What is in this article?:
- The greatest threat to early maturing wheat is a late freeze.
- Lush green plants can be a haven for insect pests and plant diseases.
- Unless there is a rust race change, we should not see stripe rust infection in most varieties.
Stripe rust (Puccinia striiformis) has infected some experiments in our research trials. We use an old susceptible SRWW variety, Patton, to evaluate foliar fungicides, and some of the plots are heavily infected with this disease. The good news is that most area growers planted varieties last fall that are resistant to this disease. Unless there is a rust race change, we should not see stripe rust infection in most varieties. The only commonly planted variety I know of that has shown some susceptibility to this disease is Terral 8558 SRWW.
We did not see much stripe rust pressure last year, so some of the newer varieties should be scouted for this pest. If the disease infects early (Feekes7 to 8), a split fungicide application (a half rate followed by a half rate 18 to 21 days later) should be considered. This program has shown to provide plant protections for 50 days. If the stripe rust shows up later (Feekes 9 to 10.5), a single fungicide application at the full rate is recommended. A single application of a good fungicide will provide 30 to 35 days of leaf protection—sufficient time to protect the leaves during the grain filling period.
Leaf rust (Puccinia recondita) has not yet been observed in this region, but warmer than normal temperatures are ideal for leaf rust development. The leaf rust pathogen thrives on the warm, wet conditions that are predicted in the 7 to 10 day forecast.
Most of the SRWW varieties planted across the region are not susceptible to the known races of the leaf rust pathogen. However, leaf rust pressure in 2010 and 2011 was light so the most current data is from 2009. USG 3295, USG 3555, and Terral LA 841 showed excellent resistance at that time. Coker 9553 and Magnolia were shown to be moderately susceptible to leaf rust, but spraying them with an inexpensive fungicide (tebuconazole) produced only a marginal profit. Pioneer 25R30 and Pioneer 25R40 are probably resistant, but they have not been around long enough to get a good assessment on leaf rust resistance.
Jackpot HRWW is highly susceptible to the leaf rust pathogen, and we have shown an excellent return by spraying it with a fungicide. Last year, over three locations, we averaged a 14-bushel increase by spraying it with tebuconazole. The other variety that should probably be sprayed is Terral 8558, as it is susceptible to both stripe and leaf rust.
Many growers have chosen to spray a fungicide on all of their wheat acreage for leaf rust as an “insurance policy” because the cost of tebuconazole is so low (at $6.00 wheat, the breakeven cost is around 1 bushel per acre). And they say they sleep better at night knowing their crop is protected in case of a rust race change. We suggest targeting that application for Feekes 9 to 10 (full flag leaf emergence to boot stage). This timing will provide good leaf protection throughout the grain filling period.