Peanut virus thwarted in trials

Row patterns, tillage and seeding rates all have been proven to have a significant impact on the incidence of tomato spotted wilt virus in peanuts, says John Baldwin, University of Georgia Extension peanut specialist.

“Over the past several years, we've been looking at all these factors to see how they fit into our Tomato Spotted Wilt Virus Risk Index. For example, we now know that we're getting less tomato spotted wilt virus with seven to nine-inch twin rows than with single rows,” said Baldwin at the recent Georgia Peanut Farm Show in Albany.

In tests conducted on more than 19 Runner and Virginia variety peanuts, researchers also have seen better yields and grades in twin-row versus single-row peanuts, he adds.

“We're getting better yields and grades 99 percent of the time with twin rows over single rows, and all of these trials are conventional-tillage and under irrigation. We're also getting quicker canopy closure — by two to three weeks — and that's helping us with weed control, especially early in the season,” says Baldwin.

Researchers also are using the same seeding rate for twin and single rows. “We arbitrarily chose our highest recommended rate for single rows, which is six seed per row foot. That's three seed for each twin row, and it gives us the same pounds per acre planted, whether it's a single or a twin row.

“We did recommend a 10 to 15 percent seed increase for twin rows. With row patterns, seeding rates are as important as plant stands. Getting an adequate plant stand is extremely important. We want at least four plants per foot.

“So, if we take six seed per foot or three on each twin row, and multiply that by the lowest allowable germination of 70 percent, it gives us 4.2 plants per foot, which would put us in the acceptable range. When we get one to two plants per foot, even with resistant varieties, we have problems with tomato spotted wilt,” says Baldwin.

Planting quality seed, in addition to planting into good moisture and warm soils, also are important in reducing the threat of tomato spotted wilt virus, he says.

It's important, says Baldwin, that growers plant peanut seed according to per foot of row rather than by pounds per acre. “It's important to know your seed count in pounds. We have some cultivars today with much larger seed size.

“To get your seed count in pounds, you first determine the seed per foot that you want to plant. If you're figuring for twin rows, you still must put in the number for single rows. In other words, if you're planting three seed on each twin row, then that's six seed per foot. We multiply that by the row length, and that'll vary according to row spacing.”

Researchers looked at the Georgia Green and AT-201 varieties in four Georgia locations this past year, says Baldwin. All of the trials were conventionally tilled and grown under irrigation, and all received a standard fungicide application, with a four-block of Folicur. Peanuts were planted in nine-inch twin rows with a Monosem planter. The same planter and land preparations were used to plant single rows.

“Ninety-nine percent of the time, we got an average yield increase of 520 pounds per acre when comparing twin rows to single rows, and that's the largest overall increase we've seen. That's just two varieties, and we looked at seven different varieties last year.

“We've looked at more than 19 varieties since 1996, and the overall average yield increase for twin rows has been 400 pounds per acre. That average actually has been higher during the past two years.”

Grades in twin row trials are running about one point higher than the grades in single rows, but there's variability among cultivars, says the agronomist.

In the Georgia trials this past year, final plant stands at harvest were 5.2 plants in twin rows versus 4.3 plants in single rows. “This is the first year I've seen a difference in plant stand, and we were planting at the same population.”

Twin rows also continue to show a lower incidence of tomato spotted wilt virus than single rows, says Baldwin. In a twin versus single-row comparison, the incidence of tomato spotted wilt was seven percent versus 19 percent in two trials and six percent versus 20 percent in another.

“For the first three years of our trials, the average reduction in the incidence of the virus was about seven to 10 percent. Now, we're getting a reduction that's almost three times that. Part of it is the more resistant varieties, and the other part is that we're working out the planting scheme to get a better plant stand in these situations.”

Many growers, says Baldwin, want to know if they'll get more yield and better grade by increasing their seeding rates in twin rows. Research looked at five locations in 1999 and 2000, with seed rates at two, three and four seed per foot in twin rows. This is equal to four, six and eight seed in single rows.

“There was no significant difference in the three and four seed rates, and we got a yield reduction when we went got to that higher plant stand. That reduction could be attributed to increased disease pressure and decreased harvest efficiency. There was no real difference in grades.”

Also during 1999 and 2000, researchers looked at the C-99R variety in various seeding rates. “We saw a trend of lower yields and slightly lower grades with two seed per foot. This is a large-seeded variety, but we'll hurt ourselves if we go down to a low plant population, and four seed is no better than three.

“If we increase our seeding rate to four with this variety, it'll cost us $35 more per acre in seed costs, and we get no advantage in yield or grade. With Georgia Green, that's an extra $28 in seed costs. If half of our acreage in Georgia was planted in twin rows, and we increased our seeding rates, that would be $7 to $10 million extra in seed costs.”

Research also is being conducted, says Baldwin, in reduced-tillage peanuts. Growers who plant in reduced tillage systems can reduce trips over the field from six or seven to two, he adds. Another advantage of reduced-tillage is a reduction in lesser cornstalk borers, he says.

In trials conducted at the Sunbelt Expo site, the incidence of tomato spotted wilt virus was reduced in a strip-tillage system, notes Baldwin.

“We're looking at twin row patterns with reduced-tillage, but we're having a few problems, mainly with getting good seed to soil contact and getting a stand. The bottom line is that we get more response with conventional twin rows than with reduced tillage twin rows.”

e-mail: [email protected]

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