Designation for defective or non-existent flowering or flower drop during or shortly after the vine blossom. Other designations are tube-flowering, leaving, trickling and, in extreme cases, passing through or trickling. The causes are weather-related influences such as frost, hail and persistent rainfall as well as chlorosis. Trickling can also be caused by pests such as mites (ruffled mites) and vine thrips, fungi such as red torch or botrytis, and various viral diseases such as brushwood disease in particular. Pruning is also favoured by excessive use in the vineyard of nitrogen, copper, sulphur or phytohormones. All this causes weak photosynthesis and poor carbohydrate supply in the plant tissue and leads to poor fruit set.