By Clint Thompson
White mold disease in peanuts has always been a problem for producers in the Southeast. University of Georgia plant pathologist Tim Brenneman is conducting research this year to see if the disease is developing resistance to the fungicides producers are already applying.
“We’ve had about 25 years of exposure, and in some cases, heavy exposure. Where we’re not seeing control, is it because the fungicide isn’t going there or is it because the pathogen is no longer sensitive to that chemical? We’ve got a large study we started last year where we collected isolates; 300 to 400 isolates that we’re going to test to make sure the fungus is still sensitive to the products we’re spraying,” Brenneman said.
Brenneman said that after the samples are collected and tested, which includes isolates from fields across Georgia where white mold is normally a problem, that UGA should have a better understanding of any disease resistance that may be occurring.
“We know (resistance) occurs in leaf spot (disease). We’ve already lost a couple of classes of our valuable chemistry. Leaf spot is a higher risk because of the exposure you get up on the leaves, and it also spreads more readily. But (resistance) can also occur in soil borne pathogens, and it’s been more than 20 years since we’ve looked at it. It’s time to look at it again,” Brenneman said.
Brenneman is no stranger to white mold research. His focus over the years at the UGA Tifton campus has been researching how to get fungicides delivered where they need to go down at the ground line, in the pod zone below the soil line. It’s difficult to do with a sprayer because there aren’t any systemic fungicides that move down in the plant.
He’s also studied night-time spraying where leaves fold up and the chemical application penetrates better. Brenneman’s also researched spray volume and spray tips to improve coverage in the lower canopy.
“White mold’s been with us forever. It’s been one of our constants in peanut production and has always been difficult to control because it can move underground. It can be in dry weather. It can be in wet weather. It’s very adaptable,” Brenneman said. “We’ve made a lot of strides. We’re doing a whole lot better than we used to with new fungicides that we have, but we still have cases where we don’t get control where we need. We’re trying to understand why that is.”
White mold is often the top cause of the loss of peanuts due to disease in a season. Sclerotium rolfsii, the causal agent of white mold, is a fungus that remains in the soil between cropping systems and waits for the next susceptible crop to be planted.
The disease becomes more problematic when growers fail to use proper crop rotations. Growing peanuts behind peanuts is highly discouraged because of diseases like white mold.
“It is very adept at killing peanuts. It produces acids that kill the tissue and enzymes that come in behind that just turn the peanuts to mush. It can grow up and down the rows and is very effective at killing peanut plants. You have these large patches of dead peanuts in your fields when you invert them. Or in the underground phase, the peanuts above them may still look okay but the pods are rotted underground. That, of course, is where your harvest is,” Brenneman said.