One of the fungicide trials that we toured during field day included several different fungicide formulations for control of dollar spot and brown patch on creeping bentgrass putting greens. In this particular trial we applied the newer fungicide Civitas + Harmonizer alongside other conventional fungicide products. As you may remember in previous posts here and here by Dr. Tredway, Civitas performed well for control of dollar spot and did not cause phytotoxicity in North Carolina trials.
In our trial this spring we observed poor control of dollar spot by Civitas + Harmonizer as a “curative” treatment. When this study was initiated we had a raging dollar spot epidemic well under way on April 18. After three applications of fungicide on a 14-day interval, most treatments still had substantial dollar spot present and poor overall turfgrass quality compared to the rotation of 3336 plus and Emerald. This included the Civitas + Harmonizer treatment which had comparable dollar spot severity and quality to the non-treated control.
Why didn’t Civatas work as well in our study as it had in other studies? Our hypothesis is that it is because the product was used as a “curative” in this case. Civitas works by induced systemic resistance (ISR), another words the product “turns on” defense responses in the turf plant. This means that the product must be taken up by the plant and elicit the appropriate responses in the plant before the plant can fight the infection by the dollar spot fungus. This process can take time in the plant. Therefore, the best results will likely be observed when Civitas is applied preventatively and the plant is provided sufficient time for the appropriate responses to be “turned on” and brought “up to speed.” In our study, Civitas was applied after the infection and the plants resistance mechanisms were not incited, which is likely why we observed very poor control of dollar spot by this product. Most of the other products applied in this “curative” fashion also provided relatively poor results with the exception of the 3336/Emerald rotation. These results further substantiate the importance of using preventative fungicide applications versus curative applications when at all possible.
In other news out of the southern plains…can you say HOT! It has been consistently in the triple digits now for several weeks in Oklahoma. June 2011 will likely go down as one of the hottest on record. In the OSU Turfgrass Diagnostic Lab we have been getting many creeping bentgrass samples with heat stress. We have also seen some Pythium blight on greens being over-irrigated to compensate for the hot temperatures. Anthracnose has also been diagnosed on several greens from the eastern part of Oklahoma.
In addition to cool-season turf samples coming in due to heat stress, we received several more creeping bentgrass samples with very high levels of plant parasitic nematodes (mostly stunt and ring nematodes). As I mentioned in my previous post, levels this high in June, will result in extremely high populations of nematodes later on in the summer when plants will already have the added stress of summer heat. Several of the courses with these problems are reporting that areas of the putting greens are beginning to fade and the decline is slowly spreading. With the continued 100 F + heat we have been experiencing in the south-central U.S. and the golfer traffic likely over the Independence day holiday, the stress that the nematodes are imparting on these greens will be further magnified. We are encouraging good cultural management including raising mowing heights (.160 in. or more would be advised), adjustment of the frequency of mowing and rolling to reduce the amount of stress applied to the turf stand, and continued frequent, light applications of fertilizer and water. Any practice that reduces stress and damage to turf plants will help plants plants in surviving the additional damage that nematode feeding causes. Hopefully we can get a break from the heat soon and reduce some of the stress on creeping bentgrass putting greens in our neck of the woods.