Watch for Rust in Wheat 

Leaf rust will continue to increase rapidly with adequate moisture and warm weather, and will provide rust inoculum for wheat growing areas further north. That’s according to the USDA Cereal Disease Lab, which monitors rust diseases in cereal grains and issues twice monthly bulletins on the spread of rust online at www.cdl.umn.edu. (click on link ‘cereal rust bulletins’).

According to the CDL, low-to-moderate levels of leaf rust infections could be found in most commercial wheat fields in Texas in late March, with high severity levels of leaf rust observed on susceptible cultivars in nursery plots. In late March in southern Oklahoma, high severity levels of leaf rust were observed in fields, but levels were much lower in north central Oklahoma. In late March, overwintering leaf rust infections were observed on lower leaves in southern Nebraska. Some wheat fields infected with rust have been sprayed for rust control in the southern U.S.

Stripe rust has also been common at various levels across the south. No wheat stem rust had been reported in the U.S. as of April 5, however.

Since rust diseases blow in from southerly winds, plant pathologists are watching the rust situation closely. “My take on this is that we need to be scouting and be ready to treat if it looks like the disease is imminent,” notes Marty Draper, South Dakota State University extension plant pathologist. “Stripe rust comes on early enough that waiting to treat at heading, as we would for scab, does not provide adequate control for stripe rust.”

Northern Plains winter wheat growers need to be particularly watchful of rust, as winter wheat fields may see rust symptoms develop before spring wheat. “We had some huge yield increases from fungicide application to susceptible winter wheat varieties in 2003 when there was early rust,” notes Blake Vander Vorst, regional agronomist with Ducks Unlimited. 

Fig. 1. Leaf rust severities in wheat fields - April 5, 2005 (light areas are trace to less than 20% and dark areas are severe, greater than 20%).

Fig. 2. Stripe rust severities in wheat fields - April 5, 2005 (light areas are trace to less than 20% and dark areas are severe, greater than 20%).