In a hot, dry year like 2006, it's easy for peanut producers to forget disease problems such as cylindrocladium black rot (CBR). But that would be a mistake, says University of Georgia plant pathologist Tim Brenneman.
“Last year wasn't a bad one for CBR. But rest assured the disease is still with us, and it isn't going away,” says Brenneman. “It's something we have to learn to live with, and we have to learn to manage.”
The disease, he says, originated in a southwest Georgia peanut field. “Georgia has originated a lot of unique things, but we might not be so proud that the CBR epidemic that affects peanuts throughout the world began here. CBR was found in Georgia in 1965 in Terrell County. In the subsequent 40 years, the disease has spread around the world. It's a major cause of yield loss throughout the world in every country where peanuts are now grown,” he says.
Brenneman, speaking at the recent Southeast Cotton & Peanut Consultants Conference sponsored by Bayer CropScience, says he tries to remind growers to return to the basics when attempting to manage CBR in peanuts. “This includes rotating crops. CBR has a very long life, and you won't get rid of it with rotation. But if you can get a good three, four or five-year rotation, you can get it down to a level where you can manage and live with it.
“We also remind growers about how the disease is spread. Try to clean your equipment, and do anything you can to keep from spreading CBR from field to field. Also, destroy or remove all peanut hay. All of these things will be very beneficial in preventing the spread of the disease,” he says.
When the disease began to be a problem in Virginia, research was conducted there on resistant peanut varieties, he says.
“We've been playing catch-up in the Southeast. We now have varieties with improved resistance. We're still not where we need to be, but we're light years from where we used to be,” says Brenneman.
Looking at other control methods for the disease, the most effective in the past has been fumigation with metam sodium or Vapam, he says. “You can get a tremendous benefit from that treatment under some circumstances. There are some cases, though, where the same fumigant can be used with no response.
“The story with Vapam has been that sometimes it is great, and sometimes it is not. It's always expensive, and it's always a pain to use. Very few of our growers are using that technology. It's used more in Virginia and North Carolina, but in Georgia, it has seen very little use because there are a lot of complications and problems with using this treatment,” says Brenneman.
The other option for suppressing the disease, he adds, is using fungicides. “Fungicides are used quite a bit on peanuts, and our only options for CBR have been Folicur and Abound. Both of these products are labeled for suppression, and that doesn't mean control. Whenever a product says ‘suppression,’ you'll probably get something that isn't in the same league as you would expect from a fully labeled material for the control of a disease.”
These products, says Brenneman, also are erratic when it comes to CBR. “We've seen a decent response in some years. In other years, we don't get much of a response from them. My advice in the past has been if you have a problem, use one or the other of these products. You'll see some benefit some of the time. But it's not something you can take to the bank.”
The first line of defense against most peanut diseases is a fungicide, says Brenneman, and growers face a huge challenge in controlling the wide spectrum of diseases found in peanuts.
“We have multiple infection ports, and we have a wide range of pathogens and sites of infection that we're trying to control when we spray a fungicide over peanuts. On top of the canopy on foliage, we have leafspot and rust. As we come down the canopy, we have diseases like limb rot. When we get down to the soil line, we have white mold that can also get below the ground, infecting pods. The hardest target of all, on the secondary roots, is where we find infections of CBR. It's a tough task for any one fungicide to cover that target.
“But we now have a product that seems to do, at least to some degree, what we've been talking about — Provost from Bayer. Basically, this product is a combination of two active ingredients: tebuconazole, which is the same as Folicur, and prothioconazole, which is a new active ingredient. It's not registered at this point, but it's expected to be registered for the coming season.”
Provost probably will be recommended and labeled in a block program, similar to the way in which Folicur currently is used. Provost has activity on leafspot and also is active on triazole-resistant leafspot, says Brenneman.
“We're seeing a trend in Georgia of triazole resistance. In various trials, products like Folicur are not doing the job on leafspot. But even in those situations, Provost still has provided excellent control.”
Going further down the plant, to soil-borne diseases like white mold and limb rot, the activity of Provost compares very well to Folicur, he says. “But the one thing that excites me the most about this product is its activity on CBR. We have seen significant activity against CBR with Provost. We do have a product here with a mixture of two triazole fungicides, so we need to consider that in our resistant management strategies.”
With one exception, there are no current treatments that can eliminate CBR infections, says Brenneman. “The exception might be if you take methyl bromide and put a plastic tarp over your field, treating it as you would a tobacco field. You can pretty much eliminate CBR, but it'll cost you $2,000 per acre. With everything else, we're talking about learning to manage and live with the disease. We're trying to buy some time for the plant, giving it a chance to grow and produce yields before CBR catches up to and kills it.”
CBR infections can occur very early in the growing season, he says, especially if there's a cool, wet spring. The fungus comes in and starts to infect young roots, gradually rotting the entire root system. Then, towards the end of the year, the plant doesn't have enough roots to sustain itself.
“If we want to head off that process and give the plant the most time to grow, the way we've found to do that is to use an in-furrow spray. The full program we're looking at is to use prothioconazole in the furrow and then use Provost as cover sprays. We have a new product that has been introduced — Proline — that is straight prothioconazole.
“The main problem with using Provost full-season and in-furrow, is that we have significant issues related to seed injury where we have put Folicur in the furrow with peanut seed. You could have late emergence, no emergence or spotty emergence, and all of those things spell trouble. We must have a good, uniform stand of peanuts to manage tomato spotted wilt virus.”
Proline can be sprayed directly in the furrow, he says, but it won't be labeled for the coming production season.
Where Proline was used with Provost in trials, the yield increase was “astounding,” says Brenneman. Similar tests in Virginia produced similar results. Also, when Vapam was added to the Proline/Provost treatment in Virginia, there was an additional response.
To summarize, Brenneman says prothioconazole is the most active fungicide available for controlling CBR. “To get consistent control of this disease, we need to use the in-furrow plus the cover sprays. If you're in a very heavy disease pressure situation, where you've used metam sodium in the past, it may pay to use a Vapam application preplant in addition to Proline and Provost. The beauty of this treatment is that it gives you the broad-spectrum control over a wide range of peanut diseases.”
In other work involving CBR, researchers are looking at the relationship between nematode damage and disease, says Brenneman. “We have a lot of nematode injury in Georgia, and a lot of those same fields also have CBR issues. They both attack the root system and are active on the same tissue of the plant.”