Biology and control of Coniophora eremophila on lemon trees in Arizona

A survey of mature lemon trees showed an average of 30% of trees with symptoms of brown heartrot caused by Coniophora eremophila. Growth of C. eremophila inoculated into branches of Valencia orange, Marsh grapefruit, Orlando tangelo, or Lisbon lemon on rough lemon rootstock was significantly higher in lemon than in other types of citrus. C. eremophila inoculated into Lisbon lemon branches on trees established on rough lemon, volkameriana, macrophylla, Cleopatra mandarin, sour orange, or Troyer citrange rootstocks showed no significant differences in growth. Somatic incompatibility tests of isolates from one mature orchard demonstrated that isolates from different trees were incompatible. In vitro fungicide trials showed that NECTEC P paste and NECTEC blank paste effectively reduced decay on lemon blocks 15 weeks after inoculation with C. eremophila. Field fungicide trials showed that NECTEC P paste with fungicides, as well as the blank paste without fungicides, significantly inhibited the advance of the fungus 7 months after inoculation. Also, propiconazole at 10,000 μg/ml, imazalil at 20,000 μg/ml, or propiconazole at 10,000 μg/ml in combination with imazalil at 20,000 μg/ml significantly inhibited the advance of the fungus.