In The Long Run

More time for disease pressure,
but better resistance – disease management
in late-maturing varieties

By Amanda Huber

 
Late-Maturing Varieties
 

Georgia-02C:
• Excellent resistance to TSWV and CBR

Georgia-01R
• Good resistance to TSWV, early and late leaf spot, white mold, CBR, leafhoppers and leaf scorch

C-99R
• Good resistance to leaf spot, white mold and rust
• Some resistance to CBR

Tifrunner
• Excellent resistance to TSWV
• Moderate resistance to early and late leaf spot

York
• Excellent resistance to TSWV, white mold and leaf spot
 

Late-maturing varieties are grown to help stretch out the harvest season so that the entire crop is not coming in at once. However, more time in the field means more time for disease problems to crop up, set in and flourish. So, the question is, “Should late-maturing varieties be managed for disease any differently than medium-maturing varieties?”

The answer, according to Bob Kemerait, Extension plant pathologist for the University of Georgia, is, “Yes.”

“The answer is ‘yes’ for two reasons,” Kemerait says. “First, late-maturing varieties have some of the best disease resistance packages of any varieties, so it may be that you will not have had the disease pressure in the field.”

Built-In Resistance
It is true that most of the late-maturing varieties are resistant to multiple diseases. For a list of varieties and the level of resistance to the various diseases, see the box on page 11. Also, consult Peanut Rx for risk levels associated with all varieties.

Bill Branch, University of Georgia peanut breeder, says that, unfortunately, germination problems have plagued some of the late-maturing varieties, such as DP-1, Georgia-0R1 and, most recently, York.

“However, Georgia-02C, C-99R and Tifrunner do not seem to have this problem,” Branch says. “Among these late-maturing varieties, Georgia-02C has the best resistance to CBR (Cylindrocladium black rot) and TSWV (tomato spotted wilt virus) and the highest yield, grade and dollar value return per acre.”

Spray Smart
The second reason Kemerait says late-maturing varieties should be managed differently is because the season does run so much longer.

“The problem you run into is if you start spraying a late variety and a medium variety at the same time, you will end up with four or five weeks left on the later variety that will still need protection,” he says. “My recommendation is to look at the resistance available in the variety, and because there is more resistance, delay the start of the fungicide spray a little.”

Kemerait says days can also be added to the intervals in between sprays.

“Instead of spraying every 14 days, go to 16 or 17 days. You will be able to stretch that disease control,” he says. “The greater risk is running out of fungicide at the end of the season.”

 
Mississippi On Board With Peanut Rx
 

What began as a collaboration between peanut researchers and specialists from the University of Georgia, Auburn University and the University of Florida for assessing disease risk and determining prescription fungicide spray programs has now expanded to include Mississippi State University.

Though MSU has been referencing Peanut Rx guidelines for several years, Mike Howell, MSU Extension agronomist, says there are several reasons for growers to get behind full participation for 2009.

“We’ve been looking at the program for several years. After evaluating and testing Peanut Rx, we’ve concluded that a reduced spray program has the potential to be a good fit for Mississippi peanut growers, too.”

Beyond the possible savings that fewer fungicide applications provide, Howell says, “Peanut Rx saves growers time when they’re not spraying every two weeks. It reduces wear and tear on their equipment and helps save fuel with fewer trips across the field.”

Peanut production has steadily increased in Mississippi the past several years, and, unlike the majority of the peanut belt, projections for 2009 indicated further expansion of peanut acres in the state. With limited alternatives, producers need the best tools available to remain profitable.

Producers in Mississippi have experienced the benefits of Peanut Rx first hand, says Howell. “We’ve got some growers, especially in our new growing areas, that have gotten by with only one or two fungicide applications a year.

We know this isn’t going to hold true as they continue to produce peanuts on those fields, but using Peanut Rx has really helped them save some money, and even some of our long-time peanut growers have been able to trim some input costs as well.”

Howell is enthusiastic about officially joining the Peanut Rx program and commends Syngenta for being the first crop protection company to support Peanut Rx since its inception in 2007.

Information provided by Syngenta Crop Protection.

Using Peanut Rx
Whether the season is short or long, growers are always going to wonder if that last spray is needed. Kemerait says whether or not you can drop an application depends on what your risk is.

“What does your disease control look like at the end of the season?” he says. “If you look like you have great control, given the current weather forecast, a lot of times you can drop the last leaf spot spray. Good management throughout the year means the last application can be dropped.”

Kemerait says late-season varieties are managed just as well with Peanut Rx as medium-maturing varieties.
“In fact, until recently, it has been the long-season varieties that have worked best with Peanut Rx,” he says.
The one pest that should be completely avoided with a late-maturing variety is nematodes.

“If you have peanut root knot nematode in a field, don’t plant a late-maturing variety,” Kemerait says. “Instead, plant Tifguard or an early variety.”

While managing disease in late-maturing varieties may not seem very different, keeping in mind these points will help keep disease under control.

The main thing with a long-season variety, Kemerait says, is that you may need to be a little more creative.

PG