Watch wheat closely for disease

By Ryan McAllister, CCA, Team Sales Agronomist, Beck’s Hybrids

Watch wheat for the possibility of disease for a better harvest.

Do you remember playing Capture the Flag when you were a kid? Well, diseases in your wheat field still like to play that game. They never grew up. Your job is to protect the flag — flag leaf that is. Most wheat fields in our eastern marketing area are in the boot stage and quickly on their way to heading. Once heading occurs, it generally takes 3 to 5 days before flowering begins. There are two considerations that you have when deciding to spray a fungicide on your wheat.

1.    Protect the flag leaf from leaf disease.

2.    Reduce the risk of head scab infection, which can lead to vomitoxin.

Fungicides with good control of head scab must be applied during flowering to be effective! With most of the wheat in our eastern marketing area as close to flowering as it is, it is wise to hold any fungicide application off until then to determine the risk for head scab rather than spraying now for leaf disease and possibly having to spray again shortly to control scab. Again, if a fungicide is applied prior to flowering for control of leaf diseases, no head scab control should be expected. I have attached a sheet that lists expected control of varying fungicides in terms of leaf disease and scab.

When you do get to the flowering window (roughly 3-5 days after heading), remember this recipe: RAIN + WARM WEATHER + FLOWERING = Increased Risk for Scab.

If temperatures remain cool during this time, or the rains stop during flowering, the risk of infection goes down. Prosaro will give you the broadest spectrum of control in terms of leaf diseases and head scab. Proline and Caramba will provide similar head scab control as Prosaro but lack control of some leaf diseases that Prosaro picks up. Many other fungicides do a great job at controlling leaf diseases if scab is of no concern to you due to conditions.

Leaf rust/Striped rust

I have heard reports of leaf rust being observed in the area and some are spraying their wheat to protect from this. Here is some yield information regarding rust infections below from http://www.ag.ndsu.edu/pubs/plantsci/smgrains/pp1361.htm:

“Yield loss and reduction of test weight are related to disease severity and time of infection. Yield losses of 30% to 40% have been recorded when severe infection occurred before flowering and damage on the flag leaf was high (> 60% to 100%). However, if severe leaf rust does not occur until dough stages of kernel development or beyond, yield losses may be in the range of 5% to 15%.”

That being said, I have seen very little rust to date (5/16/11). I have sent plant tissue to a lab for diagnosis and will report back as to the findings. Most of what I am seeing appears to be virus in nature. Fungicides do not control viruses.  If you do have rust or striped rust, you will notice raised pustules on the leaf surface.

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