From Bill Kreuser and the Turf iNfo blog from University of Nebraska-Lincoln:
The nights are getting cooler, the days shorter, students are back to school and football season has returned. While summer feels like it is winding down, there are still several turf issues that can be quite devastating this time of the year.
Gray leaf spot: Gray leaf spot was extremely devastating last fall. Particularly hard hit were lawns, sports turf, and golf course rough. Perennial ryegrass and tall fescue are the most susceptible host species. Small lesions will appear on grass leaves and can run together over time. Here are some pictures of the disease on different grass species. Disease outbreaks can develop and intensify very rapidly, especially during periods of warm weather, high humidity, and during regular precipitation. The fungicide thiophanate-methyl is considered the best option for control when the disease is first observed. The QoI (strobularin) fungicides can also be highly effective against gray leaf spot.
Fall dollar spot: The warm days, longer nights, and heavy dew in the fall can result in widespread dollar spot in late summer and early fall. While a frequent problem on golf course turf, the fall weather conditions can lead to significant dollar spot outbreaks on sports and lawn height turf. Many fungicide classes provide effective control of this disease. This is also a good time to fertilize turf with nitrogen. That added fertility can help the turf growth through this disease.
Root diseases: The heavy rains and warm soils mean that root issues like Pythium root rot can still be a concern for bentgrass greens. In addition to preventative fungicide programs, fall venting/aeration can help to improve water movement and help with these diseases. As the soils continue to cool, consider preventative fungicide applications for take-all patch on young stands of creeping bentgrass with a history of take-all. Turfgrass pathologists recommend applications be made when the soil temperature at 2 inches is between 45-60F.
Iron chlorosis occurring on lawns: There is a lot of lime green Kentucky bluegrass around Nebraska. We believe this is a root dysfunction that occurs when the soils are very warm and wet. We’ve written several Turf iNfos on the subject. The take home points are i) avoid excessive irrigation, ii) nitrogen fertilizer will make the issue worse, and iii) spray-applied iron fertilizer can help alleviate the issue. Several applications may be needed to correct this issue once it has fully developed.
Bill Kreuser, Extension Turfgrass Specialist, wkreuser2@unl.edu