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West Plains |
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| Kerry Siders, EA-IPM |
(806)
894-2406 (phone)
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(806) 638-5635(mobile)
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(806) 897-3104 (FAX)
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| E-Mail: k-siders@tamu.edu | http://lubbock.tamu.edu/ipm | ||||
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| Vol. 7, No. 9 |
1212
Houston Street, Suite 2, Levelland, TX 79336
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July
17, 2002
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CROP
& INSECT SITUATION On cotton, which ranges from first square to 2-3 boll cotton, things are getting interesting. Much concern has been generated in the eastern and southern portions of Hockley County over cotton bollworms. We have been watching our scouting fields in that area very closely. To-date we have not seen bollworm number go over 4,500 per acre. Mortality remains high from both predation and heat. Damage is minimal to fields with still exceptionally high square and boll set. |
I do not doubt however, that there are fields which may have reached economic threshold or even the chronic "nickel and dime" level for justifying a pesticide application. I warn you though that it could be a slippery slope you find yourself on if an application is not thoroughly justified. Across the whole area of Hockley and Cochran Counties though we can find cotton bollworms at less than 2500 per acre, armyworms (beet and yellow stripped) up to 15,000 per acre, very few lygus, light grasshoppers, and stink bugs. A week ago we were finding cotton aphids in good numbers scattered throughout. However, this week they are not there. We can chalk this up to beneficials. Irrigation needs to be started if not already. I am seeing too much wilt on some fields during this critical water consumption period. Weed control has been a challenge and has keep many from starting the water. But let us not sacrifice a good crop for the sake of a clean crop. Call if you need help on weed control, irrigation, insect control or any other questions I can try and provide answers to. Bollworm
and Tobacco Budworm |
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Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomic level, race, color, sex, religion, handicap or national origin. The information given herein is for educational purposes only. References to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied. |
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The Texas A&M University
System, U.S. Department of Agriculture, and the Commissioners Courts
of Texas Cooperating
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Tobacco
budworm and bollworm moths are attracted to and lay eggs readily in
cotton that is producing an abundance of new growth. Moths usually
lay single eggs on the tops of young, tender terminal leaves in the
upper third of the plant. Eggs are pearly white to cream color and
about half the size of a pinhead. These should not be confused with
looper eggs, which are flatter and usually laid singly on the undersides
of leaves. Eggs hatch in 3 to 4 days, turning light brown before hatching. Sometimes moths deposit eggs on squares, bolls, stems and, in general, lower parts of the plant. This may occur when cotton plants are stressed and making little new growth, or during periods of high temperature and low humidity. Detection of eggs and control of small worms are more difficult when eggs are deposited in these locations. Budworms are generally more resistant to insecticides than bollworms. Budworms are less numerous than bollworms until mid-August or early September, and rarely reach damaging levels. Once certain kinds of conventional insecticides are used to control bollworms and budworms, the percentage of budworms in the infestation increases with each additional application because of selection pressure. Aphid and other secondary pest infestations may increase following bollworm/budworm sprays, especially when pyrethroids are used. Management and decision making. Cotton fields should be scouted carefully every 3 to 5 days during periods of predicted moth egg-laying activity. In fields with fewer than five squares per row foot (approximately 67,000 per acre), bollworm populations often collapse and cease to be a problem. |
Eggs and newly hatched worms are usually found in the plant terminals and indicate possible outbreaks. Natural mortality agents such as weather and predators frequently control these pests before any damage occurs. Once worms have grown to larger than ½ inch long, natural and insecticidal control are less effective. Insecticides applied to control 1/2-inch long worms are only moderately effective. Frequently, examination of the upper third of the plant (leaves, stems, squares, blooms and bolls) is all that is needed to make a sound management decision. However, when eggs are being laid all over the plants or when 60 percent or more of the bolls are mature, whole plant counts should be used. Mature, unopened bolls are firm, cannot be dented when pressed between the thumb and forefinger, and cannot be cut easily with a sharp knife. Before bloom. The decision to apply conventional insecticides (as opposed to microbial insecticides, ovicides or no treatment) for bollworm and budworm control during this period should be made very carefully. Conventional insecticides often kill beneficial insects and spiders, thus allowing a rapid increase in bollworm numbers. Avoid making conventional insecticide treatments on the basis of egg numbers or first signs of crop damage. Under most conditions, do not use conventional insecticides before blooms are observed in the field. Treatment may be warranted where 15 to 25 percent of the green squares examined are worm damaged and small worms are present. Consider using a microbial insecticide to preserve beneficial insects and spiders. Microbial insecticide use is discussed further on page 14. After bolls are present. Divide the cotton field into four or more manageable sections depending upon field size. Make whole plant inspections of five randomly chosen sets of three adjacent cotton plants in each section. Count the number of eggs, worms and key predators encountered and estimate the number of eggs, worms or key predators per acre using the following formula: |
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Number
worms, eggs, or key predators counted multiplied by The plant population can be calculated on 40" rows by: counting the number of plants in approximately 13' 1" row feet. Do this in at least 4 locations and average. Multiply that average by 1000. This gives you plants per acre. As an example let us say I counted 45 plants on average in 13' 1" from 4 spots a field. I multiply by 1000 and get 45,000 plants per acre. I scouted the field by checking 40 whole plants and found 10 bollworm eggs, 3 small worms, and 12 key predators like ladybugs and lacewing. I take 45,000 plants/acre and divide by 40 plants checked to get a multiplier of 1125. I simply multiply the number of eggs, worms or predators by the 1125. Therefore, I have approximately 11,250 bollworm eggs/acre; 3,375 small bollworms/acre; and 13,500 key predators. Treatment
may be justified when counts average 5,000 or more small worms per
acre. However, if two or more key predators are found for each small
worm, control measures may not be needed or a microbial insecticide
may be used. The actual |
Bt transgenic cotton management. Research trials evaluating the Bollgard™ transgenic Bt gene technology have determined it to be highly effective against tobacco budworms. Bollgard™ cottons are also effective against cotton bollworm, but under heavy pressure from this species insecticide treatment may be needed. The entire plant should be searched for tobacco budworm and bollworm larvae and injury. A proper sample includes squares, white blooms, pink blooms, bloom tags and bolls. Scouting intervals should be reduced to 3 to 4 days during periods of increasing bollworm egg laying, especially during peak bloom. Treatment should not be triggered by the presence of eggs alone. Hatching larvae must first feed on the cotton plant to receive a toxic dose. Treatment with foliar insecticides for tobacco bud-worm or bollworm should be considered when 5,000 larvae per acre larger than 1/4 inch are present (based on a population of 40,000 to 60,000 plants/acre) and 5 to 15 percent of the squares or bolls are worm damaged. As with non-Bt cotton, a range of treatment thresholds is provided since many factors in addition to density of larvae and square damage determine the need to treat Bt cotton with insecticides. Many of these factors are the same as those listed above for non-Bt cotton. As in non-Bt cotton, predators and parasites are very important in reducing the numbers of eggs and larvae and they compliment the control provided by these varieties. The use of a non-Bt cotton refuge is a requirement for planting Bt cotton and is an important component of resistance management.
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* The synthetic pyrethroid insectidides recommended for control of bollworms also will control boll weevil. However, application intervals similar to those recommended for the traditional phosphate insecticides (3 to 5 days under heavy pressure) are necessary to provide adequate control. When treatments are to be made for a bollworm-boll weevil complex a suggested treatment regime is to use a pyrethroid followed 3 to 5 days later by a phosphate or carbamate boll weevil insecticide. Since pyrethroids are not more effective than organophosphates or carbamates for boll weevil control, but are more effective for bllworm control, they should be saved for bollworm management. We do not recommend using pyrethroids for boll weevil control alone or for early season pests because increased use may contribute to the development of resistance to pyrethroids. Bifenthrin suppresses spider mites when used for control of bollworms. The use of synthetic pyrethroid insecticides may increase cotton aphid numbers. |
Pesticides Though
pesticides pose many potential risks, they also provide the following
important advantages and benefits: Pesticides are used in IPM programs when no effective alternatives are available or alternatives are not sufficient to keep pest populations from reaching damaging levels. The emphasis is to maximize the benefits and advantages that pesticides offer while minimizing any potential risks. Whenever a pesticide treatment is needed, selection of the chemical should be consistent with the pesticide label and all state and federal laws and regulations. Additional considerations include: effectiveness against the target organism, compatibility with the host plant, effects on beneficial organisms, degree of environmental and user safety, and cost. Wherever possible, use a material that is least toxic to humans and other non-target organisms, and is least likely to contaminate ground and surface waters. |
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Why
Minimize Pesticide Use? Problems
With Overuse of Pesticides
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 Posted at this web site by: texagnet Internet Services.
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