Cylindrocladium black rot (CBR) doesn’t affect all peanuts in Georgia, but in the fields where it does occur, it can be difficult to control.
“Losses can be severe, and the survival of this fungus is long, so if you have it in a field, it’ll be there for a long while,” said Tim Brenneman, University of Georgia plant pathologist, speaking at the recent Bayer CropScience Southeast Technical Seminar in Braselton, Ga.
Other diseases, such as tomato spotted wilt virus, can closely resemble CBR, says Brenneman, so growers should be aware of the symptoms of the disease before treating, symptoms that include black discoloration in lower stems, pegs and pods. Additionally, red perithecia can often be seen on lower stems.
“We don’t have good data on where specifically the fungus is located in Georgia, but it appears to be scattered throughout the state,” he says.
When attempting to control CBR, it’s important, says Brenneman, that growers remember the basics. “With a disease like CBR, sanitation is very important because we need to do everything possible to prevent the fungus from spreading. We want to keep it out of every field possible. It’s not an epidemic, and we still have areas where it’s not present — we want to keep it that way,” he says.
Crop rotation is another means of controlling CBR, adds Brenneman.
“We’ve heard this for years, and with peanut prices where they are now, we’ve got an opportunity to maybe get in a better rotation and gain some benefits. Low peanut prices are not a positive thing, but we can make a positive out of the situation by going with a better rotation and getting a benefit. But peanut producers should stay out of soybeans if at all possible. From a rotation standpoint with peanuts, soybeans are horrible. CBR is probably the No. 1 reason why a soybean rotation is horrible — soybeans are highly susceptible to the disease,” he says.
There are other options for managing CBR, but none of them are particularly pleasant, says Brenneman. One of these is fumigation with metam sodium or Vapam. “This is not used nearly as much in Georgia as in some other places. We’ve had good results at times, but not so good at other times. Although not much of it is being used, it’s still an option in real problem areas where its use is probably justified.
“The new option we have this year is Proline, used in conjunction with Provost. In the past, we have shown some benefit from Folicur and Abound, but they were labeled for suppression only,” he says.
Another option in controlling CBR is peanut cultivars, says Brenneman. “We’re always interested in cultivars as a control measure. That’s always our No. 1 control option if they’re available. A lot of breeding efforts, by both USDA and the University of Georgia, are on-going to help us get a better CBR-resistant cultivar. Some of the cultivars with CBR resistance are being phased out, but we still have GA-02C, and that’s probably our best CBR variety right now. However, it is not highly resistant. We need better resistance than what we currently have,” he says.
Some Virginia types are resistant to CBR, but they were not developed for resistance to tomato spotted wilt virus, says Brenneman. Lines out of Florida have historically been susceptible to CBR, he says, including C-99R, Southern Runner and AP-3.
“We’re still evaluating some of the newest varieties, although the last two years have not been good ones for the disease. Weather conditions have been hot and dry, and we haven’t had the best conditions for evaluation. But the newer lines are coming out fast and furious. We’re trying to get data, and we have some tests in the greenhouse now so we’ll know more what to predict in terms of CBR as well as some of the other diseases.”
Growers also should be aware of the interaction of nematodes and CBR, notes Brenneman. “Root-knot nematodes can kill you and CBR can kill you. If you get them together, it can be a very damaging situation. We have a new option for nematodes with the Tifgard variety. It’s a runner peanut with outstanding nematode resistance. It also has strong resistance to a number of other things, including tomato spotted wilt virus. We feel like it will give us tremendous potential in managing nematode damage.
“The CBR data with Tifgard has been mixed. In some trials, it has looked good. In other trials, it hasn’t looked so good. If you’re in a field where you have CBR and nematodes interacting, Tifgard might work for you. CBR can occur on any soil type in the state — in heavy clay or deep sand. But root-knot nematodes are usually restricted to our light, sandy soils. If you’re on those types of soils and have CBR and nematodes, then by all means consider Tifgard as an option. At the very least, it’s moderately susceptible to CBR. And with the nematode benefit it brings, it could be a tremendous benefit.”
Where the problem is primarily CBR, there may be better options, like GA-02C, he says.
Turning to the fungicide aspects of CBR control, Brenneman says growers are attempting to control a range of peanut diseases, and with CBR, the infection occurs below ground.
“Everything that happens with CBR is occurring on the roots or on the pods. When we talk about fungicides and fungicide control, that’s a different target to manage. One way to do it is to get the fungicides down early, and that’s where Proline comes in. We apply it in-furrow and put it right down with the seed.
“Infection from CBR can start early on the roots as they start to develop. So we get the plant off to a healthy start and protect the young root system. We can come back in the middle part of the season with Provost, and it has the same active ingredient as Proline. So between the two, we try to start out early and then carry it on through. We’ve looked at Proline for about five years now, although it has just now been labeled.”
Research trials including programs of Bravo/Folicur and Provost and Proline are promising for the use of Provost and Proline, says Brenneman. “We’ve come a long way compared to what we were looking at with the Folicur or Abound programs. Yield response is promising. We get a boost from Folicur, another boost from Provost, and then Proline gets us up to where we need to be.”