We are seeing aphids in cotton now. Based on my last few years in Thomas County, this is earlier than normal. Jodie sent me this picture of aphids that were parasitized by wasps. The aphids turn a reddish color, then more white color. Sometimes you can see a hole on the backside where the larvae exit.
Here is some 5 – 6 leaf cotton that had ants crawling up the stalk. When we looked under the leaves, aphids are present. The reason these ants are crawling around the aphids, is that they are ‘farming’ the aphids. The aphids produce honeydew as they feed on the plant. The ants are after this sweet taste.
UGA Extension Entomologist Dr. Phillip Roberts says right now, we do need to be looking for aphids in fields. But one of the most important things we can do is watch for the naturally occurring epizootic fungus that cause aphid populations to crash. We generally see the aphids crash sometime between the last 2 weeks of June and first 2 weeks of July.
Before the crash, we may see some very small hits of aphids in ‘hot spots’. In these places, we may see honeydew (sticky, shiny material), yellowing in the terminal. We look for gray, fuzzy aphid cadavers. As aphids build, the fungus multiplies, and aphids crash. The crash happens fast and kills all aphids within a week or so. Here is a picture of the fungus on an aphid.
Dr. Roberts has completed lots of research on cotton aphids and has not seen a consistent yield response from controlling them. Controlling aphids remains a judgment call. A few points to consider if making this decision on spraying for aphids is:
- If terminal has turned yellow.
- If the whole field has aphids (instead of just hot spot.)