It seems just about every district within the Hoegemeyer trade area has areas suffering from the hot and dry weather we have been subject to this year. Damage varies from minor to total crop loss at this point. Many corn fields are or recently have reached reproduction stages (tassel/silk). It’s at this time that historically most foliar fungicide application takes place. With the hot and extremely dry conditions across much of the area, foliar fungal disease development is relatively low and/or slow to develop vs. crop stage and calendar date. Most foliar fungal pathogens in corn require moisture to either infect or progress. This is generally produced by high humidity, heavy dew, irrigation, and rainfall that wets the crop canopy for extended periods of time. Gray Leaf Spot, for example, which is one of the most common and potentially damaging foliar fungal diseases, requires somewhere around 12 hours of continued leaf wetting in order to infect. This is hard to accomplish without the aid of humidity and at least average rainfall. There are three sides to the “disease triangle”. They are 1) pathogen, 2)host plant, and 3) environment. A field with high levels of both host and pathogen will not produce heavy disease unless the environment is favorable for disease development. If one side of the triangle is low then it will lessen the amount of total disease present. That being said, southern rust has recently been confirmed at low levels within several center pivot irrigated fields in southern Nebraska which warrants monitoring. If humidity levels begin to creep higher along with the nighttime temperatures, this sporadic yet potentially damaging disease could spread more rapidly.
Disease-free ear leaf of HPT 8345 Hx/LL/RR at Hooper, NE - 7/11/12
With the current relatively low levels of fungal foliar disease, other potential benefits of fungicide applications have garnered some attention. There are various instances and even some 3rd party research trials that have shown a positive yield response to fungicides even in the absence of significant disease and/or when corn is under drought stress, however yield increases in these situations have been fairly inconsistent and much less than when disease is present. The theory is that some fungicides (strobilurins) have a positive physiological effect by aiding in more efficient respiration under hot and dry conditions and can increase water use efficiency. I feel this is valid information but applications targeted specifically for drought stress purposes alone are hit or miss and are not likely to produce consistent profitable results, especially if drought stress is at moderate to severe levels. An application will not save a severely drought-stressed crop. Fungicide applications should target disease and be timed to provide best results based off disease progression. Most current foliar fungicides have about 21 days of residual activity. Disease has been slow to develop thus far but could increase quicker if the weather pattern changes in the coming few weeks. Therefore this year, fungicide applications taking place toward the tail end of the window (brown silk) may be of more benefit in terms of disease protection than earlier applications.
Non-disease related benefits are real but should most often come along for the ride and not be specific targets of foliar disease fungicide applications when consistent yield increases are the main goal. If you have questions regarding fungicides contact your Hoegemeyer DSM or Agronomist. Now let’s get some RAIN!!!!!!!