Avoid the ‘perfect storm’ situation for a leaf spot control failure.
⋅ By Amanda Huber ⋅
Anticipating what might happen with disease pressure in your fields and providing research-based strategies to mitigate that yield destroyer are what plant pathologists do, says University of Georgia Extension plant pathologist Bob Kemerait.
The first step is looking back to the past year to see what worked and what didn’t. In 2021, it rained a lot, which made conditions throughout the season favorable for fungal diseases.
“Rains not only create conditions favorable for fungal infection and disease, but it also kept farmers out of the field and from making timely fungicide applications,” Kemerait says. “If you’re on a 14-day schedule and can’t get in the field for 21 days, there are going to be consequences.”
He also says rain makes it difficult to have adequate product drying time on leaves.
“In order to get great control, you have to have the right product, the right time and you have to be able to put the product out so that you get the right drying time. A lot of growers in 2021 did not have that.”
Anticipate Problems In 2022
Kemerait says for this season, growers should be concerned about several things.
“What’s going to be the impact of La Niña? A wetter spring is what most experts would say a La Niña weather pattern would bring,” he says.
Another concern is the impact from fertilizer costs.
“We’ll see more peanut acres, and it is anticipated that we will have shortages of fungicides and increased costs,” Kemerait says. “Expect reduced availability of fungicides and increased costs.”
He suggests that if you cannot get the fungicides you are expecting, first use Peanut Rx to determine the level of threat across your fields. Treat fields according to the risk, and put the best treatments where you need it most.
“Secondly, tailor your fungicide programs depending on that risk level.”
Kemerait says if fields are low risk, you have more flexibility to change your fungicide program. “If you have high-risk fields, you may have fewer opportunities to do that.”
Finally, he says growers must have a contingency plan.
“If you absolutely think that 60 days after planting, you’re going to use brand ‘x’ because you always do, what if you can’t get it? It’s best to know what brands ‘y’ and ‘z’ might be,” Kemerait says.
Disease Protection In Furrow
The opportunity for management of nematodes and some diseases comes one time – at planting.
“When you close that furrow, you have made decisions that you cannot go back and fix, at least easily. Take the opportunity to learn what the potential is and go from there,” Kemerait says.
In 2022, seed quality should be good, and growers have options for seed treatments that help with seedling disease.
“Recognize that what’s put on your seed before you plant can help go a long way to reducing your risk to some of these important diseases,” he says.
In-furrow fungicides such as Abound, Proline and Velum Total, enhance stands and improve vigor, but also protect seedlings against diseases such as Rhizoctonia and Aspergillus. Nematicide options include Velum, Propulse, AgLogic, Vydate-CLV and Telone II.
“You get one chance with nematodes, and when you close that furrow, if you have not used a resistant variety, such as TifNV-HighO/L, or a nematicide, there is almost no recovery. Don’t miss the opportunity.”
Kemerait says when he started in peanuts, it was primarily root knot nematodes as the microscopic pest.
“Now, in 2022, we recognize there is strong evidence to indicate that lesion nematode is also found in peanut. It makes black speckles on pods and on pegs, which possibly reduces peg strength,” he says. “Keep using what’s worked for you, and before you change products, contact your county agent to ask about the data to support the changes that you might make.”
Driving home his point, Kemerait says if you use Velum in furrow, UGA research pathologist Albert Culbreath has data that shows 90 days after planting, you may still see benefits on leaf spot from something you did before you closed the furrow.
“If you use Thimet in furrow for thrips control, you can still see some benefit as much as 90 DAP,” he says. “This doesn’t mean to start your fungicide program at 90 DAP. If you did that, you would be sorry. It just means you are still getting the benefit of that fungicide application made at planting.”
Obstacles To Leaf Spot Control
Leaf spot is the most problematic disease producers will likely face in 2022, Kemerait says. Unfortunately, there are many obstacles to good leaf spot management growers may encounter.
“A late-starting fungicide program is a recipe for disaster on leaf spot,” he says. “If you get behind because you can’t get in the field and you can’t get an airplane, there’s nothing much you can do.”
Compromised efficacy of fungicides is another problem. Kemerait says tebuconazole and some other commonly used fungicides do not provide the same level of protection as they once did.
Another problem is intentionally extending intervals between fungicide sprays.
“If you can take some defoliation, we have data that shows top yields can still be achieved,” he says. However, if a producer is trying to stretch a 14-day interval out, and then it rains, and the interval becomes much longer, that’s when leaf spot takes hold.
“It’s all about what you are comfortable with as a producer,” Kemerait says. “Not every field will work with extended interval applications. These days you also need to consider that fungicide applications do not stop at 120 days.
“A perfect storm situation is uncooperative weather, short rotations, overreliance on the same class of fungicides and stretching the intervals of fungicide programs,” he says. “We can manage all of that by being careful with what we do.”
Overreliance On SDHIs
Kemerait says producers have an expanding arsenal of fungicides; however, with all these new fungicides, there are not any new classes of chemistry.
“Whether it’s Excalia, Provysol, Sipcam — yes, there are different chemistries, but they are all the same class — the succinate-dehydrogenase-inhibitors, or SDHI class, as they are most often called.
“We are becoming increasingly familiar with and reliant on these fungicides,” he says. “And I’ll even use the term ‘overreliant’ because I think if you take shorter rotations and weather, and you rely on a single class of chemistry to carry the lot, bad things can happen. In 2021, with the rain, we saw a lot of leaf spot.”
Kemerait says no matter the cost, fungicides are needed to fight disease, but be careful to not rely too heavily on the SDHIs. “If you don’t incorporate other chemistries, resistance will develop.”
The addition of sulfur as a tank-mix partner can help with leaf spot control. However, Kemerait says certain sulfur products should be used.
“Products that offer additional leaf spot protection include Microthiol 80W, Drexel Sulfur 80W, Drexel Suffa 6F, TechnoS 90W and Accoidal 80WG.”
White Mold Still Garners Attention
Although leaf spot is the disease causing more problems in producers’ fields, some years ago it was white mold. Tim Brenneman, UGA peanut research pathologist says they are looking at some shifts in sensitivity of white mold pathogen to some of the chemistries we use.
“We have looked at several hundred isolates and we are seeing changes in sensitivity,” Brenneman says. “Looking at our database from 20 years ago, we’re seeing that those isolates are not as sensitive to some of our main fungicides like flutolonil and tebuconozole.
“We want to see how that affects control in the field and response to some of the newer fungicides like Elatus or Excalia that are in the same class of chemistry,” he says. “Does less resistance to older chemistries translate into less control in some of the newer ones? That is what we are looking at.” PG