ISSUE 8   July 2, 2009

NDSU IPM FIELD SURVEY UPDATE - JULY 1

NDSU IPM field scouts surveyed 188 wheat fields and 47 barley fields across the state for the week ending June 26. The average growth stage for wheat was still young, at late tillering, but growth stages ranged from 1.5 leaf to early flowering. In barley, the average growth stage advanced to late jointing, with a range from tillering to early heading. The range in growth stages shows the wide variation in crop development in the state in 2009.

In wheat, tan spot again was the most common disease observed, found in 87% of fields surveyed, with an average severity of 9.4%, about double the severity of the previous week’s findings. Septoria leaf blotch also was recorded in 12% of the fields, with an average severity of 6%.

Grain aphids were observed in 14 of the surveyed wheat fields, but barley yellow dwarf (BYDV) symptoms were only recorded in two fields. Scattered BYDV symptoms were observed at the Carrington Research Extension Center on June 25th.

In barley, net blotch and or spot blotch were again observed in over half the fields surveyed, with an average severity of 5%.

As the crops progress into the heading stage, field scouts will be looking for symptoms of Fusarium head blight (scab), loose smut, black chaff, ergot, and glume blotch, as well as continue scouting for leaf and stem diseases and grain insects. Only one surveyed field of winter wheat showed any symptoms of a light infection level of scab during the week of June 22-26. Scattered, but light levels of virus infections are also showing up in boot to heading wheat fields in many areas. Some of these have been positive for wheat streak mosaic virus.

 

WHEAT LEAF RUST

On June 29th, trace levels of infection of wheat leaf rust were found on Jagalene winter wheat at an NDSU/Ducks Unlimited winter wheat plot site near Lisbon, similar to the findings on Jagalene winter wheat at Ellendale, as noted in the previous Crop and Pest Report. No leaf rust was found on the other varieties at the Lisbon site on June 29th.

 

NDSU DISEASE FORECASTING SITE SHOWS REDUCED HEAD SCAB RISK, BUT STILL TAN SPOT RISK

The NDSU small grain disease forecasting web site indicates that the rainy weather the past weekend in many areas across the state bumped the risk of tan spot infection back up. Almost every NDAWN station on July 1 indicated that at least 6 hours of leaf wetness have occurred per day in the last few days. Six hours or more of dew are required for the tan spot fungus to infect.

The risk of Fusarium head blight (head scab) went down over the past week. Only a few areas that received heavy rains over the weekend had a risk of scab infection on susceptible varieties on July 1. Again, risk depends on localized weather, variety susceptibility, and crop growth stage.

For those areas that did not receive any rainfall over the weekend, and are dry, the risk of tan spot or scab remained low.

 

SOME PRELIMINARY WINTER WHEAT DISEASE OBSERVATIONS

Severe tan spot and Septoria infections were observed on most untreated winter wheat varieties in the NDSU/Ducks Unlimited winter wheat plot site near Lisbon on June 29th. For some varieties, only the flag leaf had any green tissue remaining. However, where fungicide treatment was applied at both 5 leaf stage (Stratego) and at flowering (Prosaro), an 85% average reduction of leaf spot occurred across all varieties, and leaves were visibly greener.

A few winter wheat varieties also showed symptoms of bacterial leaf blight and black chaff, primarily along plot edges where moving soil particles may have caused more wounding, allowing bacterial entry. Symptoms were light in this location, although I have heard bacterial infections are showing up in some areas where heavy rain storms went through over the past weekend. Fungicide applications do not control bacterial blight infections.

Most winter wheat varieties at the Lisbon site were in the late watery ripe stage on June 29th, a little early for good head scab evaluations. Head scab symptoms were not severe at this stage and only scattered infections were observed, in some more susceptible varieties. Joel Ransom, NDSU Extension Agronomist, will be providing a summary of data from this winter wheat plot following further evaluations and harvest.

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

 

SCLEROTINIA MAY BE A THREAT TO CANOLA THIS YEAR

Conditions may be favorable for sclerotinia infection in canola this year. For infection to occur, three environmental conditions need to be met. First, the soil needs to be moist for a week or two prior to flowering (this allows the apothecia to germinate and produce spores). The pathogen needs about of 1-2 inches of rain within 1-2 weeks to germinate and produce spores. Second, humid, foggy, or rainy conditions need to persist for a couple days while the plant is blooming (this allows the spores to geminate and cause infection). Third, sclerotinia won’t infect if it gets to hot, infection is less likely above about 85 degrees. In much of the state, there is enough soil moisture to produce apothecia. Personnel for Production Services Agronomy have found apothecia north of Minot, and I suspect apothecia are going to be formed in the NE part of the state after the recent rains.

In parts of the state canola is already blooming, and in other parts it will start very soon. If those three above conditions describe your field during early bloom, you may want to consider a fungicide application to protect the crop.

Unfortunately, we lost Ronilan® as a fungicide option. However; Endura®, Proline®, Quadris®, and and thiophanate methyl products (Topsin®, T-methyl®, Thiophanate methyl®) are available for use. We have multiple years of data on Endura®, Proline® and thiophanate methyl products, and some data on Quadris®. For management, it doesn’t really look like one product consistently rises to the top. If environmental conditions are favorable for disease, they all seem to work. The most important thing for management is to get the fungicide on at the right time. Target early bloom (20%), or at least the first half of bloom. If you miss the window, your likelihood of control goes down quickly. Always read and follow the label.

Remember, you need all three factors for disease. Even if the soil is wet, a forecast of hot and dry (low humidity as well) weather will prevent infection.

For photos of bloom stages and more detailed information on sclerotinia go to http://www.ag.ndsu.edu/pubs/plantsci/crops/pp1410.pdf.

For the 2008 ND field crop fungicide guide go http://www.ag.ndsu.edu/extplantpath/fungicide.html.

 

CANOLA RISK MAP DOWN

For those of you who have been using the risk map in previous years, I have bad news. The map is down. Those in charge of it are working on getting it up, but there is no guarantee it will happen fast enough to be useful. However, the risk assessment calculator appears to be working.

However, these two user interfaces are still based on the environmental conditions I mentioned above. You know your land better than anyone. If you think you meet the conditions and the risk assessment calculator doesn’t show it, you are probably right. The risk calculator is available at http://www.ag.ndsu.edu/sclerotinia/sclerotinia/login.html.

 

PULSE DISEASE SURVEY

Next week pulse pathologist Dr. Rubella Goswami and myself will begin a pulse disease survey in North Dakota. The focus will be on peas, but lentils and chickpeas will be surveyed as well. We will be looking for root and foliar diseases, and taking diseases tissue samples whenever possible. Our plan is to send two ‘teams’ of people out for the week, in hopes of reaching as many fields as possible. At the end of the week, we will meet for the Williston Pulse Tour on Thursday the 9th, and hopefully be able to provide a positive report of the peas.

 

MANAGING SUNFLOWER RUST

In the last week, sunflower rust pustules (uredia) have been found in sunflower fields in North Central North Dakota. This stage is the economic stage of sunflower rust, and appears as dusty cinnamon-brown pustules and dusty brown spores (Figure 1). The occurrence of uredia in fields is a couple weeks earlier than last year, and given that the crop is later in some areas, there is cause for concern. Sunflower rust has the ability to be devastating if environmental conditions are favorable and the disease is left untreated. Fortunately, fungicides are available for disease management. This article is intended to provide some critical information on the pathogen and management of the disease based on research data, observations from last year, and understanding of this and other rust systems.


Figure 1.
Sunflower rust uredia.

Assumptions. Since rust was widespread last year, it is reasonable to believe that ample inoculum to start an epidemic of rust exists in the state, particularly in areas where rust was observed last year. Additionally, since the rust pathogen has completed its sexual cycle in the last two growing seasons (evidenced by the aecial stage) we should assume that the races in North Dakota could be different than in previous years. Thus, we should assume that there is the possibility that ‘resistant’ sunflowers may no longer be resistant.

Environment. Even though the pathogen is present, and we assume the sunflower is susceptible, there is no guarantee of an epidemic. The sunflower rust pathogen needs free moisture (dew or fog) to cause infection. Rainfall itself is not necessarily important; rust can cause problems even if it dries up, but free moisture is critical. Rust likes moderate to warm temperatures. Anything below 55 or above 85 degrees is going to slow down the epidemic. Rust can spread fast in a favorable environment; the time from infection to the production of new spores in only 10-14 days in optimum conditions.

Scouting. Getting into your field and looking for rust is very important. Cinnamon-brown pustules will occur on the top or bottom of the leaves. When the plant is actively putting out new leaves, you will be most likely to find the pathogen on the lower leaves, where dew is apt to be found for longer periods of time.

Fungicides. Folicur®, Headline®, and Quadris® are all available for management of sunflower rust. All the fungicides will reduce rust, but the fungicides act differently. Folicur has good systemic activity, and has more ‘kickback’ than the other two products, and thus has more ‘curative’ activity on existing infections. As a result, Folicur® is a better product to apply if you already have a significant amount of rust in your field. Headline® and Quadris® should be thought of as protectants for rust, although they have some systemic activity. Both products are most effective if they are applied just before rust is found or when rust is occurring at a low level.

Rate. Folicur is labeled at 4-6 fl oz, Headline at 6-12 fl oz, and Quadris at 6.0-15.5 fl oz. Folicur® at 4 fl oz has has been shown to effectively manage rust in numerous crops. For Headline® and Quadris®, the length of disease management may be related to the rate. In rust trials done in North Dakota in 2008, we used a 9 oz rate for both products. Rust is a potentially serious threat to sunflowers, and I do not recommend below-label rates.

The maximum allowable rate in a season for Folicur® is 16 fl oz, 24 fl oz for Headline®, and 28 fl oz Quadris (however, if the Quadris® chemisty, azoxystrobin, is used in a seed treatment product like Dynasty® that contributes to the total allowable rate. So if azoxystrobin seed treatment was used, use 0.45 lb a.i./A to calculate the maximum allowable for the chemistry). The PHI for Folicur® is 50 days, 30 days for Quadris®, and 21 days for Headline®. However, applications made close to physiological maturity are not going to benefit the crop.

Herbicide Mixtures. With such an early occurrence of rust in some fields, there is a tendency to want to throw in a fungicide with herbicide applications. This is a potentially dangerous approach. We know fungicides should not be mixed with some herbicides (Assert®) and we have little to no data for other herbicides. Furthermore, responses from company technical representatives ranged from ‘you’re on your own’, to ‘be extremely careful’ to ‘I don’t like the idea’. Unfortunate consequences can result, especially when things heat up.

My feeling is to do a good job taking care of the biggest problems you have right now, and worry about the others when they become the biggest problem. Right now, I think weed control is the biggest problem, so do a good job with that. Timing. This is the million dollar question. We have a good idea of the appropriate spray timing when rust shows up during flowering, but have much less experience when it shows up early. Last year, personnel from industry (Vision Research Park, Northern Ag Management, some of the fungicide technical personnel) and myself watched disease progression in a field near Mohall, ND. Uredia were first found around the 4th of July, and favorable environmental conditions occurred for much of the growing season. An application of Headline® was made at the bud stage (R1), followed by an application of Folicur® approximately two weeks later at early flower (R5.1). The field averaged approximately 1400 lb/A, and we estimated the untreated strip at about 200 lb/A with unmarketable quality. There was speculation that a third application near R6 would have added some more yield. In this field, Folicur® was not labeled at the time of the first application; had it been, Folicur® would have likely been applied first and followed by Headline®.

When rust shows up later (during or after bloom), the data on fungicide efficacy is a little more clear. Approximately fifteen years ago, an Israeli pathologist developed an application threshold for Folicur®. He calculated that a spray at an average of 3% disease severity on the upper four leaves (using rust severity diagrams) would prevent economic loss. To evaluate this, and test a threshold for strobilurins (Headline® and Quadris®), timing trials were done in Langdon, Casselton, and Carrington in 2008, using Headline® and Tebuzol® (Folicur® generic), and additional fungicide trials were done to evaluate more products labeled and unlabeled products. Trials done in North Dakota in 2008 do not disagree with the 3% percent threshold for Folicur®. However, data suggested that a lower threshold (0-1% perhaps) is most appropriate for Headline®. In one timing trial using Headline® (Carrington Timing Trial 2008), disease was significantly higher when Headline® was applied a week prior to the disease symptoms, and when Headline® was applied at a severity of 7% on the upper four leaves, than an application of Headline® at approximately 1-1.5% severity. Statistically significant yield loss occurred at the 7% severity application.

In head to head comparisons (Carrington Fungicide Trial 2008) made at approximately 1.5-2% severity, all treatments reduced disease. However, rust was statistically lowest in Folicur® treated plots, statistically higher in plots treated with Headline®, and statistically higher than that in plots treated with Quadris®. Statistical differences in yield could not be measured. In a head to head comparison made within a few days of pustule development (0% severity, Casselton Timing Trial 2008), disease severity at R9 was statistically lower in plots treated with Headline® than in plots treated with Tebuzol®, although both reduced disease. However, disease severity was the same between the two products when applied at approximately 0.2-0.7% in the trial, and yield differences could not be determined.

Given this information, and what we know about the products, I believe the best threshold for a Headline® or Quadris® application is probably around 0-1%, while the Folicur® (and generics) threshold of 3% is probably appropriate. All chemicals have their benefits; Folicur ® is more effective at higher disease levels, but it is possible that the strobilurin products will protect longer, especially at higher rates.

Below are my observations and what I would recommend

1. Rust is already in some fields.

2. Don’t rely solely on resistance since we don’t know what races are present this year.

3. Scout

4. Control your weeds without fungicides (don’t mix herbicides and fungicides)

5. If rust is already present in your field.  Keep a very close eye on it. If environmental conditions are favorable, and spread is occurring, you may have to consider an early spray to protect the crop. However, if rust is light, wait until more leaves are out, or even until bud (R1).

6. If rust shows up soon in your field.  Keep an eye on dew and temperature Monitor for spread, and do not let it get out of controlConsider a spray to protect the upper leaves, perhaps as early as bud (R1) and again in early flower (R5.2 - R5.5) if the environment is favorable.

7. If rust shows up in the reproductive stages.  Keep an eye on severity in upper four leaves.  Try a 3% severity threshold for Folicur®, and a 0 to 1% (assuming rust present on mid-canopy leaves in the field) severity threshold for Headline or Quadris. If possible, wait until early flower (R5.2 or so) for the initial spray.

8. If rust shows up after flowering is complete (R6)You are most likely in the clear.

9. Don’t underestimate the disease, but don’t panic. Last year rust was very severe in some areas (Bottineau County for example), but some fields escaped totally unscathed. However, it is critical to begin scouting your fields for rust.

10. Get more information if you need advice and always read and follow the labels.

This and additional data from the 2008 ND trials is available in a research report at:
http://www.sunflowernsa.com/research/research-workshop/documents/Markell_Rust_09.pdf, or search for my name at the National Sunflower Association website to find the report.

   
Figure 2.
Sunflower rust severity diagrams.

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

 

FUNGICIDE APPLICATION FOR REDUCING LOSSES FROM PASMO DISEASE IN FLAX

Flax has been an important part of the farming landscape in North Dakota and the prairies of Canada for many years. Flax fits well in crop rotation with small grains because it is not susceptible to the pathogens that cause Fusarium head blight (scab). Flax also is seldom affected by the pathogens that cause white mold (Sclerotinia) in broadleaf crops such as canola, sunflower, dry bean, soybean, and several pulse crops. However, flax is affected by Septoria linicola, the causal agent of the pasmo disease. This pathogen infects the leaves, stems, and bolls of flax.

In 2006, the commercial fungicide Headline® (Pyraclostrobin) was applied to ‘Carter’ and ‘York’ flax varieties in the early flowering and early branching stage. The untreated flax yielded 33.5 bu/a and the Headline® treated plots 35.8 bu/a. In 2007 and 2008 the Canadian cultivars Somme and CDC Bethune and the USA cultivars Carter and York were used at the North Dakota State University Langdon Research Station to assess the effects of pasmo disease on the different cultivars. The plots were artificially inoculated with pasmo by spreading infected straw in the center of each plot 6-8 days prior to flowering at the rate of 80 grams of straw. The fungicide Headline® was applied prior to flowering, 14 days after flowering, or with two sequential applications (prior to flowering and 14 days after flowering). The cultivar Somme showed the highest level of pasmo disease in this trial. The three fungicide treatments increased total plant dry matter (not including roots), increased seed yield (see Figure), improved test weight and oil concentration of the seed, and increased the amount of fiber produced per acre.

Table 1. Test weight, oil percent, 1000 seed weight, by treatment timing averaged over four varieties, Langdon, 2007

Fungicide Timing

Test Weight

Oil

Seed Weight

 

lb/bu

%

g/ 1000

Untreated

50.7

41.1

5.02

Prior to flowering

52.1

41.9

5.43

14 days after flowering

51.7

41.4

5.58

Two applications

52.6

42.8

5.84

LSD(P 0.01)

0.6

0.8

0.13

Significant interactions (cultivars x timings x and assessment dates) were determined on leaf disease severities. Leaf disease severity at 24 Days after early flowering (DAEF) on CDC Bethune and Carter was less than 50% of the untreated control and only slightly less than 50% on York. Two sequential fungicide applications were more effective in reducing foliar disease when compared to the untreated. These results show the differences in disease susceptibility among the cultivars and between the one and two fungicide applications. Lesions from the stem disease do not become visible until much later than leaf disease lesions. The difference in effectiveness for the multiple applications may have been related to differences in susceptibility of the different cultivars.


Yield in bushel per acre averages over four flax cultivars
(Carter, CDC Bethume, Somme and York comparing untreated
flax with flax treated with Headline applied prior to flowering,
14 days after flowering and two applications at Langdon 2007
and 2008.

Fungicide application could be an appropriate management strategy to help protect flax if pasmo disease if present. Headline® is labeled for control of pasmo in flax at the 6 to 12 fl oz rate per application per acre with a maximum of 2 sequential applications (max 24 fl oz per acre). The product has a pre-harvest interval of 21 days. The label recommendation is an application at mid-flowering (7 to 10 days after flower initiation), with an option for a second application 7 to 10 days later if the disease persists or if conditions are conducive for disease development. Always read and follow the label.

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

K. Misek, Research Specialist
Langdon Research Extension Center

Sam Markell, NDSU Extension Pathologist
samuel.markell@ndsu.edu 

Hans Kandel, NDSU extension agronomist
hans.kandel@ndsu.edu

 

CERCOSPORA LEAF SPOT IN SUGARBEET

Cercospora leaf spot is the most damaging foliar disease of sugarbeet in Minnesota and North Dakota. The disease is caused by the fungus Cercospora beticola. Cercospora leaf spot results in lower tonnage, lower sucrose concentration and reduced extractable sucrose compared to healthy plants. The most common source of the pathogen is infected sugarbeet debris in the field. The fungus is spread from field to field mainly by wind. Cercospora leaf spot develops rapidly in warm, humid and wet conditions. Day temperatures of 80-90°F and night temperatures above 60°F favor disease development. Symptoms may occur about 5-7 days after infection under favorable conditions. Typical foliar symptoms are circular spots about 1/8 inch in diameter with ash gray centers and dark brown or reddish-purple borders. Research done at NDSU shows that application of effective fungicides at first symptoms, with subsequent applications based on the presence of leaf spots and favorable environmental conditions (Daily Infection Values for two consecutive days of 7 or higher – information available at http://ndawn.ndsu.nodak.edu), consistently provided the most effective and economical control.

Sugarbeet fields with more susceptible varieties (higher KWS ratings) with closed rows that are close to shelter-belts, waterways, and those close to previously infected fields should be the first to be scouted since they would be the first to become infected.

The following guidelines will help in effective disease control:

  1. The first fungicide application should be made when conditions first favor disease development or at first symptoms. If the first application is late, control will be difficult all season.
  2. Use the recommended rates of fungicides to control Cercospora leaf spot - do not cut rates.
  3. Only one application of a Topsin M in combination with a protectant fungicide (triphenyltin hydroxide) should be used in Hillsboro, East Grand Forks, Crookston, and Drayton factory districts.
  4. Never use the same fungicide or fungicides from the same class ‘back-to-back’.
  5. Avoid using fungicides of a particular class of chemistry as a stand-alone where there is known resistance or tolerance to that chemistry.
  6. Use of high spray pressure (100 psi) and high water volume 15 to 20 gal/ac will result in better disease control.

The fungicides labeled and most widely used on sugarbeet for Cercospora leaf spot control with re-entry interval (REI) and post harvest interval (PHI) are as follows:

Product

REI (hr)

PHI (day)

SuperTin 80WP and 4L

48

7

AgriTin 80WP and 4L

48

7

Headline

4

7

Gem

12

21

Inspire XT

12

7

Proline

48

7

Eminent

48

14

Topsin WSB and 4.5F

12

21

Please note that manufacturers of glyphosate do not recommend mixing glyphosate with fungicides – growers make these applications at their own risk. However, research done at NDSU indicated that the fungicides listed above mixed with glyphosate (at labeled rate) and AMS at 8 lb/100 gal did not result in any phytotoxicity and weed control was still effective (as in picture attached).

Proline is the only fungicide on the above list that will provide effective leaf spot control and Rhizoctonia root rot control if applied before Rhizoctonia infection takes place.


Plot treated with a fungicide mixed with glyphosate
and AMS at Foxhome in June, 2009.

Mohamed Khan
Extension Sugarbeet Specialist
701-231-8596
mohamed.khan@ndsu.edu


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