By Michael Plumblee
The spread and severity of foliar diseases is highly dependent on environmental conditions, with those conditions being warm and wet. Considering our weather to date this growing season, foliar diseases have been mostly kept at low levels. However, weather patterns can change quickly, just like we are seeing now with most of the state catching rains for the past week. These rains are welcome but could cause an increase in foliar disease.
Since the start of July, the agronomic crops team and I have been scouting corn, cotton, and soybean fields for foliar disease. Over the past week, we have seen a few diseases that are worth mentioning.
Corn:
The most prevalent disease we have seen is grey leaf spot, but not at levels warranting action. On August 5th in Orangeburg County, southern rust was found in corn that was nearly dried down for harvest. Due to the time of year and growth stage of most corn in the state, this detection of southern rust is not concerning. The only situation where southern rust could become an issue at this point in the season is in very late planted (currently at R3/milk or younger) corn.
Cotton:
Unlike corn, we still have a ways to go with our cotton crop. This past week, we identified target spot in cotton in Allendale and Orangeburg counties, but at low levels. Target spot is one to keep an eye on, especially if we keep catching rains, as this disease can cause premature defoliation in severe cases. That being said, once the cotton plant has reached the 6th week of bloom, spraying a fungicide for target spot is probably not necessary. Furthermore, target spot is usually found in the lower canopy, making it difficult to apply a fungicide that will reach the affected area. We have not detected areolate mildew in any of the cotton we have scouted so far.
Source : clemson.edu