Control Bacterial Necrosis of Saguaro

Gray, Fred

Brief description of causes, symptoms, disease cycle and control of bacterial necrosis in saguaros. The disease is caused by a bacterium (Erwinia carnegieana) which also causes a rotting of chol1a, prickly-pear, barrel, and organ-pipe cacti. Symptoms, usually a circular darkening and softening of the plant tissues may appear on the trunk or branches. A dark odorous material will frequently "leak" out from the plant or the soft areas wil dry and crack, revealing dark dry remains of diseased tissues. Infection begins when the bacterium are introduced into the cactus through wounds or natural openings. Many insects and small animals may serve as carriers of this soft rotting bacterium; however, it appears to be primarily carried by a night-flying moth (Cactobrosis fernaldialis) The larvae of this moth are commonly found feeding in the base of Saguaro flower buds. Later, these larva tunnel into the plant creating an open wound. Removal of the diseased tissue is the most practical way of controlling the spread of the infection. If the diseased tissues are not treated, there is no way of predicting just how long it will be before the plant is completely infected. Field studies involving 462 plants revealed that 50% died within seven years and 75% within 12 years of the first observation of symptoms.