Last week, I mentioned seeing leaf spot in the pasture. UGA Extension Pathologist Dr. Alfredo Martinez wanted to confirm what appeared to be fungal structures on the leaves as well. The last few years, we’ve looked at leaf spot pathogens in hay fields. Usually, it is leaf blight (Helminthosporium) or leaf rust. What we looked at a few weeks ago appeared to be more damaging to the lower leaves. The lesions of dollar spot are white to straw colored surrounded by a brown border. This was affecting the lower leaves bad. This is the first time I’ve seen dollar spot in pasture. It is maintained the same as helminthosporium and/or leaf rust. Keep in mind, this pasture was burned off last season.
Looking at the pasture, Tim Flanders noticed these odd structures on the leaves. They almost looked like a fertilizer granular. Dr. Martinez plated them out and did find them to be fungal related. There were basically some saprophytic fungi that ARE NOT associated with the dollar spot.
Management is strictly avoidance. Coastal, Tift 44, and Tift 85 have some level of resistance (to leafspot pathogens) while Alicia is extremely susceptible. But even less susceptible varieties are infected with leaf spot when potassium is low. Most reported leaf spot cases are directly related to low soil potash. Nutrients are removed from bermuda hay fields in about a 4-1-3 ratio of N, P2O5, and K2O with harvest. We need 75 percent as much potash as nitrogen applied each season. Split applications of K are better in sandy soils. It is also advised to remove inoculum that exists in thatch. In addition to tying up nutrients, thatch holds water and reduces air circulation. This is a conducive environment for inoculum. The only practical way to reduce thatch is burning in spring before green-up.
Visit Leafspot Diagnosis and Management in Bermudagrass Forages for more information.