Stripe Rust and Jagger Are Close Friends in the 2010 Oklahoma Wheat CropSat, 08 May 2010 22:26:49 CDT
OSU Extension Wheat Pathologist Dr. Bob Hunger offers this latest update on wheat disease conditions that he has assembled for the state of Oklahoma- as well as reports from Arkansas and Nebraska that he has received from some of his colleagues. (the picture here is of some stripe rust in our 2010 crop, courtesy of the Oklahoma Wheat Commission)
04-06-May; Dr. Bob Hunger, Extension Wheat Pathologist, Oklahoma State University: Over the last week I have visited fields and plots around Stillwater, around Marshall (30 miles west of Stillwater), Lahoma (10 miles west of Enid), Billings (35 miles northeast of Enid), Mustang , and Apache (75 miles southwest of OKC). Over most of this area wheat ranged in maturity from half to full berry (southwest of OKC) to being just at the completion of flowering and the start of berry formation.
Prevalent diseases observed included stripe rust, leaf rust, and barley yellow dwarf. Stripe rust was severe in some locations such as specific areas in fields or trials near Stillwater, Marshall, Lahoma, and Apache. Ratings of stripe rust were as high as 90 MS-S, especially in “hot spots” in some of these trials in Jagalene. Jagger would be close behind with ratings in the 65-80 MS-S range. Other Jagger derivatives were less with readings mostly in the 15-40 MS-S range. In some areas, sparse if any stripe rust, leaf rust or BYD was observed, such as in the Mustang area.
My impression is that the “shift” or adaptation in the stripe rust pathogen to the resistance in Jagalene/Jagger appears to have been highly selective to these two varieties with some type of slight “remnant” resistance still being expressed in Jagger and even a bit more resistance in Jagger derivatives; not sure how to actually explain this. In any location I have been where stripe rust is prevalent, the incidence and severity on Jagalene is greater (and earlier) than on Jagger, which is greater and earlier than the other derivatives.
Leaf rust is starting to appear in greater incidence and severity. In areas where stripe rust is not severe, Jagalene, Jagger and Overley are the three varieties on which I have seen the most leaf rust – generally in the 25-40 S range on F-1 or lower leaves.
Barley yellow dwarf is prevalent in many locations. There is not widespread stunting associated with the symptoms, indicating a later (late winter/spring) infection date. However, with some varieties in some locations flag leaves are fairly consistently turning yellow/purple and incidence of leaf rust will be less because of the reduction in green leaf tissue across the field.
Dr. Gene Milus, Wheat Pathologist, University of Arkansas:
05-May: “I found a trace of leaf rust on one leaf in plots at Fayetteville on May 4. Plants were heading to past flowering depending on the planting date and variety.
04-May: “Yesterday, I took stripe rust notes on the Arkansas variety test at Kibler and demo strips near Paris. These locations are in the Arkansas River Valley east of Fort Smith. Most varieties had flowered and the least mature ones were heading. Kibler missed the recent rains. Plots were showing symptoms of drought stress and were irrigated after I left. Paris got some rain over the weekend.
Stripe rust had moved out of the hot spots and was more or less uniformly distributed now. Very susceptible varieties were >90% severity with S to MS infection types. Susceptible varieties were approximately 70% severity with S to MS infection types. Varieties suspected of having Yr17 had variable severities and infection types and seemed to have higher severities near the hot spots and slower disease development away from hot spots. Overall, varieties suspected of having Yr17 seemed to be moderately susceptible. However Terral LA 841 that likely has Yr17 was still highly resistant. Many of the commonly grown varieties are still resistant, and at least some of this resistance appears to be adult-plant resistance. Overwintering infections in this portion of the state is a major factor for high stripe rust severities.
Some varieties that I consider resistant had 10 to 50% severities but R to MR infection types. Although these may look bad in plots and demo strips, they look good in fields. My interpretation is that spores produced on nearby susceptible and very susceptible varieties are causing these resistant infections.
Night temperatures are still favorable for stripe rust, but moisture for dew is limiting in the Delta and Grand Prairie regions of eastern Arkansas where most of the wheat is grown.
BYD is evident in every field, but severe stunting is rare. Leaf blotch is confined to the lowest leaves due to dry weather. No leaf or stem rusts yet.”
05-May; Dr. Stephen Wegulo, Plant Pathologist, University of Nebraska: “On Monday May 3, I surveyed wheat fields (all rainfed) in Saline County (southeast Nebraska (NE)) and Thayer County (south central NE). Growth stage ranged from Feekes 8 to 9. Disease levels were very low, with the most common being Septoria tritici blotch and tan spot. I did not find leaf or stripe rust. On the same day Bob Kacvinsky of Syngenta Crop Protection surveyed wheat fields in Jefferson County in southeast NE and Washington County in northeast Kansas. Growth stage ranged from Feekes 8.5 to 9.5. He found stripe rust in both counties on cultivars Art and Overland. He brought me a sample that had stripe rust on the third leaf below the top leaf. Up to 40% of the leaf surface on some leaves was covered with stripe rust pustules. Yesterday (May 4) I surveyed one rainfed wheat field in Nemaha County (southeast corner of NE). Except for trace levels of Septoria tritici blotch and tan spot, I did not find leaf or stripe rust.”
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