As cotton matures and changes, so do the pests challenging its productivity. J. Terry Pitts, Oklahoma State University Extension specialist, entomology, integrated pest management, offers an update on the 2009 cotton growing season:
"We are at or past the first bloom stage in almost all cotton fields. Cotton will no longer be vulnerable to cotton fleahoppers once the cotton begins to bloom. It is now time to look at midseason pests,” Pitts says.
"We are seeing large numbers of bollworm moths but current cotton varieties contain the Bt gene and are not vulnerable to yield-limiting worm damage.
He cautioned growers to watch for two pests that occasionally occur in cotton, cotton aphids and spider mites. “Cotton aphids are small, soft bodied insects commonly referred to as 'plant lice.' Aphids can occur on cotton in such high numbers that control methods should be implemented. Buildups are localized and usually occur after cool, damp weather or during the season after the use of certain insecticides.
"The insects are found on the underside of leaves and along the terminal stem, causing misshapen leaves with downward curl and stunted plants. The insect damages cotton directly by sucking juices from the plant and indirectly by secreting honeydew. The honeydew is slick and can lower the grade of cotton lint. A sooty mold can grow on the honeydew, further damaging the lint.” Pitts says.
"Cotton aphids can be controlled with chemical applications, but the number of beneficial insects should be taken into consideration before using a spray. It is often best to determine the aphid population level and also count the numbers and type of beneficial insects. The following week, similar counts should be made. If the aphids are not increasing in numbers, then allow the beneficials to do their job. If aphids are increasing two to three times over the last count, then a chemical application should be made. If you used a seed treatment insecticide, do not apply the same class of chemistry (such as Centric, Provado and Trimax).”
Pitts says using the same class of chemistry can result in poor control and additional spraying. “In addition, use the highest rate suggested for good control and avoid the use of pyrethroids as they can cause aphid outbreaks by removing beneficials.
"Spider mites can be distinguished from insects by their eight legs instead of six. Spider mites often attack cotton when insecticides have destroyed beneficial insects. Infestations are often aided by hot, dry weather. In most cases, infestations will be localized in a field. Spider mites damage cotton by feeding on the plant juices. Foliage will turn a reddish or yellow color with a heavy infestation. Mites are small and generally found on the underside of leaves. A close inspection is necessary to determine if mites are present.
"Chemical control should be used only if a population increase is not being held by beneficial insects,” he says. Bidrin, Captone, Comite, Cygon (Dimethoiate), Caracron, Kelthane, Zephyr and Oberon are all registered for spider mite control.
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