Disease Forecasting for Sclerotinia White Stem Rot in Canola

Around five million acres of canola are now grown annually in Alberta. Sclerotinia white stem rot is one of the most destructive diseases of this crop. To help canola growers predict outbreaks of sclerotinia white stem rot, a disease forecast system was developed. The forecast system is a checklist that assists growers to make a decision on the need for applying a foliar fungicide. The check list came into being as a consequence of disease control trials carried out in 1981 and 1982.

Table 1. Control of sclerotinia with aerial application of fungicide in canola

Fungicide	Produce rate		Minimum water volume
	(grams/acre)	mL/acre	ground	air
Benlate	405 - 605		32 - 40 L/ac	16 L/ac
Rovral	400 - 600	800 - 1200	40 L/ac	18 L/ac
Ronilan	310 - 415	–	–	16 L/ac

Figure 1. Canola field in 1 to 2 per cent bloom		Figure 2. Canola field in 30 per cent bloom

1.	Have you had good looking crops at flowering and poor yields at harvest, even though growing conditions were favorable?
	Yes – 20	No – 0
2.	Have you seen sclerotinia stem rot in your crops in previous years?
	Yes – 20	No – 10
3.	Have you heard of sclerotinia problems in your area in the past two to three years?
	Yes – 10	No – 5
4.	Have you seen black sclerotes in your harvested seed in the past two to three years?
	Yes – 20	No – 10
5.	In previous years have your canola crops lodged?
	Heavily – 20	Moderately – 10	Lightly – 0
6.	Do you see large swaths at harvest but get low yield?
	Yes – 10	No – 0
7.	If you sprayed a sclerotinia fungicide in previous years, what were the results?
	Better crop – 20	No difference – 0
. Total points for section one ______________ If you scored 60 or more in this section you probably had sclerotinia stem rot in your canola crops. Proceed to section two with a 60 or more score.
. Section two .
8.	When you walk through the crop during the morning at the beginning of flowering, are your boots and pant legs wet when you come out?
	Yes – 20	No – 10
9.	Have you had wet weather in the immediate areawithin 2 to 3 weeks prior to flowering that allowed the soil to remain moist for extended periods?
	Yes – 20	No – 10
10.	Were apothecia found in the field, around the field, or in any neighbouring cereal or canola fields where canola was grown in the previous 1 to 3 years?
	Yes – 20	No – 10
11.	Do you feel it will be dry throughout the flowering stage of the crop?
	Highly likely – 0	Moderately likely – 10	Not likely – 20
. Total points for section two ______________ . If you had a high score in section one and more than 50 for section two, you should consider applying a fungi-cide to protect your crop against sclerotinia stem rot.
. Section three .
12.	What is the condition of your stand of canola in terms of height, vigor and uniformity?
	Excellent – 20	Good – 10	Fair – 5........................Poor – 0
13.	When you walk through your crop, how dense is the canopy?
	Light – 0	Moderate – 10	Very dense – 20
14.	What is the yield potential of the stand?
	10-20 bu/ac – 0	20-30 bu/ac – 10	Greater than 30 bu/ac – 20
15.	In previous years, when your yield potential was30+ bu/ac, what were the actual yields?
	Greater than 30 bu/ac – 0	20-30 bu/ac – 20
. Total points for section three ______________

Figure 3. Apothecia – the fungus spore producing structures at the base of the crop		Figure 4. Apothecia arise from sclerotes, which may be buried in or on the soil surface (a dime)
.
Figure 5. Canola petals fall into leaf axils		Figure 6. Infection takes place in leaf axils if untreated

• Direct combining.
• Do not swath immature stands (at least 30% of the seed must be ripe).
• Do not swath if rain is in the immediate forecast.
• Avoid compacting swaths.
• Use a high cut to allow for better drying.
• Avoid heavy swaths on the turns.

Figure 7. Heavy infection can occur particularly if the crop lodges		Figure 8. Sclerotinia infection can occur under swaths especially during wet harvest seasons
.
Figure 9. Sclerotes may be harvested with the grain, but most are left in the field