Does foliar fungicide increase yield?

Gray leaf spot.

By Dave Nanda, 
Director of Genetics & Technology for
Seed Consultants, Inc.

Plant breeders try to develop new varieties with highest yield potential and select for disease resistance at the same time. However, it is almost impossible to develop resistance to all of the prevalent diseases while developing new varieties or hybrids. We have created some excellent genetic traits for insect tolerance but disease organisms are constantly changing and by the time breeders develop varieties resistant to certain disease organism, the pathogen changes. Nature has its own “breeding program” for the survival of its species. In order to maximize the potential yield of our crops, we need to protect them from diseases also and use of fungicides is one way.

Different disease organisms become more prevalent in certain growing conditions, for example, gray leaf spot likes high humidity and high temperature. Conservation tillage has also increased the incidence of many diseases. Some popular corn hybrids on the market have high yield potential but are very susceptible to certain pathogens, which increase the probability of disease development. You really don’t need to apply foliar fungicides to all hybrids if they are resistant to the diseases present in your fields but you do need to scout your fields regularly where as others might have to be sprayed with the fungicides.

Some fungicide producers have been promoting the use of foliar fungicides even at early vegetative stage to increase yields. Tests conducted by universities indicate that it is not cost effective to apply fungicides without the presence of the disease. My scouting experience during the last few years have shown that you don’t have to apply fungicides to all hybrids or even all fields planted on different dates because some fields might escape the disease The ideal time to apply fungicides on corn is after all pollen-shed is complete and silks start to turn brown.

What is the best way to apply foliar fungicides? Recent studies have shown that ground spraying is more effective than aerial application. The lesions of the fungi have to be covered with the fungicides in order to stop their growth or kill them. Fungicides don’t increase yield, but they can protect the yield potential of the crop plants in the presence of the fungal diseases. Fungicides do not protect your crops from diseases caused by bacteria or viruses.

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