NDSU Extension Service - Cavalier County

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8/27/2014

Black Canola Swaths!? Smoking Combines!!
As we return to harvest most will be surprised on what will look like combines are on fire as the clouds of black smoke (dust) will be bigger than we’ve ever seen.  In 2009 we had some real black swaths of canola where it looked like combines were on fire with the heavy black dust clouds on fields that were swathed for 3 weeks or longer before harvest.  In my opinion 99% of the blackening is from what I call sooty mold.   This mold can grow on dried down pods and can spread over a plant as it dries down, leaving whole swaths looking black. This is usually just a visual problem, but it can possibly cause pods to pop. It tends not to be on green pods.

Canola pods and plants will often darken the longer they sit in the swath, especially if conditions are moist for any period of time.   These sooty molds grow on dried down pods and can be found on seed surfaces after combining. Sooty mold is loose and crumbly and brushes off easily. Many fungi can participate in sooty mold, and some are closely related to disease causing fungi. Alternaria, for example, is a common saprophytic fungus on canola and cereals.

Wheat plants that have died prematurely are also very dark colored as a result of the sooty molds.  Standing canola fields may have scattered plants that have turned black from this sooty mold are a result of the weather condition that formed this growth on dead plant tissue.   Those back plants died from something else not the black mold!  Likely, the plants died from another cause such as blackleg, stock rot, spray damage, etc.   

In summary, sooty mold is a black, non-parasitic, superficial growth. These molds are part of a naturally occurring complex of organisms that help to decay dead plant debris. Sooty molds are most common when mature crops are subjected to repeated rains and delayed harvest. This disease also may affect plants that have been damaged by root rot.

The sooty head mold growth on small grains is normally superficial and its effect on grain is thought to be minor, but it can make for dusty harvest operations. Sooty molds can contribute to a discoloration of the grain called “black point”.

Why so prolific this year?  High humidity’s the past 2 weeks was ideal for mold growth!  Humidity average since August 10th has been well over 80% while the normal average for this same period is 66%.   Only once in the past 20 years did we have humidity averages in the 80s during this same period and that was in 2009 with humidity was in the low 80s, this year it is in the high 80s.  With this comparison of conditions that favor molds it’s no wonder dead plant tissue has taken on such a black color. 

Good News:  Yields will still be high in most all canola and wheat field harvested.  For safety when around these molds wear dust masks if possible, breathing in mold is never good for anyone.

Average Humidity Past 5 Years – August 15-25

                      2014 – 86%
                      2013 – 72
                      2012 – 62
                      2011 – 65
                      2010 – 71
                      2009 – 83

Early yields reported on canola are very good and I would expect that will stay with most of our crops.  The odd canola field may be only average yield due to heavy Blackleg disease but disease like white mold are non-existent. 

Canola Clubroot Update!  
Thank you to all who have been on the lookout for clubroot in canola fields!  Those very darken small patches in fields need to be checked out even though 99% of them fortunately are not the result of   clubroot.   The key symptom beside the swollen root club is that the plants pull up very easily as there are no fibrous roots left to anchor the plants.   The easy to pull out symptom has been questioned more since our big rain events resulting in a saturated soil where most all plants pull up relatively easy.   The club below ground root is 3-5 times larger than the above ground stem) appearance is the key symptom of club root and the center of the patch with only dead plants, which died weeks ago. 

As of this writing we have 7 fields confirmed with clubroot.  Samples for those fields have been collected and sent into the lab to determine the pathogen so we know if the resistant varieties will hold up to this disease in locations where it has been found.   I think the results will be good and the resistant varieties (though only a few) will hold up well in 2015.   

Lab analysis is very important so samples should be collected from any suspicious fields. Please keep in mind dragging plants into your truck or coffee shop is not a good idea as that will potentially spread the disease further.   I can collect the samples but if it is hard to get at or you don’t want me out, place several root samples is a sealed plastic bag (root and a couple inches of stem) then bring them to my office.   Clean your boots before leaving the field and getting into your pickup! 

Keep cleaning up the equipment as well, particularly with the wet soil conditions (mud) could
spread this problem a long distance.  Fields with clubroot confirmed should not be worked or if need be the last one of the season.  If it is earlier sanitize the equipment before leaving the field (not on the road!!) as the next vehicle driving by will pick up the pathogen and will get spread further.

Determining the pathotype we have is very important when we look at what has developed in Alberta in a matter of 10 years.  Here’s the latest new release out of Canada:

New data from the Alberta clubroot disease survey indicates some forms of clubroot resistance are no longer functioning well against a possible new clubroot pathotype in the Edmonton region.

Dr. Stephen Strelkov at the University of Alberta has investigated samples collected from several fields and verified higher levels of infection than expected in some clubroot-resistant varieties. Further studies are underway to verify the true virulence of these clubroot strains.

This risk was highlighted when clubroot resistance was first introduced in Western Canada in 2009. Researchers from Sweden had earlier observed that the clubroot pathogen overcame resistance in two crop rotations. Clubroot resistance in winter canola in the U.K. was overcome in four years. And greenhouse studies at the University of Alberta showed that some types of Canadian clubroot resistance can lose their effectiveness in as few as two canola crop rotations when under extreme pressure.

For these fields in the Edmonton area, it’s like we’re back to 2003 and clubroot has been identified for the first time. Our advantage this time is experience. We know that this disease is aggressive and spreads quickly.

The good news is that we’re likely talking about very few fields and patches within those fields. Clubroot resistance is expected to be functional in the vast majority of acres this year. But attention needs to be paid to prevent this situation from expanding. A new virulent pathotype, if allowed to spread, could set us back to the start of a new clubroot infestation.

 

 

 

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