Diseases that occasionally lead to considerable losses during storage include soft rot (Pectobacterium spp.), dry rot (Fusarium spp.), silver scurf (Helminthosporium), late blight (Phytophtora infestans), leak (Pythium) and pink rot (Phytophthora erythroseptica).
Controlling diseases in storage is hard as there are virtually no chemicals allowed nor effective. The environment within the store and during particular stages of storage are most conducive to the spread of the disease. Means to reduce incidence of storage losses are preventing diseased tubers from entering the store through proper pre-harvest control measures and the use of resistant varieties.
Silver scurf probably is the most damaging quality affecting storage disease as it decreases the quality of table potatoes by blemishing the skin, changing its hue and making it more permeable. Thus, the tubers with silver scurf lesions lose water more easily than healthy ones. Affected seed tubers produce less sprouts and yield less vigorous plants. Avoidance of silver scurf happens through two major measures: the use of healthy seed tubers and by rapid drying of the crop when it enters the store, say within five days. This assures that the store is relatively devoid of spores of the disease upon entering of the crop. Storing at as low as permissible temperatures and the use of chemicals further reduce the incidence. Imazalil (enilconazole) is a synthetic fungicide that controls the disease to some extent and also Fusarium when the tubers are atomized in a solution of the chemical upon entering the store or later after grading. Excessive use leads to exceedance of the maximum residue level (MRL), which is 3 mg/kg in Europe. Essential oils that reduce sprouting also have a negative effect on the development of silver scurf. As the fungus grows and produces spores when the skin of the tuber is moist, store keepers avoid condensation of water when warming the tubers before store unloading.
Top photo: Silver scurf caused by the fungus Helminthosporium solani thrives in humid environments, often the worst infection spread takes place in closed plastic bags during the few weeks shelf exposure in the shop.
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