Late blight in organic potato growing: managing resistance and early tuber growth

In organic potato production yields are often reduced by potato late blight (Phytophthora infestans). Two aspects are important in late blight management: a sufficiently high (field) resistance to late blight, and early tuber formation. With early tuber formation the period of tuber growth is extended at the beginning, and with a high resistance level at the end. In 2006 and 2007 experiments were carried out in which the effects of the physiological age of seed tubers on field resistance to late blight and on tuber yield of potatoes (Solanum tuberosum L.) were tested for early and moderately late varieties. The results indicate that with the use of physiologically older seed tubers (by pre-sprouting) the field resistance to late blight is generally lower than with younger seed tubers. With physiologically older seed tubers, however, yields are generally higher at the time the crop has to be defoliated because of late blight. It is concluded that especially when the growing period of a potato crop is short, for example as a consequence of an early late blight epidemic, or when a late variety is grown, early tuber growth by the use of older (pre-sprouted) seed tubers is highly important to assure an acceptable yield level at the end of the growing season. Even in years with a long growing season, a late variety like Agria may yield up to 12 t/ha more when physiologically older seed tubers are used