[Fhb-update_cgp] FHB Update from OK, 05/01/15

[FHB Update - Central GP, Hard Winter Wheat]

This past week I spent in fields/nurseries around Stillwater and also
attended field days in central OK (Caddo Cnty) and southwestern OK (Jackson
Cnty). Most of the wheat I saw was at ¼ to nearly full berry. Foliar
diseases have definitely increased.

Around Stillwater, powdery mildew is evident on the lower leaves in my
fungicide trial (approx. 25% severity). In the variety demo strips at
Stillwater, I can find severities >65% on lower leaves. However, stripe rust
is still the most evident foliar disease with mid-canopy leaves of
susceptible varieties often completely or nearly completely infected. Flag
leaves of susceptible varieties around Stillwater are beginning to show
stripe rust pustules, but that is still not uniform in all fields/locations.
Also this past week I started to see leaf rust pustules developing on lower
leaves; I only occasionally saw pustules on flag leaves with the exception
of ‘Jagalene’, which was at 90% or so.

In central OK I saw mostly the same thing. At the variety trial near
Kingfisher (Kingfisher Cnty), disease was surprisingly light with stripe
rust the most evident. Near Apache OK (southern Caddo Cnty), disease was
more prevalent with stripe rust the most severe. Varieties resistant to
stripe rust but susceptible to leaf rust (e.g., ‘Jackpot’ were beginning
to show more leaf rust pustules). Tan spot also was evident at this variety
trial as it is a no-till field.

In southwestern OK (near Altus, OK), stripe rust was severe (90% or so) on
the flag leaves of susceptible varieties such as ‘Ruby Lee’,
‘Everest’, and ‘Garrison’. Varieties with resistance to stripe rust
such as ‘Gallagher’, and ‘Billings’ showed little sporulation but
loss of some green tissue due to the hypersensitive reaction (HR).
‘Greer’ showed no stripe rust and no necrosis due to the HR. Here again,
a variety like Jackpot showed no stripe rust, but leaf rust was at a
moderate level. An interesting observation here was made by Dillon Butchee
(Helena Chemical Rep), who noticed stripe rust sporulating inside the glumes
of susceptible varieties, which I have seen only occasionally in Oklahoma.

In more northern OK, Greg Highfill (Extension Educator, Woods Cnty – near
Alva, OK) indicated 
he has seen small amounts of stripe rust in the border of the test plot near
Alva. Although temperature is increasing, the forecast for next week is
highs only in the low to mid 80s with Tuesday-Thursday being rainy again.
These temps will be lower in northern and northwestern OK. Hopefully the
rain will continue, but these conditions will favor continued spread and
increase of particularly leaf rust. For most of Oklahoma, I believe wheat is
past or quickly approaching the point where a fungicide can no longer be
applied. For a discussion of this, see “CR-7668 Foliar Fungicides and
Wheat Production in Oklahoma – April, 2015,” which is available at
http://osufacts.okstate.edu.

Finally, the diagnostic lab continues to receive samples testing positive
for Wheat streak mosaic virus. For information on mite-transmitted diseases,
I refer you to EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and
Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) also available
at http://osufacts.okstate.edu.


--Bob Hunger, Extension Plant Pathologist, Oklahoma State University

For more details, go to the FHB Risk assessment tool at
http://www.wheatscab.psu.edu

For the latest news and updates from the U.S. Wheat & Barley Scab
Initiative, go to http://www.scabusa.org