Friday, 6 November 2020
Nurturing newly-sown pasture and targeting brushweeds
Weed management in newly sown pastures is critical to the successful establishment of ryegrass and any companion species like clovers, chicory, or plantain, as well as ensuring the productive potential and quality of the new pasture is not compromised. Of course, there are other factors important to the successful establishment of a new pasture as well, such as good soil structure, fertility and moisture, grazing management, and appropriate nutrient application.
Managing weeds effectively in the previous crop or pasture will help with the weed challenge in the new pasture. Any perennial weeds with significant root systems, such as Californian thistle or docks, should be dealt with well before the new pasture is sown. This helps ensure the spray out herbicides applied will provide a clean start for the new pasture.
Time is money, so stale seedbed techniques are not as popular, however the value of double spray out programs should not be under-estimated for some situations eg when trying to eliminate old browntop.
Timing is everything and applying herbicide before the first grazing not only means the weeds will be smaller and easier to control, but will also aid the establishment of the companion species alongside the ryegrass.
The choice of herbicide will be determined by several factors including; the range of weeds that need controlling, what species are in the pasture mix and other considerations such as the growth stage of the weeds and pasture species, prevailing weather conditions and any grazing withholding period required for the herbicide. In any case several days should be allowed after application for the herbicide to work before grazing.
It should be remembered that weeds can become more palatable to grazing animals after herbicide application. Most farmers are aware of potentially toxic weeds, however if weeds form a significant proportion of the feed available there can still be metabolic effects on grazing animals even though the weeds may not be inherently toxic.
Where there are specific weeds that are more difficult to control then it may be worth considering sowing the ryegrass alone. That way more effective herbicides could be used to control the problem weeds and the clovers/herbs could be oversown once weeds are under control.
Where clover is included in the pasture mix, there are several clover friendly herbicide options available.
An MCPB/MCPA mix, (Pasture Guard Nurture) is perhaps the most commonly used of these and is good for control of seedling thistles, buttercups, and a range of other broadleaf weeds such as fathen, nightshade, hedge mustard and shepherd's purse.
Tank mixing with flumetsulam (Aim) will improve control of other weeds such as chickweed, creeping yellow cress, mallow, oxeye daisy, sorrel, spurrey (or yarr), stinking mayweed and wireweed.
An alternative to this is a MCPB/Bentazone mix (Pasture Guard Elite). This also controls a wide range of weeds including chamomiles, chickweed, cleavers, cornbind, mayweeds, nettles, spurrey, storksbill, twin cress and willow weed as well as buttercups, fathen, nightshade, shepherds purse and thistle seedlings.
The inclusion of herbs like chicory and plantain in the pasture mix, or where these are sown alone or with clover, does limit the herbicide options. Flumetsulam (Aim) is one of the few herbicides than can be safely used over seedling chicory but is considered too damaging for plantain seedlings. Bentazone is also useful in many new pasture situations but is considered too damaging for chicory seedlings.
It is possible to use 24D amine (Pasture Guard D-Amine 720) after the first grazing. The main reason for delaying application until after the first grazing is to give the clovers time to get better established so they will tolerate the 24D amine better, and the grazing helps by reducing the leaf area of clover exposed to the herbicide. 24D may be preferred for control of specific seedling weeds, such as nettles, dock, ragwort, and willow weed or other weeds that are better controlled by 24D than MCPB, Bentazone or flumetsulam. However, 24D is more damaging to herbs and red, sub and annual clovers, so would not be the preferred option where these are part of the pasture mix.
If it has not been possible, for whatever reason, to get a herbicide applied in good time, mechanical topping can be a useful salvage operation. The new pasture species will have already suffered from the weed competition, but most annual weeds do not recover from topping/grazing as well as pasture species do.
In most situations good planning and timely actions are the key to successfully nurturing new pastures.