Managing Foliar Diseases of Winter Wheat with Fungicides – Treatment Criteria, Profitability and Products

Managing Foliar Diseases of Winter Wheat with Fungicides – Treatment Criteria, Profitability and Products

November 14, 2008

Stephen N. Wegulo, Extension Plant Pathologist

With $5/bu wheat, increased profit from applying a wheat fungicide is $10 to $70 an acre for respective yield increases of 6 to 18 bu/ac.
Assumes an application cost of $20/ac

With $8/bu wheat, increased profit from applying a wheat fungicide is $28 to $124 an acre for respective yield increases of 6 to 18 bu/ac.a
aAssumes an application cost of $20/ac.

 

Leaf rust, stripe rust, powdery mildew, tan spot, and occasionally stem rust and Septoria leaf and glume blotches comprise the primary foliar fungal diseases of wheat in the central Great Plains. In southeast and south central Nebraska, leaf and stripe rusts, powdery mildew, and Septoria leaf blotch are the most common and important foliar diseases. Tan spot predominates in the dryland wheat-fallow-wheat or ecofallow cropping systems in the west central, southwest and Panhandle, and has become increasingly common in south central and southeastern Nebraska where wheat follows wheat. Fusarium head blight (scab) affects wheat heads. It is sporadic in Nebraska due to a variable climate, but can cause significant losses. The increase in irrigated wheat acreage across the entire state increases the significance of managing foliar diseases to maximize yields.

These diseases are most damaging when severity on the upper leaves reaches a high level by mid-June. This causes early loss of these leaves, which shortens the grain filling period and results in reduced yields and lower test weights. Statewide, foliar diseases usually reduce yields by about 1% annually, but from 2002 to 2006, stripe rust reduced yields in susceptible varieties by as much as 30%. In 2007 and 2008, excessive rainfall before and during flowering resulted in epidemics of Fusarium head blight in south central and southeastern Nebraska. Yield loss caused by the disease each year was about 2% statewide and up to 20% in severely affected areas. Additional loss resulted from discounts at the elevator due to vomitoxin (produced by the Fusarium head blight fungus) in grain. When May and June temperatures are moderate and precipitation is at or above normal, these diseases, particularly the rusts, pose an even greater threat. Overcast humid weather promotes the development of powdery mildew. However, if temperatures remain moderate and key rains occur during grain fill, wheat may still produce acceptable yields in the presence of moderate disease pressure.

Also see:

Treatment Criteria

How likely are you to have significant damage from foliar diseases? Irrigated wheat that is intensively managed is at greatest risk because the moisture necessary for infection is often supplied during irrigation. The greatest risk for having a tan spot or Septoria leaf blotch problem is drilling wheat into or next to standing wheat stubble. Your first approach is to monitor any rust epidemics in the southern Great Plains and local development of powdery mildew and leaf spot beginning in early May and continuing into late May or early June. This gives a good indication of the potential for foliar diseases to become a significant production factor in a field. Use the following criteria in deciding whether to treat:

 

  • Variety Planted. What is the level of resistance to the rust diseases? Those varieties that are moderately resistant or resistant to stripe and leaf rusts don't need to be treated with fungicides, unless powdery mildew or one of the leaf spot diseases is becoming severe on the lower half of the plant. However, those that are moderately susceptible or susceptible to one or both of the rusts need to be watched closely.
  •  

  • Stand Quality. In April assess the quality of the stand coming out of dormancy. Dryland wheat should have a yield potential of at least 45 bu/ac, and irrigated wheat a yield potential of at least 70 bu/ac in order to justify fungicide treatment. These thresholds can vary, depending on the expected yield increase due to fungicide application, fungicide application cost, and the price of wheat. The higher the expected yield increase and wheat price, the lower the yield potential threshold for a profitable fungicide application (Table 1).Rust epidemics in the southern plains: If either stripe or leaf rust or both are developing rapidly in Texas and Oklahoma during April and in Kansas during May, the probability is high that Nebraska will have a rust problem.
  •  

  • Timing of the Crop. If cool weather slows maturity, the window for disease development is extended and the impact on the crop is greater than if the crop is maturing early.

     

  • Weather Conditions. These foliar diseases need moist conditions, so if the long range forecast for May and June predicts above average rainfall, the disease risk is higher. Dry conditions lessen the threat to dryland wheat. Irrigated wheat is at greater risk because of more frequent leaf wetness.Excessive rainfall before and during flowering increases the risk for Fusarium head blight.

     

  • Estimated price of wheat. The higher the price of wheat, the more economical is treatment.

In general, if trace amounts of rust, powdery mildew or leaf spot are present on the flag leaf in the early boot stage of development, and infection below the flag leaf is moderate or moderately severe, the likelihood is high that severe infection of the flag leaf will occur and applying a fungicide should be cost effective. Fungicides are most effective if applied as a preventive treatment. Application after the flag leaf is already infected may result in little or no yield increase. If excessive rainfall occurs one to three weeks before flowering, applying an appropriate fungicide at early flowering will reduce damage caused by Fusarium head blight.

Treatment Profitability

In this article the estimated net profit for this practice will vary, depending on expected yield increase, expected yield goal, expected selling price and the cost of treatment. In the examples illustrated below, expected net profits varied from $25.50/ac - $61.00/ac.

Example 1: 10% expected increase X 70 bu/ac expected yield goal X $6.50 expected selling price - $20.00 application cost = $25.50/ac expected net profit

Example 2: 10% expected increase X 80 bu/ac expected yield goal X $6.50 expected selling price - $20.00 application cost = $32.00/ac expected net profit

Example 3: 10% expected increase X 90 bu/ac expected yield goal X $6.50 expected selling price - $20.00 application cost = $38.50/ac net profit

Example 4: 10% expected increase X 90 bu/ac expected yield goal X $9.00 expected selling price (seed production field) - $20.00 application cost = $61.00/ac expected net profit

However, applying a foliar fungicide to wheat does not guarantee higher yields. Consider it equivalent to health or home insurance. You pay a premium for protection that you may or may not need. If you get seriously ill or your house is severely damaged, the premiums were worth the cost, but if you don't file any claims or the claims are small, you will have paid out more in premiums than you received from paid claims. This same logic applies to treating wheat. In the event of serious disease pressure, timely application with the right product will protect yields, thus the investment was worth the cost. If you treat the field and the disease levels never develop beyond light or moderate, the return on your investment will be less and could result in a breakeven or loss scenario.

The cost of treatment will range from $18 to $25 per acre, depending on the product and application method. Many producers growing wheat under irrigation for maximum yield or for seed feel this investment is justified. However, the justification for treatment under a dryland cropping system is not as clear cut, and using the above criteria becomes critical to your decision.

Table 1 illustrates the potential net profit or loss from treating wheat with a foliar fungicide. In general treatment will be cost effective if the realized yield increase is above 6 bu/ac. Fungicide treatment will only be cost effective if foliar disease pressure is severe enough to result in a yield loss of at least 20% if the yield potential is 30-45 bu/ac or a yield loss of at least 10% if the yield potential is more than 45 bu/ac.

In seed production consider yield as well as seed quality since severe disease will reduce seed test weight. The potential net profit illustrated in Table 1 relates to sale prices of wheat in 2007 and 2008. Farmers also need to consider the crop yield effect on LDP payments and crop insurance coverage and the possible indirect effect on farm program direct and counter-cyclical payments which may make treatment a more favorable option.

Table 1. An illustration of the potential net profit from foliar fungicide treatment of wheat based on a $5 or $8 per bushel selling price at the elevator1.

Potential yield
of the field
in bushels per acre

Expected yield increase in % or bu/a due to treatment:

$ increase based on a wheat price of:

Net profit/loss ($) at a $20 treatment cost based on a wheat price of:

Net profit/loss ($)
at a $25 treatment cost
based on a wheat price of:

 
%
bu/ac
$5.00
$8.00
$5.00
$8.00
$5.00
$8.00

30

5
1.50
7.50
12.00
-12.5
-8.00
-17.5
-13.0

30

10
3.00
15.00
24.00
-5.00
+4.00
-10.00
-1.00

30

20
6.00
30.00
48.00
+10.00
+28.00
+5.00
+23.00

30

30
9.00
45.00
72.00
+25.00
+52.00
+20.00
+47.00

45

5
2.25
11.25
18.00
-8.75
-2.00
-13.75
-7.00

45

10
4.50
22.50
36.00
+2.50
+16.00
-2.50
+11.00
45
20
9.00
45.00
72.00
+25.00
+52.00
+20.00
+47.00
45
30
13.50
67.50
108.00
+47.50
+88.00
+42.50
+83.00


60

5
3.00
15.00
24.00
-5.00
+4.00
-10.00
-1.00

60

10
6.00
30.00
48.00
+10.00
+28.00
+5.00
+23.00

60

20
12.00
60.00
96.00
+40.00
+76.00
+35.00
+71.00
60
30
18.00
90.00
144.00
+70.00
+124.00
+65.00
+119.00


75

5
3.75
18.75
30.00
-1.25
+10.00
-6.25
+5.00

75

10
7.50
37.50
60.00
+17.50
+40.00
+12.50
+35.00
75
20
15.00
75.00
120.00
+55.00
+100.00
+50.00
+95.00

75

30
22.50
112.50
180.00
+92.50
+160.00
+87.50
+155.00

90

5
4.50
22.50
36.00
+2.50
+16.00
-2.50
+11.00

90

10
9.00
45.00
72.00
+25.00
+52.00
+20.00
+47.00

90

20
18.00
90.00
144.00
+70.00
+124.00
+65.00
+119.00

90

30
27.00
135.00
216.00
+115.00
+196.00
+110.00
+191.00

105

5
5.25
26.25
42.00
6.25
+22.00
+1.25
+17.00

105

10
10.50
52.50
84.00
32.50
+64.00
+27.50
+59.00

105

20
21.00
105.00
168.00
85.00
+148.00
+80.00
+143.00

105

30
31.50
157.50
252.00
137.50
+232.00
+132.50
+227.00

1 The net profit does not reflect the government subsidies for wheat as outlined in the farm bill and are based on preventive fungicide treatment before the flag leaf disease levels become severe enough to affect yield and test weight.

 

Table 2. Fungicides registered for use on wheat to control foliar diseases and Fusarium head blight.1

Product2

Target diseases

Product rate/acre

Application timing

Headline
(BASF)

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

6-9 fl oz

Up to Feekes 10.5 (heading complete)

Quadris
(Syngenta)

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

6.2-10.8 fl oz

Feekes 6 (immediately after jointing) to 10.5 (heading complete)

Quilt
(Syngenta)

Leaf rust
Stem rust
Stripe rust
Tan spot
Septoria glume blotch
Septoria leaf blotch
Powdery mildew
Spot blotch
Helminthosporium
leaf blight

7-14 fl oz

 

14 fl oz

Feekes 3-6

 

Up to Feekes 10.5 (heading complete)

Stratego
(Bayer)

Leaf rust
Stripe rust
Stem rust
Septoria leaf blotch
Tan spot
Powdery mildew

10 oz

Feekes 8 (emerging flag leaf)

Tilt
(Syngenta)

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

4.0 fl oz

Feekes 10.5 (heading complete)

PropiMax EC
(Dow AgroSciences)

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

4.0 fl oz

Feekes 8 (emerging flag leaf)

Manzate 75DF
(Griffin L.L.C.)

Leaf rust
Septoria glume blotch
Septoria leaf spot
Tan spot

2.0 lb

Feekes 10 (boot) and again at 10.5 (heading complete)

Dithane DF
             F-45
             M-45

(Dow AgroSciences)

Leaf rust
Septoria glume blotch
Septoria leaf spot
Tan spot

2.1 lb
1.6 qts
2.0 lb

Feekes 10 (boot) and again at 10.5 (heading complete)

Penncozeb 80WP
                  75DF

(Elf Atochem)

Leaf rust
Septoria glume blotch
Septoria leaf spot
Tan spot

1.0-2.0 lb

Feekes 10 (boot) and again at 10.5 (heading complete)

Caramba
(BASF)

Black point
Leaf blotch
Net blotch
Powdery mildew
Leaf rust
Stem rust
Stripe rust
Scald
Septoria leaf  blotch
Septoria glume blotch
Spot blotch
Tan spot
Fusarium head blight
(suppression only)

10-14 fl oz

Immediately after flag leaf emergence; beginning of flowering for suppression of Fusarium head blight

Multiva

Black point
Leaf blotch
Net blotch
Powdery mildew
Leaf rust
Stem rust
Stripe rust
Scald
Septoria leaf  blotch
Septoria glume blotch
Spot blotch
Tan spot

6-11 fl oz

Immediately after flag leaf emergence; apply no later than Feekes 10.5 (heading complete)

Folicur

Leaf rust
Stem rust
Stripe rust
Fusarium head blight
(suppression only)

4 fl oz

At the earliest sign of rust pustules on foliage; beginning of flowering for suppression of Fusarium head blight

Proline

Leaf rust
Stem rust
Septoria leaf blotch
Septoria glume blotch
Tan spot
Fusarium head blight
(suppression only)

4.3-5.0 fl oz for leaf and stem diseases;
4.3-5.7 fl oz for Fusarium head blight

At the earliest appearance of symptoms on leaves or stems; for Fusarium head blight suppression, from 75% heading to 50% flowering

Prosaro

Leaf rust
Stem rust
Septoria leaf blotch
Septoria glume blotch
Tan spot
Fusarium head blight
(suppression only)

6.5-8.2 fl oz

At the earliest appearance of symptoms on leaves or stems; for Fusarium head blight suppression, from 75% heading to 50% flowering

1This list is presented for information only and no endorsement is intended for products listed or 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.
2Most of the products listed in Table 2 recommend adding a spreader sticker and must be applied in sufficient water to ensure good coverage.