June 9, 2015: Wheat Pest and Disease Update

Stripe rust.

The warmer weather the past several days will likely slow the progression of stripe rust, but I really think the die is cast.  You are either going to get clobbered or you are not.

Wheat viruses

 Infected fields will show more and more damage during hotter weather.   A question came  up about  a field that was so badly infected  that it is plowed under.  Can  you then go back with millet and be OK? Millet can be infected although it is not as susceptible as wheat.  Also, if you do a good job of eradicating the wheat before planting the risk is much less.  The virus cannot persist in the soil and the mite vector will not live long without a living wheat plant (or another grass host).

Smuts

Now is a good time to start scouting for smuts.  There are two common smut fungi in Colorado.  The most prevalent is loose smut.   Plants infected with loose smut head earlier and the flowers turn into black smutty masses.   These can easily be seen before harvest because the heads are usually taller.  Stinking smut is a little bit different  – the kernels remain more or less intact until harvest and then release the black, fishy smelling smut spores that will cover healthy seeds.  Scouting for this one is tougher but very important.  Last year we had outbreaks of stinking smut in some areas of the state.  I would strongly encourage growers to be on the lookout for this disease if they had a problem last year and did not treat their seed. Walk the field and look for heads that don’t look right.  Crushing the kernels between the fingers will reveal the smut.     I am Just making up numbers here, but if you have an incidence of either smut approaching 0.1 -0.5% it is too much and you should treat seed next year if you keep your seed.

To make matters worse, Kansas is reporting a third smut called flag smut.  This smut is different in that it attacks the leaves, not the head.   It sort of looks like a black, sooty version of stripe rust. Because the head isn’t damaged, the yield losses may not be as large.  This smut hasn’t been seen in years in our neck of the woods in wheat, but I used to see this quite a bit in turfgrass in Kansas (but likely no one is interested in that but me)  Certainly if anyone sees something suspicious it should be sent to the CSU diagnostic lab in care of Dr. Tamla Blunt.  It is almost certain to be present in Colorado as well because bordering Kansas counties have confirmed its presence. For more info see the following info  from Dr. Erick DeWolf, K-State:

‘You may already know, but just in case I wanted to contact you to let you know that flag smut was detected in Kansas for the first time in many years.

I am attaching a link to a report about the initial report released by the Kansas Department of Ag.  Some of the detections are in counties adjacent to NE and CO.  The way seed industry operates in the Great Plains, I would be surprised if the disease is not also in neighboring states.’

https://agriculture.ks.gov/divisions-programs/plant-protect-weed-control/wheat-flag-smut

 

Ned Tisserat

Retired Plant Pathologist

 

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