Two sprays best with volunteer potatoes…
Two sprays best with volunteer potatoes…
By Shelley Wright
TWO sprays are the most effective approach to tackling volunteer potatoes in set-aside, according to recent SAC work.
Potato cyst nematode multiplication is prevented by the first application, and daughter tuber survival reduced by the second, explains SACs Ken Davies.
"PCN will develop and multiply as soon as a potato starts to form, so this must be controlled when the volunteers are very small.
"But the problem is that volunteers tend to come up over a long period, so you could have to repeat-spray. In set-aside that is against the rules so derogations are required.
"Exact timing of applications should be discussed with your agronomist. But an early spray, once most of the volunteers are up but before they start to form tubers, seems to work well."
Such an early knockdown also reduces early blight problems. Dr Davies recommends paraquat or paraquat + diquat at a rate of 2-3 litres/ha.
A dose of glyphosate at 4 litres/ha should follow when volunteers are flowering.
"Applying glyphosate any earlier will knock the tops down but it wont control the tubers," he warns.
With the glyphosate costing about £25/ha (£10/acre), long-term control of volunteers is not expensive in set-aside, especially given the value of seed crops, he stresses.
Another point which growers sometimes overlook is that potato volunteers do not just come from tubers; some can come from seed, he explains.
"If you have had a crop that flowered well and produced a lot of seed, you can see problems with volunteers in later years.
"So set-aside should be examined for volunteers from tubers, but also for seedlings."
For seed growers, eliminating volunteers is especially important to prevent varietal contamination, points out Dr Davies.
"Equally, for ware crops, having other varieties there can affect grading."
High volunteer potato populations can be a significant weed problem in arable crops and dense patches can act as a source of blight infection, he adds.
"Its important not only to protect potatoes growing elsewhere on your own farm, but you must also consider possible contamination of neighbours crops. There have been court cases in the past where farmers have been accused by neighbours of contaminating their crops," he warns.
Although poor lifting conditions last autumn could mean more tubers are left in the ground this spring, the cold snap over Christmas and New Year will have helped, says Dr Davies.
"At least that will have killed off the tubers near the surface," he concludes.
[as panel]
DEROGATIONS REQUIRED
Spraying in set-aside may require a derogation from your regional MAFF office or SERAD depending on the timing, warns Dr Davies. "Check with government agriculture departments to see what is and is not acceptable."
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SET-ASIDE SPUD CONTROL
* Two sprays best.
* Early paraquat/diquat.
* Later glyphosate.
* Excellent clean-up opportunity.
SET-ASIDE CONTROL
• Two sprays best.
• Early paraquat/diquat.
• Later glyphosate.
• Excellent clean-up opportunity.
Derogation need?
Spraying in set-aside may require a derogation from your regional MAFF or SERAD office depending on the timing, warns Dr Davies. "Check with government agriculture departments to see what is and is not acceptable."