Last week several areas in North Dakota received significant rainfall and severe hail events. Hail damage in crops ranged from severe to complete defoliation. We have received many questions on the use of fungicides to “rescue” the crop with a fungicide application. Below is information on fungicide use on hail damaged crops, including a summary of results of a soybean-hail study just published last month from Iowa State University.
How does hail impact plant pathogens?
Bacterial pathogens need a wound to initiate infection in field crops, whereas most fungal pathogens do not need injury to penetrate plant tissue. Consequently, we are far more likely to see disease epidemics caused by bacterial pathogens after wind-driven rain or hail than we are an epidemic caused by fungal pathogens.
As an example, severe storms a couple weeks ago have resulted in a very severe bacterial blight epidemic on dry edible beans in parts of the state, but fungal diseases like rust and white mold did not appear to have been affected.
After these storm events, it is likely that other bacterial diseases, such as Goss’ leaf blight and wilt on corn, bacterial blight on peas, and exacerbated damage on dry beans will appear.
Will a fungicide reduce disease risk in a hail damaged crop?
Fungicides are labeled for use on fungal pathogens and have little to no effect on bacterial pathogens. Other chemicals, like cupric hydroxides, have been shown to help prevent new bacterial infections, but these are only preventative and the frequency of applications needed to suppress disease development will lessen the chance of an economic benefit.
Will a fungicide application protect yield in a hail damaged crop?
In some cases, FRAC 11 fungicides (i.e. strobilurins, Headline, Quadris, Aproach, etc...) have been shown to enhance greenness in crops. However, a greener crop does not translate into higher yields.
The most realistic study we have seen on hail damaged soybeans and fungicides was just published on June 20th, 2016. Researchers at Iowa State University used a ‘PTO-powered ice-applicator’ to simulate hail events on soybeans.
The researchers then evaluated the effects of applications of Headline fungicide (among other treatments as well). Mean data from six different trials showed that the fungicide application had no statistical benefit, and numerically, the application of Headline resulted in yield values of 0.2 to 1 bushel higher than the non-treated checks. The last sentence from the manuscripts’ abstracts sums up the results of the study best -
“Based on results, R3 fungicide application to soybean injured by hail at R1 or R4 will likely provide little yield-preserving or disease-limiting benefits when foliar disease severity is low”.
A hail simulation study on corn was conducted by the University of Illinois (Bradley and Ames, 2010). While the study used different techniques, such as weed-whip damage to simulate hail, the results were the same. Fungicide applications of either pyraclostrobin (Headline) or azoxystrobin (Quadris) did not result in statistically different yields than the non-treated checks.