Plastic Covering to Reduce Sweet Cherry Fruit Cracking Affects Fungal Fruit Decay

The most common rain covering system in Norwegian sweet cherry (Prunus avium L.) orchards is a flat plastic roof raised above the tree canopies. Covering the trees from three weeks prior to harvest and throughout the harvest period reduced fruit cracking significantly in 4 out of 5 experiments. Sweet cherry fruit are susceptible to fungal pathogens during the entire fruit developmental period. Covering the trees prior harvest reduced fruit decay significantly in 3 out of 5 experiments. By prolonging the covering period for 2 weeks, a similar reduction in fruit decay was found even if I or 2 fungicide applications were omitted. All fungicide applications (3 to 6 sprays) could be omitted without any increase in fruit decay by covering during the whole period from flowering through harvest. Covering the trees during flowering or from 5 to 6 weeks prior to harvest without fungicide application between the two covering periods reduced fruit decay from 9% to 3% in the first year and from 15% to 4% in the second year. There was a further reduction to 1% or 3% fruit decay in the two years, respectively, by fungicide applications at the green fruit stage (when the covers were off). Thus, plastic covering may be both an alternative and a supplement to fungicide applications.