Growers should scout for Cercospora, other threats

FARGO, N.D. -- North Dakota State University Crop & Pest Report came out July 8. Among the report's highlights:

Gird for beet Cercospora

Mohamed Khan, NDSU extension beet specialist, says sugar beet fields rows have closed and "have the potential for record yields." Sugar prices have dropped but are relatively high. There's something to protect, he says.

Among other things, Khan says growers should scout for Cercospora leaf spot. Past control has been good and inoculums is low, but a shift to day temperatures in the 80- to 90-degree area and humid conditions makes it favorable for the disease. Growers should be prepared for fungicide applications earlier than previous years and "budget for multiple applications, should this become necessary." Look for circular spots about one-eighth-inch in diameter with ash gray centers and dark brown or reddish-purple borders.

Cercospora is the biggest leaf disease problem for beets, cutting tonnage and extractable sugar content. If first control is late, control will be difficult all season. Don't cut fungicide rates.

"Only one application of a Topsin M in combinationwith a protectant fungicide (triphenyltin hydroxide) should be used" in Hillsboro, N.D., East Grand Forks, Minn., Crookston, Minn., and Drayton, N.D., factory districts, Khan advises. He adds you shouldn't use the fungicides from the same class "back-to-back" and avoid using a particular class as a "stand-alone" where there is known resistance to that chemistry. Spray pressure of 100 psi and higher offers better control.

"The following fungicides are labeled and the most widely used on sugar beets for Cercospora leaf spot control with re-entry interval (REI) and post harvest interval (PHI)," Khan says, listing these Product REI (hr) PHI (day): SuperTin 80WP and 4L 48 7; AgriTin 80WP and 4L 48 7; Headline 4 7; Gem 12 21; Inspire XT 12 21; Proline 48 7; Eminent 48 14; and Topsin WSB and 4.5F 12 21.

"Please note that manufacturers of glyphosate do not recommend mixing glyphosate with fungicides. Growers make these applications at their own risk," Khan says. NDSU trials indicate that some fungicides mixed with glyphsate and AMS at labeled rates "did not result in any phytotoxicity, and weed and leaf spot control were effective."

Post-N for protein? Door closing

Dave Franzen, NDSU soil scientists says farmers should know that the time window for top-dressing nitrogen to enhance protein in wheat is "immediately after flowering until the wheat berries begin to turn milky," and he has strong warnings for those who apply it late.

"Application of N from milk stage to harvest may constitute fraud on behalf of the grower," he says. "Ammonia that clings to the wheat kernel may show up as a false positive for protein in elevator tests and result in the illusion of a higher protein wheat than was harvested," he says. "Do not apply any N fertilizer to wheat once the kernels begin to turn milky, except for the ammonium sulfate required to enable a preharvest glyphosate application."

The National Agricultural Statistics Service on July 4 said 13 percent of the North Dakota's spring wheat crop was in milk stage, up from 3 percent the previous week. Some 49 percent was heading, compared with 22 percent the previous week.

In Minnesota, 91 percent of the spring wheat had headed, up from 73 percent the previous week, and 5 percent was ripening, compared with zero the previous week.

Continue scouting wheat midge

Wheat midge emergence is "well under way and should be peaking in the northern tier," says Janet Knodel, Extension Service entomologist.

Wheat is susceptible in heading to early-flowering "when the wheat midge were at peak emergence in many areas. Apply insecticide during heading and when adult midge density hits one midge to four or five heads of hard red spring wheat, or one midge per seven or eight heads for durum. Avoid late application to avoid killing natural parasites. Midge feed on kernels and reduce yield.

Soy aphid numbers still low

Knodel says daytime temperatures of 90 degrees-plus aren't "optimal" for soybean aphid reproduction, delaying "any economic field infestations" in the state. Continue scouting until the R6 (full seed) growth stage.

Moths show in sunflower traps

Adult moths of banded sunflower moth and sunflower moth were trapped and detected for the first time this season. The moths migrate from the South and catches are "very low" so far. Scouting is critical at the R3 bud stage, when an immature bud is elongated about 2 centimeters above the nearest leaf.

Thistle caterpillars in sunflowers

Painted lady butterfly or thistle caterpillar apparently have blown from the south into parts of North Dakota. Now, caterpillars "have been observed causing defoliation" in sunflowers in the southwest part of the state, Knodel says. They've also been noted on canola and soybeans.

Eggs are spherical and white. Larvae are brown to black and spiny with a pale, yellow stripe on each side. At maturity, they're 1.25 to 1.5 inches long. The chrysalis, or pupa, is "molten gold and about 1 inch long." Insecticides generally are "not warranted," but "spot treating may be necessary" in instances of "high localized infestations" and "within certain fields." Sample 75 to 100 feet from a field margin. Look where Canada thistle is abundant. The economic threshold is 25 percent defoliation provided that most of the larvae still are less than 1.25 inches long. After that, the feeding is mostly done and control isn't economical.