Rust Update 4/15/11

April 15, 2011

Xianming Chen

Yesterday, I was checking stripe rust in wheat fields in northern Idaho and eastern and central Washington. Only a few spring wheat fields have been planted and some with plants just emerged in central Washington. In eastern Washington and northern Idaho, spring wheat basically has not been planted due to fields too wet and temperatures too low. Winter wheat growth stage ranged from Feekes 3 to 6. The growth stage was mostly related to planting date and less so to regions. Some fields in northern Idaho and eastern Washington reached Feeks 5 and 6, but most fields are in the earlier stage. The relative lower-than-normal temperatures since mid February have kept crop growing slowly and also made stripe rust develop slowly. Otherwise, stripe rust could have exploded. However, stripe rust is widely occurring in these regions (more than 70% of wheat fields checked yesterday had stripe rust), plus southern central Washington, western and northeastern Oregon, and southern Idaho, which have been previously reported for stripe rust. Fields in western Washington have not been checked because a recent heavy snow and almost every raining day have delayed field activities, but stripe rust should have occurred there as usual.

Stripe rust started developing in the Palouse region (eastern Washington and northern Idaho). Rust was found in commercial wheat fields around Pullman, Colton, Uniontown, Colfax, Palouse, and Dusty WA (Whitman Co.) and Moscow and Viola, Idaho (Latah Co.). In the Palouse region, stripe rust incidence was generally less than 0.1% and rust was just found in low leaves. These rust spore-producing leaves were infected before the winter and now producing spores to infect more leaves. This is the earliest date when stripe rust have been first observed in spring for many years, about one month early than last year in this region. Just little bit to the south of the Palouse region, stripe rust was reported last week in Lewiston, ID (Nez Perce Co.).

Stripe rust was found almost in every checked field near Washtucna, Kahlotus, and Connell in central Washington (Adams and Franklin Cos.) with incidences generally in the range of 1 to 10%, except that one field had more than 30% incidence. Stripe rust started showing up on upper leaves in some fields.

As stripe rust has widely survived the winter and has started developing, many fields in the central and southern central Washington, and some fields in the Palouse region have been sprayed with fungicides mixed with herbicides. For fields that have not been sprayed, growers should check for stripe rust and consider spraying fungicides when apply herbicides.

In some early planted fields in central Washington, barley yellow dwarf was severe. Hot spots could be seen from distance. Do not mistreat barley yellow dwarf from stripe rust. The viral disease does not produce powdery rust dust and yellow symptom starts from leaf tips and moves to the middle of leaves, and more severe along field edges. Considering the heavy aphid infestation in early planted fields in the Horse Heavy Hills region (south-central Washington) observed in November, barley yellow dwarf could be severe there and in the nearby areas (I did not check the Horse Heavy Hills region yesterday). These fields should be sprayed with insecticides when later on aphids start showing up.

Just one pustule of leaf rust was found in a field planted with Farnum northeastern Connell. Last year, leaf rust was severe in two fields grown with Farnum southeastern Connell (Franklin Co.).

Nationally, stripe rust have been reported in Arkansas, California, Idaho, Louisiana, Mississippi, Oregon, Texas, Tennessee, and Washington. Based on reports from these states and crop stages, stripe rust will unlikely cause as severe damage as in the last year in the south-central states. However, because of the recent tornadoes and heavy rains in the north part of the Great Plains and eastern and north-eastern states, stripe rust spores could have been spread to and infected crops in these regions from the south, stripe rust epidemic is likely. In the western states, stripe rust has been severe and widespread in California and the disease pressure is very high in the Pacific Northwest as stripe rust has started very early and abundant precipitation so far and forecasted for the next two weeks will provide moist conditions favorable for stripe rust development well into the late crop season.