Forward oilseed rape crops need managing this autumn

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.

Robert Hurren, who advises farmers in Suffolk along with his five colleagues in Apex Agronomy, says that the autumn weather has favoured rape this year. "Most crops were early drilled into moisture and the unseasonably high temperatures have encouraged rapid growth. The earliest drilled rape has 10 leaves, but most has around 6 leaves and in my view already has sufficient canopy to go through the winter. What I want now is for the plants’ energy to be diverted into creating a more robust rooting system, so that the crop can get through the winter and withstand any drought in the spring. I don’t want much more leaf growth. This is where metconazole comes in. Our field experience shows that metconazole has the ability to promote root growth and create a more compact canopy, just what I am looking for."

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.

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.