As we move into July, here are a few things to be looking for in cotton. Much of the earlier planted cotton is blooming and setting bolls. Some cotton fields are still in the seedling and early growth stages.
INSECTS
Aphid populations have been building in cotton of all sizes and growth stages. Some fields have been treated, and more may require treatment, but hopefully soon the fungus will be “taking out” those that are in cotton fields.
Another insect that can cause damage to bolls and reduce yield is the stink bug. A few years ago, the dynamic threshold was developed to help growers in making treatment decisions. The steps for scouting and the threshold damage levels, based on week of bloom, are shown in the image. This is a great guide to go by when scouting for stink bugs and making treatment decisions. Scouts/Growers need to be aware of other insect pests that may be present in the field if stink bug treatment is needed.
While silverleaf whitefly (SLWF) has not been an issue to this point in the season, be aware if they are present or not in the field. Their presence will be a factor in the stink bug insecticide decision. If we start seeing SLWF population building, we will notify growers in the area.
DISEASES
Dr. Bob Kemerait mentioned some foliar diseases that can affect cotton during this time. A couple that may require treatment are target spot and areolate mildew.
Target spot will usually occur in fields with good growth and yield potential, and warm, humid conditions. Most of the time it begins lower in the canopy and moves its way up in the plant. It can cause premature defoliation when conditions are favorable. The first week of bloom is an excellent time to begin scouting for target spot, as the canopy is closing. If present at first bloom, fungicide treatments can begin. However, if not present, growers can continue to scout for the disease and treat at onset. Based on the research, the single most important timing for fungicide application is at the 3rd week of bloom. More than one application may be needed for continued protection. After the 6th week of bloom, growers should not need to continue protective treatments.
Another disease that we have seen more the last couple of seasons is areolate mildew. This disease looks a lot like powdery mildew, and can be seen higher in the cotton plant. If the cotton is within 4 weeks of anticipated defoliation, it may not need treating; but if it occurs earlier, a timely fungicide application can protect potential yield.
Here are some tips from Dr. Kemerait:
Because of crop development, it is important during July to consider protecting a cotton crop with fungicides. There are 5 steps. First, scout the field and determine what diseases are present. Second, decide on management options. If the disease is Stemphylium leaf spot, then a fungicide will not control the disease. If the disease is target spot or areolate mildew, then a fungicide could be beneficial. Third, consider the crop before applying the fungicide. Does the field have a reasonable chance for good yields? How advanced is the disease? Fourth, decide on a fungicide. Priaxor is the best fungicide for management of target spot, though other fungicides, to include Headline and Quadris are also good. These fungicides will control areolate mildew as well, though areolate mildew is easier to control than is target spot. Fifth, timing of fungicide application is critical. If applied too late, there will be little hope for controlling the disease and protecting yield.
Please contact Worth County Extension if we can be of assistance.