Disease-resistant varieties have revolutionized peanut production, in some cases de-emphasizing the importance some growers place on control measures.

But all of the same diseases are still relevant, and to ignore any one of them would be a mistake.

In looking back over this past year, Auburn University Extension plant pathologist Austin Hagan says extremely high temperatures prompted a resurgence in white mold disease on peanuts.

“We didn’t see a lot of tomato spotted wilt virus (TSWV). But in the past, the disease pressure was so bad that some fields had to be plowed under,” says Hagan. “Just because we didn’t see much last year doesn’t mean it’s gone — it could come back.”

Peanut producers have replaced the once-popular Georgia Green with varieties that have higher levels of resistance to the disease, he says. “We should be in pretty good shape as we shift over to these new varieties. In the Peanut Rx, we assign point values as far as sensitivity or susceptibility to TSWV. Georgia Green is up to 30 total points, and all of the newer varieties look very good.”

Many fungicides are now available for leafspot, and that’s probably the disease growers should be most concerned about, says Hagan.

“Many new products are out there, and they all will control early leafspot — which is the main concern — and late leafspot. There are a lot of alternatives depending on what type of program you want to put together. We have generic products that’ll be relatively inexpensive, generic chlorothalanil and the generic Folicur-type products, and we have the brand-name materials. So there are a broad range of costs out there when you look at leafspot control,” he says.

Need-based point system

The Peanut Rx program, explains Hagan, is a need-based, point system that allows growers to use some of the name-brand products but reduces the total application costs.

“We’ve had very good luck using these programs in trials. The four or five-spray programs with a resistant variety have worked very well in comparison to the seven-spray program. The main sprays you cut out with the Peanut Rx program are sprays of chlorothalonil. If you’re talking about a generic chlorothalonil, you’re talking about $5 per product per application, and if you’re talking about Bravo Ultrex or Bravo WeatherStik, you’re talking about $7 or $7.50. You’re probably going to save no more than $15 per acre when shifting to this program, but it is an option. The other option is to go the generic route.”

As far as leafspot resistance, the best variety bets, says Hagan, are GA-07W, FLA-07 and Tifguard. “These varieties give you added security as far as slowing down leafspot. That’s especially helpful if we have a tropical storm or hurricane that keeps you out of the field for a couple of weeks.”

(For a look at how growers figure the value of peanut variety resistance see http://southeastfarmpress.com/peanuts/placing-value-disease-resistant-peanut-varieties-0).

If you were going to look at a prescription program where you use reduced fungicides for leafspot control, you’re probably better off using one of those varieties as well, he says.

“These varieties give you an extra margin of safety over Georgia Green. Basically, from our standpoint, looking at diseases, GA-06G is every bit as susceptible to white mold and leafspot as Georgia Green.”

Looking at leafspot ratings at the plant breeding unit in Shorter, Ala., the highest came in for Georgia Green and the lowest for Tifguard, with many of the other varieties falling somewhere in between, he says.

“A grower might have a problem with white mold if he has a history of soybean production, or he’s back for the third time with peanuts, or he has had some history with vegetables in the field, especially if it becomes hot and dry at pegging time.”

One way to suppress white mold is to plant later, says Hagan. “Down in the Wiregrass region of southeast Alabama and in other areas, growers are wanting to move their planting dates earlier to give them a little more flexibility at the end of the season with harvest operations. With those late April to early May planting dates, they’re more likely to run into problems with white mold because the peanuts have been setting their pods in late August and early September, when temperatures are really hot, particularly at night.

“If we plant in the middle of May to the end of the month, then the peanuts are maturing in late September up until the first of October, the soil temperatures will be dropping, and the risk of white mold will go down on its own.”

As for varieties, Georgia Green and Georgia Greener tend to have more issues with white mold than almost all of the others, he says.

Many products out there

“There are a lot of white mold products out there. If you look at economics, the least expensive products are the generic Folicur ones. Tubuconazole is a fairly cheap product right now. In some trials, it doesn’t do quite as well as some of the name-brand products. When you look at costs, you could put together a white mold/leafspot program with generics at a much lower cost than a name brand. You need to look at it on a field-by-field basis.”

One new fungicide product that growers will see on the market for next year is Fontelis from DuPont, says Hagan. “It is a premium product. Its yield response and level of disease control is comparable to products like Provost, Abound and Convoy.”

For the past couple of years, says Hagan, researchers have been looking at peanut seeding rates in Headland, Ala.

“A number of years ago in the mid-1980s, there was work done about reducing seeding rates. They were able to show that with planting Florunner at 70 pounds of seed per acre, they were able to make the same yields as with about 100 pounds per acre. After the work was done, TSWV came on the scene, and that was the end of cutting seeding rates, because with susceptible varieties, whenever you started thinning the stand, the amount of virus increases dramatically. So we pushed people to plant six seed per foot of row.”

In 2010, researchers planted GA-07, GA-06G and Georgia Green. “GA-07 and GA-06 outyielded Georgia Green. Also, we had a little bit less disease with the low seeding rate, but the yields were the same across all seeding rates. I’m not suggesting you go to two or three seed per foot of row, but there is some margin for working within seeding rates as a means of saving a little bit of money. If TSWV comes back, we’ll have to jack up seeding rates. If we’re in a situation where virus is declining, this may be a place where you might save a little bit of money. We got the same results in 2009 as in 2010, and we’ll repeat this trial this year.”

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