Beat the Heat

One of the keys to Effective harvest management

Published in the July 2012 Issue Published online: Jul 12, 2012 Jeff Stark, Universtiy of Idaho Variety Developmen

One of the biggest challenges potato growers face each year is dealing with the wide variations in temperature and moisture that are so common during harvest.

Whether hot or cold, wet or dry, the only weather characteristic that is consistent is its inconsistency.

Growers can maximize their ability to adjust to changing weather conditions during harvest by doing the things necessary to promote tuber maturation and skin set. This includes using optimal N and irrigation rates, completing N applications well in advance of vine kill and allowing adequate time after vine kill before harvesting. Keep in mind that high soil temperatures and excessively dry or wet conditions can slow skin set, thereby making tubers more susceptible to skinning and scuffing.

Growers should take appropriate steps to remove field heat and excess moisture with adequate air flow after tubers are placed in storage. An adequate period for wound healing at 50-55 degrees F is also essential to allow for suberization and wound periderm formation, which helps reduce disease progression and slows the rate of tuber water loss.

Cracks, wounds or breaks in the skin provide easy access points for rot organisms to invade the tuber, and, if not allowed to heal properly, can substantially increase storage rot development. They should also monitor their potatoes often during the first couple of months of storage to determine the potential for rot development, which can vary considerably with the amount of shatter bruise, leak or soft rot going into storage.

A key factor in the management of soft rot in fresh pack operations is tuber pulp temperature. Soft rot progress is greatly retarded, even stopped completely, when pulp temperatures approach 50 degrees F. Often, tuber temperature is much warmer than this critical temperature while they were being handled, washed and packaged. Realistically, 50 degrees may be difficult to achieve, especially in the early part of the harvest season. However, tubers should be cooled as rapidly as possible to get them to 55 degrees F or cooler, to greatly help reduce this rot problem.

The soft rot bacterium is also favored by wet conditions on the tuber surface, something that is impossible to avoid when washing potatoes. Wounds or natural weak areas in the skin of the tuber, like the lenticels, are particularly vulnerable to soft rot invasion. The bacterium has the ability to thrive either with or without oxygen and by immediately placing wet tubers into poly bags, an environment very conducive to soft rot is created. Add to this scenario the excessively high pulp temperatures, and the result is a lot of rotted potatoes. This situation can be remedied to some extent by maximizing the chlorine content of the wash water but tuber pulp temperatures are probably the major contributing factor.

Coping with the ever-changing weather conditions is a fact of life growers will always have to deal with, but a key guiding principle of harvest management is to properly manage those factors that can be controlled to increase one's ability to deal with the unexpected. 

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