18 It’s Farming. And It’s Better. Better Farming | June/July 2024 Managing risk Tar spot risks significant yield drag in corn crops. The factor that has the largest effect on this risk is weather. “The spread of the disease is dictated, overwhelmingly, by favourable environmental conditions,” says Hooker. “If weather conditions are favourable for the development of the disease, and if the pathogen or disease is present in the field, then an application of an effective fungicide may be warranted between the VT and R2 stages of corn development. The fungicide application at this time would offer two to three weeks of protection of non-infected leaf area during the critical phase of corn development and delay the onset of disease development through the grain-fill period.” Thirlwall adds that fungicide application is the primary approach to managing tar spot. “You can’t really minimize the spread. If the climate is right, it’s going to be there,” says Thirlwall. “The main way to minimize tar spot is to use a fungicide that is registered for control of tar spot. Delaro Complete from Bayer is registered for control of tar spot in corn.” Tenuta notes that in addition to Delaro Complete, it’s been found that Veltyma (BASF), which is registered for control of tar spot, and Miravis Neo (Syngenta), which is registered for suppression, have also shown success in managing the fungal disease. Thirlwall says that the timing for spraying for tar spot lines up with most producers’ current fungicide programs. “The best timing for Southwestern Ontario to spray is at R1 timing or Silking, which we also use for protection against ear moulds and DON suppression,” says Thirlwall. Tenuta says that the Crop Protection Network has also reviewed residue management as a strategy for managing tar spot, but found a welltimed fungicide application was significantly better at reducing the risk to the crop. “What we’ve seen at our trial locations with very little residue – 20 per cent or less – is that we still observed tar spot development,” says Tenuta. “Residue management can reduce tar spot slightly, but not to the point where it’ll drastically reduce your risk. You don’t need a lot of tar spot in your field to develop it, and the impact of residue management is limited.” He shares that the Crop Protection Network has been investigating tolerance in corn hybrids to give grain farmers another tool for managing tar spot. “The good news is that we have the tools to manage tar spot already. We’ve been doing a lot of work with seed companies and breeders to evaluate hybrids,” says Tenuta. “We’ve been testing around 100 different commercial hybrids in our nursery or tar spot location at Rodney, Ont., and we see variation in terms of tolerance. We see some with greatly reduced tar spot levels and some that are very susceptible. We are working to make sure this information is available in areas with higher risk for growers that need it.” As producers monitor their own crop through the summer, it is beneficial to know the status of tar spot in surrounding regions. Thirlwall says that one easy-to-access option for monitoring the disease is the Tar Spotter app. “Many agronomists in Ontario are scouting for tar spot in their customer’s fields. There is also the Tar Spotter app to follow the spread of the disease and see if there is a risk in your local area,” says Thirlwall. The Crop Protection Network has also developed maps on the Corn ipm PIPE website to show yearly historical and current tar spot infection in the U.S. and Ontario. These tools allow growers to stay up to date on the risk to their fields and help them develop a strategy for fungicide application. Tenuta says collaboration with researchers in the U.S., who managed tar spot for five years prior to its arrival in Ontario, has yielded information to help Ontario farmers without the usual delay associated with research on emerging diseases. “Because of our collaboration with the U.S., we were ready to go right away. We had trials lined up and were ready to go,” says Tenuta. “This really helps us get that info and those tools out to Ontario growers as soon as possible. They don’t have to wait two to three years, because we are already a part of the planning process to deal with diseases such as tar spot.” By staying informed about the status of tar spot and reviewing the available options for risk management, grain farmers can protect their corn crop against yield losses from tar spot. BF Better Farming and Farms.com are accepting applications/resumes for the following position. It’s Farming. And it’s Better. APPLY TODAY TO JOIN OUR TEAM: Paul.Nolan@Farms.com FARMING JOURNALIST New full-time or potential part-time home-based role with popular farming magazine. You love farming and can write engaging, insightful stories about our industry and its farming families. You possess a professional, team-oriented attitude with strong language skills. You are comfortable proofing copy for errors and factchecking for accuracy. You enjoy taking interesting farm photos with your mobile device. If this sounds like you, please let us know! EMILY CROFT Emily lives on a beef farm, raising Red Angus and Simmental cattle. She holds a Master of Science in Animal Biosciences from University of Guelph, with a focus on ruminant nutrition. Tar Spot
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