Stripe Rust is Developing on Irrigated Spring Wheat 5/16/03

May 16, 2003

Xianming Chen

Since stripe rust was first observed on spring wheat in eastern Washington on May 8, the disease has been developing rapidly in irrigated spring wheat fields. In several irrigated spring wheat fields planted with ‘Express’ and ‘Scarlet’ around Connell, stripe rust of 15-40% incidents, 5 to 10% severity, and highly susceptible reactions was observed on May 18. The uniform distribution of the rust in the fields indicated that the infections were from spore showers produced in the nearby early infected winter wheat fields. Similar rust situations were reported for fields planted with ‘Alpowa’ in the area. The current rust levels and stripe rust-favorable conditions forecasted for the following 10 days warrant a fungicide application in these spring wheat fields.

Except for the irrigated area, spring wheat in Franklin, Adams, and Whitman counties was generally too small (one leaf to early tillering stages) to see stripe rust. However, with the widespread precipitations early this week, spring wheat infection could have occurred in many areas. Widespread stripe rust in spring wheat fields may be visible in two to three weeks.

As expected, I found stripe rust widely occurring in winter wheat fields, mostly in very low levels, in eastern Washington. Resistance in most soft white winter and club wheat varieties is effective. Stripe rust was developing in some triticale lines near Connell.

High level (up to 100%) of stripe rust was reported on some susceptible winter wheat lines in nurseries near Pendleton, Oregon.

In the past, we generally recommended one fungicide application for control of stripe rust in eastern Washington because the disease usually developed to 5 to 10% of incidence and severity in late stage. This year stripe rust on spring wheat occurred or will occur early, we need carefully considering number of applications to effectively control the rust and also make profit. There is no a single answer for various regions and various varieties. The currently labeled foliar fungicides are systemic and can protect plants for about a month. For varieties with high-temperature, adult-plant (HTAP) resistance (e. g. Alpowa and Express), one fungicide application before the boot stage can protect plants up to the late stages when the HTAP resistance starts working. Therefore, second application for these varieties may not be necessary. For varieties that do not have adequate HTAP resistance (such as Scarlet and ‘Zak’), a second application about a month after the first one may be necessary to protect plants during grain filling. Weather conditions should also be considered. In the late growth stages, cool temperatures (especially night temperatures below 60 oF) and frequent rains favor rapid development of stripe rust.

If you have any questions about stripe rust, please feel free to contact me by phone (509-335-8086) or e-mail (xianming@mail.wsu.edu).