East: Aphid and slug pests continue to threaten crops

Generally crops look well, but we have had to work hard to achieve this! Pests continue to keep us busy during a mild autumn as we continue to chase high populations of aphids and slugs. If Mother Nature could send a cold blast it would be mighty helpful.

Hopefully temperatures are now starting to decline, but whilst conditions remain relatively mild we must stay on our toes. Slugs continue to graze some crops despite repeat doses of metaldehyde; currently later-drilled second wheats are most at risk as they establish. As conditions become cooler and wet the ferric phosphate-based pellets will become a better choice – although more expensive. These pellets work by stopping the slugs feeding. so disappointingly there is no satisfaction of finding slime trails and dead slugs, but grazing will stop.

Risk of barley yellow dwarf virus (BYDV) infection has been high this autumn. On mid-September sown Deter (clothianidin) treated crops a top up of foliar insecticide is recommended as high populations of aphids continue to migrate in the mild conditions. Non-Deter treated crops also need follow up sprays to maintain protection until the migration tails off.

Propyzamide (e.g. Kerb Flo) applications should be stalled until soils cool. Propyzamide is more effective when applied in cool conditions as this improves its persistence and weeds are more easily controlled when their growth is less active, but not entirely shut down. Firm seed-beds, high soil moisture content and recent frosts also improve the efficacy of these actives.

Phoma is now developing quickly in previously untreated crops, so any outstanding treatments should be applied soon. In crops where the phoma threshold has not yet occurred, a latent infection will be developing within the plant. In these cases a pragmatic approach to control is advised, by mixing the fungicide with a scheduled propyzamide application for grassweed control, for example.

On cereals heavy pre-emergence herbicide applications have worked reasonably well. Some herbicide “stacks” have caused transient phytotoxic effects, particularly when delayed until early post-emergence, but this is to be expected. As feared in some situations blackgrass is now emerging through these treatments. Planned autumn applications of sulfonylureas for blackgrass control (e.g. Atlantis) should be completed soon whilst the weed is still actively growing. Results can be disappointing if applied when the plant is on the verge of shutting down. Remember the usual mantra regarding the importance of good application techniques and spray times that enable the spray to dry on the leaf before the evening dew settles.

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