STEM-END NECROSIS

Press, Volume CVIII, Issue 31676, 11 May 1968, Page 9

STEM-END NECROSIS

“This year a number of potato crops are showing damage at the heel or stemend of the tuber,” says Mr C. M. Driver, leader of the potato section at the Crop Research Division at Lincoln.

“It may be little more than a spot at the point of attachment of the stolons with a little browning under the skin, to a severe necrosis and rotting. Usually the damaged portion becomes sealed off and rots away, leaving a hollow in the end of the tuber, but occasionally some other soft rots can enter the damaged area and rot the whole tuber.

“The condition is confined to crops which have been sprayed off to check growth and prevent tubers growing too large. Hence it is most common in seed crops. It results from a too rapid killing of the tops, especially if done when the tops are actively growing. Rua is probably most affected because Rua tubers grow quickly and reach a desired size while the tops are still very young. When a period of dry weather and slow growth is followed by wet weather and rapid growth, the tubers become especially susceptible to damage. “The tubers in the accompanying picture came from a crop which first had grown poorly, but which after rain had put on six inches or so

of new growth before being sprayed off. In another case spraying during hot northwest weather gave an almost instantaneous kill. “The aim should be to spray under conditions that give a slow kill of the tops. If there has been a spurt in growth with new foliage developing, it is better to wait until growth has slowed down before spraying. Alternatively, if they can be sprayed within a day or two of the rain it may be possible to check them before new growth occurs.

“A variety such as Rua would be better late planted (late November). It would grow more slowly and would not be ready to spray until later in the season when growth had slowed and weather conditions were not so conducive to a very rapid death.

“In affected table tubers, the affected portion can be cut out, and the rest of the tuber will be quite acceptable, except that it may have a greater tendency than normal to fall to pieces on cooking.

“If seed tubers are carefully stored and handled they should be perfectly satisfactory to use next year, but with poor storage some of the worst affected tubers may rot, and the vigour of the rest be impaired. Any severely damaged tubers should be rogued out before sale, but provided they are still sound at planting time, they could be used if necessary. If used it is suggested they be planted a little closet together than normal and not more than two inches below the soil surface to allow for quick emergence and establishment

“In America there are many areas where spraying off is never done because of stemend necrosis and it would seem we have to exercise care here,” said Mr Driver.