Diseases and Insects As with most crops, cranberries have a whole host of insects and diseases that attack various parts of the plant. Rather than a single disease, this is a complex of several different fruit decaying organisms. Phyllosticta and Glomerella are just two of the more troublesome fruit rotting diseases. In many instances, although many rots are present, one or two of them tend to dominate any specific site. Knowing this information is essential in formulating a proper fungicide control strategy.
Most growers are under a three or four spray program for field rot control.
Sprays commence early in the season at bloom time which precedes fungal growth and infection times. One disease that is becoming more troublesome is Phytopothora which causes large die back areas in the vines. Proper drainage and fungicide applications can help control this water mold fungi. Black-headed Fireworms are insects that can cause damage to cranberry leaves and terminal buds. The Sparganothis fruit worm and the Cranberry fruitworm both can injure fruits and are characteristically identified by the berries turning prematurely red.