ISSUE 13   August 13, 2009

NDSU IPM FIELD SURVEY FOR SMALL GRAINS WINDING-DOWN

The NDSU IPM field scouts are finishing their small grain survey within the next couple of weeks, with wheat and barley fields ripening fast, and most of the scouts heading back to college soon.

Growth Stages: For the week ending August 7, the scouts surveyed 75 wheat fields and 4 barley fields. The average growth stage over all the wheat fields surveyed was early dough stage, and for barley, mid-to late dough.

Wheat: The late season diseases observed in wheat included Fusarium head blight (head scab), a little leaf rust, bacterial stripe, loose smut, barley yellow dwarf and wheat streak mosaic. Head scab was observed in 11 wheat fields (14.7% of fields surveyed), with an average field severity of 2.4%.

Wheat leaf rust was observed in four commercial fields of spring wheat in the southwest region, with an average leaf severity of 4%. Loose smut was observed in 23% of the surveyed wheat fields this past week, with 6.6% of the plants in these fields, on average, showing symptoms. Bacterial leaf stripe was observed in 14.7% of fields surveyed, with 50% of the plants in those fields showing symptoms.

Barley yellow dwarf virus symptoms were observed in 29.3% of the wheat fields, with an average of 15.5% of the plants showing symptoms in those fields, and wheat streak mosaic virus symptoms were observed in 13.3% of the fields, with an average of 8% of the plants in those fields showing symptoms.

Barley: Only four un-ripened barley fields were surveyed last week. Barley yellow dwarf virus symptoms were observed in one field, bacterial leaf stripe in one field, and Fusarium head blight was observed in one field.

A summary of season-long wheat and barley disease observations and implications for management for next year, will be given in the next NDSU Crop and Pest Report edition, which will be on August 27th.

 

WINTER WHEAT AND FUNGICIDE RESULTS, LISBON, ND, 2009

Disease notes were taken on winter wheat variety x fungicide plots near Lisbon, ND on July 13th. Tan spot pressure was high in this location, and leaf rust and head scab were present, but at low levels. Symptoms of wheat streak mosaic and barley yellow dwarf virus also were observed, and these viruses will most likely impact yield in these plots.

Tan spot, leaf rust and Fusarium head blight were scored across the 20 varieties, for both the untreated plots and fungicide treated plots, on July 13th at soft dough stage. The fungicide protocol applied was an early application of Stratego followed by a flowering application of Prosaro. Flowering applications were made according to the flowering date of each variety. The following table summarizes the results across all 20 varieties in the trial.

Fungicide effects on fungal diseases in winter wheat, averaged
over 20 varieties, Lisbon, ND, ‘09

Treatment

Leaf rust %

Leaf spot %

Fusarium field severity %

Untreated

3.7

30.7

0.24

Treated*

0

2.2

0.02

LSD 0.05

3.2

5.4

0.08

* Treatment was an early application of Stratego at the 5 leaf stage, followed by an application of Prosaro fungicide at 6.5 fl oz/acre, at flowering stages of individual varieties

The above information indicates that fungicides controlled leaf rust by 100%, leaf spot diseases by 93%, and Fusarium head blight (head scab) by 91%. For varieties that had the most fungal leaf spot in untreated plots, such as CDC Falcon (56.7% severity) or Yellowstone (42.5% severity), the fungicide treatments still resulted in 90%+ control. Leaf rust levels in untreated ranged from 0% to 28.3% (Jagalene), but fungicide treatment resulted in 100% control, even in the most susceptible cultivars.

These levels of control of leaf rust and fungal leaf spot control with fungicides are not uncommon with good application techniques, rates, timings, and products. For Fusarium head blight, however, levels were not high in any variety this year; the highest Fusarium head blight field severity level [(incidence x head severity)/100] was less than 1% (Wesley = 0.6%). So, the 91% percent control achieved with fungicides may be high; under more severe Fusarium head blight levels, levels of control have averaged between 55-80%, depending on severity, year, location and variety.

Dr. Joel Ransom, NDSU Extension Agronomist, will be providing more information on these winter wheat plots, once harvest data is analyzed. Dr. Ransom has coordinated these plots, in conjunction with Blake Vander Vorst of Ducks Unlimited.

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

 

DRY BEAN RUST IDENTIFICATION AND SCOUTING

Since the identification of a new race of common bean rust last fall, rust has been on the minds of many bean growers, and rightly so. The new race has the ability to cause disease on virtually all varieties grown in our area, and the environment has been reasonably favorable for disease development (not too hot, areas with significant dews). We too are scouting fields for rust, and paying particular attention to areas near locations rust was reported last year, or in areas where suspicion of rust exists. Additionally, we are scouting ten sentinel plots up and down the valley and in the Fessenden area. Last week, 35 fields were scouted. To date, we have not been able to confirm rust in ND. This is not to say that it is not out there, but we have yet to been able to find it either through our own survey, or samples or fields from growers, agents, or consultants. However, we have been seeing other symptoms that can be confused with rust.

Rust symptoms include a small rust pustule with cinnamon brown spores in the center. These spores can be rubbed off with a finger or a nail, leaving a dusty streak of spores behind (Figure 1 and 2). However, the pustule will remain, although may appear lighter colored (maybe dark yellow). The early symptoms of brown spot (Pseudomonas syringe pv syringe) can be remarkably similar to early rust infection. These young symptoms produce a small, circular, discrete necrotic lesion surrounded by a yellow halo (Figure 3 and 4). However, the brown spot pathogen will not produce a pustule with spores, and if you rub your finger or nail over the necrotic spot, it remains unchanged and no spores will be dispersed. The early stages of other bacterial blights may appear similar to rust as well, but from what I have seen in the field so far this year, brown spot appears to have the most similar symptoms. Additionally, splashing soil after thunderstorms can look similar to rust pustules. The easiest way to distinguish soil from rust is to rub it off. Soil can be rubbed off in its entirety, whereas when a rust pustule is rubbed, spores are removed but a spot remains.

I strongly encourage growers to scout their beans. It is still early enough in the season that an epidemic could cause problems. Research done the last time rust epidemics were common suggested that until pintos reached striping, yield loss from rust could occur. One last point about scouting, when I look for rust, I tend to concentrate on the middle canopy, and make certain that I examine undersides of the leaves. Conditions in the canopy and on the undersides of leaves are more frequently favorable for initial disease development.


Rust symptoms include small pustules
with cinnamon-brown spores.


Spores rub off pustules leaving a dusty streak of spores.


The early symptoms of bacterial brown spot can resemble rust.
However, no spores will be present in the central necrotic area.


Close-up of third figure

 

DRY EDIBLE BEAN DISEASE SURVEY BEGINS NEXT WEEK

A disease survey of edible beans, led by Dr. Rubella Goswami will begin next week. A minimum of 30 fields (likely 50 total) will be scouted throughout the dry bean growing areas in North Dakota. The goals of the survey are to assess the impacts of different diseases on edible beans, detect any new diseases, and collect any diseases that attract our attention. It was during this survey last year that the new race of rust was collected and identified, thanks in a big part to several consultants and growers who had pointed us to several suspect fields or sent us samples. The data generated here helps us develop management strategies and determine future pathology needs. Thanks to all the anonymous growers whose fields we visit and thanks to Northarvest Bean Growers for support.

 

SOYBEAN DISEASE SURVEY BEGINS THIS WEEK

As soybeans are approaching the R3 and R4 stages, we are beginning a disease survey aimed at 1) detecting diseases we don’t want and 2) quantifying the diseases we know we have. The goal is to survey a minimum of 60 fields in the southeastern 12 counties this week (approximately R3), and survey a minimum of an additional 60 fields in a couple weeks (R4-R5). Diseased tissue will be collected and pathogens will be identified and stored. The survey is essential for development of management recommendations and determination of future pathology needs. We thank all the anonymous growers whose fields we survey and the North Dakota Soybean Council for support.

Soybean Rust Update

Plant pathologists have been monitoring the spread of soybean rust in the United States and Mexico for many months. In North Dakota, we survey weekly for the disease in the southeast part of the state and bi-weekly in other soybean growing counties. To date, soybean rust has not spread beyond the southern United States and was only first reported in Arkansas this week. Given the lack of disease spread in the United States and the lateness of season, it is safe to assume that soybean rust will not be an issue this year in our region. A current map of soybean rust spread (Figure), disease information, and photographs are available at www.sbrusa.net. The national and North Dakota efforts are sponsored by the North Dakota Soybean Council and the North Central Soybean Research Promotion Board.


Soybean rust distribution in the United States
as of August 12, 2009. Red counties indicate
positive soybean rust finds and green counties
are negative for soybean rust.

 

SUNFLOWER RUST UPDATE

Conditions have been, and are, optimal for sunflower rust development and spread. In fields where rust has already been found, I would expect the disease to appear to ‘blow up’ within the next week, and in fields where rust has not yet been found, conditions have been/will be optimal for spread of the disease.

In localized areas in the state, particularly in the North Central counties, rust was identified as early as June. However, abnormally cool temperatures slowed (but did not stop) the development and spread of the disease. The recent moisture (rain or dew) and relative warmth last weekend likely provided an optimal environment for rust infection. With temperatures pushing 90F this week, those new infections will develop very quickly. Under these conditions, the time between infection and pustule formation may be as short as 7-10 days. Therefore, I am expecting many new pustules to become apparent next week.

In fields where rust has already been observed in the lower or middle canopy, it is very possible that pustules will begin to appear on the upper leaves. Yield and quality losses are possible when rust appears on the upper leaves at this early growth stage, and the earlier rust appears in a field, the more likely yield losses are to occur. Tebuconazole (Folicur® and generics) and two strobilurin fungicides (Headline® and Quadris®) are labeled for use on sunflowers. Based on fungicide trials performed in North Dakota and other locations, a tebuconazole can be sprayed at 3% pustule coverage on the upper four leaves for optimum control, but the strobilurins need to be sprayed earlier (either as a preventative or up to maybe 1% or 2% pustule coverage) for optimum control. In studies done overseas, rust did not impact yield after approximately 4 weeks post flowering.

In a Headline timing trial done in Carrington in 2008, fungicide applications made at 1-2% severity were found to reduce disease and protect yield as much as when three sequential fungicide applications were made prior to disease onset, at 1-2% severity, and at 7% severity (Table 1). In trials at Casselton 2008, fungicide applications reduced disease, but yield differences between the untreated control and treatments was not observed (Table 2). This was likely due to a lower disease severity at the time of applications (0 to 0.6%), and the influence of phomopsis in the trial. As demonstrated by these two trials, high rust severities at season’s end do not impact yield, but can make a big difference in our current growth stages. More information, including photos of symptoms and diagrams of rust severity, are available in the July 2, 2009 issue of the Crop and Pest Report and at the National Sunflower Association web site, www.sunflowernsa.com. Additionally, the complete fungicide trial report is available at the NSA website.

Sunflower rust trial timing in Carrington 2008. All applications were 9 fl oz Headline®. Disease severity was calculated as the average pustule coverage on the upper four leaves. AUDPC is a cumulative disease severity index. Letters following number indicate statistical differentiation by the LSD value.

Treatment
(Headline 9 fl oz)

Disease severity (upper four leaves)

 

R3.5

R5

R7

R9

AUDPC

Yield (lb/A)

Untreated Control

0a

1.8 ab

8.7 a

16.5 a

264 a

1501 a

1 wk before disease occured (R3.5)

0a

0.8 bc

4.1 b

13.9 a

169 b

1720 ab

1-2% severity (R5.2)

0a

0.8 bc

1.3 c

3.6 bc

54 c

1899 b

7% severity (R6)

0a

2.7 a

6.0 b

4.6 b

150 b

1440 a

R3 + R5.2 + R6.0

0a

0.4 c

0.4 c

0.9 c

17 c

1941 b

LSD

0

1

2.4

3.4

64

306


Sunflower rust trial timing in Casselton 2008. Disease severity was calculated as the average pustule coverage on the upper four leaves. AUDPC is a cumulative disease severity index. Letters following number indicate statistical differentiation by the LSD value. Tebuzol® is a tebuconazole product (UPI).

Disease severity (upper four leaves)

Treatment

Timing

R5

R7

R9

AUDPC

Yield (lb/A)

Untreated Control

NA

0 a

1.46 a

24.88 a

291.2 a

2236.4 ab

Headline @ 9 fl oz

1 wk before disease (R5.0)

0 a

0.03 c

0.82 d

9.3 cd

2295.0 ab

Headline @ 9 fl oz

0.2-0.4% (R5.9)

0 a

0.75 b

6.49 b

83.4 b

2288.4 ab

Headline @ 9 fl oz

0.3-0.6%(R6)

0 a

0.49 bc

3.26 bcd

44.3 bcd

2165.9 b

Headline @ 9 fl oz

R5.0, R5.6 and R6

0 a

0.05 c

0.59 d

7.3 d

2582.8 a

Tebuzol @ 4.0 fl oz

1 wk before disease (R5.0)

0 a

0.29 bc

5.38 bc

62.4 bc

2462.6 ab

Tebuzol @ 4.0 fl oz

0.2-0.4% (R5.9)

0 a

0.48 bc

2.41 bcd

35.1 bcd

2383.6 ab

Tebuzol @ 4.0 fl oz

0.3-0.6%(R6)

0 a

0.61 b

1.012 cd

23.2 cd

2147.3 b

Tebuzol @ 4.0 fl oz

R5.0, R5.6 and R6

0 a

0.08 c

0.27 d

4.6 d

2196.7 b

LSD

 

0

0.4843

4.4145

53.80

361.22

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


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