East: Blackgrass emerging quickly in cereal crops

Already the landscape is green with well-established rapeseed and first wheats. We have been blessed with a long, dry spell that has enabled good progress, although this has bought about its own challenges and dilemmas.

Holding back feisty growers wanting to drill earlier than is comfortable in moderate blackgrass situations is a dicey business, requiring careful negotiation and compromises. Some seed-beds have been dry and difficult and in the main these have been left until rain, resulting in the “easier” situations being drilled first into good seed-beds.  Slug activity has been relatively quiet over the last few weeks but, populations are high and activity will increase quickly as soils become moister, particularly after oilseed rape.

With no rain on the forecast it seemed too risky to hold cereal pre-emergence herbicides until the soil was moist, and so sprayers have kept pace with drilling. Blackgrass is emerging quickly and it’s my understanding that although most residuals perform less well in the dry, they perform much better pre-emergence of the blackgrass. Hopefully the dry conditions have favoured good tri-allate activity.

The amount of blackgrass in some rapeseed crops is terrifying and more “early” blackgrass sprays of clethodim and carbetamide have been scheduled this year than before. This will be followed by propyzamide later this autumn.

In cereals, aphid populations are high and easily found on volunteers. All non-Redigo Deter (clothianidin + prothioconazole) cereals should be treated for aphid/BYDV control from early full emergence; repeat treatments will be required until the end of the migration. Crops treated with Redigo Deter will be protected for at least six weeks after emergence. Early September-drilled crops will need a follow up foliar insecticide towards the end of October.

Rapeseed in my area falls into two categories; fantastic looking crops and those that are pest-beaten and or were drilled later. These need the favour of a few more warm days and nights. In some areas cabbage stem flea beetle (CSFB) remains a nuisance and continues to hold crops back. They will also need a non-pyrethroid insecticide active against Myzus persicaethe primary vector of TuYV – as populations are building and the timing of treatments will be largely driven by aphid trapping. How much activity these will also give against CSFB larvae already in the plant is not clear, but I fear it will be small.

As mid-October approaches some growers will start to consider bean drilling. Check the thousand grain weight of seed stocks and plan the seed rate according to establishment technique. Aim to establish 18 plants/sq m. Plan a robust pre-emergence herbicide tailored to the likely weed profile, post-emergence options are limited, expensive and often unreliable. Those drilling early are reminded that it is still too warm to apply Kerb.

In some beet crops rust infection is relatively high this season. Post-Christmas-lifted beet may need a third fungicide. Always check product labels for maximum doses and observe harvest intervals.

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