Still going strong controlling volunteer potatoes and thistles in sugar beet – Dow Shield 400

Sugar beet is an uncompetitive crop, particularly during the first eight weeks of growth when weeds with a high biomass can establish and compete. These weeds, volunteer potatoes and thistles, as well as competing for nutrients can impede crop growth create shade, block out sunlight and have a detrimental effect on yield. Research shows that 5 potato volunteers per square metre can result in yield loss of 16.5 t/ha of beet, as well as running the risk of being a source of potato blight and Potato Cyst Nematodes (PCN).  “Because there is an overlap between sugar beet and potato growing areas, beet will always run the risk of potato volunteers as a potential weed problem,” according to Peter Waite from DowDuPont.

Economics dictate that growers strive for yield to optimize margins. This year’s 2017/18 harvest saw the national yield increase to 83.4 t/ha up from 79.8 t/ha in 2016/17. “It’s important to constantly review both fixed and variable costs to maximise margin.” Peter advises against trimming some variable costs such as herbicide inputs as this may lead to a reduction in yield. He says this means using the right herbicide early and often enough on the most competitive weeds, particularly those that grow above the canopy. “It is widely documented that one tall weed per square metre can cost 11% of yield. So we need to deal with these to make a difference to gross margins.”

“Dow Shield 400 (clopyralid) is the most important herbicide to reduce volunteer potatoes in sugar beet. We have seen best control is achieved by making the first 0.25 L/ha application when emerging volunteer potatoes are 5-10cms tall, followed by another application at 0.25 L/ha 7-10 days later,” says Peter.

Another tall weed which is a real nuisance are thistles.  “Just one creeping thistle stem per square metre can reduce beet yields by 1 t/ha. Dense stands of tall sappy stems compete directly with the sugar beet and weed control should start when the weeds are small.”

“Creeping thistles, spear thistles and sow-thistles can all be controlled by Dow Shield 400 at 0.25 L/ha applied to weeds at rosette stage followed by an application of 0.5 L/ha 3-4 weeks later to complete creeping thistle control. Consider combining your first spray with metamitron programme, this not only controls thistles but also boosts the performance of your programme against key annual weeds such as polygonums. In addition Dow Shield 400 will control corn marigold, groundsel, pineapple weed, scented mayweed, scentless mayweed, black-bindweed, pale persicaria and redshank.”

Peter reminds growers that Dow Shield 400 has been reformulated into a double strength formulation and is available in a bottle container with no induction seal or foil to get rid of. “Dow Shield has been available to growers for over 42 years and it has covered all the hurdles for re-registration. It will be around for a few more years yet.”

The NFU sugar board reminds us that the UK sugar industry is one of the most efficient in the world, contributing £700 million to the economy each year, supporting 9,500 jobs.

“UK sugar prices are strongly correlated to world prices, which brings more volatility and the need to produce high yields to make profits,” says Peter.


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About The Author

John Swire - Deputy editor of Agronomist and Arable Farmer as well as responsibility for the Agronomist and Arable Farmer and Farm Business websites. After 17 years milking cows on the family farm John started writing about agriculture in 1998 and has since written for a variety of publications and has developed a wide circle of contacts within the industry. When not working John is a season ticket holder at Stoke City and also of late has become a fitness freak, listing cycling, swimming and walking as his exercises of choice.