Early Herbicides in OSR
24 Aug 2017
Pre-emergence herbicides in oilseed rape often come under question but they have an important role to play and have been shown to increase yield potential.
The use of pre-emergence herbicides in oilseed rape, or “front-loading” herbicide costs, can be viewed as a challenge by some growers, as it means alternating between spraying, finishing harvest, cultivation work and ensuring attention to detail in the preparation of seedbeds. However, Clare Tucker, BASF Business Development Manager, explains how getting it right using dimethenamid-P products* such as Springbok, can increase yield potential.
Ms Tucker outlines the benefits of early weed control, which can also be seen here:
Why consider early herbicides?
- Oilseed rape is very sensitive to early weed competition with losses in the region of 1.0 – 2.0 t/ha not uncommon.
- Patches of weeds result in patchy crops making the timing of other inputs throughout the year difficult.
- A rapidly established crop is the best defence against CSFB and the crop quickly becomes competitive, helping to suppress later weed germination. Other benefits of good, even establishment include – easier disease control and better tolerance to slugs, pigeons and wet winters.
- The main post-em option, Astrokerb, is typically applied in November, when spraying conditions can be poor and it has key weed gaps (e.g. shepherd’s purse, cleavers, crane’s-bill and established speedwells and deadnettle). Even where Astrokerb is planned, a reduced dose early herbicide will allow good early crop growth and better overall weed control.
- Paying attention to the seedbeds favours both crop and herbicide. A good seedbed increases the reliability of the herbicide and offers flexible rate options.
Why Dimethenamid-P (DMTA-p) products?
Wider weed spectrum
- DMTA-p controls the same range of broad-leaved and grass weeds as metazachlor. In addition, it’s strong against crane’s-bill (all species), shepherd’s purse and adds to poppy and cleaver control. For the best persistence against poppies and cleavers, include quinmerac.
- DMTA-p provides a good start to the black-grass programme. If the seed bed is good, a product such as Shadow can give 80% control. Surviving black-grass plants don’t grow so quickly, making them an easier target for the next herbicide applied and increasing the likelihood of better control.
More reliable control
- DMTA-p products are less affected by drier conditions, a common occurrence in early autumn. DMTA-p is taken up by both roots and young shoots of the weed; metazachlor is taken by the roots. DMTA-p is not so reliant on ‘chasing’ the roots down through the soil but waits for the shoots to reach it.
- DMTA-p products can be used pre-emergence or ‘just at emergence’
- For applications pre-emergence of the crop, ensure 15mm cover of settled soil, or for applications at emergence, spray at expanded cotyledon, just as rows become visible.
- To get the best weed control DO NOT delay any further. The temptation is to delay the ‘just at emergence’ spray, in order to tank-mix with a graminicide for volunteers – this compromises weed control.
In all cases, do not apply if heavy rain is forecast within 48 hours of planned application – wait until afterwards, particularly if the soil is very dry. In addition to crop safety, this adheres to the ‘H20 OK?’ VI water protection guidance to reduce metazachlor loss to water.
Some autumn and winter applied pesticides can be lost from the field when drains are running, so drained land is much more likely to pose a risk to water than undrained land.
To reduce this risk on drained land including mole-drained:
- Where possible, avoid use of metazachlor or quinmerac after 30th September and do not use after 15th
- In high risk areas (ie. Drained fields in Safeguard Zones) do not use metazachlor or quinmerac after 30th September.
*Dimethenamid-P products include: Springbok (dimethenamid-P + metazachlor), Shadow (dimethenamid-P + metazachlor + quinmerac), Elk (dimethenamid-P + metazachlor + quinmerac), Katamaran Turbo (dimethenamid-P + metazachlor + quinmerac), Tanaris (dimethenamid-P + quinmerac), Topkat (dimethenamid-P + quinmerac), Banastar (dimethenamid-P + quinmerac). All products are registered trademarks of BASF
Astrokerb contains aminopyralid + propyzamide.