Control of volunteer potatoes and thistles in sugar beet for over 4 decades

volunteer potatoes in sugar beet 2Cast your mind back to 1976! It was the era of the Three day week and the Soweto riots in South Africa. But it would probably be remembered more for the famous UK summer drought – still the worst on record. It resulted in stand pipes in the street and plagues of ladybirds. Gardeners saw their lawns go brown; Farmers watched their crops die on their feet and sugar beet and root crops suffered. Beet yields in 1976 were down to just 30 tonnes/hectare. In 1976 there were 15,000 growers providing beet for 17 beet factories. Now 40 years later we have just 4 factories and 3,000 specialist growers growing 75 t/ha average yield. The progress in yield has been outstanding; increasing by 2% each year and that has been brought about through the introduction of new varieties and cost-effective inputs. For example now it is a quite normal and widespread practise to use several fungicides in sugar beet to not only control disease but to keep the crop greener for longer. Forty years ago no-one did this. However forty years ago sugar beet growers could use Dow Shield (clopyralid) for the very first time to control thistles. 1976 was the same year that Dow Shield was registered. Further investment saw volunteer potatoes added to the label in 1991. And growers today are still able to use this effective herbicide.

Sugar beet has always been a very uncompetitive crop, particularly during the first eight weeks of growth when weeds with a high biomass are able to flourish and compete. These weeds, such as volunteer potatoes and thistles, will impede crop growth and shade the canopy, blocking out sunlight and having a detrimental effect on yield.

“With lowering sugar beet prices, the way of making a good margin is to grow the heaviest crop you can, whilst carefully managing some key costs; for example I would advise looking at fixed costs rather than variable costs which could lead to a reduction in yield,” says Peter Waite from Dow AgroSciences. Based in Cambridgeshire, Peter says “this means using the right herbicide early and often enough on the most competitive weeds, which are those that grow above the canopy. 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.”

Being more specific, 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. This year we haven’t had sufficient winter frosts to reduce the viability of daughter potato tubers in the ground, so we will be anticipating even more volunteers than usual.”

Dow Shield 400 is considered to be the single most important herbicide to use on volunteer potatoes in sugar beet. Used as a part of an integrated control programme across the rotation, in beet it has a significant impact in reducing the populations of these weeds. Best control is achieved when applications begin when emerging volunteer potatoes are 5-10cms tall, and sugar beet is at cotyledon stage. A second application should be made when the volunteer potatoes are 10-20cm tall usually 7-14 days after the first application.

Dow Shield 400 can be used at any time during the classic sequential low dose programme at 0.25 l/ha initially with the residual metamitron plus oil spray and thereafter with other products in the programme, applied in 80 to 100 l/ha of water. Controlling these pernicious weeds with a timely herbicide programme, you can expect to protect your sugar beet yields,” says Peter. “You need to finish spraying Dow Shield 400 by the end of June,” he remarks.

Another tall weed which can be a real nuisance are thistles. “Just one creeping thistle stem per square metre can reduce the beet yield by 1 t/ha. Dense stands of tall sappy stems compete directly with sugar beet and control should start when weeds are small. Creeping thistles, spear thistles and sow-thistles are all controlled by Dow Shield 400 at 0.25 l/ha plus a coformulation of desmedipham + ethofumesate + phenmedipham at 2 l/ha at rosette stage of the crop. This must be followed up by Dow Shield 400 at 0.5 l/ha 3 to 4 weeks later. No more than 0.75 l/ha of Dow Shield can be used per crop. In addition Dow Shield 400 will control corn marigold, groundsel, pineapple weed, scented mayweed, scentless mayweed, black-bindweed, pale persicaria and redshank.”

Peter Waite reminds growers that Dow AgroSciences has continued to invest and support Dow Shield 400 through re-registration by reformulating it to double strength formulation and by packaging it in a new style container with no induction seal or foil to get rid of. “We have invested in Dow Shield throughout all the rigorous registration challenges over the last 40 years and we are anticipating that it will be around for many more years to come.”

William Martin, the NFU sugar board chairman, is optimistic for the future of sugar beet. “We have a quite a way to go to reach the theoretical potential for sugar beet yields, which is

thought to be 150 t/ha. In parts of California they are growing 120 t/ha and even in France the average sugar beet yields is 90 t/ha. Yield is down to genetics and inputs.”

“As an example, a future significant jump would come from GM beet that is winter hardy and could be planted in the autumn and with a longer growing season its yields would be potentially much higher. This year is the last year of beet quota and set prices. The UK grower is one of the most competitive growers now, with yields in sugar cane levelling out, and with our highly efficient processor in British Sugar, we will be in a strong position on the global market. The end of quotas should be seen as an opportunity to thrive. The UK grower is highly skilled and knowledgeable in growing beet and I predict the industry will have a positive future.” William who farms in Cambridgeshire has grown sugar beet for thirty years and he uses Dow Shield every year for controlling thistles and volunteer potatoes. “It is a regular part of my programme,” he says.