I saw some areolate mildew in cotton at 5th week of bloom earlier today in Bulloch County (Figure 1). The best management of areolate mildew is with judicious and timely fungicide applications. Cotton can be effected by areolate mildew until within four weeks of defoliation. When defoliation reaches 25% or so – the chances of slowing it down with a fungicide decreases.
Source : uga.edu