Spray Pressure and Nozzle Types

​This time of year, I receive many questions about what fungicides to apply. I get fewer questions about how to apply fungicides. Below, I will try to address how to apply fungicides.

Many years ago, I was told that to successfully use fungicides on vegetables, one must use high spray pressures and hollow cone nozzles. However, I had trouble finding any research on this topic, just rumors. So, I did my own research.

Dennis Nowaskie, Superintendant at the Southwest Purdue Agricultural Center (SWPAC) built a single row sprayer that could be used to vary nozzle types between flat fans and hollow cones and spray pressures from 30 to 150 PSI. We used the sprayer to conduct experiments on Alternaria leaf blight of muskmelon during three years of field tests. The fungicide we used to try to manage this disease was the contact product chlorothalonil (trade names include Agronil®, Bravo®, Echo® and Terranil®). Phillip Harmon, now a professor at the University of Florida, was my co-author on this paper.

Try as we might, we could not find any statistical differences in disease severity or yield between any of the nozzle type or spray pressure treatments. We also used water sensitive paper to measure coverage at each treatment. Regardless, of the nozzle type or spray pressure there was no statistical difference in coverage.Surprisingly little research has been done by other researchers on this subject (there just isn’t much money to support such research). However, the little research that has been done has resulted in similar findings. University of Florida researchers lead by Tom Kucharek found that regardless of whether flat fan or hollow cone nozzles were used, no difference in disease severity was observed in the following diseases: early or late leaf spot of peanut, bacterial spot of pepper and blast or purple blotch of onions. Kucharek also found that spray pressures ranging from 50 to 250 psi made no differences in disease control in early or late leaf spot of peanut.

I was not able to obtain funding for the question of how much water per acre to use for fungicide applications. My observations are that one should use between 20 and 50 gallons per acre. My personal opinion is that the more the better, within this range.

The timing of fungicide applications is usually more important then nozzles and pressures. Some of my thoughts on fungicide timing are given in the article on fungicide application hints in this issue of the Hotline.

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