ISSUE 10   July 17, 2008

WINTER WHEAT DISEASE RATINGS - LISBON, ND

A winter wheat variety trial at the Randy Mair farm near Lisbon, ND, was rated for disease pressure on July 9th, at early soft dough. The following data shows the ratings of untreated plots and plots treated with fungicides (early season application of 3 fl oz/A of Headline followed by flowering application of Prosaro at 6.5 fl oz/A). Disease levels were relatively low on July 9th. At a field tour of this same site on July 14, however, disease levels had approximately doubled, by late dough stage.

Fungicides controlled scab levels by 83%, leaf rust by 100%, and leaf spot diseases by 76%. The varieties with the most susceptibility to diseases generally were Jagalene and Wesley, but individual varieties, such as Radiant, CDC Falcon, and Expedition showed considerable leaf rust and/or fungal leaf spotting. Radiant also showed stem rust infection. These plots are a cooperative effort among NDSU Extension and Ducks Unlimited, with support from BASF and Bayer Crop Science.

Lisbon Winter Wheat Disease Ratings, July 9, 2008

Named Variety

Untreated

Fungicide Treated*

Scab index (%)

Leaf rust  (%)

Leaf spot (%)

Scab index (%)

Leaf rust (%)

Leaf spot (%)

Roughrider

0

8.5

6.5

0

0

0.9

Jerry

0

1.9

6.4

0

0

1.2

Darrell

0

7.8

2.9

0

0

0.6

Overland

0

0

5.4

0

0

1.4

Radiant

0

13.3

12.6

0

0

1.8

Alice

0.03

6.2

6.8

0

0

1.4

Millennium

0.03

1.1

6.1

0

0

0.7

CDC Buteo

0.03

6.8

5.5

0

0

2.3

Expedition

0.1

14.5

13.8

0.1

0

0.8

CDC Falcon

0.1

1.0

13.2

0

0

2.8

Hawken

0.9

0

5.8

0.8

0

2.0

Yellowstone

1.3

5.1

5.4

0

0

4.9

NuDakota

1.9

0

6.7

0

0

1.6

Jagalene

3.0

18.9

6.8

0.03

0

1.5

Wesley

4.2

3.5

8.7

0.9

0

1.6

 

NDSU IPM FIELD SCOUTS RESULTS

NDSU field scouts surveyed 88 wheat fields and 29 barley fields during the second week of July. Nine percent of the wheat fields showed wheat leaf rust, while two of the barley fields showed barley leaf rust. Only one occurrence of scab was recorded, in a winter wheat field at low severity.

Field scouts are noticing more bacterial blight (stripe) symptoms in fields now, with 8% of wheat fields and 18% of barley fields with symptoms . High winds with rain result in more leaf wounds, which allow for bacterial infection and spread. Symptoms are brownish, necrotic streaks on the leaves, often with dried, shiny bacterial colonies still evident on the leaf surface.

Bacterial infection on wheat
Bacterial infection symptoms on wheat leaves.

Marcia McMullen
Extension Plant Pathologist
marcia.mcmullen@ndsu.edu

 

EARLY APPEARANCE OF SUNFLOWER RUST IS A CAUSE FOR CONCERN IN NORTH DAKOTA

Sunflower rust is a disease that is capable of causing significant yield loss to sunflowers. Sunflower rust appears most years in North Dakota, but isnít usually observed until late July or early August. However, the presence of sunflower rust in North Dakota was recently brought to my attention by crop consultant Mike Hutter (Renville County), and the disease has since been observed in other counties throughout the state.

Symptoms. Rust will often appear initially on the lower leaves and spread upward as new leaves are produced. The disease produces small (approximately 1/16 inch) dusty cinnamon-brown pustules full of brown spores (Figure 1). Brushing your thumb across rust pustules will leave a dusty brown streak on it. Rust can also infect the stems, bracts and head.

Rust pustules
Figure 1

Disease Cycle. Once pustules are observed, they each are capable of producing many more spores and many cycles of infection. These spores can be dispersed long distances by wind, which may rapidly spread the disease to other fields. Spores need a minimum of 2-3 hours of free water (either dew or rainfall) to germinate, but 6-10 hours of free moisture will produce higher levels of germination and infection. Optimal temperature for infection ranges from 60-75 F, but can occur between 39 and 86 F. At temperatures above 90 F, rust spores do not germinate on sunflowers. Once infection occurs, temperature is the only environmental factor that will determine how fast the disease progresses. During cool conditions (65 F day/55 F night) it may take up to 14 days for new pustules to form, but at warm conditions (85 F / 75 F) new pustules can form in as few as 8 days. Thus, warm temperatures will often speed disease development.

Fungicides. We have almost no fungicide data from early rust epidemics, simply because they are rare. However, after conversations with colleagues in other sunflower growing states and provinces, I would recommend being aggressive controlling this disease. We have a long growing season in front of us, the disease is well-known to cause yield and quality losses, and the price of sunflowers is high enough to justify managing the disease. I think it is important to scout your fields weekly for the disease, and use the figures in this article to help assess severity (Figure 2). In fields where rust is not found, be happy and scout again next week. In fields where rust is found, you likely need to consider a fungicide application this season.

Rust severity
Rust severity
Rust severity
Rust severity
Figure 2

Currently, Headline and Quadris are labeled for rust control. If rust is absent or present at very low levels, it may be prudent to wait until the upper leaves have emerged. However, if severity on the lower leaves is higher (3-5% or more average for all leaves) and favorable conditions for disease exist (prolonged dew and relatively warm days), a fungicide application to arrest the development of the disease may be warranted. In this case, a follow-up application could be necessary later, depending on severity and plant growth stage. Headline is labeled at 6 Ė 12 oz/A and Quadris has a North Dakota Section 2(ee) label at 6 - 7 oz/A, but both disease control and residual will be better if a higher rate of either product is applied (9 oz/A or more for Headline). Remember to read the label, follow directions, and pay attention to the PHI.

In some fields, a threshold model for rust control developed by researchers in Israel in the mid 1990ís may be useful, with some modifications. The model is based on fungicide timings around flowering, so it may be relevant in some areas. The research group found that yield loss was limited if a fungicide application was made when the upper four leaves had an average pustule coverage of 3% (Figure 2). They also found that at 27 days after flowering, a fungicide application no longer benefitted the crop, since the seed filling period was largely finished. However, two things about this study suggest to me that we might want to be more aggressive than this. First, this data was based on an application of a triazole fungicide (Folicur, which is not labeled on sunflower), which has been shown to have more curative activity than strobilurins (Headline and Quadris) on rusts of other crops (strobilurins should be viewed more as a protectant for sunflower rust). Thus, an application before the 3% severity threshold is reached is critical when using the strobilurins, and I would strongly encourage the use of a higher application rate. Second, we should expect our climate to be more conducive to disease development, further suggesting that an application before the 3% severity threshold is reached would be prudent.

If rust is in your area and you are considering a preventative application, I would recommend waiting until early flowering. That way you protect the upper leaves for a prolonged period of time, removing much of the window for new infections to cause damage.

Sam Markell
Extension Plant Pathologist
samuel.markel@ndsu.edu


NDSU Crop and Pest Report Home buttonTop of Page buttonTable of Contents buttonPrevious buttonNext button