Spraying fungicides on drought-stressed corn
click image to zoomFigure 1. Corn showing symptoms of moisture and heat stress. Indiana's "second" corn crop that was planted in late May or early June is at or approaching the tasseling and silking growth stage. In many areas, this late-planted corn is short, uneven in growth stage, and is experiencing nitrogen or other nutrient deficiencies. These problems are compounded by the fact that the tasseling and soon to tassel corn is going through pollination under high temperatures and low soil moisture (Figure 1). Extension corn agronomists across the Midwest have been discussing the impact that the heat and lack of moisture can have on corn yields: http://graincrops.blogspot.com/2011/07/high-temeperatures-could-hurt-corn.html. The bottom line is that yields may be impacted not only by the late planting date, but also by the current weather conditions. Growers interested in maximizing remaining yield potential may be considering spraying this corn with a fungicide in the hopes that these applications will improve plant water use efficiency, and/or alleviate plant stress through grain fill.
click image to zoomFigure 2. Lower leaves of corn plant with little or no gray leaf spot lesions present (Picture taken in Northeast IN on 8/1/11). Applying fungicides for purposes other than disease control has not proven to be consistently profitable in replicated field research trials across the Midwest. As we have reported in previous articles, the most likely chance to recoup the investment from a fungicide application is when fungicides are used in response to disease presence or disease risk factors. Across Indiana, development of foliar fungal diseases such as gray leaf spot and northern corn leaf blight has overall been low. Disease development is slowed under high temperatures (above 85-90°F) and dry conditions, and in many fields, lesions of gray leaf spot are well below the ear leaf, or hard to detect (Figure 2). Our scouting thresholds (http://extension.entm.purdue.edu/pestcrop/2011/issue15/index.html) would indicate that in these situations there is not enough disease pressure to warrant a fungicide application.
Additionally, there are very few replicated field research trials that examine the true effects of fungicides on plant water use efficiency and ability to alleviate drought stress. If fungicides will be applied to corn for these purposes, it would be beneficial to work with the applicator and leave several untreated strips within the field that can be harvested and yields averaged to determine if there was an actual yield benefit due to the fungicide application. This does require additional planning and effort, but it can mean the difference between knowing if the fungicides were worth the investment and whether or not they work under your specific production conditions.