WHEAT DISEASE FORECASTING 

Many growers currently are contemplating the use of a fungicide to control scab and leaf spot diseases in wheat. General guidelines include high yield potential (40 bushels/acre or greater), leaf spot disease present in crop, and favorable weather conditions (immediate past, currently, and forecasted in the near future) for disease infection and development. An aid in forecasting favorable conditions for leaf spot disease (tan spot, septoria, and leaf rust) and scab infection is available from NDSU at the following website:

 

As an example, at Carrington during June 18-29, 10 of 12 days had favorable conditions for tan spot infection in wheat. Unfortunately, the Carrington site does not include scab infection forecasts so other sites will need to be checked for a forecast for this disease.

 

SMALL GRAIN FUNGICIDE RAINFASTNESS

 

Rainfall following a fungicide application in wheat or barley is certainly likely given our recent wet cycle. Protectant fungicides (e.g. mancozeb) are readily washed off the treated crop if a substantial rain occurs within 8 hours of application. Retreating the field may be required for maximum protection.

 

Eighty percent of locally-systemic fungicides (e.g. Folicur, Tilt, and Benlate) are absorbed by the plant within the first hour after application. The remaining fungicide is absorbed in time and the optimum rainfastness is reached at 4 hours after application. Retreating the field is not needed if it rains 1.5 to 2 hours after applying these fungicides.

 

WHEAT MIDGE EMERGENCE OCCURRING

Orange wheat blossom midge are being found in our area, but currently at very levels. Adult female midge emergence begins at about 1300 degree day (DD) units at a base temperature of 40 F. The following is a listing DD units accumulated on June 29, based on the ND Ag Weather Network, for selected south-central ND locations: Oakes = 1549; McLeod = 1512; Linton = 1422; Edgeley = 1365; Carrington, Dazey, Jamestown, McHenry, Robinson, and Streeter = 1304-1331; and Harvey = 1244.

Scout wheat fields for the presence of wheat midge from head emergence until 80 percent of the heads have anthers visible (flowering). Field scouting must be in the evening from 9 p.m. until midnight. Wind speeds should be below 6 miles per hour and temperatures above 59 F. Visit three or four different sites in the field. At each location, count the number of midge on several sets of wheat heads (4 to 5 heads per set). Record and calculate your average for the field.

If monitoring shows that the action threshold of an average of 1 adult midge per 4 to 5 heads has been reached, producers should consider the following guidelines for treatment with Lorsban 4E-SG:

*If 30 percent of the wheat is heading, wait up to four days and then apply insecticide.

*If 70 percent of the wheat is in the heading to flowering stage, optimum control should be achieved by treating.

*If 30 to 60 percent of the heads are flowering, and at least one anther is visible, spray immediately, though control is likely to be reduced.

*If 80 percent of the heads are flowering, treatments are not recommended.

Additional details on wheat midge scouting and management may be obtained from NDSU Extension Service offices.