18 August 1995

Potato rain dilemma

DROUGHT-hit potato growers may want rain to bulk crops. But once it arrives quality could suffer as secondary growth and cracking sets in.

Large yield increases can be expected once "significant" rain arrives, advises ADAS. For many the dilemma is whether to defoliate before then and harvest a low yielding but quality sample or to wait for rain to stimulate further growth and risk quality penalties.

Sprouting in the field is also a worry – a feature of the summers high temperatures. Symptoms are now apparent even in moderately well irrigated fields. Maris Piper, King Edward and Cara are suffering most, says ADAS. Second earlies seem less affected.

Most affected crops are below a marketable yield, so bulking is required. Further secondary growth and chain tuberisation can be expected. That will result in starch moving from the first-formed tubers, leaving them "glassy" with quality implications.

For crops which are not at marketable yield and have at least four weeks of growth before the start of senescence or desiccation, maleic hydrazide (Fazor) may suppress sprouting, suggests ADAS. Growers should check with buyers whether such use is acceptable, it adds.

Trials show the optimum period for application is at the beginning of the label window of 3-5 weeks before the anticipated start of crop defoliation. But treatment should not be more than six weeks before planned desiccation. &#42