Serving the Big Horn Basin for over 100 years
Serving the Big Horn Basin for over 100 years
A doctor of plant pathology with the University of Wyoming, Jean Williams-Woodward, gives a presentation to local sugar beet farmers about cercospera, a fungal infection that Big Horn Basin sugarbeet growers battle each year. The presentation took place at the Washakie Museum during WESTI Ag Day on Feb. 3.
Proactive spray application is best practice
During WESTI Ag Day on Feb. 3, an associate professor with the University of Wyoming gave a presentation about a type of fungal infection that has become the No. 1 enemy of sugarbeet farmers in the Big Horn Basin: cercospera leaf spot (CLS).
CLS is caused by fungi in the genus cercospera that have found a niche living in the tissue of beet leaves, and it has become a common pest in areas of sugarbeet production. Symptoms of a cercospera infection begin with small brown spots on the leaf, and end with leaves that are shriveled and dry, as if they were burned. Affected beet plants synthesize less sugar due to leaf loss, meaning infected fields can have their yields greatly reduced.
Parasitic cercospera doesn't reveal any symptoms until its reproductive stage; by the time you notice spots, the fungus is already releasing millions of spores on the underside of infected leaves, dispersing them to the wind. This makes the disease easily transmitted between neighboring fields.
Cercospera species complete this reproductive cycle in just two weeks during their host plants' growing season. Afterwards, the fungal spores lie dormant until the next growing season. They can even stay dormant for years until conditions are right, meaning that removing the pest completely is an impossible task.
Dr. Jean Williams-Woodward has spent her professional career dealing with CLS, and research she is involved in is leading the way in developing methods for farmers to control the disease.
For farmers attending her presentation hoping to hear about a way to eradicate the fungus, she didn't have good news. She said, "One thing you have to remember, fungicides do not kill this fungus. What they do is keep it static; they hold a fungus in suspension for a while, as long as that fungicide residual is there, and for that time it isn't reproducing. Once that fungicide residual wears off, that fungus is able to come back to life and start reproducing again."
Williams-Woodward did, however, present some management strategies that would help farmers to control the disease.
She said, "With the data we have from the Red River Valley, recoverable sucrose in beets is highest when fungicide application begins in the fourth week after planting ... We have data going from 2017 to 2023 that supports that ... We also have data showing that if you don't apply anything until late in August, you've reduced your recoverable sugar by at least a third. So getting out early is a better option for you to try to reduce the amount of infection, reduce the amount of spores getting produced, and then you're kind of ahead of the disease, as opposed to chasing it."
She added, "We're still researching how to manage this, stay tuned and hopefully we'll have some of this information. But the goal for any kind of disease management is prevention. If you are waiting too long, you've already got a lot of spots, you're not going to control that, and your sugar is going to be reduced."
She said that irrigation method and timing can affect cercospera transmission, saying that the fungus thrives in a wet environment and water splashing will enhance transmission by knocking spores loose. She said that irrigation methods that keep the leaves dry works best for managing cercospera, and allowing the field to dry during the day shortens the time spent in a wet, cercospera-favoring environment.
Williams-Woodward also stressed the importance of following application of one pesticide with another that uses a different mechanism to control the fungus. She showed example data that identified 46 different kinds of cercospera fungi in one field, and spoke about how their fast reproductive cycle gives them advantages in developing fungicide resistance. One fungicide application would leave some fungal colonies unharmed that have evolved resistance, but another fungicide application using a different mechanism can target them. By rotating applications in this manner, farmers can get the best results in controlling cercospera in their fields.
She said that data on the cercospera problem in the Big Horn Basin is limited, but expressed that she wants to work with local growers to gather that data, and generate some more detailed management plans in the future.
