Evaluation of a Factor Exclusion Experiment Designed to Assist in Elucidating the Etiology of Citrus Blight

Abstract

In 1986, 42 Delta Valencia trees on rough lemon rootstocks were planted at random in a 25-yr-old Valencia orchard affected by citrus blight. The trees were planted on sites from which blight affected trees had been removed. Five chemicals were used to treat 24 of the experimental trees. The chemicals used were Temik®, Rugby®, Benlate®, Ridomil® and Azodrin®. The other treatments included trees planted in holes (3 m × 3 m × 1 m deep) filled with virgin soil; trees planted in insect proof cages; and untreated controls. Based on zinc analyses, canopy rating and water uptake, only two trees have been identified with apparent blight. Serological assays conducted in 1997, 1998 and 2001 were, however, negative for all trees. There appears to be no relationship between the type of treatment and incidence of blight. The low incidence of blight may be as a result of the physiological changes brought about by severe pruning of the scions and root systems following relocation, owing to a severe drought.