story and photography by Janelle Kluz
La Verne’s trees are suffering. A close inspection tells a different story than the traditional changing of the season color and molting of leaves. The harsh truth is that some of La Verne’s trees are very sick. Since 2010, the Southern California drought has caused La Verne to lose an abundant number of trees, such as oak and liquid amber. Stressed by the extreme drought, complications have occurred, further weakening them. According to Jay Jones, professor of biology and biochemistry at the University of La Verne, the pathogen known as “Xylella Fastidiosa” is a main contributor to the recent decline of trees. Xylella Fastidiosa lives in the xylem tissues of host plants, where water and nutrient processing takes place. The pathogen causes diseases such as Bacterial Leaf Scorch (BLS) and leads to premature thinning of leaves with the potential to eventually kill the trees.
Many misdiagnose this disease as symptoms of fall, but the difference is that BLS infected trees have leaves that are scorched around their edges during the middle of summer. It begins with the older leaves before spreading to newer ones. Soon vast expanses of the canopy are affected. It is common for the disease to develop soon after a known stress, such as drought. BLS has been identified in the urban forest throughout the eastern United States and as far west as Texas. Xylella Fastidiosa also resides in “alternative” hosts, and the bacterium is transmitted by insects that feed on xylem fluids of the affected plants. Insects such as leafhoppers, or sharpshooters, are known to carry this pathogen.
The blue-green sharpshooter is most common in dense tree growth areas with vines and shrubs. Because it feeds on new growth with soil moisture and shade, it is seldom found in unshaded, dry locations.