Light bits and heavy hits
Light bits and heavy hits
Blueprints may be out of fashion, but for sugar beet weed
control a look at two typical regimes – one for light land, the
other for heavy – is a good starting point for planning
field-specific programmes. Morley Research Centres
Martin Lainsbury serves up his recipes
Heavy land hard hits
OUR first field is a typical clay loam in Suffolk. The weed spectrum on this site is cleavers, mayweed, chickweed, and some annual meadow-grass. Like many fields in this area there is also a legacy of previous cropping, volunteer oilseed rape, to deal with.
Because the soil is heavy and travel opportunities may well be limited, a pre-emergence herbicide is essential, if only for the insurance value. But the farm is using Gaucho-treated seed so Venzar (lenacil) is not an option.
Morleys recommendation is a chloridazon product such as Pyramin DF at 2.5 kg/ha. Besides offering good early control of weeds in a wet season, if it turns out to be dry it also helps to sensitise the weeds to the first post-emergence application.
Cleavers and volunteer oilseed rape mean Debut (triflusulfuron-methyl) must feature in the programme but we would not include it in the first post-emergence spray. Cleavers will not have developed their first whorl at that time and more rape is likely to emerge, so what shall we use?
Something with good contact activity is needed to combat the emerged weeds. A mix of 1kg/ha Goltix WG (metamitron) and 1.2 litres/ha of Betanal Flo (phenmedipham) is our suggestion, applied when the first flush of weeds have fully-emerged cotyledons, with or without 0.5 litres/ha of oil, depending on the weather.
The Goltix deals with any mayweeds and annual meadow-grass that is escaping the Pyramin and should check the early volunteer rape. It will also help the Betanal Flo take out the chickweed.
Timing of the second post-emergence treatment will be 10-14 days later, by which time the cleavers will have at least one whorl. Debut at 30g/ha, phenmedipham EC at 1.5 litres/ha and 0.4 litres/ha of Venzar Flo is a good start on the cleavers, but for reliable control a total Debut dose of 60 g/ha, and more in wet seasons, is needed.
The third post-emergence spray delivers this, using an identical mixture to the second. We are using Venzar (lenacil) as Debut and phenmedipham have no residual activity and there are reports of antagonism between metamitron and chloridazon. While Venzar is the least soluble of the residuals, this heavy soil is slow to dry out.
That application will easily control all the volunteer rape present and completes a programme strong enough to deal with most weeds for under £110/ha (£45/acre). Hopefully, we can shut the gate on the crop.
Light land
little bits
FOR our second case study we move much closer to Morleys home in Norfolk, to a light sandy soil field with good drainage. Here we can travel even after rain, given normal amounts.
Our main weeds are fat-hen, knotgrass, mayweeds and black bindweed and the field is close to the farmyard. The grower is a keen sprayer so this is an ideal place to practice the little and often FAR technique. First year BBRO-funded work at Morley last spring showed how competitive this approach can be. (see p67)
Weekly applications of phenmedipham, ethofumesate and a residual component are made to very small weeds until it is no longer possible to hit them. That may be because the canopy has closed or because weed emergence is complete and all weeds have been killed.
Normally, four applications are required but this can vary by season, soil type and by weed burden. Because low rates are applied each time, the cost of a single application is not high. Therefore the cost of that last treatment which makes all the difference is not prohibitive.
The first application is made as soon as the weeds are visible. A close inspection of the soil surface is needed, as weeds will only be the size of a pinhead. If the cotyledons have expanded you have left it too late.
We recommend using a mixture based on the new phenmedipham Flo formulations as this is safer for the sugar beet. Betanal Flo at 0.5 litres/ha mixed with 0.5 litres/ha of 200g/litre ethofumesate and 0.5 kg/ha of Goltix (metamitron) can be applied at any crop growth stage as the Betanal Flo reduces any slight crop vigour effects. The key is to go at the first sign of the weeds.
Seven days later apply the same mixture but add 0.5 litres/ha of esterified vegetable oil to improve activity. Repeat as each flush of weeds emerge.
Last season three such sprays finished off all the weeds at Morley in the BBRO work and it looked as though it would be an incredibly cheap programme. But then rain stimulated a late flush, demanding a fourth application. However, even after that fourth round, the cost is only about £60/ha.
If potatoes were present in the rotation and emerged in the beet, then oil could be replaced by 0.25 litres/ha of Dow Shield (clopyralid) once the potatoes were 10cm tall. But a total of 1.0 litre/ha of Dow Shield is needed for complete control, adding considerably to the cost of the programme. However, daughter tuber viability is dramatically reduced which benefits any following crops. *
HEAVY LAND
• Clay loam in Suffolk.
• Cleavers, mayweed, chickweed, AMG, volunteer osr.
• Pre-emergence essential.
• Debut definitely at T2 and T3.
• Cost kept to £110/ha.
LIGHT LAND
• Free-draining Norfolk sand.
• Fat-hen, knotgrass, mayweed, black-bindweed.
• FAR most cost-effective.
• Repeat pinhead sprays.
• Add clopyralid for vol pots.
Morley message
Mr Lainsburys recommendations are a typical Morley approach to sugar beet weed control on two very different soil types, based on historical trial results and on recent BBRO-funded work at Morley. Members of the Norfolk-based research centre benefit by seeing work in progress, discussing individual strategies with Morley staff and often having trials information on new products before they are commercially available, he says.