Thankfully bollworm pressure in south and central Alabama was relatively light this year, and we did not receive any calls on escaped worms in those regions. However, we have received reports from the Tennessee Valley of bollworm egg lays from 5 to 20 percent over the past 7 to 10 days.
Currently, we are still recommending allowing the Bt technologies in two-gene cottons the opportunity to control these populations. In fields that have been treated for other pests, such as plant bugs or stink bugs in the past 2 weeks with hard chemicals (e.g., pyrethroids, organophosphates, or neonicotinoids), we recommend treating when 5 small larvae are found per 100 plants.
In fields that have not been sprayed in the last 2 weeks, we recommend treatment when 10 small larvae are found per 100 plants. The reason for the difference is the presence of beneficial insects that should be in fields that haven’t been treated recently. You can watch Eddie McGriff’s presentation on beneficial insects on YouTube.
Current recommended thresholds, insecticides and rates can be found in the Alabama Cotton IPM Guide.
Spider mites are still building in areas of Alabama. Spider mite infestations are rarely evenly distributed throughout the field and are almost always in clumps either near field edges or scattered randomly throughout the field. Our threshold in the Alabama Cotton IPM Guide says to treat fields when mites are widely distributed and mottling of leaves is common.
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Determining when to implement controls can be difficult when trying to decide how many ‘hotspots’ suggest mites are “widely distributed” and justify a spray. Spider mites prefer hot, dry conditions and typically can be suppressed by a rainfall event.
Fields with spider mite hotspots should continue to be monitored after rain, because populations can build back after several days of hot, dry conditions. Spider mites also tend to build following broad-spectrum insecticide applications for other pests.
To scout for spider mites, look for leaf stippling or reddening on the top of leaves. If these symptoms are observed, look on the underside of leaves for spider mites, which will be a yellowish color with two black “spots” on each side of its back.
Exposing the underside of leaves to the sun may agitate mites, making them easier to see. Also look for mites one or two nodes above the most symptomatic leaves as they may have moved up to fresh leaves. There are a few miticides labeled for use in cotton that can be found in the Cotton IPM Guide.
Abamectin (e.g., Agri-Mek 0.15EC) at 8 to16 ounces per acre is the most economical option but rotating chemistries is necessary if multiple applications are needed. Historically, lower rates of abamectin (8 to 10 oz) have provided adequate control in younger cotton, while higher rates (12 to 16oz) are needed later in the season when plants are larger.