counts and multiply by 1,000. This gives an estimate of the number of plants, squares, etc., per acre.
Insect pests to expect at different stages of plant development: Based on historical data, the following pests could be expected at different stages of plant development. This is a generalized statement; your conditions may be different.
|Stage of Plant Development||Major Pests||Occasional Pests|
|Emergence to fourth true leaf||thrips||aphids, cutworms, armyworms, saltmarsh caterpillars, grasshoppers, spider mites|
|Fourth true leaf to first square||none||plant bugs, spider mites, aphids, armyworms, saltmarsh caterpillars, grasshoppers|
|First square to first bloom||bollworms, plant bugs, tobacco budworms||spider mites, aphids, fleahoppers, armyworms|
|After first bloom||bollworms, tobacco budworms||aphids, whiteflies, plant bugs, beet armyworms, loopers, spider mites, fall armyworms, stink bugs|