East: Phoma and LLS threat increases in oilseed rape


Mild weather so far this autumn would suggest an early onset of phoma, but dry conditions have delayed the disease.  Two weeks with wet weather now mean close monitoring of OSR crops is required.  Phoma can move 5mm/day at 15?C therefore to prevent the disease travelling to the axial and causing cankers later on, smaller leaved, backward crops should be prioritised.  In some cases this may be a percentage of the total field population as dry weather has caused uneven emergence in places; some crops still range from cotyledon to two true leaves plants within a field.

Now is also the time to refer back to HGCA varietal resistance scores for both phoma and light leaf spot (LLS).  Being aware of a crops susceptibility to LLS infection in early November whilst bearing in mind thresholds for phoma now will enable planning of an efficient and cost effective autumn fungicide strategy.  Wet conditions are starting to bring down soil temperatures, which at present are around 12?C.  This is too warm for propyzamide, but allows backward crops the opportunity for more development before winter.

Winter barley crops are growing fast and can therefore be prone to manganese deficiency.  Bearing in mind soil type and seedbed consolidation, plan now for an application where the deficiency is likely to present itself; symptoms go hand-in-hand with increased chances of mildew infection, and some of the most susceptible land can also be the hardest to travel over during winter and early spring.

Conditions have been conducive to high aphid populations that can be found in many cereal and OSR crops.  Non-deter dressed crops will require an insecticide at around the 2 leaf stage, with A follow-up 4 weeks later.  Where resistance is suspected or poor control is achieved after a pyrethroid, alternative products may be required.

Across the region slugs have caused varying levels of damage.  They are certainly more widespread after higher than normal populations this spring.  Some cereals after oilseed rape have already required multiple applications of pellets to allow crops to get out of the ground.  The problem has been compounded by dry, cloddy and trashy seedbeds that have slowed crop emergence.  These remain the areas that need monitoring for ongoing problems.  Reduce the pressure on metaldehyde by using ferric phosphate pellets, targeting these applications on headlands and fields where there is an increased risk of products reaching watercourses.

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