That’s the view of Agresearch weed specialist Trevor James, who says while the weed probably won’t be much of a problem in pasture, its long seed-life and capacity to limit crop options for decades to come mean dairy farmers must sit up and take notice of MPI’s management plan.
The plan recommends stock that have had access to velvetleaf-contaminated paddocks should be put in a designated holding area for 24 hours and, if stock are to be trucked, “inform MPI of your plan to move the stock”.
Truckies need to be told effluent could be velvetleaf-contaminated and should be disposed of in a designated area. If stock are walked from contaminated paddocks the route should be accurately recorded, and there’s extensive advice on how velvetleaf-affected paddocks should be grazed.
Whether these measures will become mandatory remains to be seen but as the number of velvetleaf affected paddocks continues to climb that seems increasingly likely.
Within-farm movements from affected paddocks are also subject to the 24-hour holding period advice and subsequent movements of that mob of stock around the farm should be recorded.
MPI says the time for seed to pass through a cow is not known exactly and “somewhat a matter of probability”. What is known is that both excreted seed, and seed from ensiled crops, remains viable.
If importing lifted beet from contaminated paddocks, contractors should avoid contaminated areas, leaving at least a 1m buffer, and beet should be bought washed, if possible. Record where lifted beet is stored and fed.
Dairy NZ’s David Hodges says MPI’s advice must be followed.
“Velvetleaf is concerning because the seed can persist for decades and it survives digestion by the cow and the silaging process. When it germinates it is very invasive because it grows very rapidly and takes up space, water and nutrients that should be there for the crop.”
In pasture he says it shouldn’t pose too much of a problem because it will be easy to spot and relatively easy to treat with herbicides, although any clovers and herbs in the seed mix could be taken out by the herbicides.
However, James warns against returning contaminated paddocks to pasture, as does MPI’s management plan.
“The problem is if it was allowed to seed and you put the paddock into pasture you are not in an eradication scenario, you are merely postponing it,” James says.
“In 10 or 20 years when you next plough that paddock up you will have a problem.”
If seed is left near the surface typically more than 80% will germinate within five years and it might last 60 years, especially in America and Europe, where resistance to atrizine in maize crops is widespread. Herbicide resistance status in NZ has yet to be established.
Feeding contaminated crops
If some of your feed crops are contaminated with velvetleaf, MPI advises grazing uncontaminated paddocks first to allow grazing plans for contaminated paddocks to be formulated and assessed. It’s not clear whether that assessment will be by a ministry or other biosecurity official.
When grazing contaminated paddocks, MPI says:
• If practical, do not allow access to areas where velvetleaf seed has dropped. A buffer of at least 1m is required between possibly contaminated soil and single-wire fences.
• Do not pull and feed beet plants from contaminated areas because seed could be embedded in leaves or soil attached to the beet.
• Plan grazing to finish in a clean area of paddock to maximise chances of ingested velvetleaf seed being excreted before stock move to other paddocks.
• If multiple paddocks are infested, graze sequentially rather than alternating with clean paddocks.
• Keep the same mob of cattle on contaminated paddocks.
• Use back fences to minimise spread of soil across paddock.
• If possible, graze close to contaminated areas first, and work away so back-fences act as a secondary barrier between stock and the contaminated area(s).
• If multiple contamination sites make fencing off impractical, plan grazing to finish in a clean area. Such paddocks will need an active management plan to deal with plants that germinate the following year, including: avoiding deep cultivation; not sowing tall crops such as maize, sweetcorn, forage brassica or triticale; selecting annual crops that are harvested December-January before velvetleaf flowers.
Adapted from MPI Biosecurity Response document Velvetleaf Farm Management Advisory, released April 6. Go to www.mpi.govt.nz/protection-and-response/responding/alerts/velvetleaf/
