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| Wednesday, January 03, 2007 |
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Frequently Asked Questions - Sclerotinia Stem Rot Forecasting in Canola What
is the risk of sclerotinia in canola in 2006? To get an answer
to your own question, click here
What is the risk of sclerotinia in canola in 2006? The risk of sclerotinia is moderate in 2006 in the main canola production regions of the province. The conditions that favour sclerotinia infection are: (1) the release of air-borne ascospores during canola flowering, and, (2) prolonged rainfall before and during canola flowering. Fungicide control of sclerotinia stem rot in canola will not be effective once the symptoms are observed, so it is important for growers to assess their sclerotinia risk at early flowering. The best control measure is a couple weeks of dry, warm weather during the bloom of canola. Apothecia are small mushroom-like structures that germinate from sclerotia (the over-wintering body of the fungus) at the soil line. Figure 1 below shows that apothecia are shaped like golf tees and have a flesh tone colour. The cap is about 1-4 mm diameter across and they are produced on short stalks. The recent wet conditions and moist soil surface have favoured the production of apothecia. Apothecia release ascospores, which become airborne. Ascospores use canola petals as a food source, carrying the disease down into the canopy with petal drop (Figure 2).
What yield loss can be expected from sclerotinia? The rule of thumb is that yield loss is approximately one-half of the percentage of infected plants observed in a field. Of course, this is impossible to determine within a given year since symptoms aren’t visible until pod development, which is too late to be spraying with a fungicide. Hence, one has to look at typical yield losses in a region to guesstimate loss in 2005. The table below provides survey data from recent ‘wet’ years in specific regions and what an extrapolated yield loss may be:
**Yield loss is approximately ½ of disease incidence; use more accurate figures based on your experience.
What tools are available to help determine disease risk? 1. Sclerotinia Stem Rot Checklist The checklist is available on the Canola Council of Canada’s website at: http://www.canola-council.org/sclerotiniaforecast.aspx This checklist should be conducted at early flower. The checklist asks questions related to yield potential, density of the crop, history of sclerotinia in the area, and the weather forecast. 2. Petal Test Kit Petal test kits are available from Discovery Seed Labs in Saskatoon: (306) 249-4484; Email: info@seedtesting.com . The kit costs $46.95, which includes materials and instructions to sample one canola field. The purpose of the kit is to test canola petals for the presence of fungal ascospores. What foliar fungicides are registered for sclerotinia control in canola? There are four fungicides registered for sclerotinia stem rot control in canola: Lance, Ronilan EG, Quadris, and Rovral Flo. The window for application is between 20-50 per cent bloom, with optimum timing at 30 per cent bloom. The idea is to spray when the crop is as yellow as possible to ensure that the greatest majority of the petals will be covered with the fungicide. Some of these products are registered for split application, which is an advantage as it would provide longer protection if the bloom period is extended due to cool, wet conditions. I have heard that calcium controls sclerotinia, is this true? No, don’t use an unproven product that is not registered for this use. There is no valid research to indicate that calcium will control sclerotinia in canola in a field situation. Of course, the cheap price relative to fungicides is attractive, but if disease pressure is high, it will not be able to hold the disease in check. Calcium is a component of plant cells walls and the acid produced by the attacking sclerotinia fungus degrades this structure; so the theory is that applying calcium would bind the acid and prevent degradation. Some work has been done by the North Dakota State University (NDSU) on this, but disease pressure was not high enough to favour any of the treatments. The NDSU also conducted trials using calcium for white mould control in field bean. They found that calcium applied with fungicides somewhat enhanced disease control, but the belief was that calcium’s role was more that of a nutritional supplement. There is interest by researchers and agri-retailers to experiment with calcium this year, so stay tuned. How do I determine whether or not a fungicide application is economical? Canola Council of Canada research indicates that it may be economically justifiable to apply fungicide when field scouting indicates that disease levels will reach 15 per cent in Brassica napus (Argentine canola) and over 30 per cent in B. rapa (Polish canola) by crop maturity. This figure is based on an $8 return per bushel ($353 per tonne) and an application cost of the fungicide at around $22 per acre ($55 hectare). Growers can determine their own “break even” point by using the following calculations. Determining the economics of a fungicide application is difficult as it depends on the price of canola, cost of the fungicide and disease pressure – all of which are variables that change or are hard to determine. Use your own values in the formulas to determine the point where fungicide application becomes economical:
Note: Refer to Table 1 for a range of potential yield loss for your region.
If this value is lower than the cost of a fungicide application/acre – DO NOT APPLY A FUNGICIDE.
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