You Are Here: Management Updates 2000 Archive June 30, 2000

Date: June 30, 2000
Category: Diseases
Subject: Summer Diseases, Dollar Spot, Brown Blight, Animal Urine Injury

A very hot and humid weekend led up to spectacular fungal activity on Monday. This could have led to serious disease problems if the weather had not broken and returned to warm and relatively dry (late day thunderstorms) with comfortable, cool nights. Even so, DOLLAR SPOT (see last paragraph) and RED THREAD were very active. Unfortunately, the variable weather makes identification of problems more difficult unless you know exactly when they first made their appearance. Here are a few highlights from the past week.

ANTHRACNOSE is finally becoming more widespread- not wishing it on anyone, but the continued moisture made us expect more sooner. Most samples are from poorly drained, compacted areas. Most samples are also of the much more problematic basal or crown rot stage. The long term solution is to really fix the turf growing conditions- better aeration and drainage. When you can see massive root growth in the aeration holes, you get an idea of how restricted plants away from those holes are. Short-term, raise the mowing height, divert traffic, wash mowers before moving on to new areas, and delay sand-topdressing, especially brushing it in.

BROWN BLIGHT is a common spring leaf spot specific to ryegrass (Drechslera/Helminthosporium siccans). It makes numerous chocolate brown spots that can progress into melting-out and crown rot. Cool, wet conditions and high nitrogen fertility favor the disease. The good news is that it is NOT GRAY LEAF SPOT. We'll be watching for that later.

ANIMAL URINE INJURY can cause confusing symptoms. Watch for a central straw-colored burned spot surrounded by the extra green fertilizer effect as you look out radially from the center. Usually, only a couple of spots will be in an area (unless you have a dog in a restricted yard) rather thansomething widespread like dollar spot. The only other common cause of extra greening in rings is FAIRY RING. There are many reports of this recently, which is probably related to the rainfall this year. These soil saprophytes are busy breaking down organic matter in the soil and releasing N fertilizer to the grass. The rings may be very round or quite irregular, 6-12" diameter or many feet across. As long as they remain green, they should not be a significant problem, but watch these areas for hydrophobic soil problems if the weather becomes hot and dry.

Be on the watch for the new disease BENTGRASS DEAD SPOT. We originally were calling this disease "fall spot." It is usually first noticed in the fall, but once it is established, it can be active from June through the fall. The disease was diagnosed this week in Pennsylvania. It looks like very distinct dying or dead spots, similar to ball marks. They are slow to heal, do not usually coalesce into larger areas, and no mycelium is seen in the morning. The fungus produces numerous small black flask-shaped fruiting bodies, but they may not be visible at this time of year.

One last comment should be made about fungicide control on golf courses. There has been a lot of rain and a lot of turf growth this year. These two factors will shorten the control interval for contact fungicides which only coat the grass blade with a protective layer. No resistance in DOLLAR SPOT has been reported for chlorothalonil. Systemic (penetrant) fungicides offer longer control, but run the risk of resistance, so alternate chemical groups when using these. Spoon-feeding of quick release N fertilizers and whipping or dragging dew from turf on non-mowing days are excellent cultural practices for dollar spot.

- Submitted by: Dr. Gail Schumann