Despite the name, diamond scale is not an insect pest. Instead the fungusPhaeochoropsis
neowashingtoniae(previously calledSphaerodothis neowashingtoniae) causes this common foliar disease, which derives its name from its characteristic diamond-shaped fruiting bodies.
Diamond scale attacks primarily the California fan palm (Washingtonia filifera) in coastal regions and the
intermediate and interior valleys of California subject to marine influence; it rarely occurs in arid regions such
as the Central Valley or the deserts of Southern California.
Sooty mold is the common name applied to several species of fungi
that grow on honeydew secretions on plant parts and other surfaces. The
fungi’s dark, threadlike growth (mycelium) gives plants or other
substrates the appearance of being covered with a layer of soot.
Sooty molds don’t infect plants but grow on surfaces where
honeydew deposits accumulate. Honeydew is a sweet, sticky liquid that
plant-sucking insects excrete as they ingest large quantities of sap
from a plant. Because the insect can’t completely utilize all the
nutrients in this large volume of fluid, it assimilates what it needs
and excretes the rest as “honeydew.
Powdery mildew is a common disease on many types of plants and is prevalent under the diverse conditions found in
many areas of California. Different powdery mildew fungi cause disease on different plants. These fungi tend to infect
either plants in the same family or only one species of plant.
You can recognize this disease by the white, powdery mycelial
and spore growth that forms onleaf surfaces
and sometimes on flowers and fruits. Powdery mildews may infect new or old foliage.
Fire blight, caused by the bacteriumErwinia amylovora, is a common and frequently destructive disease of pome fruit trees and related plants. Pear (Pyrusspecies) and quince (Cydonia) are extremely susceptible. Apple, crabapple (Malusspecies), and firethorns (Pyracanthaspecies) also are frequently damaged. Fire blight is less common on hawthorn (Crataegusspecies),Spiraea,Cotoneaster, toyon (Photiniaspecies), juneberry or serviceberry (Amelanchierspecies), loquat (Eriobotria), mountain ash (Sorbus
Anthracnose is a group of diseases found on many deciduous and evergreen trees
and shrubs; some trees such as sycamore, ash, and evergreen elms can be
noticeably blighted. Often called leaf, shoot, or twig blight, anthracnose
results from infection by any of several different fungi, includingApiognomonia errabunda, A. veneta, Discula fraxinea,
Glomerellasp.,Gnomoniasp., andStegophora ulmea,depending on the tree attacked. Infections on
deciduous plants are more severe in areas where prolonged spring rains occur after new growth is produced.