ISSUE 8   July 1, 2010

MANAGING PASMO DISEASE IN FLAX

Pasmo disease in flax, caused by the fungus Septoria linicola, can cause significant yield loss when conditions are favorable. Recently, a fungicide label was granted for Headline fungicide. This article discusses pasmo management and summarizes a fungicide trial conducted at the Langdon Research Extension Center in 2009.

Pasmo overwinters on the flax stubble, spores are splashed or blown to plants, and infection can occur on all the above ground plant parts. Symptoms include dark brown to black lesions on leaves and dark brown to black bands on the stems resembling a barber pole appearance (Figure 1). Small black bumps can be observed in lesions.


Figure 1.

Infections may start early in the season and are favored by warm weather with some rain events throughout the growing season. The disease is very common in our region. In Manitoba, Dr. Khalid Rashid conducts regular diseases surveys; pasmo was observed in 60-100% of the fields surveyed between 1996 and 2009, with disease incidence ranging from 20% to 80% plants infected and disease severity ranging from 10% to 40% stem and leaf area affected.

Treatment plots (cv. CDC Bethune) were inoculated with pasmo by spreading infected straw collected from 2008 in the center of each plot 6-8 days prior to flowering. An impact-type sprinkler system was installed to wet the residue and to create a favorable environment for disease development. Treatments included different rates and timings of the Headline (Pyraclostrobin, BASF) and a non-treated control (Table 1). Pasmo disease was assessed on leaves on August 19th and 31st . The leaves and stems were assessed using the 1-9 scale with 1 = no sign of disease and 9 = high disease severity resulting in leaf or plant death.

By the 19th of Aug, high rates of Headline were managing disease more effectively than low rates. Similarly, late bloom applications and multiple applications were managing pasmo better than early single applications. Post bloom timings were most effective in reducing disease severity at the 31 Aug assessment date. Stem infection was managed best by later application timings and Headline rates 6 fl oz/acre or greater. All treatments increased yield and test weight except Headline at the 3 fl oz/acre. Oil concentration was increased over the non-treated with split fungicide applications of Headline, and by 9 and 12 fl oz rates of Headline at early and late bloom.

Recommendations

Fungicide application is an appropriate management strategy to protect flax plants if pasmo disease is present. Headline is labeled at the 6 to 12 fl oz/A (max 24 oz/A season) and off-label rates (3oz) were demonstrated in this trial to not be effective. The label is recommends application at mid-flowering (7 to 10 days after flower initiation) and a second application is if the disease persists or if conditions are conducive for disease development. This data generally support the label recommendations for effective management of the disease. Trials at the Langdon and Carrington REC’s are being conducted again this year. Always follow complete label instructions.

Scott Halley
Crop Protection Scientist
Langdon Research Extension Center
Scott.halley@ndsu.edu

Kevin Misek
Former Research Scientist
Langdon Research Extension Center

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

Hans Kandel
Extension Agronomist
Hans.kandel@ndsu.edu

 

Table 1. Effect of different application timings and rates of Headline for management of pasmo disease of flax in Langdon, 2009. Leaf and stem disease severity, yield, test weight and oil concentration presented.

     

Pasmo Disease Severity

     
 

Fungicide

Application

Leaves

 

Stem

Yield

Test Weight

Oil

Fungicide

Rate

Timing

19-Aug

31-Aug

31-Aug

(bu/a)

(lb/bu)

%

untreated

   

9

9

7

50.9

51.1

46.2

Headline

3 fl oz

early bloom

8.3

8.8

4.8

53.5

52.1

47.5

Headline

3 fl oz

herbicide

8.8

9

6

55.2

51.1

47.4

Headline

9 fl oz

early bloom

7.5

8.8

3.8

56.8

52.7

48.2

Headline

12 fl oz

late bloom

3.8

4.8

1

56.9

52.8

48

Headline and

3 fl oz and

herbicide and

           

Headline

6 fll oz

early bloom

6.8

8.8

3

57.4

52.3

48

Headline

12 fl oz

post bloom

5.8

5.8

1

59.2

52.6

47.4

Headline

6 fl oz

early bloom

6.5

8.3

1.8

59.3

52.7

47.4

Headline

12 fl oz

early bloom

5.8

7.5

1.3

59.4

52.5

48.7

Headline

6 fl oz

late bloom

7.3

8.5

1.3

59.5

52.5

48.3

Headline

9 fl oz

post bloom

6

6.3

1

60.4

53.4

48

Headline

9 fl oz

late bloom

4.8

7.5

1.3

60.9

52.9

48.8

Headline

6 fl oz

post bloom

6

7

1.5

61.5

53.1

47.7

LSD(P=0.05)

   

1.7

1.6

2.3

6

0.6

1.4

%C.V.

   

19.2

14.7

62.1

7.3

0.8

2

 

FUNGICIDE AND HAIL DAMAGED PEAS

In this past week I have received numerous calls about the potential for the fungicide Headline to positively impact hail-damaged peas. To my knowledge, NDSU (or any other University in the U.S.A. for that matter) has no data on hail damaged peas and any fungicide.

Fungicides are excellent tools that have been developed for disease management and/or prevention. Recently, an interest has increased in fungicide applications in the absence of disease -for physiological plant effects - (i.e. Plant Health). In NDSU trials, yield increases have been observed in the absence of disease in some crops and environments, but a yield increase has been inconsistent and hard, if not impossible, to predict. Statistically significant yield increases have occurred only in the minority of trials we have conducted at NDSU. Additionally, to the best of my knowledge, the trials NDSU has conducted in the past have been on non-hailed crops.

We do not have any data on the effects of fungicides on a hail damaged crop, and as such could not support spraying hail damaged peas with a fungicide. Fungicides are very good at managing diseases. However, when hail occurs on pea fields the most frequently observed disease is bacterial blight; fungicides will not have a meaningful effect on bacteria. There could be an increase in mycosphaerella or ascochyta, but it would be a stretch to make a recommendation on the potential increase in disease pressure. Additionally, yield potential in hailed fields can be reduced, and it seems illogical to put another input into a crop that may be significantly impaired.

 

DOWNY MILDEW IN SUNFLOWER APPEARING

Downy mildew is starting to appear in sunflowers. The disease is more common when soils are wet, so the appearance of the disease is no surprise. The disease causes a thickening of the leaves and stunting of the plant (Figure 1). The upper side of the leaves will become yellow from the stem outward (Figure 2), and on the undersides of the leaves you may see a white cottony appearance (spores) (Figure 3). An extension publication with detailed information and numerous photos of downy mildew is available at www.ag.ndsu.edu/pubs/plantsci/rowcrops/pp1402.pdf

The pathogen is soil-borne, and the infection takes place through the roots. No foliar fungicide application will rescue a plant from downy mildew. Downy mildew infected plants will usually have significantly reduced yield. However, since downy mildew plants are usually stunted and unthrifty, nearby non-infected plants may compensate. The biggest yield losses are observed when large patches of sunflowers are infected.

Many downy mildew resistance sunflower hybrids are available and widely used. However, a new race that can overcome the resistance was identified last year. It is unlikely the race is widespread, but if a downy mildew resistant hybrid has symptoms, the new race may be present. Dr. Tom Gulya is will be coordinating a survey effort this summer to try and assess the geographic distribution of the new race. However, if you observe downy mildew in a resistant hybrid, your help in this process would be greatly appreciated. If possible, please place sporulating leaves (leaves with the white cottony growth) leaves in a zip lock bag, keep cool, and mail as soon as you are able to Tom Gulya at the address below.

Dr. Tom Gulya, Research Plant Pathologist
USDA,ARS,NCSL; 1307 18th St. N.; Fargo, ND 58102-2765
Thomas.Gulya@ars.usda.gov


Figure 1.
Healthy (left) and downy mildew infected (right) sunflowers, note stunting.


Figure 2.
Downy mildew infected plant with chlorotic leaves.


Figure 3.
Downy mildew infected leaf with white-cottony sporulation on underside of leaf.

We thank you for help.

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

 

RECENT WHEAT RUST OBSERVATIONS

Stem rust was observed (M. McMullen) for the first time in ND this year, on Yellowstone winter wheat, at the Casselton Seed Farm on June 29. Incidence was 50%, severity was 5% on the flag leaves, with a only a very few pustules seen on the stems. No stem rust has been observed in any commercial winter wheat field. Samples from this variety will be sent to the Cereal Disease Lab for race identification, to determine which common race it is.


Stem rust pustules on the upper surface of a
the flag leaf on Yellowstone winter wheat.


Stem rust pustules on the underside of the
flag leaf on Yellowstone winter wheat.

Stripe rust continues to be detected in winter wheat plots across ND, with the most recent observation of severe stripe rust in Darrell winter wheat at the North Central Research Extension Center, Minot, observed by Sam Markell. Stripe rust evaluations at the Hettinger Research Extension Center, by NDSU field scout Dixie Denis, on June 29, indicated that stripe rust was found in 14 of the 23 lines in variety plots, with the highest incidence (78-90%) and severity (5-8%) in Jagalene, Hawken and Darrell, followed closely by Striker (76% incidence, 4% severity). Stripe rust severities of >40% were observed in Hawken in Cass Co. on June 29. Most of the varieties are in the soft dough stage now.

Stripe rust also was observed (McMullen) at the Carrington Research Extension Center in a few spring wheats on June 24, mostly in RB07, but at very, very low levels. Most of the stripe rust has been observed in winter wheat and spring wheat varieties not commonly grown in ND.


Stripe rust on Hawken winter wheat, Cass Co.

Common leaf rust is rarely seen so far this year in spring wheat. Low levels have been observed in Jagalene, Darrell, and a few other winter wheats.

 

FUSARIUM HEAD BLIGHT (SCAB) RISK

The Fusarium head blight risk maps indicate a moderate to high risk of infection today (June 30), but the www.wheatscab.psu.edu website indicates that the risk will go down dramatically over the next few days, primarily because of the high winds and high temperatures that are occurring today, and predicted for July 1-2.

For producers who have wheat just starting to flower, I recommend that they re-assess the risk this Friday through Monday (July 2-July 5), as the wind speeds decrease and chance of showers returns. Infection is not occurring during these days of high winds and temperatures, as even night time dew periods and relative humidities are low. When night time relative humidities are above 80% for extended times is when infection is more likely.

Producers also should not try to spray when winds are high, as this is against ND pesticide laws and also won’t do any good, as the fungicide won’t reach its target. If infection doesn’t occur within the next few days, and it shouldn’t, then, if risk returns because of return to heavy dews and low winds, producers can still apply fungicides to heads that have been flowering for a few days.

 

NDSU IPM SURVEY RESULTS, JUNE 25th

NDSU IPM scouts looked at 97 wheat fields the past week, with the average growth stage of these crops at boot, but ranging from 5 leaf up to soft dough. As in previous reports, tan spot infection is by far the most common disease observed. Only a few commercial wheat fields have shown symptoms of stripe rust, none were reported with leaf rust, and a few had powdery mildew symptoms and a few with loose smut infections.

Bacterial stripe also is common in some fields, especially in winter wheats that had tender flag leaves several weeks to a month ago.

Bacterial stripe infection close up (shiny leaf appearance and dried bacteria on leaf surface, plus some stripe rust infections).

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

 

POTATO LATE BLIGHT UPDATE

The wet spring conditions across North Dakota and Minnesota have been favorable for the development of Potato Late Blight, a disease caused by the fungal-like organism Phytopthora infestans. Late blight has been confirmed in a potato field from Dickey County in southeastern North Dakota as well as in western and central Manitoba. No late blight has been reported in Minnesota.

Late blight attacks the leaflets, petioles, and tubers of potato plants and thrives when warm days and cool nights are combined with high relative humidity. Late blight lesions (Figure 1) will generally occur 3 – 5 days after infection, and sporulation (Figure 2) will soon follow with favorable conditions. Fields should be scouted as often as possible to increase the chance of early detection. Samples should be placed in a plastic bag, kept cool, and brought to the Plant Pathology Department at NDSU for confirmation. Areas within fields that provide a favorable environment for late blight development include:

  • Low-lying areas
  • Areas next to shelter belts
  • The inner span of pivots
  • Areas around pivot tracks
  • Under the corner system on a pivot
  • Areas around power lines
  • To aid growers in their blight fight, fungicide recommendations and current late blight severity values can be found on the Late Blight Hotline at http://www.ndsu.edu/potato_pathology/ or by calling 1-888-482-7286.


    Figure 1.
    Late blight lesions on upper part of leaf.
    (Note the lesions cross the midrib of the leaflets
    and the yellow halo surrounding the lesions)


    Figure 2.
    Late blight lesion on the underside
    of a leaflet. (Note the white "fuzzy" material
    around the lesion. This is late blight sporulating)

    Nick David
    Extension Potato Agronomist
    (701) 799-8457
    nicholas.david@ndsu.edu


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