The View from Teagasc: Crops are very well established this year as many crops are knee high with full ground cover. Where weed control has not been carried
out, your options are limited once the weeds are past the two-leaf stage.
In contrast to last year, crop competition should smother most broad-leaved weeds. However, grasses, cleavers, thistles and so on, remain a serious threat. Salsa works best in mild conditions and is effective on Charlock, Runch, Cranesbill and some other difficult weeds.
Where volunteer cereals, grasses, chickweed and speedwells are the main problem, propizamide (Kerb and so on) will do a good job. Mayweeds and all the thistles can be controlled with Shield. Graminicides (Aramo, Fusilade and so on) will effectively control grass weeds but watch latest timings of Aramo on forward crops.
Canopy and disease management
Most crops are very leafy and tall. Generally there is no need for specific autumn growth regulators but assess crops for lodging risk. Plant growth regulators (PGRs) will be more effective (against lodging) when applied in the spring, so an autumn PGR will have to be followed up with a spring PGR in most cases.
Modifying your spring nitrogen strategy will do more to prevent lodging than an autumn-applied PGR. Autumn PGRs primarily influence rooting and winter
hardiness and do not slow down internal plant development.
Most rape crops will benefit from an autumn fungicide. Phoma is common this year. It looks like Septoria in wheat (black pycnidia in a white lesion). On big leafy crops, you only need to spray when 20 per cent of plants show visible symptoms.
The threshold is 10 per cent on small crops. Light leaf spot is difficult to see in the autumn. Put some rape leaves in a warm plastic bag and see if spores (small white salt grains) appear. Spray if more than 25 per cent of leaves have symptoms.
See more details here.
0.6L/ha Prosaro (PGR effect)
0.75L/ha Folicur (PGR effect)
0.75L/ha Caramba (PGR effect)
0.4L/ha Punch C
0.4L/ha Magnello (PGR effect)
Oil seed rape in flower in April. Photo O’Gorman Photography