24 August 2001

Vital to keep on top of volunteer control…

VOLUNTEER potatoes are becoming more of a problem, particularly as milder winters favour their survival. But a planned multi-season approach can keep them at bay.

"There is scope to improve control, but growers have to keep on top of the problem and work in successive crops and not think they can do it all in one hit," says Mike Abram, senior trials officer for Agrovista.

He is running a major BPC-supported trial on volunteer control at Saxham, near Bury St Edmunds, Suffolk, where the plots clearly show the scope for maximising volunteer potato control in certain crops.

Not surprisingly, best control was achieved in set-aside. In the trial, Cheminovas new environment and operator friendly easy-flowing glyphosate formulation, Envision, likely to be available next year, was used at 3.2 litres/ha. When applied at the T1 hook stage of the volunteers it gave near total haulm control to prevent daughter tuber development.

But there were survivors. "The question is how many late emerging volunteers, or small plants that are covered and not hit by the spray are left uncontrolled?" asks Mr Abram. "Would a T4 spray when tubers are 45mm be better for getting the herbicide down into all the tubers to ensure they all rot?"

The best compromise may be 3.2 litres/ha at T1 and T4, suggests Mr Abram. "Given the price of glyphosate, it might be worthwhile."

All the plots in the trial will be harvested and surviving tubers tested for viability the following season to find out.

In sugar beet, 0.35 litres/ha Shield three times from the hook stage of the volunteer potatoes reduced tuber number and size much more than cereal treatments. Adding Betanal Progress (ethofumesate) accelerated haulm knock-down and also including Debut gave even better haulm control and more cracked and distorted tubers – but at twice the cost of Shield alone.

In cereals, 2 litres/ha Starane (fluroxypyr) gives much the best control, knocking haulm back hard and reducing daughter tuber number and size, so any plants emerging in the following crop should be easy to control.

But cost is over three times a single sulfonyl urea, and £12/ha more than the standard approach of Ally + 1litre/ha Starane, so it is unlikely to appeal unless the problem is very severe.

In the Saxham trial, DP928 (Ally + Prospect) and DP911 (Ally + Quantum) offered no benefit over Ally alone for haulm control. But there were fewer daughter tubers which were more misformed. &#42

Glyphosate applied at T1 took out most "volunteer" potatoes in the Saxham trial, but escapees could still set seed, warns Agrovistas Mike Abram. A T1 + T4 spray would ensure any tubers set by survivors from the first spray still get a full dose of glyphosate to encourage rotting.

HITTINGVOLUNTEERS

&#8226 Worsening problem.

&#8226 No single solution.

&#8226 Set-aside best chance.

&#8226 Get timing right.

&#8226 Multi-year strategy.