When a plant cannot function normally, it is diseased. The primary causes of disease in trees are pathogens and environmental factors. Trees have many disease pathogens: viruses, bacteria, fungi, nematodes, mycoplasma-like organisms, and parasitic higher plants. Fungal pathogens are the most prevalent. They cause seed rots, seedling damping-off, root rots, foliage diseases, cankers, vascular wilts, diebacks, galls and tumors, trunk rots, and decays of aging trees. Unfavorable weather and environmental factors such as temperature and moisture extremes, high winds, or ice can damage trees directly and predispose the trees to pest attack. Destruction of already-formed wood, which generally refers to losses caused by heart-rots that kill or ruin wood. Therefore, the degradation of live trees is a sort of loss that is unique from all others. The organisms inducing nursery diseases are unlike those that cause diseases of trees within forests. They are similar or the same as those pathogens that cause diseases of agricultural crops. Pathogens associated with nursery-grown seedlings are usually not problems once seedlings are planted in forest areas. Management procedures to reduce impact of diseases within forest nurseries are similar to those used to control agricultural pests. Methods like Cultural help in disease prevention which is the main objective of cultural management of nursery diseases. Reduce inoculum in growing areas and avoid conditions which promote disease spread. Sanitary practices including greenhouse, containers and seed. Next is biological control and last is Chemical methods in which Fungicides often are specific to a particular group of fungi, as are the application methods so a proper diagnosis is very important. Therefore, many of the chemical and non-chemical control methods used in forest nurseries have been adopted from agricultural system that have similar pathogens.