Last year, Dale Holland got a little antsy around the end of April and it cost him. Like many of his Virginia peanut-growing neighbors, Holland fumigated some of his land when the soil temperature was below 65 degrees Fahrenheit, too early for effective cylindrocladium black rot (CBR) control.
He won't make that mistake again this year in the fight against one of the top yield-robbing diseases in the Virginia-Carolina area. He's already watched the medium-range forecast and made sure it's going to be 65 degrees or above before heading to the field to fumigate.
“On the fields where we applied metam too early last year, we had yields of 2,850 pounds per acre,” Holland says. “Our average is 3,700 pounds per acre. If we hadn't used any Vapam on any of our peanuts, we would have probably lost over half our yield.” Holland points out that in a normal year, he's able to control CBR by fumigation and rotation.
CBR is a perennial problem for growers in the V-C area. The soil-borne fungus that causes CBR is noted for yellowing and wilting plants, and yield losses of 50 percent or more.
CBR-infected plants dot the field like a patchwork quilt of brown in a sea of green. Entire plants die at an alarming rate when drought conditions follow excessive rainfall. Below the ground, roots become black and rotten. Above ground, small, reddish-orange fruiting bodies of the fungus are the size of a pinhead and develop on the stems and pegs. These bodies enable an accurate field diagnosis of CBR infection. Otherwise, CBR can be confused with TSWV in the field.
To combat the problem, growers fumigate at least two weeks before planting with 7.5 to 10 gallons of metam sodium when the daily average soil temperature is above 65 degrees and the seven-day forecast is likely to sustain these temperatures, says Patt Phipps, Virginia Tech Extension plant pathologist. Soil temperature reports for 11 locations in Virginia are posted daily at www.ipm.vt.edu/infonet on the Internet. The medium-range forecast is at www.weather.com or www.weatherunderground.com. Phipps says growers should avoid heavy rainfall or cold fronts when fumigating.
The first line of defense against CBR, however, is a good rotation, the longer the better. Extension specialists recommend varieties with resistance to the pathogen. In the past several years, researchers have also noted that CBR can be spread at low frequencies by speckled seed infected with the pathogen.
This has brought about the recommendation for seed producers avoiding harvesting CBR-infected areas of a field where disease exceeds more than 28 CBR-infected plants per 100 foot of row, Phipps says.
Last year's CBR epidemic in the V-C area was the result of unexpected cool weather in April and periods of heavy rainfall, Phipps says.
For Holland, peanuts begin to call him to the field in late April. When the usual warm weather in the Tidewater area didn't appear last year, however, the calendar still said it was April.
“We were getting to the end of April and I knew I would have to wait two weeks before I got in the field to plant peanuts after fumigating,” says the City of Suffolk producer who farms with his son, Jason. Holland injected the fumigant under cold, wet and muddy conditions. “I shouldn't have done it,” he concedes. “You get excited and nervous sometimes and you just start too soon.” Because of the wet weather, Holland delayed some of the fumigation until later. “On the fields where we applied the fumigant a little bit later, we had better control of CBR.”
Because of CBR pressure, Holland continues to bottom plow his peanut land. On his corn acreage, he has gone to strip-till. “I would probably be one of the first ones to go no-till or strip-till on peanuts if we had some way to inject Vapam,” Holland says, noting that he was the first grower in Virginia to work with Phipps when farmers began to notice CBR in the early 1980s
As far as what happened last year, Holland says yields were off 850 pounds in those fields where he fumigated too early. The Hollands normally average about 3,700 pounds per acre.
Phipps, Virginia Tech's Extension plant pathologist in Suffolk, says the weather was, by far, the most important factor in last year's outbreak of CBR. “Above-normal rainfall almost all the way through the season favored the disease.” The timing of fumigation also played a critical role in the outbreak.
The main line of defense against the soil-borne pathogen is metam sodium. Seventy-five percent of the acreage in Virginia is fumigated with 42 percent metam sodium, injected eight inches deep at a rate of 7.5 gallons per acre, Phipps says. Metam works best when soil temperatures are 65 degrees or above.
Last season, April was a cold and wet month. Soil temperatures for April of 2000 were in the 50s in Virginia. “In the fields that were fumigated in April, by and large, we didn't see good control. On top of the soil temperatures, we also had too much water.”
A farmer would fumigate one day and get a two-inch rain that night, adding to an already saturated soil. The result: The fumigant became diluted and dispersed out of the row, Phipps says.
The farmers who fumigated fields the first week in May saw marked differences in control, Phipps says. “By May 5 last year, soil temperatures jumped up to 70 degrees, and the result was better control and much better yields.”
In producer meetings this winter, Phipps urged producers to monitor the weather at www.wunderground.com, and fumigate when the soil temperature is near 65 degrees. Phipps and his colleagues used this Website in developing their frost advisory. By typing in your zip code, you can get the five-day forecast for your area.
“We'd like to see a forecast that indicates temperatures are going to stay in that range for five days, with no rainfall in excess of an inch,” Phipps says.
The first line of defense, Phipps says, is a three-year rotation.
The Hollands of the City of Suffolk have about half of their 458 acres of peanuts on a three-year rotation, following two years of corn. The remaining acres are on a two-year rotation. That additional year makes a huge difference in yield and CBR incidence, Holland says. “A lot of times, we get a 1,000 pound per acre yield increase with that extra year of rotation.” They plant NC-11, VA-C 92R and VA-98R.
“For one reason or the other, we have some fields where half of the field is under a two-year rotation and the other half is under a three-year rotation,” Holland says. “When you hit the dividing line between the two-and three-year rotation, you can tell where the disease pressure started in the two-year rotation.”
Phipps is recommending a three-year rotation in the battle against CBR, for both seed growers and commercial growers. Seed growers and peanut farmers in general should avoid harvesting areas that have 28 CBR infected plants or more per 100 feet of row.
“We have found that level of disease can result in about two percent speckled seed at harvest,” Phipps says. Research by Phipps and graduate student Debbie Glenn in Virginia confirms that speckled seed are infected with the fungus that causes CBR. The fungus will survive in some of the speckled seed through winter storage and cause infection in the field, Phipps notes.
In tests, the fungus survived best when the peanuts were stored at or near-freezing temperatures. Phipps and Glenn also found that commercial seed lots stored in a vented building with temperature controls caused a reduction in survival of the fungus.
Seed treatments with Vitavax PC reduced CBR incidence. No fungicide offers complete control of the pathogen in speckled seed, but Phipps and his graduate student are currently looking at different combinations of Thiram, Raxil and Maxim, a new fungicide. “We're getting good results in our seed treatments with CBR,” Phipps says.
There's also good news on the variety front. Perry, a new Virginia-type peanut with good resistance to CBR and partial resistance to Sclerotinia, is on the horizon, being produced on about 3,500 acres for seed increase this season. “There should be some of this variety available for planting by farmers next season,” Phipps says.