Causal Agent

Xylella fastidiosa subsp. fastidiosa 

 

Hosts

Xylella fastidiosa is a bacterium that has several subspecies or strains. The host ranges of the different strains are currently being researched. The Pierce's disease strain falls within X. fastidosa subsp. fastidiosa. In Oklahoma, we have confirmed Pierce's disease only in grape. Other hosts that may be hosts of the Pierce's disease strain include alfalfa, maple and almond. 

 

Symptoms

Pierce's Disease is caused by a bacterium that lives in the xylem (water-conducting) cells of plants. The symptoms are observed in late summer and fall and include marginal leaf scorch (browning) that is frequently bordered by a red or yellow halo. Entire leaves may turn brown and drop, leaving the petioles attached to the plant. Fruit clusters may shrivel and shoot growth is of ten stunted. Plants generally perform poorly and often die within a few years. 

 

The disease is transmitted by xylem-feeding insects including sharpshooters and leafhoppers. Long distance movement is due to infected plant material. 

 

Pierce's Disease was first identified in grapes in Canadian County, Oklahoma in 2008 in a home garden. At this time, we do not know the distribution of Pierce's Disease in Oklahoma. Other strains of Xylella fastidiosa that affect shade trees have been routinely found throughout Oklahoma. This indicates that the grape-infecting strain could survive throughout the state. The strain of the bacterium that affects shade trees does not cause Pierce's Disease.

 

Control

Growers should plant certified, disease-free plants. Pruning tools should be disinfected with a bleach solution (1 part household bleach, 9 parts water) between cuts. Infected plants should be removed and discarded. 

 

If Pierce's Disease is found in the area, it may be helpful to monitor for xylem-feeding insects that transmit the disease using yellow sticky cards. If the disease is found, other plants including grape should be sampled to determine the extent of the pathogen in the area.