May 17, 2015: Wheat Pest and Disease Update

From Ned Tisserat, Retired Plant Pathologist, Bioagricultural Sciences and Pest Management

Stripe rust

As expected the wet weather of the past 10 days has aggravated the strip rust epidemic.  The most intense area of the disease appears to be in a triangle from DIA to Wiggins then south to I70.  Counties that I know that have  stripe rust include Morgan, Washington, Weld, Kiowa, Prowers Arapahoe, and Adams, but I suspect  it is more widespread than that.  Nevertheless, it appears that many areas are not hard hit yet. The relative cool weather and periodic rains will continue to favor stripe rust development.   If you have stripe rust in your field and have the potential for high yields, then a fungicide application may be warranted.   If you don’t have rust in the field yet, then the decision is trickier.  If you are a gambler, then you may want to see what happens in the next week.  As I have mentioned many times in the past, if stripe rust comes in after flowering, its impact on yield is much, much less that if it shows up earlier.  If the level of stripe rust is low to non-existent in the field now, then it may not get to damaging levels in the future.  I have had non-treated plots that were severely rusted after flowering but sustained no yield loss compared to fungicide treated plots. Go figure.

Virus diseases

Another, often overlooked problem are the virus diseases. While there is nothing you can do about it, there presence can influence management decisions.

Some barley yellow dwarf has been observed in the southeast part of the state.  Look for purpling and yellowing of the leaves along with stunted plants.  This virus is aphid transmitted.  I think we are also going to see a lot of mite transmitted virus problems (wheat streak, triticum mosaic and high plains) as well.   If you have these virus diseases in your fields, I am not sure I would make a fungicide application for stripe rust.  It is much harder to recoup costs in these fields that will likely yield low anyway.

Ned Tisserat

Retired Plant Pathologist

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