AbstractA fairly large number of grafted mango seedlings, kept under partial shade in the Fortuna Substation, were damaged by a serious die-back disease which caused death of the scions and necrosis of the wounded tissues of the root-stocks. In the orchard, trees of the susceptible variety Jacqueline developed very serious die-back symptoms and stem cankers. The disease was prevalent during December 1965 and January 1966. The high percentage of natural infection can be attributed to the wide-spread occurrence of the parasite, Physalospora rhodina. The imperfect stage of the organism, Diplodia, is endemic in the Island, and was repeatedly isolated from the following hosts: avocado, orchids, pigeon peas, papaya, alfalfa, mango, and sugarcane. Six distinct physiologic races were recognized when using the aversion test. The perfect Physalospora form was produced when the physiologic races were cultured independently on caimito fruits or in young papaya stems and petioles. This organism is a wound parasite and capable of causing great damage under certain favorable conditions, as when grafted mango trees are kept in a humid propagation shed. In the nursery the disease was controlled by practicing such preventive methods as: Selection of scions from healthy trees, sterilization of the budding knife with alcohol, keeping the grafted trees in a relatively dry environment, and gradual exposure of grafted mangos in plant beds to full sunlight. In the orchard, control was attained by spraying the mango trees periodically with copper oxichloride sulphate (3 lbs./100 gal.) and by paintings of the stems frequently with a thick paste of the above mentioned fungicide.
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