With the extreme winter weather across most of North America, I have fielded many questions about the influence of winter on diseases such as dollar spot, Pythium diseases and nematodes damage. I understand that record cold temperatures and uncharacteristic snowfall amounts are wreaking havoc on our everyday lives. A few weeks ago we received about 5 inches of snow fall in the Raleigh area. Many people were stuck in traffic for three to four hours and some even abandoned their cars. I also understand that many golf course superintendents are very concerned about the health of their turf. I think as a way to spread positive vibes through our industry, many of the trade magazines are asking turfgrass pathologists about the viability of pathogens after this horrible winter.
This is a difficult question to answer. For instance, we store many fungi on filter paper at temperatures of -112oF. Although the hyphae is dried down prior to storage, that is still an extreme temperature. My student Renee Rioux examined overwintering of the dollar spot fungus in plants and found a reduction in isolation frequency from fall to spring in a three-year study. In one year we observed a drastic reduction in isolation from the same area from fall to spring and it happened that it occurred after the coldest winter of the study. We think that overwintering of the dollar spot fungus is affected by environmental conditions, but the key point is each year we were able to isolate the fungus from symptomatic and in some cases asymptomatic tissue.
In a recent nematode management trial we observed something very interesting. In early September we established a trial to investigate the effects of experimental products on sting nematode populations. We collected samples for nematode enumeration prior to initiating the experiment and again in January. We were shocked to find that average sting nematode counts ranged from 260 to 400 in January, which was very similar to averages we collected in September. Even a nematode that loves warm weather can survive unusually cold winters. The bottom line is do not expect that a cold or mild winter for that matter will influence pest problems for the upcoming spring and summer. These organisms unfortunately are extremely reliant and really the potential for causing sleepless nights relies on what mother nature gives us this spring and summer.