CAUSE OF DAMAGE TO SWEET CHERRY FLOWER BUDS IN SOUTHERN NORWAY

Commercial production of sweet cherries in the southern coast region of Norway has been inhibited by the high risk of crop failures due to extensive damage to flower buds. The aim of this investigation, which was begun in 2000 and will continue into 2002, was to survey and study the factors associated with damage of flower buds across this region. Thus far, the following results have been documented: 1) bud damage occurs at least two months before bud break; 2) sites with more stable, less fluctuating winter temperatures show less damage; 3) those sites along the coast (e.g., Lindesnes) with a boreal climate and those 60 km inland from the coast had very little bud damage (<20%); and 4) orchards between the coast and inland had significant damage (>50%). All of the orchards investigated suffered from Zn deficiency, except the orchard in Lindesnes which had no significant (<5%) flower bud damage in either 2000 or 2001. All orchards with >50% damage to flower buds had leaf analyses indicating Zn deficiency, as well as infections with bacterial canker (Pseudomonas syringae). Plastic rain covers to protect against fruit cracking have become a standard practice in Norway. The potential use of similar covers in early spring may be a strategy for reducing the infection pressure of diseases caused by fungi and bacteria. Such covers also might offer opportunities to modify the climate in ways leading to less damage of flower buds before and during flowering, resulting in better pollination and fruit set.