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
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Table I. Fungicides commonly used to manage foliar diseases of wheat in Nebraska.* |
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Product** |
Rate/Acre |
Application timing for optimal disease control |
Max. no. |
Max. |
Pre-harvest interval (PHI) |
Diseases controlled |
|
Headline |
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 |
|
Quadris |
4 to 12 fl oz; |
Apply prior to disease development starting at Feekes 6 (first node of stem visible) |
2 |
24 fl oz |
14 days(hay); |
-Leaf rust |
|
Quilt |
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 |
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 |
|
Stratego |
10 fl oz |
Apply preventively when conditions favor disease development |
2 |
20 fl oz |
35 days — apply no later than Feekes 9 (ligule of flag leaf just visible); see label for grazing restrictions |
-Leaf rust |
|
Tilt |
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 |
|
PropiMax EC |
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 |
|
Dithane DF |
2.1 lb |
Apply at first appearance of disease in the tillering to jointing stage |
3 |
6.3 lb |
26 days — apply no later than the beginning of flowering (Feekes 10.5) |
-Helminthosporium |
|
Manzate 75 DF |
2 lb |
Apply at first appearance of disease in the tillering to jointing stage |
3 |
6 lb |
26 days — apply no later than the beginning of flowering (Feekes 10.5) |
-Helminthosporium |
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*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. |
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Table II. Efficacy ratings for wheat foliar fungicides.* |
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|
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. |
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