Volunteer Potato Problems Grow

Cambridge (June 28, 2003) - Volunteer potatoes are emerging as a serious problem for more and more arable growers across the country, according to latest Monsanto studies, revealing populations as high as 200,000 tubes/ha in some cases.

Conducted through the company's technical advice service, the studies highlight the extent to which higher harvesting specifications, milder winters and inappropriate cultivation practice are causing an upsurge in volunteer problems.

"Far more undersized tubers are being returned to the soil these days as a result of modern harvesting specifications," explained technical advice service co-ordinator, Manda Sansom. "Mild winters are encouraging high survival rates. And we've seen a continuing legacy from the many unharvested crops during the terrible winter of 2000/2001.

"Tubers can survive to emerge in several flushes of growth over several years," she pointed out. "The fact that varieties like Cara and Maris Piper produce many more small tubers than others, and Majestic, Romano and Pentland Dell are more prone to dormancy complicates matters. As does burial through ploughing which induces dormancy."

Mrs Sansom stresses that volunteer potatoes are not inherently hard to kill. The real control challenge, however, arises from the numbers of tubers being left in the ground and the unpredictability of their emergence over an extended time. Which means at least two glyphosate treatments are likely to be needed within the rotation.

"Of the three main rotational opportunities to tackle potatoes, set aside is undoubtedly the best," she advised. "Removing the annual weed cover with an early mid-April to mid-May application encourages maximum emergence of the volunteers. They can then be hit with a full rate perennial weed dose of Roundup between mid-June and mid-July when the foliage is fully developed and uptake optimal.

"Pre-harvest Roundup applications to cereals as part of a harvest management programme are also valuable for controlling volunteer potatoes; as are late-autumn cereal stubble applications ahead of late-sown winter cereals or spring crops. In each case, it's essential to use the 3.2 l/ha rate of Roundup Gold or equivalent to ensure complete tuber kill.

"Where there's no tuber problem the 1.2 l/ha rate on stale seedbeds will give excellent control of the seedling potatoes which can be very numerous.

"Minimising tuber return in potato harvesting is, of course, also important," Mrs Sansom added. "And shallow cultivation rather than ploughing ahead of the following crop will keep the tubers near the surface where frosts and vermin can markedly reduce viability."