16 March 2001

Planting patience is a must say agronomists

Potatoes are arguably the most management responsive crop grown on many farms. In this

special feature we focus on agronomy angles to help you make the most of this seasons

plantings, with advice on irrigation, disease control, computer support systems, volunteer

eradication and integrating crop management. But first Edward Long asks two leading

agronomists how best to start the season. Edited by Andrew Swallow

PATIENCE is the watchword when planting potatoes this spring.

But while planters stand idle in the shed, seed can be managed to compensate for the late start, say agronomists.

"After last seasons experience no one wants to risk another late harvest," says Abbey Growers Simon Bowen.

But if growers do not wait for land to dry to depth both yield and quality could be compromised, he warns. Agronomy needs to be tweaked to minimise any knock-on effect on maturity.

"It is better to plant two to three weeks later than to go too soon. But contingency plans need to be laid now with seed management the first priority," he says.

Unchitted seed needs to be kept cool to prevent sprouting. But chitted seed will have a 10-day advantage once planted, and if done properly provides a very useful way of advancing the season.

"It is preferable to seed not growing as it sits in cold wet soils," he notes.

But where late planting is anticipated, growers should tray up seed slightly later than usual to avoid putting on too many day degrees. Early trayed stocks should be held in a cold and well-lit store.

"If sprouts become too long and weak they will be knocked off at planting, losing all the advantage and cost of chitting."

To offset a late start and match a shorter growing season nitrogen and potash fertiliser rates could be trimmed, he says.

"That should ensure the crop is mature at lifting. It is best to split the N with the first dose going on at planting and rest at tuber initiation."

Andy Wells, of ADAS Gleadthorpe, echoes Dr Bowens patience message.

"Patience will be a real virtue this season. There is a real risk growers will feel pressured to make a prompt start and wreck the potential of a high cost crop before it is even planted.

"Much of the organic manure normally applied will be going on late so will provide significantly more nitrogen for the crop," he adds.

"Rates of inorganic N will have to be trimmed otherwise die-back will be delayed by 2-3 weeks leading to immature crops at lifting, or another late harvest."

Fertiliser placement provides a small yield benefit, particularly where residual reserves have been depleted by winter rain, he adds.

Seed rates may also need altering where planting is delayed.

"For longer season crops it may be worth widening spacings, allowing room for plants to produce a decent sized sample. That is particularly important for bakers."

Not planting too deeply on medium to heavy soils will help late-planted crops emerge rapidly, says Mr Wells. But with crops emerging in as little as two weeks growers will need to be ready with pre-emergence herbicides at the first hint of surface movement. &#42

PLANTING POINTERS

&#8226 Wait for fit seed-beds.

&#8226 Slow chitting if necessary.

&#8226 Trim N on late plantings.

&#8226 Beware extra N from late spread manure.

&#8226 Cut seed-rate for bakers?

New PDQ mix

Potato contact herbicide PDQ (diquat + paraquat) is in a new formulation this spring, offering better control of larger, more vigorous broad-leaved weeds at lower rates, says Syngenta. "Tank-mixing with Opoguard will provide the optimum contact and residual control combination," says potato product manager Ben Miles.

Risks of rushing

Little land intended for potatoes was prepared over winter and in the few cases where ground was worked, beds have slumped and additional cultivation could be needed to dry them out, says Dr Bowen. But growers should not attempt to use the plough, bed formers, or de-stoners until soil beneath the surface has dried out for fear of smearing. Smeared soil will restrict rooting, impair canopy development, cut yield and reduce tolerance of stresses such as drought or PCN. Also crops planted into poor seed-beds are more vulnerable to wet weather diseases such as powdery scab and blackleg. Cold soils make crops slow to emerge and vulnerable to canker, adds ADASs Andy Wells. But where soils are fit, an early start will spread workload. Large seed should be used, as it is has more reserves and split grading could prove worthwhile. More robust varieties such as Cara can cope with 5-7C soil temperatures, but varieties such as Estima, Dell and Saxon should go into seed-beds at 7C minimum, adds Dr Bowen.