)
Small Grains
Management Program for Powdery Mildew of Wheat
Cause and Occurrence
Cause:
Blumeria graminis f. sp.
tritici
(formerly
Erysipha graminis f. sp.
tritici) Occurrence: May to July, during periods of overcast, humid, moderate weather
Key Symptoms
Most conspicuous on
upper leaf surfaces and heads; also present on stems.
Heads on the later,
shorter tillers can become heavily diseased because they remain lower in the
wheat canopy where humidity is high.
Fungus initially forms
cottony white patches which later turn light gray or buff-color.
When severe, individual
patches often merge and cover large areas of the leaf surface and head.
Leaf tissue on the
opposite side of the mildew pustules becomes yellow, later turning tan or
brown.
As the season progresses
the older, gray colonies of powdery mildew become dotted with small black
bodies called cleistothecia.
Cultural Management Practices
In most years powdery
mildew will not be a yield limiting disease in Nebraska; however, sporadic
widespread, moderately severe outbreaks may occur as in 2004.
Dense stands of heavily
fertilized, irrigated wheat are most prone to mildew.
In Nebraska some of the
better yielding and more popular wheat varieties are susceptible to powdery
mildew; so growing mildew resistant varieties is an option, but rust resistance
(definitely stem and possibly leaf and stripe) is the top priority in selecting
disease resistant varieties.
Use a balanced fertility
program based on soil test analysis. Heavy applications of N and high seeding
rates produce a dense canopy that favors mildew development.
Fungicide Treatment Program (Table 1)
Scout fields for mildew,
rust and other leaf diseases and assess incidence and severity from tiller
elongation through flowering.
It is important to keep
disease levels on the top two leaves (flag and flag-1 leaves) and the head to a
minimum to prolong the grain filling period.
Base the decision to
spray the field on the level of disease present, susceptibility of the variety,
stage of development, the potential yield and the current selling price of the
grain.
Table 1. Fungicides
registered for foliar diseases of wheat.*
Product
Rate/acreTiming
|
Quilt
(azoxystrobin
+ propiconazole)
(Syngenta)
|
7-14
fl oz
|
Up
to Feekes 9 (ligule of flag leaf just visible) growth stage
|
|
Quadris
(azoxystrobin)
(Syngenta)
|
6.2
- 10.8 fl oz
|
Feekes
6 (immediately after jointing) to 10.5 (late head emergence)
|
|
Headline
(pyraclostrobin)
(BASF)
|
9
fl oz
|
Feekes
10.5 (late head emergence)
|
|
Stratego
(propiconazole + trifloxystrobin)
(Bayer)
|
10
oz
|
Feekes
8 (emerging flag leaf)
|
|
Tilt
(propionazole)
(Syngenta)
|
4
fl oz
|
Feekes
8 (emerging flag leaf)
|
|
PropiMax
EC (propiconazole)
(Dow
AgroSciences)
|
4
fl oz
|
Feekes
8 (emerging flag leaf)
Has
a Section 24C label to apply up to Feekes 10.5 in Nebraska
|
|
Manzate
75DF (mancozeb)
(Griffin L.L.C.)
|
2
lb
|
Feekes
10 (boot) and again at Feekes 10.5 (late head emergence)
|
|
Dithane
DF
F-45
M-45
(mancozeb)
(Dow
AgroSciences)
|
2.1
lb
1.6
qts.
2
lb
|
Feekes
10 (boot) and again at 10.5 (late head emergence)
|
|
Pencozeb
80WP
75DF
(mancozeb)
(Elf
Atochem)
|
1-2
lb
1-2
lb
|
Feekes
10 (boot) and again at 10.5 (late head emergence)
|
|
*Fungicides listed represent the best
information available. No criticism is intended of products not listed, nor
is endorsement by the University of Nebraska given to those listed.
|
Application
Apply sufficient spray
solution to ensure good coverage of the leaf surface.
Read and follow all label directions for mixing and applications. Apply fungicides in sufficient enough water to ensure good coverage of the leaves and heads.
Categories: Disease, Powdery Mildew, Wheat
Date: 06/16/2005
