Crop Watch: Cold weather welcomed by agronomists

The recent cold weather has been welcome, say this week’s Crop Watch agronomists, checking forward crops and high disease levels.

“The cold weather has finally brought the green area index (GAI) of oilseed rape crops back to somewhere close to where we would expect them to be at this time of year,” says Tim Bullock of Agrovista, working in the south. “Over the last month they have lost 0.75-1.0 GAI.

“It has helped with weed control, allowing carbetamide applications to hit the ground where needed and activating bifenox on charlock,” he says.

Unfortunately the cold weather has brought pigeons with it, adds Mr Bullock, although they are still lower than he would expect for this time of year.

“As long as they aren’t eating the crown of the plants they won’t be doing any major damage, however, be ready to control them,” he says.

Despite the cold weather Paul Sweeney, an independent agronomist covering Cheshire and Lancashire, expects aphid numbers to remain high.

“Unless this bit of winter lasts and we get some serious cold without snow cover, we can expect the risk of barley yellow dwarf virus (BYDV) to be really high,” says Mr Sweeney.

This is situation that has been witnessed in trials by South West Agronomy’s Stephen Harrison. “In South Wales in a BYDV trial, untreated plots and the guard area around those plots were heavily infected,” he says. “Plants in these areas had roughly half the biomass of those in the treated areas.”

In the East of the country, disease levels have been on the rise, particularly yellow and brown rust. “Many had resisted the urge to apply a fungicide up until this point on the advice of experts,” says Brian Ross of Frontier.

“This spell will certainly put a brake on things and may well bring things back to where they should be disease wise. Time will tell,” says Mr Ross.

The use of a robust T0 treatment will still be the key to fungicide programmes, says Mr Bullock. “Disease risk is still high,” he says. “The longer the cold weather lasts though, the more normal timings will become for disease programmes as at the moment things will start considerably earlier.”

Plant growth regulation and nitrogen programmes will have to be planned carefully to reduce the lodging risk later in the season says Mr Harrison.

“Don’t forget that the HGCA lodging rating is not an absolute figure and can vary by several points depending on sowing date and shoot numbers.

“Root lodging is likely to be most severe in early sown, over thick crops so take every step to keep them in check,” he says.

Fungicide choice is also an interesting debate, with new SDHI chemistry available to growers this year.

“None of the older fungicides have retired yet, but a few are showing their age,” says Mr Harrison. “The triazoles certainly need more help to be as effective as they were 10 years ago.”

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