Friday, April 27, 2012

Wheat Freeze Damage more Apparent, so are Viruses

Chad Lee, Extension Agronomist, University of Kentucky
Bleached head from freezing temperatures.
Source: Kenny Perry, Graves County ANR Extension Agent
The freeze damage on wheat became more apparent this week. The damage is spotty and tends to be more severe in the low areas of fields. Much of the wheat appears to have survived, but scouting to assess damage within fields is difficult. In order to understand the extent of damage within fields, almost the entire field needs to be walked. At the very least, the highest and lowest elevations need to be examined.

Bleached heads are a clear indication of freeze damage to heads. Girdling around the stem would be another indication of freeze. Heads that appear bent over may be a sign of damage to the stem directly beneath the head. As more days pass,  symptoms will become more visible (if damaged occurred). For more on wheat freeze damage, visit the Wheat Science Newsletter.

In central Kentucky, we are seeing a lot of Barley Yellow Dwarf Virus (BYDV) on wheat. In some cases, fields were sprayed with an insecticide. In at least one case, the field was sprayed twice. In other cases, people scouted fields, followed aphid thresholds and elected not to spray. In all cases, the warm winter most likely elevated aphid levels and climate and biology overwhelmed chemistry.
While BYDV is being observed on a lot of plants in many fields, the severity of the symptoms are relatively low, indicating that minimal yields losses should be expected in most cases. In some fields, wheat plants with BYDV also have Wheat Spindle Streak Virus. Again, the severity is rather low and expected yield losses should be low.

Considering the very warm winter season, followed by the late spring freezes, perhaps we should be thankful that much of the wheat crop survived the freeze and has only minimal damage from the viruses.

Barley Yellow Dwarf on Wheat in Southern Kentucky.
This field was sprayed twice with insecticides to control aphids. 
Wheat that tested positive for both
Barley Yellow Dwarf and Wheat Spindle Streak.

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