Peach leaf curl is a disease that affects peach and nectarine trees. Although you may not see symptoms right now in the dormant season in California, it's time to think about treatment, especially if your tree had the disease last year.

Symptoms of this fungal disease include distortion, thickening, and reddening of foliage as trees leaf out in the spring. As weather warms, damaged leaves that die and fall off trees are replaced with new, usually healthy leaves. However, after several years without treatment, peach leaf curl will cause tree decline and reduced fruit production.

Avoid peach leaf curl by growing varieties resistant to the disease. For nonresistant peach and nectarine trees, consider spraying with...

This time of year, you may notice a white, powdery looking growth on fruit, vegetable plants or ornamental plants in your garden. What is it? It could be powdery mildew.

Powdery mildew is caused by several different fungi that may attack plant leaf surfaces, shoots, fruits, and flowers. There are several species of powdery mildew; all are spread by wind and thrive in shady areas when temperatures are between 60-80 °F. The fungi attack both new and old foliage, and can be a problem on certain plants. The disease usually occurs first on new leaves, before spreading to older parts of the plant. This is why over fertilizing worsens powdery mildew. 

Ornamental Plants

Many woody and herbaceous...

[From the December 2016 issue of the UC IPM Green Bulletin]

The Polyphagous shot hole borer (PSHB) (Fig. 1) and Kuroshio shot hole borer (KSHB) are invasive wood-boring beetles that attack dozens of tree species in Southern California, including commercial avocado groves, common landscape trees, and native species in urban and wildland environments. Both beetles spread a disease called Fusarium Dieback (FD), which is caused by pathogenic fungi. Trees that are FD-susceptible may experience branch dieback, canopy loss, and tree mortality (Fig....

Today's post for National Invasive Species Week highlights two ambrosia beetles that are detrimental to certain trees. Ambrosia beetles are highly specialized beetles that excavate tunnels in usually weakened or dead trees and cultivate fungal gardens, which they feed upon. Below are two such invasive beetle-fungal complexes that are currently impacting trees and forests in California.

Walnut twig beetle and thousand cankers disease. Walnut twig beetle, Pityophthorus juglandis, is a tiny bark beetle that attacks only walnut trees. The beetle has been in California for many decades but recently became associated with a new fungus, Geosmithia morbida. The fungus kills the phloem and cambium of...