The storm system that swept across the region weekend of May "undoubted carried" wheat rust spores up from southern plains states, says SDSU Small Grains Pathologist Jeff Stein.
Depending on temperature and moisture, leaf and/or stripe rust could develop on the Dakota wheat crop within the next week or two.
Lyman County Extension Educator Bob Fanning says tanspot and Septoria leaf spot, since they are residue-borne diseases that are able to overwinter in South Dakota, already have a start in some fields. Those diseases may continue to develop if moisture conditions are favorable. Limited leaf rust has begun to appear as well.
Fanning says a general starting point for considering a fungicide application to protect wheat is when the crop has a yield potential of 45 bushels an acre.
"That 'magic 45' should be a floating number when wheat prices are volatile. A yield response of 5 bushels an acre is worth a lot more when the grain is $5 per bushel than when it is $3," Fanning says.
There's increased opportunity for fungicides to return a profit on wheat when wheat is planted in corn or wheat residue, when disease present on lower leaves at jointing, and when there's an extended period of wet weather after jointing.
A major consideration in applying a fungicide is to get the product on at the right time, Fanning says. The flag leaf is said to be responsible for 50-75% of the yield, so you'd like to keep if free of disease. The ideal situation for flag leaf applications is to get the fungicide applied to the flag leaf as it is emerging or soon after it emerges.
Source: SDSU AgBio Communciations