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ISSUE 9  June 29, 2000

 

FULL SECTION 3 REGISTRATION GRANTED FOR RONILAN ON CANOLA

    By now, almost everyone may know that a section 3 (full registration) was granted on June 21 for the application of Ronilan on canola for suppression of Sclerotinia stem rot. It has the advantage of being highly effective over a wide window of application: 20-50% bloom. Other products registered in the US and Canada provide good management when applied early, but do not provide the same broad window of application; this may be one reason for the consistent performance of Ronilan
over a wide range of locations and environmental conditions.

    Ronilan is to be applied at 20-50% bloom. Ronilan is less effective if applied after 50% bloom. It is to be used at 10.6 to 16 oz/A. These rates are consistent with the Canadian label. Ronilan has consistently provided excellent Sclerotinia management at the 12 oz/A rate. I would suggest that the 12 oz rate be used in most situations. A higher rate, such as 14 oz, might be considered under extreme conditions such as high yield potential (over 2,000 lb/A, especially if the potential is near 3,000 lb/A)
and high disease potential. High disease potential situations include a field that had severe Sclerotinia in that or nearby fields in recent years, a heavy crop canopy, and 4-5 inches of rain in the past 2 weeks.

    Ronilan was being stockpiled in the area even before the section 3 was granted. Consequently, the Ronilan in warehouses does not contain the supplemental label for canola. Growers and applicators who use Ronilan will need the supplemental label. This label is available on the website of the North Dakota Dept. of Agriculture:        

                                         http://www.agdepartment.com/pestlbl.html

and the website of the NDSU Extension Service Pesticide Program:

                                http://www.ag.ndsu.nodak.edu/aginfo/pesticid/LabelPage.htm.

 

SOFT ROT AND BLACK LEG OF POTATO

    The Erwinia bacteria that cause soft rot of potato seed pieces and also black leg of potato are favored by heavy rains shortly after potato seed pieces have been planted. Rains which cover the seed piece with a film of water establish anaerobic conditions (conditions without oxygen) around the seed piece. These conditions prevent normal healing of the seed piece, but do not affect the Erwinia bacteria. Blackleg symptoms include wilted tops, a shiny black stem below the wilted area,
and often a seed piece with bacterial soft rot.

 

SUNFLOWER DOWNY MILDEW

    Sunflower downy mildew is a water mold (see Crop and Pest Report No. 5), favored by saturated soils before or slightly after emergence. Heavy rains over the past several weeks may have triggered downy mildew in some areas. Expect to see gaps in the row from plants that died from pre emergence or post emergence damping off. Stunted plants may have yellow areas along the main veins on the upper leaf surface and a downy white growth on the lower leaf surface opposite the yellow on the upper leaf surface.

 

POTATO LATE BLIGHT POTENTIAL HIGH

    Information on the potato late blight hot line (see Crop and Pest Report No. 6) indicates that many sites, both irrigated and non-irrigated, have exceeded 15 severity values, indicating that late blight could appear soon. No late blight has been confirmed yet, but spray schedules are critical at this point.

 

ASCOCHYTA BLIGHT ON CHICKPEA

    Ascochyta blight is now present on chickpea across much of western North Dakota and eastern Montana. Bravo is not specifically registered for chickpeas, but is covered by the crop sub group "beans". Either Bravo Ultrex or Bravo WeatherStik Zn can be used. Both are labeled for dry beans and for Ascochyta. According to the fungicide branch of EPA, no supplemental
labeling is required. The other Bravo formulations cannot be used as they are labeled for beans: navy, pinto, etc. and are not registered for Ascochyta. Usually Bravo is applied at early bloom; if disease pressure is high, a second application may be needed. Bravo is a protectant and does not cure established infections. If Ascochyta appears before flowering, the first application should be made at that time. It is essential to apply as soon as the first Ascochyta infections appear.

 

SECTION 18 GRANTED FOR FOLICUR ON SUNFLOWER

    A section 18 was granted for the use of Folicur on sunflower for the control of rust. The section 18 allows for the application of Folicur at 4 fl oz/A, with a maximum of 8 fl oz/A per year. In many cases, only one application will be needed unless an application is required in the bud stage. The greatest damage and yield losses from rust occur when rust develops in the bud stage or the bloom stage. If more than 3% rust appears on the upper four leaves, then an application of Folicur will be economic. NDSU Extension Circular PP-998, Sunflower Rust, has illustrations of various levels of rust, for reference purposes.

    Folicur should not be applied within 50 days of harvest. Usually this occurs at about ray petal wilt, which is the stage at which there is no longer an economic return from the use of a fungicide.

    Sunflower rust is a hot weather disease. If cool weather continues, this disease will progress very slowly, and may not cause much damage. If hot weather develops and persists, this disease could explode and become devastating.

 

CERCOSPORA MANAGEMENT IN SUGARBEET

    The rows of early planted beets are beginning to close, which suggests that the Cercospora season is about to begin. Warm, rainy, humid weather will also increase the Cercospora potential. There are two important concepts to keep in mind with regard to Cercospora: 1) disease management and 2) resistance management. The two are closely related.

    1) Disease management. Once a canopy forms, the humidity remains high in the canopy, and conditions favoring Cercospora increase. Scouting for Cercospora is essential. Be especially careful to monitor next to last year’s beet fields, near shelterbelts and around low spots. The first application of fungicide should begin as soon as Cercospora is found in the field, or is being seen in other fields in the area. Good disease management depends on a timely first application of an effective fungicide. If the first application is late or the fungicide is not highly effective, Cercospora gets a head start and you spend
the rest of the season trying to "catch up". After a timely first application, subsequent applications should be made based on the Cercospora advisory and/or the recommended application interval for that fungicide. Fungicide rates and application intervals are discussed on pages 86 and 87 of the 2000 Sugarbeet Production Guide, also known as the "pocket guide". It may be possible to stretch intervals in dry weather if disease pressure is low, but do not attempt to stretch intervals if disease
pressure is high or if conditions are favorable for Cercospora.

    2) Resistance management requires a timely first application with an effective fungicide so that Cercospora populations stay low. For the same reason, intervals should be closely observed. Since we have a section 18 for Eminent, it should be one of the major components of a disease management program. For purposes of resistance management, Eminent should always be used in alternation with a fungicide with a different mode of action. Data from the 1999 trials clearly indicated that it would be best to start with Eminent in the southern Red River Valley (south of Highway US 2), and then alternate with TPTH. In the northern valley (north of Highway US 2), it may be possible to start with either TPTH or Eminent, and alternate with the other product; a single application of Topsin M or Benlate in a tank mix with mancozeb or TPTH could be used as the second spray. Even in the northern Red River Valley, if TPTH tolerance is high in a particular locality, I believe it would be best to start with Eminent; in areas where TPTH tolerance is low it would be possible to start with TPTH, as shown by research results. Details on resistance management can be found in the 2000 Sugarbeet Production Guide, pages 79-83.

 

USE OF QUADRIS FOR SCLEROTINIA

    Quadris fungicide provided good suppression of Sclerotinia in a 1998 North Dakota trial by Kent McKay and Jan Knodel. It has also provided good Sclerotinia suppression and yield response in some Canadian trials. Reports from last summer indicate that grower experience with Quadris was variable. Timing of application may have had a role in the varied experiences, since timing is so important.

    Timing is Critical. The Quadris label states that Quadris should be applied at 10-25% bloom, or 3-7 days after the onset of bloom. Of course, the number of days to reach a certain bloom stage will vary with temperature. The 10-25% bloom stage is a narrow window, and it would be easy to miss the window of application. Late application could lead a grower feeling that the product was not effective, when, in fact, the window of application was missed. In the 1998 North Dakota trial, Quadris provided good suppression when applied at 20% bloom at the 9.6 fl oz rate, but not when applied at pre bloom. Applications later than 20% bloom were not tested. Yield with Quadris applied at 20% bloom at 9.6 fl oz/A provided slightly better (not statistically significant) yield than Benlate, which was in the trial for comparison.

    A recent experience in Manitoba illustrates the importance of timing with Quadris. A variety trial was sprayed with Quadris last summer. Of 12 varieties in the trial, only 3 were sprayed at the 20-25% bloom stage – all others were sprayed later. Disease suppression was good in all 3 varieties sprayed within the window of application. These 3 varieties had an average of 41% infected stems in the untreated, compared to 14% in the Quadris treated plots. By contrast 8 varieties sprayed at 30-40% bloom (an apetalous variety is not included in calculations) had 39% Sclerotinia in the untreated and 32% in the Quadris treated plots. In the plots treated at 20-25% bloom, Quadris performed as well as Benlate, slightly better than Rovral, and slightly less well than Ronilan. The other three fungicides performed as well or slightly better at 30-40% bloom as at 20-25%.

    Keep in mind that Quadris has a different mode of action from the other three fungicides. Benlate also has a different mode of action from Ronilan and Rovral. According to Zeneca, since Quadris inhibits respiration, it is most effective when the fungus has a high metabolic activity, such as during spore germination and penetration. Thus, Quadris needs to be applied earlier than some of the fungicides currently used in Canada. Keep this information in mind when canola begins to bolt. Canola should be checked daily so that the onset of bloom can be recorded accurately. This information will signal that the crop needs to be sprayed with Quadris in 3-7 days, if conditions favor Sclerotinia. More information on Sclerotinia is available in NDSU Extension Report 54, Sclerotinia Stem Rot of Canola.

Art Lamey
Extension Plant Pathologist
alamey@ndsuext.nodak.edu

 

SMALL GRAIN DISEASE UPDATE

    Leaf rust: Jack Rasmussen, NDSU Plant Pathologist, rated the winter wheat nursery at Prosper on Monday, June 26th for leaf rust. He found 20-50% severity of leaf rust on flag leaves of susceptible winter wheats. Last week, Jim Miller, USDA Rust Pathologist, reported that leaf rust went from trace incidences and severities up to 20% severities and 100% incidences in a
matter of 12 days at the Casselton winter wheat plots. Mike Peel, NDSU Extension Agronomist, observed extensive leaf rust development on winter wheat in Sargent Co. on June 26.

    In spring wheats, Jerry Schneider and Matthew Gregoire, NDSU Extension Field Scouts, are now finding leaf rust at around 5% severity and 20-75% incidence in SE and SC counties. Terry Gregoire got a call from Jay Schindle, and he reported some leaf rust in Gunner spring wheat. Leaf rust has not been seen by the scouts in the NC and NW regions. Although rust levels are still generally low, they are definitely on the rise.

    Stem rust and stripe rust: Jim Miller also observed a demo trial of winter wheat varieties in Sargent Co. A winter wheat variety from Kansas (2137) had a trace level of stem rust and stripe rust, as well. Our wheats generally have resistance to stem rust; all are potentially susceptible to stripe rust.

    Septoria (Stagonospora): Septoria (Stagonospora) avenae f. sp. triticea was observed on barley plots in Fargo and Septoria (Stagonospora) nodorum was observed on wheat in plots at Fargo on June 26. Jochum Wiersma, Area Small Grains Specialist, Crookston, is also reporting Septoria spore detections. He also is seeing quite a bit of powdery mildew in lush crops.

    Head scab: On June 26 I observed some scab infections on barley heads in plots planted back into corn ground, at Fargo. Mike Peel saw low incidences of scab in winter wheat in Sargent Co.

    BYDV and WSMV: These two virus diseases are quite common in the western part of the state, as observed by Amy Dukart and Roger Ashley. Yield losses from these two virus diseases will be dependent on when the crop was infected; infection in the 4-5 leaf stage (up to 50% loss or greater) will be much more damaging than infection at flag leaf stage (5%). Nothing can be done now to contain the wheat streak. Volunteers and grassy weeds will have to be controlled this fall
to prevent spread into next year’s crops. It may be getting too late to prevent BYDV transmission by aphids, as well.

 

FUNGICIDE APPLICATION

    Wheat and barley crops with good yield potential in areas of saturated (but not drowned-out) soils are good candidates for fungicide protection this year. Diseases have been low so far, but detections are certainly on the rise.

    Questions have come in about timing of application. The optimal timing for head scab control in NDSU tests in recent years has been the early flowering period, when 10-25% of heads are showing the anthers (in barley it is when full head emergence has just occurred). See tables below. This timing has worked very well for leaf diseases, too. The tables also show it is better to err on the early side than late side, especially when fields are wet and it will be difficult to get applications on or airplanes scheduled.

Field Severity* of Head Scab when Fungicide**
applied at 3 different growth stages, Fargo ‘99

Feekes*** stage of fungicide application

Grandin HRS wheat

Munich durum

Robust barley

Untreated

7.0

32.1

3.2

10.3

1.6

16.4

1.5

10.51

0.5

3.5

1.3

10.54

7.0

22.5

1.9

LSD =.05

3.9

17.2

2.8

*Field severity = % heads infected x head severity
** Folicur at 4 fl oz/acre
*** Feekes growth stage 10.3 = 1/2 heads emerged;
10.51 = early flowering in wheat, head fully emerged in barley; 10.54 = kernel watery ripe

Effect of Fungicide* timing on Scab Inoculated Robust barley,
Fargo ‘99 (Barley heads emerged)

Timing of fungicide

treatment in relation to time of inoculation

% Scab Field severity

Untreated

7.9

Day of Inoculation

4.0

2 Days After

3.1

3 Days After

8.2

4 Days After

11.7

LSD p>0.05

5.2

* Folicur (4 fl oz/A + 0.06% Induce) applied with
track sprayer at 18 gpa, 40 psi

 

FUNGICIDE RATE QUESTIONS

    The label rate of fungicides generally provides the greatest disease control. The following table has information from one test done at Fargo in 1999. In another test in 1999, John Lukach at the Langdon Research and Extension Center compared 2 fl oz of Folicur to 4 fl oz of Folicur, applied at several flowering stages of spring wheat.

    He found that the 4 fl oz rate resulted in 2.1-2.5 more bu/acre than the 2 fl oz rate. One ounce of this product costs about $2.38. These tests were done under low scab pressure. The untreated yield at Langdon was 47.4 bu, the treated yields ranged from 59 to 74.4 bu/acre, depending on flowering stage applied and rate.

Effect of Folicur Rate on Wheat Disease and Yield

Folicur
Rate/A

%
Scab
Severity

% leaf
spot on Flag lf

 

% Leaf
rust on
Flag lf

Yield
bu/A

4 fl oz

1.6

6.5

0

44.2

3 fl oz

4.3

12.0

4.3

43.1

Grandin HRSW, field applied, Fargo 1999

Marcia McMullen
Extension Plant Pathologist
mmcmulle@ndsuext.nodak.edu

 

PLANT DIAGNOSTIC LAB

    Samples seen in the lab this past week include: Cottonwood (salt injury); Insect ID (longhorned beetle in fir); Plant ID (eastern black nightshade); Spruce (animal feeding injury, high water, Cytospora); Apricot (fireblight); Birch (transplant shock); Elm (DED); Canola (sulfur deficiency, growth regulator herbicide); Corn (Roundup drift, high salts); Durum (BYDV); Potato (rhizoctonia root rot, drowned out, mechanical injury to leaves); Soybean (growth regulator herbicide, rhizoctonia root rot); Sugarbeet (rhizoctonia seedling rot, pythium root rot); Sunflower (dinitroanaline injury, compaction, deep planting); Wheat (BYDV, common root rot, Roundup drift injury); Winter Wheat (WSMV).

Cheryl Ruby
Plant Diagnostician
diaglab@ndsuext.nodak.edu


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