Post-drilling and pre-crop emergence, an application of two litres/ha of Nortron (ethofumesate) is a good start to a control programme, delaying weed emergence.
Clomazone – as in Magister or Director – is an alternative or it can be added to Nortron, helping control cornbind, groundsel, twin cress, henbit, shepherds purse and speedwells.
However, use on soil with cation exchange capacity under 10 or more than 30 is off-label and Schrader said he wouldn’t use it unless comfortably within those limits.
An insecticide should go on with the pre-emergence herbicide to protect beet seedlings from pests including nysius and springtails.
“The crop’s slow to develop and you have so few plants you don’t want to lose any.”
That slow development and wide-row spacing is why effective weed control is crucial too.
Grass weeds are easy to take out from around fodder beet but trickier are broadleaved weeds.
Other crops that are sown more densely are more competitive with weeds and soil is quickly shaded cutting weed germination, whereas beet can take three months to close across rows.
The crop is also highly sensitive to many herbicides, limiting the armoury available. Schrader said a post-emergence herbicide should be applied as soon as another flush of weeds emerges, ideally with the weeds at cotyledon to two-leaf stage.
Meanwhile, the crop needs to have at least its first true leaves emerged for it to be safe from herbicide damage, hence why the pre-emergence spray is a good idea.
“It buys you a bit of time before that first flush of weeds occurs.”
Depending on the weed spectrum a two, three or four-way mix of ethofumesate (as in Norton), metamitron (as in Goltix), phenmedipham (as in Betanal) and desmedipham (as in Betanal Forte) is the usual first post-emergence spray.
“You can buy pre-formulated products or mix your own. The danger with the mix-your-own approach is they’ve all got surfactants added and you can increase the risk of burning the crop.”
Usually a second post-emergence herbicide is needed, sometimes as little as a week to 10 days after the first.
“You need to be walking your crop weekly or more often if you can early in its development. Taking out the weeds while they are small is the key to good control.”
Product choice is similar to the first post-emergence spray but should be fine-tuned to what’s still emerging.
While many growers achieve good control with a pre-emergence herbicide followed by two post-emergence sprays, paddocks should continue to be walked weekly until the crop closes across the rows because if a late flush of weeds does emerge – fat hen is the most likely one – control will depend on spotting it early and getting another herbicide on before it’s too big.
However, once beets start forming a bulb no herbicides are approved so there’s nothing that can be done on-label if any really late flushes occur, Schrader added.
“That’s what happened with a lot of crops in the wet December and January this year.”
Herbicide history
Agronomist Dave Schrader advises engaging an agronomist to check the herbicide history of an intended fodder beet paddock going back a minimum of three years, preferably four.
Aminopyralid-based herbicides such as the Tordon range raise a red flag as do sulfonylureas such as chlorsulfuron (eg: Glean, Telar) or tribenuron-methyl (eg: Granstar, Thor, Granit).
Liming – common practice ahead of beet given its preference for pH 6.2 – can exacerbate problems, locking herbicides into the soil so they persist longer.
Dicamba within a year of the beet crop and products containing picloram can also cause problems.
“Even MCPA [herbicide] within a month or so of sowing can be a problem. It’s a complex area affected by soil type, rainfall, and cultivations so if in any doubt, get a professional agronomist to check it out,” Schrader said.
First fungicide approved
Bayer Crop Science’s fodder beet fungicide Escolta has become the first fungicide approved for use on the crop in New Zealand.
The 160g/l cyproconazole, 375g/l trifloxystrobin formulation has a recommended rate of 0.35l/ha with rust, powdery mildew, cercospora and ramularia control on the label.
“The first application should be at first sign of disease with a second application three weeks later,” Bayer’s Chris Miln said. A withholding period before grazing of 42 days is required.
The approval is subject to a maximum residue limit being established and accepted but Miln said that that should be achieved well before December, which is when the first applications are likely to be needed.
Beating weeds in beet
- Pick paddocks to avoid problem weeds
- Use glyphosate to create a stale seed bed if possible
- Pre-emergence herbicides buy time for a crop to emerge and become safe for post-emergence sprays
- Walk crops at least weekly until canopy closure
- Hit weeds as soon as possible with herbicides, ideally at cotyledon stage, and
- Little and often, and pre-formulated products are safest for crops.
