Managing Foliar Diseases of Wheat With Fungicides

Managing Foliar Diseases of Wheat With Fungicides

March 16, 2007

This year's growing season follows a fairly wet winter for Nebraska and continued wet conditions this spring will affect the development of foliar diseases in wheat. The risk of disease development is higher in irrigated than in dryland wheat, especially in areas that usually receive less than adequate rainfall.

The major fungal diseases likely to develop early in the growing season are powdery mildew and tan spot. Powdery mildew usually is more prevalent in the eastern half of Nebraska while tan spot can occur throughout the state. Development of leaf rust and stripe rust will depend on when spores wind-blown from southern states arrive in Nebraska. Stripe rust has occurred sporadically since 2000.

Fungicide applications are aimed at maximizing green leaf area of the top leaves during grain fill. In wheat, the flag leaf contributes the most to grain fill, followed by the flag-1 leaf. Therefore, to maximize yields, fungicide applications should be timed to protect the flag leaf.

The fungicides used to control foliar diseases of wheat in Nebraska include Headline (pyraclostrobin), Quadris (azoxystrobin), Quilt (azoxystrobin + propiconazole), Stratego (trifloxystrobin + propiconazole), Tilt (propiconazole), PropiMax (propiconazole), Dithane (mancozeb), and Manzate (mancozeb) (Table I).

In general, it is economical to apply a fungicide only if the return from fungicide application exceeds the cost of buying and applying the fungicide. A general rule is that yield potentials should be 40-50 bu/ac for dryland wheat and 75-85 bu/ac for irrigated wheat for a fungicide application to be profitable. The higher the price of wheat, the more profitable a fungicide application be.

If conditions are favorable for disease development early in the season, it may be beneficial to apply a fungicide for early season disease suppression and follow up with a second application at flag leaf emergence. If a decision is made to apply two or more sprays, care should be taken not to exceed the maximum product rate for a single growing season (Table I). Also adhere to restrictions on the interval between two spray applications.

Results from fungicide efficacy trials may vary with location and year. Table II is a general guideline on the relative efficacy of five fungicides in controlling specific foliar diseases of wheat.

Stephen Wegulo
Extension Plant Pathologist

Table I. Fungicides commonly used to manage foliar diseases of wheat in Nebraska.*

Product**
(Company)

Rate/Acre

Application timing for optimal disease control

Max. no.
of sequential applications

Max.
product rate/Acre/
season

Pre-harvest interval (PHI)

Diseases controlled

Headline
(BASF)

6 to 9 fl oz

Apply prior to disease development; immediately after flag leaf emergence (Feekes 8)

2

18 fl oz

Apply no later than the beginning of flowering (Feekes 10.5); 14 days (wheat hay or green-chopped feed)

-Black point
-Leaf rust
-Powdery �
mildew
-Septoria leaf
and glume
blotch
-Spot blotch
-Stem rust
-Stripe rust
-Tan spot

Quadris
(Syngenta)

4 to 12 fl oz;
7.5 to 11 fl oz for powdery mildew control

Apply prior to disease development starting at Feekes 6 (first node of stem visible)

2

24 fl oz

14 days(hay);
45 days (grain and straw) - apply no later than the beginning of flowering (Feekes 10.5)

-Leaf rust
-Powdery
mildew
-Stripe rust
-Stem rust
-Septoria leaf
and glume
blotch
-Tan spot

Quilt
(Syngenta)

7 to 14 fl oz for early season suppression of powdery mildew, Septoria leaf and glum blotch, and tan spot;

14 fl oz for control of leaf diseases

For maximum yields, apply when the flag leaf is 50% fully emerged

2
(Minimum interval between applications is 14 days)

20.5 fl oz

45 days - Apply no later than the beginning of flowering (in wheat, at Feekes 10.5; in barley, rye and triticale, apply no later than Feekes 9 (ligule of flag leaf just visible)

-Kernel blight
-Leaf rust
-Net blotch
-Powdery
mildew
-Septoria leaf
and glume
blotch
-Spot blotch
-Stem rust
-Stripe rust
-Tan spot

Stratego
(Bayer)

10 fl oz

Apply preventively when conditions favor disease development

2
(Minimum interval between applications is 14 days)

20 fl oz

35 days — apply no later than Feekes 9 (ligule of flag leaf just visible); see label for grazing restrictions

-Leaf rust
-Powdery mildew
-Septoria leaf
and glume blotch
-Stem rust
-Stripe rust
-Tan spot

Tilt
(Syngenta)

2-4 fl oz for early season suppression of powdery mildew, Septoria leaf and glume blotch, and tan spot;

4 fl oz for control of foliar diseases

Apply at first appearance of disease; for maximum yields, apply at Feekes 8 (flag leaf emergence)

2

4 fl oz

45 days — apply no later than the beginning of flowering (Feekes 10.5) - wheat only; on barley, rye and triticale, apply no later than Feekes 9 (ligule of flag leaf just visible)

-Leaf rust
-Net blotch
-Powdery mildew
-Septoria leaf
and glume blotch
-Spot blotch
-Stem rust
-Stripe rust
-Tan spot

PropiMax EC
(Dow AgroSciences)

4 fl oz

Apply at first appearance of disease; for maximum yields, apply at Feekes 8 (flag leaf emergence)

1

4 fl oz

Apply no later than Feekes 8 (flag leaf emergence

-Leaf rust
-Net blotch
-Powdery
mildew
-Septoria leaf and glume blotch
-Spot blotch
-Stem rust
-Stripe rust
-Tan spot

Dithane DF
(Dow AgroSciences

2.1 lb

Apply at first appearance of disease in the tillering to jointing stage

3
(7- to10-day interval between sprays)

6.3 lb

26 days — apply no later than the beginning of flowering (Feekes 10.5)

-Helminthosporium
leaf spot
-Leaf rust
-Septoria leaf and
glume blotch
-Tan spot

Manzate 75 DF
(DuPont Crop Protection)

2 lb

Apply at first appearance of disease in the tillering to jointing stage

3
(7- to10-day interval between sprays)

6 lb

26 days — apply no later than the beginning of flowering (Feekes 10.5)

-Helminthosporium
leaf spot
-Leaf rust
-Septoria leaf and
glume blotch
-Tan spot

*This list is presented for information only and no endorsement is intended for products listed nor is criticism meant for products not listed. Consult the product label before buying and using a specific fungicide. Read and follow all label directions and restrictions.
**Addition of a a spreader-sticker is recommended for most products listed. Sufficient water should be added to ensure good coverage.

Table II. Efficacy ratings for wheat foliar fungicides.*

Product

Leaf rust

Stripe rust

Powdery mildew

Septoria leaf and glume blotch

Tan spot

Headline

E**

E

G

VG

E

Quadris

E

E

F(G)***

VG

E

Quilt

VG

VG

VG

VG

VG

Stratego

G

VG

G

VG

VG

Tilt

VG

VG

VG

VG

VG

*Source: Management of Small Grain Diseases (NCERA-184), developed by a multi-state team of researchers.
**E = Excellent; VG = Very Good; G = Good; F = Fair; P = Poor.
*** (G) indicates greater efficacy at higher application rates.

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