Weeds are an unwanted addition to any paddock. Their emergence can seem inevitable, but controlling weeds on your farm is possible with planning and a herbicide programme. Planning your weed control strategy, before drilling, is time well spent.
Planning
Before planning, it is important to know the history of the paddocks and what weed species are likely to be present. Then consider any factors affecting the efficacy of herbicides such as soil pH, soil structure, weather, water quality, spray quality and size of the weeds. All should be considered when working out your spray programmes. A spray out with an appropriate companion herbicide can be extremely beneficial.
Drilling
Establishing a uniform population of 90,000 to 100,000 plants per hectare or nine plants per m2 is a big factor in driving high yields in fodder beet. The other factors are the correct seed rate, creating a good seed bed, and ensuring accurate drilling speeds (five to eight kph). Nitrogen (N) applications help control weeds by ensuring rapid canopy expansion to achieve closure in good time to shade out weeds.
Pre-emergence herbicides
Building up the residual herbicide levels in the soil helps your overall spray programme. The use of a pre-emergence herbicide lengthens the time available to apply post-emergence herbicides. It sensitises emerging weeds by making them more susceptible to post-emergence sprays. With herbicide resistance on the rise in New Zealand, a robust pre-emergence spray containing different herbicide modes of action reduces the chance of resistance occurring. A fine, consolidated, moist seed bed maximises the effectiveness of pre-emergence sprays.
Post-emergence herbicides
Do not delay implementing your weed control program, especially if weeds have emerged. Metamitron is a useful holding spray with its residual and contact activity, it is effective on difficult weeds like wireweed.
Ideally, you want to begin controlling weeds at the cotyledon or first true leaf stage. You do not want them growing too large. Regularly monitor the crop before following up with a post-emergence spray.
Be on the lookout for virus vector aphids and, if necessary, use an insecticide that does not kill beneficial insects.
Post-emergent spray intervals
Stay on top of your spray intervals because delays invite difficult weeds, like fat hen, to reach four-true leaves where they become much harder to control. By this time, fat hen becomes quite waxy and getting the herbicide to penetrate the cuticles becomes much harder. When weeds are under abiotic stress they will naturally become waxed up so a suitable adjuvant will be required to assist herbicide efficacy.
Best practice is trying to control weeds at the cotyledon or first true leaf stage. Check regularly. If the interval is extended, an oil or suitable adjuvant is required. Avoid crop damage by not spraying when air temperatures are above 21 degrees.
British Beet Research Organisation, Weed Control Key Messages
