The attention given to foliar fungicides for soybean production following the discovery of Asian soybean rust has in part caused growers to evaluate if there's potential to increase yields in the absence of ASR, says Dean Malvick, assistant professor of plant pathology at the University of Minnesota. One initiative growers are evaluating is a foliar fungicide application for a "plant health" benefit.
"Some in the industry perceive that soybean yields haven't increased like they could and some are looking at more intensive management," Malvick says. "They're looking to see if there are additional management tactics or tools that can be used to increase soybean yields economically."
Rather than focusing on single inputs or factors that influence soybean yields, Malvick and many others prefer to look at multiple ways of achieving increased yields of soybeans. This approach incorporates the contribution of genetics, multiple diseases, nutrition, soil types, water, nematodes, insects and stress to produce the final yield of a soybean plant.
Marty Draper, plant pathologist at South Dakota State University, summarized foliar soybean fungicide trials conducted in 2005 by multiple investigators at 65 locations across the north-central region of the Midwest. While all trials were absent of ASR, some identified measurable levels of other diseases. Other trials may or may not have contained some level of secondary disease; however, they were not reported one way or the other.
Trial reports show that a foliar application with a strobilurin fungicide yielded at least 4 bushels per acre more than the unsprayed control only about one-third of the time. However, another one-third netted a positive effect on yield below 4 bu/acre; and the final one-third showed a yield loss versus untreated soybeans.
"What I see for the future is that additional trials will help us get a handle on when and where we might expect to see an economic and yield advantage of using fungicides," Malvick says. "It's clear they don't work well everywhere and in every situation.
"But there are some situations where they might be beneficial. Trying to understand what those situations are and where those locations are where growers could see a relatively high probability of return is being explored. There's a quest to narrow down that window of where we can have a higher likelihood of getting a positive return."
Malvick stresses that it's important for growers to remember that the primary function of fungicides is to control diseases. This follows the argument for growers to follow Integrated Pest Management (IPM) principles, so the decision to use a control strategy is triggered by an identifiable problem. Elements of IPM include scouting and identifying pests or limiting factors, and then implementing appropriate strategies to reduce their impact.