Cotton Insect Pests
Overview of Cotton Insect Management in Mississippi
Insect Pests: Cotton is subject to attack by more than a dozen different species of insect pests in Mississippi (Table 1). The tarnished plant bug is considered to be a key pest of Mississippi cotton because the early season treatments that are often necessary to control plant bugs destroy beneficial insects and thus increase the potential for outbreaks of pests such as aphids and tobacco budworms. In terms of annual estimated yield loss, the tobacco budworm/bollworm complex and the boll weevil have historically ranked among the top three most damaging pests, where they often are accompanied by the tarnished plant bug (Table 2). However, in recent years the boll weevil has disappeared from this table due to a statewide boll weevil eradication program that has reduced boll weevil numbers to the point that they are no longer economically damaging and promises to eliminate all boll weevils from the state within two to three years.
Each of the pests listed in Table 1 is capable of causing economic yield loss in cotton, and some, such as tobacco budworm or boll weevil, potentially can cause 100 percent yield loss in individual fields. Because growers may invest in excess of $500 per acre in producing a cotton crop, and because the crop is at risk from insect damage throughout the growing season, insect management is an extremely important component of cotton crop production. The major challenge facing producers and professional pest managers is to avoid excessive economic losses to insects while keeping the total costs of insect management at a profitable level. Currently, profit margins are quite narrow, and excessive insect control costs can destroy profit potential, even if little or no insect related yield loss is sustained.
Scouting: Knowing pest insect population levels at any given time in the growing season is the key to achieving the dual goals of avoiding excessive yield loss to insects and avoiding excessive control costs. Having accurate estimates of pest insect populations allows growers to make informed insect management decisions. Cotton insect scouting methods vary considerably depending on stage of crop development.
Cotton insect management is both information intensive and time sensitive. Because of the high egg laying capacity and rapid development rate of most insects, fields must be scouted every 3 to 4 days. Because of the low treatment thresholds for many cotton pests, sampling procedures are quite time consuming. For example, sampling for tobacco budworm/bollworm requires examining randomly chosen plants for the presence of eggs and newly hatched larvae that are less than 1/4 inch in length. Scouts must keep a running count of the number of plants examined and the number of insects found so that results can be reported as percent infested plants.
Because the treatment threshold for tobacco budworm on non-Bt cotton during the boll setting period is only four larvae per 100 plants, a relatively large number of plants must be checked in order to obtain accurate counts. As a minimum it is recommended that scouts examine an average of 1 plant per acre (100 plants per 100 acre field) when sampling for budworm/bollworm. However, additional samples may be needed when populations are near the treatment threshold.
Taking these type samples is a time consuming process that can take approximately 1 hour per 100 plant sample. In addition, scouts must also collect information on populations of other insect pests present in the field. Fortunately sampling for other pests can be combined with the budworm/bollworm sampling process with little increase in time.
Because of the time involved in making these insect counts, most Mississippi producers contract the services of a professional crop consultant, usually for a per acre scouting fee, to monitor insect populations and make treatment recommendations. Most consultants employ several summer scouts to help make insect counts. From a grower's perspective, this use of summer scouts is highly desirable as it allows for more intensive, more efficient scouting. More importantly, it is desirable to have more than one individual making counts in a given field, because a single individual, no matter how experienced, may occasionally overlook a developing pest problem.
Integrated Pest Management: Successful cotton insect management requires the use of an integrated approach to insect control and integrated pest management is utilized on 100% of the state's cotton acreage. Simply defined, integrated pest management or IPM refers to the use of several different methods of controlling a particular pest or group of pests, rather than relying solely on a single method of control. Certainly, insecticides are an important component of cotton IPM, but there are several non-insecticidal components of IPM, many of which can be implemented at little or no cost, (Table 3) that producers can utilize to reduce insecticide use.
However, because of the relatively high unit value of cotton and the fact that many cotton insects feed directly on the fruit, the treatment thresholds for many pests are relatively low. Consequently, insecticide applications are often necessary to control pest populations that exceed the economic threshold, despite the other IPM tools that are used, and most of the money spent by growers to control insects goes to purchase insecticides or to pay for fees or costs of insecticide application. Recommended treatment thresholds, insecticides, and rates are listed in the Cotton Insect Control Guide, which is revised annually to include recent research results and newly labeled insecticides.
Cost of Insect Control: Per acre costs of insect control can vary considerably from year to year, depending on weather and other factors that influence insect populations. However, since 1992 there has been a sharp increase in insect control costs. This increase in costs of insect control is largely due to the development of insecticide resistance in pests such as tobacco budworm, tarnished plant bug, and cotton aphid.
Insecticide Resistance: Insect control costs increase sharply in response to resistance because of the need to shift to more costly treatments or use combinations of two or more insecticides, to use higher rates, or to apply treatments more frequently. Development of resistance to older insecticides can also influence pricing of new insecticides simply because the value of newly developed insecticides is greater if older alternatives are not effective. However, the most important result of the development of insecticide resistance is the increased risk of insect induced crop disasters that growers experience. Inability to control pests, such as tobacco budworm, can result in crop failures despite high control costs.
Cotton producers can slow, but not necessarily avoid, the development of insecticide resistance by following resistance management plans structured to use different classes of insecticide chemistry against different generations of pests. Such plans are most effective when practiced by all producers in a relatively wide geographic area.
New Management Tools: Recently several new management tools have become available for control of the tobacco budworm/bollworm complex and other cotton insects. These include transgenic Bt cotton and several new foliar applied insecticides. Because these tools are relatively new, insects have not yet developed resistance to them and they are quite effective against the primary target pests. Availability of these new pest control tools has helped lessen the risks of insect related crop failures but has had less effect in reducing costs of cotton insect control.
Transgenic Bt cotton refers to cotton varieties that have been genetically modified by the insertion of genes from the naturally occurring bacterium, Bacillus thuringiensis. These genes allow the production of the Cry1 Ac Bt toxin within the transgenic cotton plants. When it was first introduced in 1996 only two varieties of Bt cotton were available, however in 2000 approximately a dozen cotton varieties of Bt cotton were available.
Bt cotton producing the Cry1Ac protein is highly effective against tobacco budworms (Heliothis virescens) and provides significant control of bollworms (Helicoverpa zea). However, when bollworm infestation levels are moderate to high, enough larvae may survive on Bt cotton to cause economic damage, and supplemental foliar treatments are often required. Since it was first introduced in 1996, Bt cotton has maintained a record of requiring fewer foliar applied caterpillar treatments, while also sustaining much less caterpillar induced boll damage.
Bt cotton also provides limited suppression of other caterpillar pests, such as loopers and armyworms, but it's efficacy against these pests is relatively low, and both groups have the potential to cause damaage to Bt cotton. Bt cotton has no activity against non-caterpillar pests, such as tarnished plant bug and cotton aphids.
Since it's introduction Bt cotton has proven very useful in reducing the risks of excessive yield losses to tobacco budworm and other caterpillar pests, particularly in areas involved in the early years of boll weevil eradication. In 2000, approximately 75% of Mississippi's cotton acreaage was planted to transgenic Bt varieties. The average fee paid by growers to use this technology was approximately $30 per acre.
An improved form of Bt cotton, BollGard II, which contains genes for the simultaneous production of two Bt toxins, CrylAc and Cry2Ab, is currently in the development and testing stage. Initial results indicate that this product has similar efficacy against tobacco budworm, but is much more effective against bollworm and other caterpillar pests. Like its predecessor, BollGard II does not control non-caterpillar pests. Cotton seed containing the BollGard II gene are expected to be commercially available within two to three years. The improved control provided by these dual toxins is expected to result in reduced caterpillar damage and enhanced resistance management.
During recent years, several new insecticides have been developed and introduced for control of cotton insect pests. These include the biologically derived foliar insecticide spinosad (Tracer), which was first introduced in 1997, and indoxacarb (Steward), which was first labeled for use in 2001. Both of these products are primarily labeled for control of caterpillar pests, although indoxacarb (Steward) has some activity against tarnished plant bugs.
Two insect growth regulators: tebufenozide (Confirm) and methoxyfenozide (Intrepid) have also been recently labeled for control of caterpillar pests. These growth regulators are primarily useful against armyworms and/or loopers.
Availability of these new insecticides and transgenic cotton varieties, along with the continued availability of many older pest management tools, provides cotton producers with more options for cotton insect management than have ever been available before. Successful eradication of the boll weevil will enhance these options even more. Thus by wisely using both Bt cotton varieties and non-Bt varieties in combination with other available insect management tools, Mississippi cotton producers have a better opportunity than ever before to effectively control cotton insect pests and to successfully practice resistance management.
One trait shared by these tools is that they are very target specific, providing control of many caterpillar species but having little activity against non-caterpillars. This narrow spectrum of activity has both advantages and disadvantages. It allows control of caterpillar pests without affecting survival of most beneficial insect species, but non-caterpillar pests, such as tarnished plant bugs and cotton aphids which may also be present in damaging numbers, are not controlled without the use of a second insecticide.
Boll Weevil Eradication: As of August of 1999, all Mississippi cotton is involved in a Boll Weevil Eradication Program. Mississippi is divided into 4 Boll Weevil Eradication regions. Eradication efforts began in the eastern portion of the state (Regions 3 and 4) in August of 1997 and in the South Delta portion of the state (Region 2) in August of 1998. The initiation of boll weevil eradication efforts in the North Delta (Region 1) in August of 1999 marked the beginning of the end of boll weevil infestations in Mississippi cotton. These 5 year eradication programs are primarily funded by per acre assessment fees paid by producers.
Eradication is accomplished by using boll weevil pheromone traps on all cotton fields within an eradication area to determine whether or not fields within an eradication area are infested. Fields that are infested are treated with ULV malathion insecticide treatments. During the early years of an eradication program the total number of insecticide treatments applied to control boll weevils may be somewhat higher than what growers would normally apply in the absence of an eradication program. However, as the eradication program progresses into the 4th and 5th years the number of treatments required declines sharply and reaches or approaches zero. Progress of Mississippi's boll weevil eradication program is evidenced by the fact that no economic yield loss was attributed to boll weevil in the 2000 growing season.
During the first and second full season of an eradication program, growers often experience increased problems with secondary pests such as, tobacco budworm, beet armyworms, aphids and whiteflies. This is due to the increased number of insecticide treatments applied during these years and the resulting impact on beneficial insect populations. However, the long term impact of successfully eradicating the boll weevil, and eliminating the early season treatments routinely required to control this key pest, is to greatly reduce secondary pest problems, insect related yield losses, and control costs.
More Current Information: For more timely information on the cotton insect situation in Mississippi check the Mississippi Crop Situation Newsletter, which is produced weekly during the summer months. Also check the Cotton Insect Hotline 1-800-445-4931, which provides a 3 to 5 minute taped message on the current cotton insect situation that is updated 1 to 3 times weekly on an as needed basis.
Insect Species Attacking Mississippi Cotton
| Common Name | Type of Damage |
|---|---|
| Thrips (several species) | adults and immatures cause distortion of leaves and terminal of seedling plants |
| Cutworms (several species) | larvae feed on seedling plants, cutting mainstem at or just above ground level |
| Boll Weevil | adult feeds on squares and bolls, larvae develop inside squares and bolls |
| Tarnished Plant Bug | adults and nymphs feed on small squares causing them to abort, also feed on bolls |
| Bollworm | larvae feed on squares, bolls, and terminals |
| Tobacco Budworm | larvae feed on squares, bolls, and terminals |
| Cotton Aphid | adults and nymphs suck sap from leaves, producing honeydew and sooty mold |
| Whiteflies | adults and nymphs suck sap from leaves, producing honeydew and sooty mold |
| Spider Mites (several species) | adults and immatures of this tiny arthropod suck sap from leaves |
| Beet Armyworm | larvae feed on leaves, causing defoliation, also feed on squares, blooms, and bolls |
| Fall Armyworm | larvae feed primarily on blooms and large bolls, occasionally feed on squares |
| Yellow-striped Armyworm | larvae feed primarily on leaves, occasionally feed on squares, or bolls |
| Cabbage Loopers | larvae feed exclusively on leaves |
| Soybean Loopers | larvae feed exclusively on leaves |
| Stink Bugs (several species) | adults and nymphs feed primarily on bolls |
Ten year summary of the top three most damaging cotton insects in Mississippi
| Rank in Terms of Estimated Yield Loss |
| Year | 1st | 2nd | 3rd |
| 2002 | Budworm/Bollworm | Plant Bug | Thrips |
| 2001 | Plant Bug | Budworm/Bollworm | Stink Bug |
| 2000 | Budworm/Bollworm | Thrips | Fall Armyworm |
| 1999 | Budworm/Bollworm | Cotton Aphid | Plant Bug |
| 1998 | Budworm/Bollworm | Boll Weevil | Cotton Aphid |
| 1997 | Budworm/Bollworm | Boll Weevil | Plant Bug |
| 1996 | Boll Weevil | Budworm/Bollworm | Plant Bug |
| 1995 | Budworm/Bollworm | Boll Weevil | Cotton Aphid |
| 1994 | Budworm/Bollworm | Plant Bug | Boll Weevil |
| 1993 | Beet Armyworm | Budworm/Bollworm | Boll Weevil |
Some Non-insecticidal Components of Cotton IPM
| 1. | Scout fields twice per week to monitor pest populations |
| 2. | Use economic thresholds to determine need for treatment |
| 3. | Follow recommended guidelines for resistance management |
| 4. | Preserve beneficial insects by using target specific insecticides |
| 5. | Monitor beneficial insect populations and utilize when possible |
| 6. | Plant early maturing varieties to escape late season pests |
| 7. | Plant varieties with insect resistance traits, smoothleaf, etc |
| 8. | Plant varieties with transgenic insect resistance, Bt-cotton |
| 9. | Destroy stalks promptly after harvest to reduce overwintering insect populations |
| 10. | Practice fall or early spring tillage to reduce overwintering insect populations |
| 11. | Avoid excessively dense or sparse plant stand densities |
| 12. | Manage the crop agronomically to promote vigorous growth and early maturity |
| 13. | Terminate insecticide treatments as soon as crop maturity allows |
| 14. | Practice border vegetation management to minimize alternate hosts |
| 15. | Be aware of naturally occurring insect diseases and utilize when possible |
| 16. | State and Federal Quarantines prevent entry of new pests |
| 17. | Boll weevil eradication |
Glossary:
Honeydew: Due to the relatively low protein content of plant sap, aphids must consume high quantities in order to obtain adequate protein. Aphids excrete the excessive sugars contained in the plant sap as a sticky liquid known as honeydew. Excessive accumulation of honeydew on the lint of open bolls can result in an undesirable condition known as "sticky cotton" which causes milling difficulties and hence, grade reductions.
Sooty Mold: The honeydew excreted by aphids accumulates on leaves and other plants where it supports the growth of a group of fungi known as sooty molds. These sooty mold fungi develop on the honeydew, consuming it and eliminating the stickiness it causes, but do not attack the cotton plant itself. Growth of sooty mold results in a black, powdery or sooty layer of growth over the leaves, which when excessive can interfere with photosynthesis.
Key Pest: This term does not necessarily apply to the pest that causes the most damage or is the most costly to control. Rather this term is reserved for a pest that has the potential to cause excessive yield loss and that routinely exceeds the economic threshold early in the season, thus requiring insecticide treatments at a time when insecticide use would not be otherwise necessary. These insecticide treatments destroy populations of beneficial insects that would otherwise aid in suppressing populations of secondary pests and thus increase the frequency and intensity of secondary pest outbreaks.
Treatment Threshold: This term represents the pest population level at which treatment must be applied in order to avoid sustaining economic loss that would be greater than the cost of treatment. Thresholds can vary depending on: pest species, stage of crop development, cost of treatment, price of cotton, potential for flaring secondary pests, ability to control secondary pests, and a variety of other factors.
Integrated Pest Management: Integrated Pest Management or IPM refers to the use of more than one method of managing a pest or complex of pests, rather than relying solely on a single method of control, such as repeated insecticide applications. In an IPM system growers may use a variety of non-insecticidal management tools, such as planting resistant varieties, managing for early maturity, and utilizing naturally occurring beneficial insects to reduce pest numbers and the number of times that pests populations exceed economic thresholds. Insecticides are a necessary and very important component of IPM and are the most common method of control against pest populations that have exceeded treatment thresholds.
Insecticide Resistance: Insecticide resistance refers to an increase in tolerance of a given species of pest to a particular insecticide or class of insecticide chemistry to the point that insecticide rates that initially provided effective control no longer do so.
Secondary Pest: This term is reserved for pests which, in the absence of insecticide treatments for other pests, normally would remain below the economic threshold due to the control provided by naturally occurring predators and parasites. Disruption of these naturally occurring predators and parasites by insecticide treatments targeting other pests allows the secondary pest to build to damaging populations. Tobacco budworm, beet armyworm, and cotton aphid are examples of secondary pests in cotton. Populations of these secondary pests and the number of insecticide treatments required for their control are increased as a result of insecticide treatments applied to control key pests, such as boll weevil and tarnished plant bug.
Resistance Management: A structured plan of pest management designed to delay the development of resistance to key insecticides or other pest management tools. Such plans are usually designed to avoid exposing a portion of the pest population or one or more generations of the pest population to the insecticide or tool in question. Resistance management is most easily practiced when there is a diverse array of management tools available for control of the pest in question. Effective resistance management requires the participation and cooperation of all producers in a relatively large geographic area.