Poor Growing Conditions Continue To Plague Turf Professionals

 

Peter H. Dernoeden, Ph. D.

We have had endlessly poor growing conditions for turf in the mid-Atlantic. Winter winds, and a cold and wet spring, slowed turf green-up and growth. There are numerous environmental stresses; however, among the most underestimated stresses includes extended periods of warm and overcast weather, especially when combined with rain. Overcast and warm weather stimulates a lot of excessive leaf growth, at the expense of roots, and slows bermudagrass coverage The only good weather this spring occurred during the week of June 11 to 16 (i.e., Open Week). Thereafter, it turned very hot and humid, and then we had several more days of overcast and rainy weather. It has been a difficult time just keeping-up with mowing. Weeds are going berserk and diseases like brown patch and dollar spot are having a field day. I’m seeing stress related diseases like Curvularia blight in annual bluegrass and lots of mower damage. Some clubs managing bermudagrass fairways seem to have a mess on their hands.
Common bermudagrass fairway treated with ammonium sulfate eliminates annual bluegrass and open areas became evident in June.
Bermudagrass took a hit this year, and not so much from spring dead spot, but from winter desiccation (i.e., the drying of crowns due to a relatively open and windy late winter). Winter cart traffic added to the problem. Bermudagrass needs about 100 days of warm and sunny weather, as a well as freedom from competing weeds, to achieve optimum cover before autumn.  Ammonium sulfate, in my view, is one of the best nitrogen (N) fertilizers to use in promoting bermudagrass growth; however, you need to keep it off cool-season grasses during warm, moist and overcast weather. Cool-season-grasses on close cut golf turf contacted with ammonium sulfate (unless immediately irrigated) during warm and humid weather are likely to be “smoked.”   Fairways with high populations of annual bluegrass may suddenly collapse from ammonium sulfate, revealing a large loss of winter damaged bermudagrass. This is good and bad. Eliminating annual bluegrass as a competitor  is very important in achieving faster bermudagrass cover. On the downside, if you have much more annual bluegrass than you realized, the result is open and ugly fairways. With open fairways, another problem is weed breakthrough, especially goosegrass and sedges. It is tough medicine, but applications of about 1.0 lb. water soluble N/ 1000ft2 every 2 to 3 weeks are needed until bermudagrass coverage is achieved.
Tillered goosegrass and other weeds invade open bermudagrass.
Mower damage on collars and approaches has been commonplace. The combination of prolonged warm, wet, humid and overcast weather, caused turf to become puffy and very susceptible to scalping. It can be devastating in summer to mow perimeters, collars, and approaches when turf  is hot and soggy wet. This is especially true for pocket greens (i.e., those surrounded by brush and trees and/or low lying).
Mower damage in collars and perimeter cuts common due to overcast
and wet conditons that promoted  puffy growth.
Two of the most usual maladies I have seen this week are Curvularia blight in annual bluegrass on greens and a mushroom fungus infesting fescue lawns.  In both cases they are not pathogens, but are fungi that are saprophytic (i.e., they attack weak, stressed and dying tissues for nutrients). In annual bluegrass on greens, Curvularia blight can appear in distinct spots or be diffuse and mimic anthracnose, summer patch or even Pythium blight. Discoloration of affected areas is reddish-brown, bronze or yellow. Looking closely, you should observe that the fungus is specific to annual bluegrass and generally bentgrass is unaffected. It occurs mostly in the perimeter cut of greens or areas prone to scalping. The discoloration is due in large part to the fungus’s ability to produce enormous masses of spores on dying leaves. Spores are dark-brown, but enmasse, they appear black. Again, this fungus is present due to severe stress in the annual bluegrass. I found that most stem bases of Curvularia-affected plants have white buds – meaning recovery should be possible, at least those areas not showing bare-ground. You must alleviate stress and the best way is to increase height of cut and mow the perimeter and collars every other day or two using a walk-behind greens mower with a solid roller until damage has recovered. Do not mow if areas are spongy wet or wilted.
Curvularia blight spots selective to annual bluegrass can appear
like early stages of Pythium blight.
Bronzed-colored annual bluegrass affected by Curvularia spp.
can appear like anthracnose, June 2018
Diffuse and spot symptoms of Curvualia blight in annual bluegrass.
Stems have white buds and recovery should be poosible.
Curvularia blight is not likely to respond in a dramatic way to a fungicide application. However, it is prudent, especially during overcast and humid weather, to tank-mix broad-spectrum fungicides to target likely diseases (e.g., brown patch, dollar spot, Pythium blight and other common diseases on your greens) to reduce the potential of primary pathogens getting involved in the complex.

Warm, overcast and humid weather has promoted many disease and weed problems in lawns as well. Heavy rains and overcast weather, which stimulates excessive leaf growth, have caused a rapid depletion of nitrogen, and many lawns are turning yellow too early. We see lots of mushrooms/toadstools in lawns these days. An unusual mushroom is active on fescues. It is an interesting site, with heavy clusters of small mushrooms with long stems (stipes) growing out of old and dying leaf sheaths. My mentor, Dr. Noel Jackson (RIP NJ) said they likely were a Marasmius spp. On necrotic tissues, small white and older orange-colored and umbrella-shaped mushroom caps with spore-bearing gills are produced. The lifecycle is unknown. In some unfathomable way, spores fall into thatch, germinate and begin to live off dead organic matter. When overcast and warm conditions are just right, the fungus grows from thatch onto dying/dead leaf sheaths, penetrates and produces numerous bunches of mushrooms and thus new spores, and the cycle continues. Like most other toadstools in lawns (except fairy ring) there is no harm to turf, and mushrooms rapidly disappear  in sunny weather.

Small, white and orange capped mushrooms in a fescue lawn; June 21, 2018.
Long,dark-colored stipes (left) and umbrella like caps growing
from necrotic fescue leaf sheaths, June 21, 2018.

 

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