Knowing field history of diseases can help peanut growers

Growers get the most benefit from fungicides by knowing what kind of disease pressures they’re facing and the field history, says Pat Phipps, Virginia Tech Extension plant pathologist.

“Fungicides have their own special strengths and provide a good spectrum of activity,” Phipps says. “The key is using them when you need them and addressing the problems that are there.”

In the Virginia region, Cylindrocladium black rot (CBR) is the worst of the soil-borne diseases. Sclerotinia comes in second, with white mold and rhizoctonia coming in third in regard to importance.

With CBR, the grower needs to think first about variety selection. Perry is a good choice because it has resistance to CBR, Phipps says. The second consideration is fumigation.

“Perry will respond to soil fumigant with metam sodium in fields with a two-year rotation and heavy disease pressure,” Phipps says.

“On peanut fields with a four-year rotation and lower levels of disease pressure, Perry may perform well without soil fumigation. That’s something the grower has to determine.”

Foliar fungicide sprays offer a bit of suppression of CBR, Phipps notes, but “it’s minimal and won’t handle a severe problem. Fumigation becomes the most important tool for those fields that are heavily infested.”

CBR turns plants light green or yellow. The plants wilt and die. A blackened root system is characteristic of this disease. The fungus produces numerous brick red, pinhead-sized structures on crowns, lower stems and pods. If these fruiting structures are not visible, late-season wilting and root rot symptoms of CBR and TSWV can be confused.

Fields with a history of 1 percent to 10 percent of CBR should be planted to a resistant variety.

Sclerontinia is another soil-borne disease important in Virginia. It comes in August. Vines must be pulled back to reveal cottony growth of Sclerotinia on straw-colored stems. The end portion of infected limbs may remain green and look healthy for several days before wilting is evident. Small black sclerotia that are irregular in shape can be seen both on and in infected tissues. The disease favors cool and wet conditions.

For Sclerotinia, there are two fungicides available: Omega and Endura.

Omega needs to be applied with a leafspot funigicide. These funigicides have good activity on white mold and rhizoctonia, even though these problems need to be addressed in July and early August.

Endura has some activity on leafspot.

For leafspot, Headline and Abound are strobulins. Folicur is a tebuconazole. Stratego is a mixture of both the strobulurins and tebuconazole.

“They all do a good job on leafspot,” Phipps says. In Virginia, the use of Folicur is recommended with a low rate of surfactant “because we have had some problems with leafspot control when we didn’t use the surfactant.

Abound, Headland and Folicur have activity on some soil-borne diseases. Folicur and Abound excel on white mold, Phipps says. Artisan is a mixture of Tilt and Moncut and is also a very good candidate for white mold or rhizoctonia.

For the biggest payback, “use fungicides to address specific problems,” Phipps says.

In Virginia, growers can get by with three to five sprays. One of those sprays would need to be a chlorothalonil such as Bravo. “That one spray is positioned at the end of the season for resistance management because fungicides need a resistance-management strategy in place.”

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