Last year North Carolina was fairly mild with above average precipitation. At least in Raleigh, precipitation was 13.32 inches above normal in 2014. Basically it was not a great year to be a turfgrass pathologist in the Southeastern US, which in turn is great for golf course superintendents. Although our sample numbers were down, there were still some interesting observations we’ve made the past two years. If you recall, 2013 was a fairly mild summer in the Southeast as well.
For those still managing creeping bentgrass putting greens, the two most frequent diseases we see in the lab are Pythium root rot and anthracnose. Both of these diseases are associated with summer stress and even in mild years we still have our fair share of stress. It is extremely important to note that in both years, 50 to 60% of the samples we received did not have a disease. In other words, we did not find enough evidence to implicate a specific disease.As I have mentioned in previous posts, that does not mean pathogens were not present. Quite the contrary, many different fungi and bacteria, both pathogenic and non-pathogenic, may be present. During the diagnostic process we gather evidence and then use that evidence to determine what caused the issue. Most of the time, we cannot find enough evidence to implicate a disease. For example, we need to be able to link the symptoms with the signs and the environmental conditions-both macro and micro- in order to confidently and accurately diagnose a disease. We take many things into consideration like time of year, condition of the root zone, depth of organic layer, soluble salts, health of root system and observations from golf course superintendents. The point here,diseases are a rare event in nature even on golf course putting greens.
With Pythium root rot we showed that applications of Segway starting in mid-May kept root rot at bay. Keep in mind that only 3 applications of Segway are allowed in a season. Therefore we suggest starting root rot programs with Segway then rotate to Subdue MAXX and Banol. Mid-season we saw significant improvement with Segway’s efficacy when we tank mixed a QoI. Then if more applications are needed rotate in the other Pythium chemistry once more. Anthracnose still remains problematic for creeping bentgrass in the transition zone. Fungicides have not lost effectiveness; rather a greater emphasis on cultural practices is needed. Dr. Bruce Clarke’s lab has done tremendous work with cultural management of anthracnose. Sand topdressing at 1 ft3/1000 ft2 every 14 days significantly reduced anthracnose severity. Moreover, more frequent nitrogen applications or slightly increased nitrogen amounts also reduced anthracnose severity. Although it gets exceptionally hot in NC, it is important to maintain topdressing and nitrogen applications during the summer months.
For those managing ultradwarf bermudagrass putting greens did you notice the number of abiotic diagnoses are less,yet the percentages increased slightly from 2013 to 2014? Only time will tell if other issues develop on our relatively new bermudagrass putting greens.Even with a grass that is more suited to hotand humid summers, abiotic issues are still problematic. The main diseases we see on ultradwarf bermudagrasses are leaf spots, Pythium blight, leaf and sheath spot (aka mini-ring) and cream leaf blight. Entering another season it is very important to note that the stand symptoms of leaf spot and Pythium blight on ultradwarf bermudagrasses are extremely similar. So similar in fact, that I suggest applying a tank-mixture of fungicides for both diseases during conducive conditions. Both diseases develop when bermudagrass is slow growing in the spring, fall, or during periods of extended cloud cover, thus before these conditions develop make a preventative application for both diseases.
A final note, we typically only receive the most interesting and difficult problems. We rarely see diseases like brown patch and dollar spot. We mainly receive turf samples that struggle despite excellent fungicide and many times excellent agronomic programs. There are plenty of times when turfgrass plants just succumb to environmental pressures despite the best effort of the golf course superintendent.