STRAIGHT FROM THE HORSES MOUTH

Duane A. Lienemann, UNL Extension Educator, Webster County May 22, 2010 Edition What a difference one week can make when it comes to wheat and wheat diseases. I had a feeling we would start seeing some problems and have been encouraging producers with wheat to periodically check their wheat and in particular the flag leaves as that is what we need to protect. We have been finding tan spot, septoria, and some leaf rust all along, but not to the degree that was of major concern to me other than in very isolated situations. I have actually early on talked more to producers about the yellow color and stunting of wheat, which seems to be more environmental, rather than diseases. Now the environment is dealing wheat another problem. Let’s see what that may be. Wheat Stripe Rust: Cool, wet weather has always given concern towards, in my opinion, one of the nastiest wheat fungus problems and right now it looks like this disease has hit us. That disease is Wheat Stripe Rust. Stripe rust, caused by the pathogen P. striiformis, normally occurs in Nebraska during cool periods in early June. That is what is surprising to me, as I did not really expect to see it in the middle of May. I believe I remember a rash of it in 2001- 2003. During these years, cool, wet weather in Texas during April and early May resulted in the extensive development of stripe rust inoculums that blew north and affected production throughout Nebraska, even though we were in the beginning of a long drought. This disease is also called yellow stripe rust. That is mostly because the pustules are light yellow and occur on leaves in distinct, straight-sided stripes about 1/16 inch wide and of irregular length. Pustules also may develop on the heads, which of course compounds the problem with this disease. Stripe rust develops at slightly cooler temperatures (55-75°F) than does leaf or stem rust. The good news is that once temperatures exceed 75°F, stripe rust develops very slowly and in fact during years when June temperatures are in the high 80s and 90s, only trace levels of stripe rust can be found. Unfortunately June is still a ways off, and of course we live in Nebraska, so you can always expect the unexpected when it comes to crops, and it always seems to start in Webster County, although this time Nuckolls may get the credit (a field just outside of Webster)! This past week UNL Extension plant pathologist, Dr. Stephen Wegulo, and I looked at some fields in the Lawrence and Guide Rock areas and along the eastern half of Webster County. As you might suspect, we found stuff that I really didn’t want to see. The producers we visited with, of course, didn’t want to see it either! It didn’t take long to find this disease in some fields and in fact one field was about 100% infected, while we found other fields that were clean, and others with percentages of infection of varying degrees. I had earlier looked at some fields across the south central Nebraska area and found some solid evidence of concerns so made a call to Dr. Wegulo. I have since found more fields with Stripe Rust in the western half of Webster County from Bladen south to the Kansas border, while others seem clean or with minute pressure. This cool wet weather we have been having has caused stripe rust to be widespread in wheat in south central and southeast Nebraska. During the survey of fields in south central Nebraska on May 18 with Dr. Wegulo, we found stripe rust ranging from low to covering more than 70 percent of the plant. What is perplexing is that symptoms are ranging from no visible symptoms to isolated spots showing yellow leaves to large affected areas. In one field, there was a sharp contrast between a susceptible variety and one planted next to it that appeared to have some resistance. In talking to Dr. Wegulo, wheat stripe rust has the potential to cause 100 percent loss of a wheat crop. The prolonged cool, wet weather has favored and continues to favor development and spread of stripe rust. He says that if you see stripe rust in your field, you need to apply a fungicide to protect the flag leaf. Even if the variety you planted is known to be resistant, it may still be affected by damaging levels of stripe rust because of the possibility that the stripe rust we are seeing may consist of a new race or races. Wegulo suggests that if wheat is headed and or is beginning to flower, you should apply a fungicide that has good to excellent efficacy against both stripe rust and Fusarium head blight, or scab. Please note however, a fungicide application will not be effective if stripe rust has already progressed to severe levels. The optimum timing for a fungicide application is when the disease is just beginning with trace levels of severity or before disease symptoms are observed. If disease severity is low to moderate and the top three leaves are still green, some yield loss will be prevented by a fungicide application. He goes on to say that yield loss also will be prevented by a fungicide application only if small areas of a field are affected by severe stripe rust. In this case, the fungicide will protect the wheat crop that is not yet affected within the field. There are several fungicides that work well at this juncture, but the one most often suggested is a product called “Prosaro”. The product you may choose to use will mostly depend on how close your wheat is to flowering. If it is headed and will be flowering soon, producers may want to wait until it begins flowering and use Prosaro, Caramba or perhaps Proline/Folicure mix that provides prevention for head scab in addition to killing wheat stripe rust and other fungal diseases on your leaves. If you feel that you have a few more days before flowering, you may want to consider other fungicides. Dr. Wegulo has several items in the CropWatch web site, and there are other discussions that will be of aid to wheat producers at http://cropwatch.unl.edu. I also have a lot of good material in my office with pictures, explanations, etc. Just give us a call and we will get it out to you. Whatever you do, check your wheat – and not from the pickup window! The preceding information comes from the research and personal observations of the writer which may or may not reflect the views of UNL or UNL Extension. For more further information on these or other topics contact D. A. Lienemann, UNL Extension Educator for Webster County in Red Cloud, (402) 746-3417 or email to: dlienemann2@unl.edu or go to the website at: http://www.webster.unl.edu/home