Knowing where nematodes are in a cotton field can help you control thrips more efficiently, regardless of whether in-furrow or seed-coated insecticides are used.
In a year in which cotton acreage is likely to be down again and in which profits are going to be tougher than ever to come by, growers simply can’t afford unnecessary inputs or to lose yield and quality to early season insects — primarily thrips.
A recent series of tests by Clemson University Entomologist Jeremy Greene indicates that thrips control is intrinsically tied to your nematode control program and that precision application of insecticide/nematicides can increase profits by increasing yields or reducing inputs.
“We have two delivery systems for cotton insecticides and nematicides. Avicta and Aeris are seed-treatments which can control thrips and low levels of nematodes. Temik 15G applied in-furrow at-planting has been the long-time standard for both thrips and nematode control in cotton.
“The driving factor for seed-treated insecticides is convenience and timing. We estimate that 25 percent or more of the cotton grown in South Carolina is planted with Avicta or Aeris-coated seed.”
“Both seed treatments performed well when used in statewide trials if nematodes were not present or present below damaging levels. However, these seed treatments can require supplemental foliar sprays for thrips more frequently than Temik 15G, and at least one of the labels specifically recommends supplemental control of thrips with foliar sprays,” Green says. He goes on to say that neither of the popular seed-treatments significantly out-performed the other in terms of thrips control. There are strengths and weaknesses for both under certain conditions, but overall growers have two equal options for seed-coated insecticides to suppress thrips, he contends.
“In fields where nematode pressure is high, these seed treatments are not likely to be enough to prevent some level of damage from the combination of thrips and nematodes. Knowing where higher rates of Temik 15G are needed to control nematodes is critical to profitability,” he adds
Combining Temik 15G with one of the seed treatments to achieve higher levels of nematode control may not always be successful.
In a test run in 2007 the combination of in-furrow Temik 15G and either of the seed treatments did not result in higher yields than Temik 15G alone. “However, in a similar study in 2008 in fields with light to moderate thrips pressure and heavy nematode pressure we saw a significant yield increase when Temik 15G was combined with Avicta compared with Avicta alone. In this test we had a 170 pound ($100) per acre increase with the Avicta-Temik 15G combination.
“In fields with light nematode pressure where higher rates of Temik 15G are not needed for nematode control, we have data that shows either of the seed-treatments are as good as Temik 15G for thrips control. In fields with heavy nematode pressure, controlling nematodes takes precedence over thrips control in selecting pesticides. If nematode pressure is severe a soil fumigant, such as Telone II, may be needed to ensure adequate yields. In this case either Temik 15G or one of the seed treatments can be used in combination with the Telone II to provide a total early season pest management package.”
Nematode distribution can be predicted. In one test, a Veris 3100 soil sampling system was used to measure electrical conductivity (EC) of the soil and to map the soil in EC zones. In this particular field, high levels of thrips were detected in low EC zones, which are sandier, less conductive soils.
In a second test in another part of the state, there was no direct correlation between the low EC zones and thrips damage. In the second test thrips pressure was much lower, indicating that pressure from thrips may influence this trend of having more thrips damage in sandier soils.
Testing for nematodes is as simple as taking a shovel of dirt, putting it in a plastic bag and sending it to a lab for sampling. To sample a lot of acres can make it considerably more difficult, costly and time-consuming, however.
Regardless of the time and cost involved in sampling for nematodes, the knowledge a grower gets as to what levels and what species of nematodes in the soil are essential to cost-effective management of thrips and other early season insect and disease pests.
Any time a plant’s root system is damaged, especially early in the growth cycle, the more open that plant is to damage from any pest.
Thrips are attracted to flower pollen, but both immatures and adults feed mostly on plant tissue. These tiny insects feed by using rasping/sucking mouth parts to extract plant fluids.
Though small in size, heavy infestations of thrips can cause big damage to young cotton plants. Though the threat of feeding damage from thrips is significantly reduced by delaying cotton planting, large acreages and conflicts with other crops often lead growers to plant early.
Feeding injury from thrips typically occurs when cotton plants are small and tender. Feeding appears as coarse stippling on the leaf surface. Large populations of thrips cause serious plant injury, which results in a silvery or scratchy appearance on leaf surfaces. Thrips also feed on flower tissue which causes marginal necrosis of petals and petal browning.
Once cotton plants reach the five true leaf stage, damage from thrips is typically minimal and the plant tends to recover with little yield or quality loss. However, cotton plants appear to be both more vulnerable to thrips damage and less likely to recover from feeding damage prior to the five-leaf stage.
Nematodes can make thrips damage much worse. In the Southeast, growers have to contend with three primary species of nematodes: Rootknot, Columbia lance and sting.
Though management of each in terms of pesticides used are similar, there are significant differences that growers need to know — information that generally requires a professional laboratory analysis.
Knowing the enemy is a big part of winning the battle and Greene stresses the importance of knowing population levels of species in cotton fields.
“This year will not be a good year to risk thrips damage, because you don’t supplement seed treatment with Temik or other effective nematacides. Or to use a combination of these materials in fields where either seed treatments or in-furrow treatments will work equally as well to manage thrips,” he concludes.
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