Where Sclerotinia is a severe problem year after year, a two-spray fungicide programme is the way to minimise its impact on rape yields, according to a Scottish agronomist.
Jonathan Cahalin of Agrovista advises farmers in both high and low Sclerotinia risk areas. "Aberdeenshire is a hot spot for Sclerotinia every year, mainly due to the crop rotation which includes vegetables, peas and potatoes, all of which suffer from Sclerotinia and all of which will add to increased disease pressure in oilseed rape. Last year 60% of crops in Aberdeenshire were affected by Sclerotinia. This year could be even worse as there will be large reservoirs of sclerotia in the soil, ready to attack susceptible crops, when the weather comes right. In other parts of the country Sclerotinia can be more of a moveable feast, but not in the North-East of Scotland."
Although the area of rape is down a little from last year the rotation is still 1 in 3, which is not sufficient to get rid of the threat of Sclerotinia. Nor is it sufficient to minimise another important soil-born disease, club root. Those farms that adopt a wider than 1 in 5 rotation could reduce the risk of both these diseases, points out Jonathan.
"The only way to control Sclerotinia adequately in high pressure areas is to adopt a two-spray fungicide programme starting with a mid flowering spray of Filan followed three to four weeks later by a second spray of Compass. In the North we have longer flowering periods and this means that the crop is exposed to disease for a longer period. A single spray can't cover this extended period," he explains.
"Filan is a good protectant fungicide that not only protects against Sclerotinia but also beefs up the control of Alternaria and Botrytis as well. It is recommended at a dose rate of 0.5 kg/ha at early to full flowering before disease symptoms are seen. Compass which contains iprodione and thiophanate-methyl has also performed well, particularly in HGCA fungicide performance trials last year when disease pressures were so high."
"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 certainly justify a two-spray programme, especially with oilseed rape pricing as it is. Perhaps a two-spray programme would have been more difficult to justify when rape was £120/tonne but at £350/tonne it is well worth protecting. We are in a New World when it comes to return on investment," say Mr. Cahalin.
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 which is 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 two or three times in the one crop, exerting pressure on all diseases with regard to resistance. It is important to give the crop a break from triazoles and use something different and effective such as boscalid. It can also be tank-mixed with a pyrethroid insecticide for pest control, unlike triazole fungicides."
According to Clare, Compass provides cost-effective control against late diseases and helps keep the canopy green for yield building. "Rates of 2–2.5 l/ha will give the best persistence, with the higher rate being used where Alternaria is the key target. In the HGCA fungicide performance trials Compass reduced the percentage of plants infected from 25% down to just 5% and its use resulted excellent yield response of over 2 t/ha when used at full rate."
Sclerotinia monitoring is well underway this season at 5 sites including one in Scotland. These sites monitor germination of the pathogen's resting stage, the sclerotia, and has proved to be a useful management tool to assess disease risk and the need for treatment. Sclerotia germination increases once the soil temperatures has reached 10˚C provided the soil surface is moist. The sclerotia then release air-borne spores which then infect oilseed rape petals. Cool April temperatures have delayed germination but once temperatures rise spore release is likely to be high in May. Farmers and advisors can access this information on the web site www.totaloilseedcare.co.uk.
Background Notes - Filan contains 50% w/w boscalid, formulated as a water dispersible granule, packed in a 2.5 kg pack. It is recommended in oilseed rape for the control of Sclerotinia stem rot and Alternaria. It is a protectant and systemic fungicide. It is recommended in high disease risk situations at early to full flowering (BBCH Growth Stage 63-65) at a dose rate of 0.5 kg/ha in 200 litres of water. It has no LERAP.
Compass contains 167 g/l iprodione and 167 g/l thiophanate-methyl formulated as a suspension concentrate, packed in a 5 litre pack. It is recommended in oilseed rape for the control of dark leaf and pod spot (Alternaria brassicae), grey mould (Botrytis cinerea), Sclerotinia stem rot and late light leaf spot (Pyrenopeziza brassica). Compass has protectant and systemic activity. It has a harvest interval of three weeks and has no LERAP.