Managing Target Spot and Areolate Mildew in Cotton Kemerait
Target spot (Corynespora cassiicola) and areolate mildew (Ramulariopsis gossyppii) are the two most important diseases affecting cotton in Georgia later in the growing season. For both target spot and areolate mildew, judicious use of fungicides not only protects the crop, but can increase yield profitability as well. Another disease, Stemphylium leaf spot, is often even more common than either target spot or areolae mildew in Georgia’s cotton crop. However, as Stemphylium leaf spot results from a deficiency of potassium within the plant, to date use fungicides has not proven to be an effective management strategy. Target spot has been found widely found in cotton growing in southern Georgia. Abundant rain, high humidity, and rank growth of some cotton all contribute to the increased importance of target spot this season. Areolate mildew is also showing up. Presented below is a slide of the fungicides currently labeled for management of target spot and results from recent on-farm trials conducted in Colquitt County with UGA Extension agent Jeremy Kichler. The two fungicides that have performed “best” against target spot have been Priaxor and
Miravis Top, close behind this pair has been Headline. Unfortunately, if seems that none of these fungicides
are readily available this season to cotton growers in Georgia. This leaves azoxystrobin (sold under various trade names). Azoxystrobin is a fair-to-good fungicide for control of target spot; it is a good-to-very-good fungicide for control of areolate mildew. Amistar Top, a combination of azoxystrobin and difenconazole, is another fungicide that could be considered when Priaxor, Miravis Top, and Headline are in short supply. The use rate for Amistar Top is 8-11.6 fl oz/A. Growers should consider protecting their cotton crop from target spot between the 1st and 6th weeks of bloom IF the disease is present, or is likely to develop, and conditions are favorable for development and spread,
and IF the crop has good yield potential. (As from earlier, conditions for development and spread of
target spot are EXCELLENT in 2021.) Judicious use of fungicides can protect as much as 250 lb of lint where
target spot is problematic. Where the crop is suffering from drought or poor growth from other causes, protection against target spot with a fungicide may not be warranted. Recently Colquitt County agent reported defoliation at already 40% in one cotton field crop that was in the 4th week of bloom.