Beef + Lamb New Zealand has produced a factsheet outlining winter weed control options (PDF, 302Kb) to help growers determine the best agrichemicals for their specific situation.
A number of factors need to be taken into consideration when selecting agrichemicals, these include the age of the stand, the grazing pressure it has been under and the weed profile.
Standard control options include Paraquat, Atrazine, Simazine and Terbuthylazine.
Before spraying, lucerne stands should be grazed to remove all leaf. Ideally, rain after grazing will help wash away dirt from the surface area of both the lucerne plant and weeds, as this dirt can deactivate agrichemicals.
Application should be delayed until after any frost has thawed.
Paraquat will dessicate all green plant tissue, but it is deactivated with soil contact, so is non-residual. This means it is not effective enough on its own to kill weeds with taproots or rhizomes. It is typically used in a mix.
Atrazine has a large weed spectrum of broadleaf weeds and easy to control grasses. It has good knockdown and moderate residual activity with a soil half-life of 35-50 days.
Simazine, with a soil half-life of up to 107 days, has good residual control but has limited knockdown ability. It is recommended for use where there is not a lot of weed cover or on lighter soils.
Terbuthylazine has both root and leaf uptake with a residual soil half-life of 30-60 days. It does have a four-week withholding period for grazing. It is the best triazine to use on catsear, dandelion, storksbill, cocksfoot and grasses but it can affect lucerne so should be applied as early in winter as possible.
Other options and decision support tables are included in the factsheet.
After spraying, it is recommended that lucerne stands are left ungrazed throughout winter, as grazing will impede spring production.
While there may appear to be a green pick, these are the growing points on the plants and removing these will stop the plant from producing green leaf in the early spring period.
The plants have nodes that respond to air temperatures. In temperatures above 5 degrees Celsius, the plant will produce a green leaf which is held in compact form over winter. In spring these leaves elongate and this is what provides the high-quality spring feed that makes lucerne such a valuable forage crop.
For more information see:
- Factsheet outlining winter weed control options (PDF, 302KB)
- Knowledge Hub resources
- Sign up to our lucerne text service (note you need to be logged into the the B+LNZ website to subscribe).
- Video: management and grazing of dryland pastures with Professor Derrick Moot.