Do foliar fungicides provide enough bang for the buck?

There has been a lot of discussion about applying reduced rates of foliar fungicides, usually a half rate at the T1 stage or at the time of herbicide spraying. 


The practice has become common in the past few years, but the question remains: “Are you getting an economic bang for your buck?” 


Kelly Turkington of Agriculture Canada has studied propiconazole at various rates when tank mixed with herbicide at the herbicide application timing, T1, or fungicide alone at the flag leaf stage, T2, for leaf spot control in AC Metcalfe barley. 


“We observed no, or rarely, any benefit to applying fungicide at the herbicide application timing,” said Randy Kucher of the University of Saskatchewan, who participated in the study. 


“For optimum leaf spot control in barley, we continue to observe the best results at the flag leaf fully unfurled.”


However, it seems to me that there may be exceptions.


A farmer might consider applying a fungicide at the T2 stage under the following conditions: the crop was planted into infested cereal stubble, it has a dense and moist canopy and lesions are observed on the newest leaf growth. 


If this isn’t the case, the producer should save the fungicide until the application will provide with the greatest economic return at flag leaf or anthesis.


Timing is also a factor when applying fungicides with a herbicide application. 


Early weed removal has significant benefits, but fungicide success also appears to increase as the crop stage advances because of the increased amount of plant material to be protected and the increased likelihood of infection. 


These two dynamics work against each other. From an economic standpoint, it does not make sense to delay a herbicide application to improve the benefits of a fungicide application.


Disease resistance management must be another consideration.


There has been confirmed resistance to most groups of fungicides among all common cereal leaf diseases. Growers can help reduce the threat of fungicide resistance by avoiding the use of very susceptible varieties, treating seed with effective seed treatments and, where sprays are required, rotating with the fungicide groups. 


“(However), the more a fungicide is used (numbers of applications), the greater the risk that the pathogen population will become insensitive (resistant) to the product,” Kucher said.


Three Agriculture Canada studies have found no economic benefit to this practice, but Marcia McMullen, a plant pathologist with North Dakota State University’s extension service, said studies in that state have found benefits.


I have observed numerous fields this year with heavy infection of leaf diseases, mostly tan spot on wheat and net and spot blotch on barley. Both diseases prefer the showery, wet conditions we have been experiencing.


These diseases are worse on crops grown on their own stubble. I’ve noted that wheat on a cereal stubble or barley on a cereal stubble, while not as bad as on its own stubble, is worse than when grown on a broad leaf stubble like canola or peas. 


As well, disease infections are highest on crops that are under stress, either moisture or nutrient. 


Diseases such as scald on barley have been observed in other parts of Western Canada,.


Producers should scout fields, properly identify diseases and use effective control measures that will provide the best return when making disease decisions.

Thom Weir is an agronomist with Farmer’s Edge. He can be reached by emailing [email protected]

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