How to identify verticillium stripe

Researchers detected verticillium stripe, caused by the pathogen Verticillium longisporum, in canola in Manitoba in 2014. The disease is now across the Prairies and will cause yield loss.

The soil-borne fungus infects roots and travels up the water-transporting xylem in the stem. It will eventually plug the xylem, cutting off the flow of nutrients.

The Canola Encyclopedia has a disease cycle graphic.

(Verticillium stripe, caused by V. longisporum, is the verticillium disease of canola in Western Canada. Verticillium wilt, caused by V. dahliae, is a common disease in various other crops around the world.)

This Identifying Verticillium Stripe video shows you how to identify verticillium stripe and how to differentiate it from other common canola plant diseases.

field scouting guide for verticillium stripe and blackleg in canola — This field scouting guide helps you identify verticillium stripe and distinguish it from blackleg disease symptoms.

Key distinguishing features

Stem striping

When the crop is full height but still green, canola plants infected with verticillium stripe will often have a two-toned stem – half healthy and green and half discoloured and drying down. This half-stem senescence is where the “stripe” name comes from. You will not see half-stem senescing with blackleg or sclerotinia stem rot. Sclerotinia will cause stem discolouration, but it will not stripe half the stem.The only other disease to cause similar symptoms is fusarium wilt, but current canola cultivars all have resistance to that pathogen.

Stem cross section discolouration

Verticillium stripe infects roots and enters the plant’s vascular system. Verticillium hyphae and conidia fill up the vascular system, restricting the passage of water and nutrients throughout the plant. This gives the stem cross section a greyish colour that is easily confused with blackleg. We have two tips to distinguish the pathogens:

With blackleg, stem tissue infection tends to be darker and cause distinct black wedge shapes. Verticillium is lighter grey, more general throughout the cross section and can present in more of a starburst pattern.
Blackleg stem discolouration is confined to the crown area at the base of the stem. Verticillium darkening can extend well up the stem.

Stem peeling and weakening

Peeling stem skin is a symptom of verticillium stripe. Under that peeled outer layer will be the microsclerotia, often taking the shape of faint black vertical striping. Severely diseased stems may break off and can be confused with lodging. Sclerotinia stem rot will also cause weakened brittle stems, but sclerotinia will not have the stripy, speckly microsclerotia. Sclerotinia stem rot will cause the entire stem tissue to shred, not just the outer layer.

Black specks

How to collect canola samples for verticillium stripe testing video.

As verticillium infection advances, microsclerotia will form on the underside of peeling stem skin. These can be found all the way up the stem. Verticillium specks may seem similar to blackleg pycnidia, but they’re much smaller – more like powdery pepper. In some cases, blackleg pycnidia will have a purple-pinkish ooze of pycnidiospores around them. Blackleg pycnidia are also confined to a lesion no more than a couple centimetres in size. If you see pink and specks confined to a lesion, it’s blackleg.

Scouting and testing

The disease is easiest to scout just prior to or just after harvest when symptoms are most obvious. The Identifying Verticillium Stripe video provides key scouting tips for effective scouting of this disease.

For a final confirmation, some labs (PSI Labs, Discovery and 20/20) will test plant tissue for the verticillium pathogens.

Verticillium stripe infects up the stem — Verticillium stripe infects a long way up the stem, unlike blackleg which is confined to the crown.

stem cross section comparison of verticillium stripe and blackleg — Cross section comparison showing verticillium stripe, blackleg and a healthy stem.

Late season verticillium stripe symptoms: Peeling outer layer of skin with tiny black specks called microsclerotia. — Late season verticillium stripe symptoms: Peeling outer layer of skin with microsclerotia – the tiny specks.

Outer layer of canola stem skin peels back to show microsclerotia underneath — Before and after pealing the epidermis to reveal microsclerotia; Photos (and layout) credit: Justine Cornelsen

Differentiating between verticillium stripe, sclerotinia, blackleg, grey stem and fusarium wilt

wdt_ID	Plant Disease	Sclerotinia	Blackleg	Blackleg	Verticillium Stripe	Grey Stem	Fusarium Wilt
1	Species	Sclerotinia sclerotiorum	Leptosphaeria maculans	Leptosphaeria biglobosa	Verticillium longisporum	Pseudocercosporella capsellae	Fusarium oxysporum
2	Stem Symptoms and distinguishing features	Bleached white appearance. Infected stems tend to shred and shatter very easily. White mouldy growth. Black sclerotia bodies will form inside the stem.	Stem lesions with pycnidia (black spots) forming inside the lesion. Base of stem (crown) becomes woody. Cross section cut reveals blackening.	Shallow stem lesions with pycnidia	Shredding of the stem tissue. Tiny black microsclerotia form beneath the peeling outer layer.	Large purple to grey-speckled stem. Pod lesions are also possible.	Discolouration of the stems; yellow or reddish-brown streaks on stems.
3	Pod	Withered pods if branch below is infected. Sometimes white mould, lesions.	No symptoms	No symptoms	No symptoms	Grey speckled pods.	No symptoms.
4	Crown (base of stem) exterior		Cankering
5	Crown cross-section	Clean, dried down	Solid black sections, often pie shaped. Fully black in extreme cases.	Typically does not reach stem in time	Greyish hue across entire cut. Gets darker as microsclerotia build up. Can extend many inches up the stem.
6	When to scout	Prior to swath timing	Prior to swath timing, 60% SCC.	Prior to swath timing, 60% SCC	Easier to ID post-harvest	Prior to swath timing, 60% SCC.	Prior to swath timing, 60% SCC.
7	Yield Loss	Potential yield loss in a field can be determined by: % Potential Yield Loss = % Infection x 0.5	For every unit of increase in disease severity, a 17% loss in plant seed yield can be expected.	Comes in too late in the season to cause a significant impact	Does occur but no system to measure at this time.	Not known.	Varieties are resistant, rare to find.

Management

Verticillium microsclerotia are soil-borne, so steps to keep soil in place could provide some reduction in spread. Two- or three-year breaks between canola crops are good disease management in general, but verticillium microsclerotia can remain viable for many years. Plant tolerance or resistance is likely to provide the best solution, and plant breeders are looking into this trait.

No fungicide or soil amendment is known to be effective on verticillium stripe.

Blackleg and sclerotinia stem rot, if those are the diseases present, are more manageable through genetic resistance, crop rotation and fungicides.

Canola Research Hub verticillium stripe research summaries.
- It also features the Verticillium stripe: Researching a new canola disease threat blog.
The Canola Encyclopedia’s Verticillium stripe chapter provides a succinct disease overview.
This video summarizes verticillium stripe research projects.
- Also see the Verticillium Stripe in Canola – Lifecycle and Disease Severity video.
The full Verticillium Stripe Workshop recording increases understanding of this disease.

Key distinguishing features

Stem striping

Stem cross section discolouration

Stem peeling and weakening

Black specks

Scouting and testing

Management

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