Sarah Cook
The ran has set off weed germination and emergence.
In oilseed rape it is important to remove weeds before they start to compete with the crop, this is particularly important where volunteer levels are high e.g. after combine swaths. The table below details the graminicides available for use in the crop.
There are wide range of herbicide options for weed control in oilseed rape, the approach taken depend primarily on the presence of flea beetle. Where they are a threat, the trend is for post emergence treatments otherwise pre-emergence herbicides are an option. Difficult to control weeds are shepherd’s purse, poppy, charlock and crane’s bill. Poppy control is best undertaken either using Astrokerb, the timing is usually early November when temperatures have cooled, or Belkar (Halauxifen-methyl + picloram) as a split dose - 0.25 L/ha after 1st September to 31st December when 90% of the crop at BBCH 12-14. A further application of 0.25 L/ha can be 2 weeks after the first application. Alternatively a single application of 0.5 L/ha can be applied from 15th September - 31st December when 90% of the crop is at BBCH16. Other weeds controlled include cleavers, crane's-bill, fumitory, shepherd's purse, scented and scentless mayweed, field pennycress, and chickweed.
The best option for charlock control is to hope for a very cold winter or opt for a Clearfield variety where the use of Imazamox should give good control.
When applying herbicides always pay attention to weather conditions:
• If conditions are unsuitable for a pre-emergence timing, either because of very dry soil conditions or heavy rain forecast then metazachlor or co-formulations of metazachlor should be applied when the crop is at the fully expanded cotyledon stage.
• The only exception is any application containing clomazone either as the straight or in co-formulation which must be applied pre-emergence of the crop.
Table: Grass weed control in oilseed rape – contact herbicides
| Active substance | Weed growth stage | Crop timing | |
|---|---|---|---|
| Cycloxydim | 2lf<1 node | Cots to crop canopy covers weeds | |
| Propaquizafop | 2lf-1 node | cots to before flower buds visible | |
| Quizalofop-P-ethyl | 2lf<1 node | Cots to 11 weeks before harvest | |
| Quizalofop-P-tefuryl | 2lf<1 node | Cots to before flower buds visible | |
| Fluazifop-P-butyl | 2lf<1 node | 1lf to before flower buds visible | |
| Clethodim https://www.upl-ltd.com/uk/product-details/centurion-max for stewardship details. | Minimum 3lf actively growing 3lf<early tillering –amg | From 2 leaves to before stem elongation. Do not apply after the 15th October or 6 leaf stage of crop. No spring applications No crop stress or pest damage. Adequate crop waxing and crop nutrition | A 10 day no spray period is in place before clethodim. • A 14 day no spray period is in place after clethodim for other Plant Protection Products. • After 7 days, application of nutritional products and insecticides is permissible. |
Several of the key residual grass weed herbicides for use in oilseed rape are being found in water e.g. – metazachlor, carbetamide and propyzamide. Unless extreme care is taken to protect water from these herbicides, there is a serious risk that their use will be restricted. The Voluntary Initiative has published information for Metazachlor, Quinmerac and Propyzamide which provides advice on how to protect water. This information can be found on the Voluntary Initiative website www.voluntaryinitative.org.uk.
| ACTION - Remove weeds before they start to compete with the crop - Follow the Voluntary Initiative to protect herbicides |