A leading East Anglian agronomist from the newly formed affiliation of independent agronomists, Apex Agronomy, will be applying SunOrg Pro (metconazole) to the majority of his winter oilseed rape this autumn as most of his crops are already over 5 true leaves and need managing to create the optimum canopy for maximum yields.

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Robert also points out that, in addition to the positive PGR effects, metconazole also has good Phoma activity. "I have seen very few Phoma lesions in the field as yet, but the added disease control will be welcome – a double benefit."

As forward crops are those that will benefit from growth regulation the most, Robert estimates that around 70-80% of the rape he looks after this year will receive metconazole. "This is the first year in the last four years where I can foresee most crops benefiting from autumn metconazole."

"Last year although crops looked well in the autumn, the winter closed in very early, lasted for a long time and was very cold. The previous two years saw very difficult drilling conditions and poor establishment leading to small crops. Such crops didn’t need PGR’s. The few crops that won’t require metconazole this year are those that were later drilled and struggled in the dry conditions or are suffering from rabbit, pigeon or slug damage." he says.

"In these circumstances I would avoid using a PGR fungicide, but will use an alternative fungicide with no growth regulatory effects such as prothioconazole, if and when Phoma problems become more severe. If high levels of Phoma and Light Leaf spot do develop, I will add in prothioconazole to the metconazole for its curative activity."

With the vast majority of rape crops giving full ground cover now, we need to focus on increasing roots and not increasing the canopy, he advises.

ADAS research supports canopy manipulation

Dr. Peter Berry of ADAS agrees that there are many more advanced rape crops that will require growth regulation this autumn. "Research work by ADAS has shown that small canopies produced the best yields and the autumn is the time to start manipulating big crops to optimise these canopies."

Dr Berry points out that metconazole is a proven PGR fungicide. "Metconazole inhibits the plant hormone gibberellic acid, which slows down stem elongation and reduces leaf expansion. Metconazole regulates plant height, keeping the canopy closer to the soil, and reduces stem extension. This helps the crop through the winter. Shorter and thicker lower stems mean better winter hardiness resulting in crops which are also less prone to lodging. Metconazole also increases rooting at depth which helps anchor the plant and may help the plant withstand drought in the spring."

This year Dr Berry thinks that many rape crops are already way too big and will need two PGR applications, one in the autumn and one in the spring. "What we are trying to do is to create an optimum sized canopy with a Green Area Index (GAI) of 3.5 at flowering, so that yields are maximised. At the moment we are seeing rape crops that are already well over 2 GAI and there is a clear danger they will overshoot. Advanced crops need to be regulated now in the autumn with a very effective PGR fungicide to have a chance of keeping them down to the optimum GAI later in spring. Our trial results have shown that metconazole fits this bill perfectly."

Sunorg Pro’s double benefit of growth regulation and disease control is needed in many rape crops which have established well and are advancing rapidly this year.

Sunorg Pro contains 90 g/l metconazole, formulated as a soluble concentrate and packed in a 5 litre pack. It is recommended in winter oilseed rape, spring oilseed rape, winter wheat, winter barley and spring barley, field beans, peas and lupins. Sunorg Pro is a broad-spectrum fungicide with curative and protectant activity. In oilseed rape, it can be applied as soon as diseases develop at a dose rate of 0.8 litres/ha in 200 litres of water. It is subject to LERAP B.