Care essential in winter oilseed rape
Growers must focus on creating an optimum sized canopy and minimising disease and weed threats in winter oilseed rape this spring, says ProCam UK Agronomy Manager Nick Myers.
With current reports of fresh Phoma infections in rape crops, particularly where the second autumn fungicide was missed when the season closed in, attention to detail is the only way to maximise yields and profits, he says.
"The cold winter put paid to some treatments and then the unseasonably warm, wet weather in January, which has seen temperatures 3-4ºC higher than the long term average, has encouraged new infections.
"There is quite a bit of Light Leaf Spot about, too. On both counts, there is a strong case for a stem extension fungicide, based on flusilazole - not least because of the high potential value of the crop this year."
A lot of winter oilseed rape crops are forward this year and there is a definite need for a PGR fungicide based on metconazole or tebuconazole, which could be combined with the flusilazole treatment, he says.
"These PGR’s take the height out of the crop and manipulate the canopy. Large canopies need reining back as they will lodge and light penetration is impaired.
"By using a PGR fungicide, the canopy structure can be optimised, making it more open and able to intercept the maximum amount of light, resulting in better yields."
Crops with a GAI (Green Area Index) of at least 1 in March or over 2 in April will give an economic response to PGR fungicides of up to 0.5 t/ha, Nick says.
"Some crops are already at GAI of 1 in the latter part of February, so action will be needed as soon as the weather warms up and ground conditions improve. Crops have not yet started stem extension, but we are just starting to see a hint of new green growth in the crown of the plant, so it won’t be long."
The GAI of crops can be measured using reference photos or by using the online tool developed by BASF and ADAS on www.totaloilseedcare.co.uk.
Although most crops are more forward than last year, some later drilled ones will not need so much PGR fungicide.
"These crops could benefit from an application of phosphite and other micronutrients to stimulate growth and help create a better rooting system. In oilseed rape, phosphite can be applied as a one shot approach early but it is better utilised as part of a programme at stem extension followed by a second application pre/early flowering."
Another activity that needs attention and planning now is the control of difficult large fleshy or climbing weeds, such as thistles, sow-thistles and cleavers, Nick points out.
"These weeds are very competitive to the crop and cause damage at harvest when they interfere with combining. Galera (clopyralid and picloram) has an appropriate weed spectrum for the early spring, including cleavers, sow-thistles, thistles and groundsel."
However, the timing for Galera can be a challenge, Nick Myers points out.
"The spray window can be quite tight. Weeds need to be actively growing and temperatures need to be warm enough. The manufacturers recommend that Galera is applied when day and night temperatures are above 6°C and rising.
"But then the herbicide must be applied before the official cut-off, which is up to flowers buds visible above the crop canopy - quite a small window of opportunity, but one worth taking if you have these weeds.
"It will be well worthwhile inspecting your rape for weeds, and indeed diseases, making a note of which fields need treatment and ordering the necessary product in advance," Nick Myers concludes.
