by Ned Tisserat
There are now reports filtering in from northeastern Colorado of both leaf rust and stripe rust. The amount of rust in the fields, for the most part, is at a very low level. These infections probably were associated with the wet weather in early June, with rust spore showers, moving in on the weather fronts. It is possible that with the current weather that these rusts could intensify in the next 10 days and there may be hot spots where damage could be serious. However, in general the amount of damage these rusts could potentially cause is much less now than, say, a couple of weeks ago. I do not foresee the extent of damage that occurred last year. The debate on whether to spray at this late date is probably moot, since most of the fungicides have harvest restrictions of 30 days after spraying. We are running late on wheat maturity, but it would be a close call to make an application now.
We continue to receive samples of mite transmitted viruses. These include wheat streak mosaic, triticum mosaic, and High Plains. The symptoms of these viruses were very slow to develop this spring due to the cooler than normal temperatures in May. So if your crop looks like it is going backwards now, you may want to test for virus . We have also seen more barley yellow dwarf virus this spring.
I have attached a PDF of two publications you might find useful. The first publication Stem Rust Information (79) covers facts about black stem rust. This disease has been almost completely controlled for the last 60 years by resistance and has been rare in Colorado. However, a new race of the stem rust was discovered in Africa several years ago that can ‘break’ the resistance found in most of our varieties. There is concern that this race will somehow manage to make it to North America. Also, some varieties, like Bill Brown, may not have resistance to this species of rust (i.e. the stem rust). There is also a nice table in this publication that lists the harvest restrictions of some of the wheat rust fungicides.
The second publication is a very nice resource to help in identification of wheat diseases. This is one you really should download. Wheat Disease Identification (80)
Ned Tisserat
Extension Specialist and Professor
Bioagricultural Sciences and Pest Management
Plant Sciences 1177
Ft. Collins CO 80523
Ned.Tisserat@colostate.edu
970-491-6527
970-491-3862 (FAX)
