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Are spider mites snacking on your cotton?
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High numbers of spider mites can affect your cotton - both yield and quality.
Spider mites are small arthropods that feed on the underside of cotton leaves - using their piercing mouthparts to suck out the contents of leaf cells. This removes chlorophyll from the leaves and causes a reduction in photosynthesis.
There are three types of spider mites - two-spotted spider mites (the main pest species; pale green with two distinct dark green spots on either side); bean spider mite (red in colour) and strawberry spider mite (pale green with three dark green spots on either side). They all cause different amounts of damage, so correct identification is important to help you make the correct control decision.
The CottonInfo team have spotted spider mites in different valleys. The increased prevalence this season may be linked to increased spraying for pests such as Green Vegetable Bugs (GVBs). The registered control options for GVBs are known to be disruptive to various natural enemies that would normally suppress mite populations.
Is your cotton affected? Here's what you need to know:
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What to look out for? Symptoms and sampling.
All three species feed on the underside of leaves, but they cause different amounts of damage. Two-spotted mites cause damage that appears as brownish areas on the lower leaf surface, causing reddening on the upper surface. If damage is allowed to continue, leaves will become completely red and fall off.
To sample for two spotted mites in cotton, sample leaves from 3, 4 or 5 nodes below the plant terminal. Check on the underside of each leaf and score as present if any mite life stage (eggs or motiles) is found. Repeat this weekly on 50 leaves per field from at least four sites (depending on the field size).
Refer to the Cotton Pest Management Guide for a detailed description of how to sample for spider mites in cotton.
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When do I need to act? Thresholds and control.
Thresholds and yield loss charts have been developed for two-spotted spider mites. Yield loss due to mites depends on when (and how quickly) mite populations begin to increase.
At this stage in the season, when cotton is starting to open, control is only warranted if mites are well established (greater than 60 percent of plants infested) and are increasing rapidly. Beyond 20 percent open bolls, control is no longer warranted.
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Where do I go for more?
The Cotton Pest Management Guide contains all the information you need on identifying, sampling, and controlling spider mites. It also talks about the key beneficial insects that can help you naturally protect against mites.
The Guide also contains the full sampling protocols for mites, a table outlining estimates in yield reduction, and control methods to help you make the best decision for your farm.
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Check out these three short videos:
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