The spray window for producers to decide if they are going to use a fungicide to prevent disease development on wheat flag leaves is occurring right now instead of in May, when it more typically occurs. This week Extension Plant Pathologist Stephen Wegulo and I surveyed quite a few wheat fields in Saline County and found stripe rust widespread.
Stripe rust, caused by P. striiformis, normally occurs in Nebraska during cool periods in early June. It’s unusual and unfortunate to see it this early. Stripe rust develops at slightly cooler temperatures (55-75°F) than does leaf or stem rust. Once temperatures exceed 75°F, stripe rust develops slowly. Cool temperatures and moisture during the last one two weeks have been conducive to stripe rust development.
The decision to apply a fungicide should be based on the amount of disease in the field, the yield potential, and the susceptibility of the variety planted. Fungicides are most effective if applied when disease levels are still low and flag leaves are out and still clean. One of the fields we surveyed near Tobias had high yield potential but was a susceptible hybrid with early onset of disease at high levels in the lower canopy. While the decision to spray seems appropriate, we can’t say with certainty that it will pay to spray. That assessment will come at harvest.
With stripe rust already present in many fields, it is important to note that you need a fungicide with both preventive and curative activity. Most of the grain fill period will occur in May this year instead of in June. High wheat yields are possible if adequate moisture and mild weather occurs during grain fill, the same weather that favors stripe rust. If adequate moisture occurs, double cropping opportunities will exist with an expanded growing season window that we normally don’t see.