Pests and diseases are beginning to take hold in oilseed rape while slug control and herbicide applications take precedence in cereals, say our Crop Watch agronomists.

In Hampshire, slugs had started to wreak havoc in cereals after oilseed rape, said Agrovista agronomist Swaran Bachoo. “Where they are damaging the crop, apply slug pellets but take into account the new guidelines for metaldehyde-based products. In my experience methiocarb slug pellets work better in wet conditions.”

Growers should also be looking out for peach potato aphids that transmit turnip yellows virus as oilseed rape seed dressings would soon be running out of steam, he said. “Turnip yellows virus has symptoms of reddish purple mottling on the leaf, and looks a little like phosphate deficiency can lead to devastating yield loss.”

Losses of 20% to 30% were not uncommon, he added. “Insecticides such as Markate (lambda-cyhalothrin) or Biscaya (thiacloprid) give good control. The latter also takes care of resistant aphids which are steadily becoming more prominent.”

In Lincolnshire, Farmacy agronomist Philip Vickers said he had seen sawfly larvae in two oilseed rape crops. “Both crops are very forward, but the pest will be closely monitored given the level of damage it can cause in a very short time.”

His blackgrass resistance test results had also arrived, allowing him to build effective pre-emergence chemical programmes for each client. “They have highlighted considerable differences in resistant populations both between and within farms,” he says. “As effective chemical options decrease, attention to detail must increase.”

In Yorkshire, leaf miner damage had been much higher than in previous years, but hadn’t yet had a dramatic effect on the crop, said Arable Alliance agronomist David Martindale.

Phoma was also appearing, but was not yet approaching the 10 plants infected threshold, he said. “Therefore fungicides are likely to be needed towards the end of the month or in early November.”

Graminicides were giving indifferent blackgrass control putting more pressure on residuals such as propyzamide or carbetamide, he added. “These need to be applied when the soil temperature is below 10C, which is likely to be later this month.”

Agronomist Dan Dines from Wessex Agronomy Services in Wiltshire was finding good activity from pre-emergence herbicides. “Where they have been applied they appear to be doing a good job, with grassweeds looking sick.”

His policy was not to apply Atlantis (iodosulfuron + mesosulfuron) to a field in two consecutive seasons. “So we are stacking residuals, a strategy that has not made easy by the shortage of flufenacet products.”

Where autumn Atlantis was going to be applied, he needed to strike a balance between waiting for all blackgrass to emerge, avoiding plants being too large when applied, and making sure conditions were mild and good for growth.

Spud Special

Potato harvest was in full swing in Scotland and soil conditions were improving slowly, said SAC’s Mike Inglis.

“On the whole, the quality of crops being lifted is good. There are a few rots, mainly water-logging related and lenticels are open in many crops which may lead to rots or disease developing if wetter weather returns.”

Common scab levels were moderate to high in some crops, but powdery scab levels were low, he said. “Some seed that has to be loaded for early export may have a problem with soil sticking to the tubers. Positive ventilation following harvest is helping to reduce this.”

In this week’s video clip David Martindale looks at leaf miner, barley volunteers and phoma in oilseed rape.