[Fhb-update_cgp] FHB Update from OK, 05/09/19

Thu May 9 17:10:07 EDT 2019

This past week in addition to looking at wheat around Stillwater, Dr. Tom
Royer (OSU Entomologist) and I were at field days on Monday (6-May) near
Kildare in north-central OK (Kay County) followed by a stop at the
Experiment Station near Lahoma (15 miles west of Enid) and another field day
near Cherokee in Alfalfa County (north and west of Enid and about 20 miles
south of KS). That was followed on Tuesday by a field day at Kingfisher
(about 25 miles northwest of Oklahoma City) and field visits northwest of
Kingfisher near Loyal. Across these areas wheat ranged from heading to full
kernel formed (watery to start of milky). In southwestern OK, wheat ranges
from ¼ kernel to milky whole kernels with the dough stages approaching
quickly.

In southwestern OK, leaf rust, stripe rust and Septoria tritici blotch have
become severe according to both Heath Sanders (SW OK Area Extn Agronomy
Spclt) and Gary Strickland (Extn Educator; Jackson Cnty). Gary indicated
that this is only the second time he has seen Septoria tritici blotch severe
on flag leaves. Leaf rust also is severe. Both Heath and Gary also indicate
they have started to see more powdery mildew in fields, but have found it
severe on the mid and lower leaves in only one field.

In north-central OK near Kildare, wheat was mostly clean with Septoria
tritici blotch being the most noticeable disease on lower leaves. No
significant stripe or leaf rust was observed, and powdery mildew could be
found but was sparse. By contrast, wheat at Lahoma showed significant leaf
and stripe rust with leaf rust being the most prevalent. However, whereas
the rusts could be found in many of the wheat breeding nurseries, both rusts
were lacking in the large variety trial with stripe rust being present at
only a low severity. In some varieties and breeder lines, leaves were
quickly deteriorating. At Cherokee, heavy rain on Sunday had saturated the
area and more rain fell on Wednesday. Rust was light in the variety trial
with stripe rust again being the most prevalent albeit again at a low
incidence and severity. At Kingfisher on Tuesday, leaf rust was the most
prevalent foliar disease with Septoria tritici blotch also present on lower
foliage. In a field near Loyal, OK, Dr. Royer found a high incidence of
armyworms especially along the field’s edge. As he moved into the field,
the incidence of worms dropped, but he felt like a field such as this was
approaching the spray threshold and should be watched closely to monitor if
the spray threshold was reached. For more information on armyworms in wheat,
including threshold numbers and control options, see Pest eAlert Vol 18, No.
14, EPP-7094 “Common Small Grain Caterpillars in Oklahoma” and CR-7194,
“Management of Insect and Mite Pests in Small Grains.”

In addition to army worms, a physiological leaf spot (PLS) was observed on
wheat leaves around Kingfisher and Loyal. As indicated in my last update
(http://entoplp.okstate.edu/pddl/2019/PA 18-16.pdf), PLS has been observed
in a number of fields across several varieties. There can be many causes of
PLS, one of which is chloride deficiency. Chloride deficiency tends to be
variety specific. Years ago in Oklahoma, the varieties ‘Payne’,
‘Cimarron’ and ‘Century’ all would show PLS due to chloride
deficiency. Cimarron and Century both had Payne as a parent in their
pedigree. Hence, although chloride deficiency can cause a PLS, there are
other causes as well, and this year I believe that the PLS being observed is
too widespread and across to many varieties to be attributed to only a
deficiency of chloride. For more information on chloride and its role in
PLS, see Kansas State University’s recent extension publication MF 2570;
Chloride in Kansas: Plant, Soil and Fertilizer Considerations (Dorivar A.
Ruiz Diaz), which can be found at:
https://www.bookstore.ksre.ksu.edu/pubs/MF2570.pdf

A report of increasing foliar disease also came in from Lanie Hale (Wheeler
Brothers; west central OK) who reported,
“In my last report April 26, I told you I found 3 fields with rust. Those
3 fields were out of a total of 23 fields scouted. Those 3 fields have been
sprayed. Yesterday, May 6th, I looked at the 20 fields where I found no rust
April 25th. 11 of those 20 had stripe rust and/or leaf rust. Since the 30
day window is upon us, the farmers are spraying all 20 fields. In the fields
I looked at yesterday, I would estimate 75-80% of the flag leaves had some
kind of dis-coloring issue ranging from light flecking to stripe rust, leaf
rust, Tan Spot, or Septoria tritici blotch. (1&2) I noticed many of the
stems have dark spots below the flag leaf; (2) I’m assuming that is also
Septoria tritici blotch. Several fields had small circular spots that appear
to be Barley Yellow Dwarf Virus hot spots. (3) The head count in all the
fields I’ve scouted, regardless of the location, is tremendous. If we can
maintain the flag leaf health we have today, yields and grain quality will
also be tremendous.”

These and additional reporting by Josh Bushong (NW OK Area Extn Agronomy
Spclt) all indicate that foliar wheat diseases, especially Septoria tritici
blotch, leaf rust, and stripe rust are increasing greatly in incidence and
severity across Oklahoma. With continued wet and cool weather, the
incidence/severity of these diseases will continue to increase across
northern OK and the OK panhandle. The spraying window across much of
Oklahoma is now getting quite tight, and a producer needs to be certain to
follow the fungicide label regarding when a fungicide can be applied in
order to be in compliance with the label. For more information on applying
fungicides and their relative effectiveness in managing foliar diseases, see
OCES Current Report (CR-7668) that can be found at:
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-4987/CR-7668web2019.pdf

Finally, in addition to the rusts, Septoria tritici blotch and powdery
mildew, other diseases that have been observed include an occasional loose
smutted head as observed by Zack Meyer (Sales Agronomist with CHS) near
Hennessey, OK. I also have seen an occasional head of loose smut this year
in various fields. It merits to mention that if you see loose smut or common
bunt in a field, do not save seed from that field for planting the next year
as that will lead to increasing that smut or bunt. If that field is planted
again in wheat, be sure to plant seed treat at a high rate with a fungicide
effective against the bunts and smuts. Barley yellow dwarf also has been
seen in various fields and trials around the state but is much less
prevalent than typical as are the mite-transmitted viruses, especially wheat
streak mosaic virus.

--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 https://www.scabusa.org