Post-emergence grassweed control in cereals, phoma in oilseed rape and barley yellow dwarf virus have occupied our Crop Watch agronomists this week.

Phoma had reached unprecedented levels in some Sussex crops, said Tod Hunnisett, agronomist for Chichester Crop Consultancy. “In some situations, 50-60% of plants are infected with up to 10 lesions on some leaves.”

Prompt action with robust rates of flusilazole or prothioconazole was required, he warned. “Some fields, especially those with smaller plants, will need re-treating in four to six weeks time.”

Winter beans were being planted and would receive a pre-emergence residual herbicide, he said. “In the past, I’ve used pendimethalin/clomazone based mixes, but this year I’m trying some prosulfocarb with pendimethalin (off-label) – I’ll tell you the results in July.”

Seed treatment or a foliar spray should be used to protect cereals from BYDV, said Prime Agriculture agronomist Marion Self from Suffolk.

“If conditions remain mild, then early September-sown crops treated with Deter (clothianidin) should receive a pyrethroid insecticide to continue protection until aphid migration ceases.”

Blackgrass was emerging in wheat crops with some plants at the two-leaf stage or beyond, said Ms Self. “An autumn application of Atlantis (mesosulfuron + iodosulfuron) should be considered where blackgrass and sterile brome are the target weeds.” Applications should be made at the one to three leaf stage when weeds were actively growing, she added.

Phoma infection was visible in most oilseed rape crops, but small crops were most vulnerable. All untreated crops should be sprayed soon, she said.

In Devon, phoma lesions had started to appear in many oilseed rape crops, but not at the high levels reported in other areas, said Matford Arable agronomist Neil Potts.

Winter barley crops had emerged and pre-emergence herbicides appeared to be working well. However, he didn’t know if Deter seed treatments would be persistent enough to stop aphids. Monitoring weather over the next fortnight would help him decide if a follow-up aphicide would be required for BYDV control.

First and second wheats had emerged and pre-emergence herbicides had worked well. But brome species were starting to appearing in earlier-planted crops, meaning post-emergence sprays needed to be applied at optimum timings.

Potato harvest was making good progress and was nearing completion in some parts of the country, said John Sarup, senior potato consultant for SAC. “Rain has made conditions somewhat tricky in places, but generally the amount of soil going into store has been minimal.”

Size and quality was inconsistent with signigicant differences in yield. “Interestingly, there seems to be a trend towards crops grown from larger seed outperforming those grown from smaller seed,” he said. “Any crops with underlying stress issues seem to have suffered worse this year and it really does bring home the fact that attention to detail is key.”

VIDEO: Marion Self’s top tips for optimising post-emergence grassweed control

See our Crop Watch reports in full:

• West: Drilling “completed” in superb conditions
• South: Phoma continues to spread
• East: Autumn workload is back on track
• Spud special potato yields extremely variable