Accurate placement of pre-em OSR herbicides is key

Optimum establishment and rapid early growth are increasingly important to help oilseed rape crops outgrow cabbage stem flea beetle attacks as growers face a further season without neonicotinoid seed treatments.

A healthy young crop also copes better with slugs and diseases like downy mildew, and is likely to have improved overwintering capacity, says Agrovista technical manager Mark Palmer.

Choosing vigorous varieties and sowing them into good seedbeds on well-structured and well-fed soils are obvious pointers to improve early vigour.

Good herbicide practice is perhaps a less well-known but important factor in determining crop vigour, to ensure weed competition is reduced as much as possible while minimising crop check from certain pre-emergence herbicides, says Dr Palmer.

“The key is to get as much active ingredient onto the soil as possible to optimise weed control. Pre-em sprays are very prone to drift and turbulence, which can result in poor coverage of the soil.

“We then want to keep those actives in the top couple of cm of soil, to ensure there is enough chemical present to kill emerging weed seeds and to reduce the chances of damaging the emerging crop.

“Some active ingredients, such as clomazone, metazachlor, dimethenamid-P and quinmerac, can cause phytotoxicity in young seedlings, particularly if heavy rain follows application, reducing growth rate.”

Dr Palmer recommends Remix, a long-chain paraffinic oil that reduces spray drift, improves spray deposition and increases adsorption to soil particles, improving weed control and crop safety by binding the active ingredients in the spray to the top layer of soil particles.

Improved weed control in a range of independent and Agrovista trials has typically added 0.2-0.4t/ha in yield, says Dr Palmer.

Extensive trials over several years also show that using Remix reduces phytotoxicity when added to herbicide, resulting in increased chlorophyll content of the young plants and increased plant weights.

For example, trials in Austria in 2014/15 showed phytoxicity fell from 27% to 7% when adding Remix at 0.4 litres/ha to a Centium (clomazone)/Fuego (metazachlor) mix (0.25 and 1.5 litres/ha respectively) and from 40% to 28% to Springbok (dimethenamid-P + metazachlor) at 2.5 litres/ha.

The pattern was repeated in Ukraine trials in 2016 following 25mm of rain after spraying. Phytotoxity fell from 30% after using KalifMega (clomazone + metaxachlor) at 1.25 litres/ha to 18% when Remix was added.

Total chlorophyll and caretinoids increased as a result, reaching about 7.7mg/g of dry matter in the latter plots 25 days after treatment, compared with 6.8mg/g in the herbicide-only plots.

Dry matter rose by 95% in the Remix plots, compared with 73% in the herbicide plots over the same period.

These are typical findings, says Dr Palmer. Overall, Remix-treated crops have been shown to make more of favourable September growing conditions, resulting in bigger, healthier plants with improved winter hardiness, he adds.

This can be further improved by using the spray application aid Velocity during routine autumn disease control programmes. The product, which is specifically designed to partner fungicides, reduces spray drift and contains a blend of adjuvants that improve coverage over the leaf surface and increase penetration through oils that soften the outer leaf layer and aid penetration and organo-silicones that improve coverage.

This not only results in better phoma control, as illustrated in Agrovista’s own and independent trials over many years, but also improves root growth.

“Velocity alters the shoot to root ratio, increasing the root mass,” says Dr Palmer. “For example, in trials in the Czech Republic in 2012, roots accounted for 15% of the total dry matter in untreated plots. Adding tebuconazole increased that fraction to 18%, while the same fungicide plus Velocity raised it to 21%.

“The result is an increase in the root neck diameter of the oilseed rape plant,” says Dr Palmer. ‘We want a diameter of 5-6mm in late autumn – plants of this size have a much greater chance of survival.”