Short rotations and longer flowering mean high risk for Sclerotinia

Jim Rennie, Technical Director for CSC, is advising growers in Scotland and Northern England to take action against Sclerotinia and to use a two-spray fungicide programme where short crop rotations, longer flowering periods and high levels of sclerotia in the soil means higher disease risk.

"In the North we have a number of unique factors that all add up to a potentially higher risk of Sclerotinia. The first is the tight rotations in which rape is being grown, with a 1 in 4 rotation being common and rape being a key break crop. The inclusion of other susceptible crops such as vegetables, peas or potatoes in the rotation and the susceptibility of certain weed species such as mayweeds, fat hen deadnettles and cleavers adds up to increased disease pressure in oilseed rape," he says.

"The second is that we have much longer flowering periods for rape in Scotland and the North. From first petal to final petal fall can be between 7 to 10 weeks, compared with 5 to 8 weeks in the South and this means that the crop is exposed to disease for a much longer period."

"The third is the high levels of Sclerotinia we have suffered in rape in the past which means that there are large reservoirs of sclerotia in the soil, ready to attack susceptible crops, when the weather comes right. And the weather conditions are just about there, with soil temperatures moving into double digits and sufficient soil moisture."

"The way to control Sclerotinia adequately in such high pressure areas is to adopt a two-spray fungicide programme starting with an early to mid flowering treatment before disease can take hold. In the North the longer flowering periods can’t be protected by a single spray and all sprays are largely protectant, so timeliness of treatments is vital," Jim Rennie explains.

In Jim’s view oilseed rape crops in the high risk areas of Scotland will benefit from a two spray programme. "In the higher rainfall and higher risk areas at least 80% of crops would justify a two-spray programme. In my experience in Scotland in 4 out of 5 years Sclerotinia has a very significant effect on yield, but in the higher risk areas it is 7 out of 8 years."

Jim Rennie looks for consistency in performance when it comes to fungicides. "You really need to look at a whole gamut of trials and field experience over a number of years to gauge the best performers. Over many years the protectant fungicide Filan (boscalid) has been the best and the most consistent fungicide against Sclerotinia and certainly has the edge over the others. It also performs strongly in dose rate trials which gives a good indication of its longevity of activity. I would see Filan as the foundation of my Sclerotinia programme adding strobilurins or triazoles where required. For instance I may add a triazole to it if Light Leaf Spot was a particular problem or where autumn sprays were not applied."

Clare Tucker, Agronomy Manager for BASF says that Filan is the proven Sclerotinia fungicide, providing greater persistence that allows application at early flowering. "In the HGCA fungicide performance trials Filan gave one of the top performances against this disease. It also offers an alternative mode of action required in Scotland where fungicide resistance has become an issue. In Scotland triazoles are widely used for Light Leaf Spot control and can be applied a number of times in the one crop, exerting resistance pressure on all diseases. If possible , it is important to give the crop a break from triazoles at the flowering timing when all diseases may be present. If Sclerotinia is the key target, using a different mode of action such as boscalid is the preferred approach. Ideally the key Light Leaf Spot sprays should have been applied earlier; Filan will give activity against any residual Light Leaf Spot still remaining "

Clare reports that the impact of Sclerotinia in rape can be devastating, with 50% yield loss or more. Even moderate infections can result in 10-15% yield loss. "Such losses would easily justify a two-spray programme, especially with oilseed rape pricing at around £250/tonne. In addition to good disease control, Filan has been shown to produce an average extra yield of 0.25 t/ha in the absence of disease through its strong physiological effects, making it an economically viable treatment whatever the season brings. Its physiological benefits include increasing chlorophyll and nitrogen content in the pods, which increases the crops’ potential to use sunlight more efficiently and so improve photosynthesis. It also reduces the production of ethylene which plants will produce in response to stress such as lack of water and it has been shown to stimulate the plants’ own defence mechanisms. Filan offers the whole package with broad disease control (Alternaria and Botrytis in addition to Sclerotinia) and strong physiological effects, "she says.