Fungicides & Phomopsis
Burying infected stalks via tillage can be an effective cultural practice in reducing possible infection in subsequent crops. Infected stalks that are buried even an inch below the surface will not be able to release spores. Obviously, this is an alternative in areas were tillage is a common cultural practice.
In both 2010 and 2011, Phomopsis fungicide trials were established at the North Dakota State University Research Extension Center, Langdon, in collaboration with Sam Markell, NDSU extension plant pathologist. Phomopsis-infected stalks were placed throughout the nursery to initiate disease. But in both years, the disease did not develop. However, an inoculated rust trial (under pivot irrigation) at the center had good levels of Phomopsis (as well as rust) in 2011. A number of fungicides and application timings were evaluated in the trial.
Phomopsis disease ratings were taken using a rating scale of 0 to 4, with “0” having no disease and “4” representing a lodged, nonharvestable stalk. In this study, the nontreated control had a Phomopsis rating of 2.95 (stem turning brown from infection), while the fungicide treatments varied in disease ratings from a low of 0.43 with three applications of Headline® to a high of 2.1 from a single application of Headline applied at the R-1 (early bud) growth stage.
Scott Halley, crop protection specialist at the Langdon R&E Center, concludes that a single application at R-1 is too early to control Phomopsis. He likes two fungicide applications with one at the R-2 or R-3 growth stage and the second application at early bloom (R-5.0).
While Headline was tested in this study as the principle fungicide, Folicur® would be an alternate option for the first application. “Folicur is inexpensive, and it will stop early rust development as well,” Halley observes. He would come back with Headline, Quash® or Endura® at early bloom. “In addition to Phomopsis, Headline is effective against rust; Quash would be effective against additional infections of rust, Phomopsis and suppression of Sclerotinia head rot. Endura would be effective on head rot but was not tested in this study,” Halley says. Endura is presently labeled on sunflower, but a Quash sunflower label is not expected until the 2014 season.
This strategy depends on a grower’s history of these diseases, the weather conditions, whether the field is irrigated or dryland, yield potential, hybrid tolerance and planting date. Some seed companies do rate their hybrids for tolerance to Phomopsis.
Halley has observed that the best chance for Phomopsis disease development at his northeastern North Dakota location is on early planted sunflower . “We planted the rust nursery in mid-May and had good Phomopsis infection. We planted another study specifically to evaluate Phomopsis in early June, complete with inoculum, and had almost no Phomopsis disease,” he reports. Halley does believe fungicides play a role in controlling Phomopsis.
— Larry Kleingartner
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