As seen in the liquid amber leaves, the drought has caused a multitude of trees across the city to be infected with bacterial leaf scorch, caused by the bacterium Xylella fastidiosa. Scorched leaves develop when sufficient water does not reach the leaf margin cells. / photo by Janelle Kluz
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.
Found on the sap of a pine tree at Kuns Park in La Verne, a nymph blue-green sharpshooter gains its nutrients by feeding on plant fluids in the water-conducting tissues of a plant (the xylem). When Sharpshooters feed, they can inject the disease-causing bacterium Xylella fastidiosa, which then multiplies in the tree’s water-conducting system and causes further water stress beyond existing drought conditions. / photo by Janelle Kluz
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.
Sitting on a branch of a dying tree at the crossroads of Hawthorne and Park avenues in La Verne, the white-winged Phoebe scans the area in search of insect food. Phoebes are native to North and South America and belong to a small bird group in the genus “Sayornis.” / photo by Janelle Kluz
Sharing his knowledge of the effects of the Xylella Fastidiosa pathogen, Jay Jones, professor of biology and biochemistry at the University of La Verne, discusses the causes and the possible effects the loss of city trees will have on the environment. In his professional life, Professor Jones holds public lectures year round to inform others of the ever escalating, significant damage to the ecosystem. “It’s a pretty grim picture that we live in. We forgot that human life depends on nature, and soon it can all be erased forever.” / photo by Janelle Kluz
Trees at Foothill Boulevard and D Street visibly show stress. The city of La Verne has more than 11,000 street and park trees. A 2015 study conducted by West Coast Arborists, Inc., calculated these trees to be valued at nearly $40 million. / photo by Janelle Kluz
Observed on Seventh Street in La Verne, California, vines have been affected by the pathogen “Xylella Fastidiosa,” which is carried by leafhopper insects known as sharpshooters. So-called leaf scorches begin to appear by early summer and increase through fall, causing clusters to dry. / photo by Janelle Kluz
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