As we hoped, plant bug numbers have dwindled for now, and things have been relatively quiet in the cotton field. However, I have seen a few things that I think we need to acknowledge.
Two-Spotted Spider Mites
It seems that spider mite infestations in cotton fields are higher than normal this year. After conversations with Dr. Phillip Roberts, he agreed and said it is a widespread occurrence. Although there may be mites in most fields, to my knowledge, we have only treated a handful of fields. Treatment should be triggered when 50% of plants are symptomatic and populations are growing. Part of the reason we are seeing high numbers is likely due to the number of fields treated for plant bugs this year. Many of the insecticides we used for plant bug control also took a toll on our beneficial insects. As we know, many of our beneficial insects in cotton are natural predators of spider mites. So as a result, spider mite infestations are especially evident in plant bug-treated fields.
We have not had to worry about corn earworm in cotton since the release of Bollgard cotton back in the 90s, which only had one Bt gene. We now have cotton with 3 Bt genes, which include the same gene that was originally in Bollgard. Over time, resistance develops, and we now have evidence to concur that the initial Bt gene provides very little control of corn earworm. That being said, 3 gene Bt cottons still provide excellent control of corn earworm, but most of that can be attributed to the addition of the third Bt gene. The point is, resistance will develop to this gene as well, and we need to be scouting our fields for occasional slips as you see in the pictures below. There was a field of 3 gene Bt cotton in Georgia last year that had to be treated for corn earworm. These cottons are not immune. I am not sounding the alarm by any means, but I want it to be understood that we need to be aware and scouting our fields.
Target Spot and Areolate Mildew
The first target spot and areolate mildew was found this week in cotton in Bleckley County. Dr. Bob Kemerait had the following to say about the two diseases:
Cole Moon in Bleckley County has found target spot on cotton AND our first report of areolate mildew. Target spot can be and IS a problem many times when it occurs early enough in the season (somewhere around the 3rd week of bloom). AREOLATE MILDEW is ALWAYS are problem when it occurs in a cotton field in Georgia with more than a month to go prior to defoliation AND otherwise good yield potential. I believe in La Nina and El Nino and that a changing climate is going to mess up our crop production in GA. UGA on-farm research tells us that well-timed fungicide applications (Priaxor, Miravis Top, Headline, azoxystrobin) will make you yield and money. I am not saying every cotton grower needs to spray for areolate mildew. I am saying, based upon what Cole in Bleckley Co found yesterday, the areolate mildew genie is out of the bottle in Georgia and we need to be prepared.
There are many fields in our county that will need to be treated this year for these foliar diseases. I hope to start researching this topic next year in some on-farm trials to look at different fungicides and the timing of application in the efficacy of control of these diseases.