Plant Diseases

Results of 2025 UC Cooperative Extension field trials to evaluate tolerance of lettuce varieties to Fusarium wilt in Monterey and Santa Barbara counties.

A fungicide efficacy trial was conducted at the Emerald Seed Co. research farm in El Centro, CA, from September 2025 to March 2026 to evaluate the effectiveness of various fungicide treatments against onion downy mildew (Peronospora destructor) under field conditions. The trial included 9 treatments across 4…

Looking to keep your brain stimulated this summer? Need information about garden pests? Join us every third Thursday of the month from 12:00 to 1:00pm PST to learn about a wide range of urban pest management topics. This series is free and open to the public, but advance registration is …

A warm March followed by rain in April and May in many parts of California has set up the perfect conditions for the development of an unsightly and damaging tree disease called fire blight. Pome fruit trees like pear and apple, and other related trees like pyracantha, are all susceptible to this bacterial…

If you are noticing droopy, dried-out flower clusters on your pears, Asian pears, quince, apples or crabapples, fire blight may be the cause. Fire blight is caused by a bacterium and is a common and frequently destructive disease that usually shows up in April and May, but during dry spell, it may appear in…

Have you seen white powdery-looking patches appearing on the leaves of your roses or sycamore trees? While home gardeners may be familiar with this sign of the plant disease powdery mildew on their veggies, ornamental plants and landscape trees can also be infected. In addition to those powdery spots, the…

Reflections on thrips and INSV during the 2025 Lettuce Season Dylan J. Beal, Daniel K. Hasegawa, Yu-Chen Wang INSV: Early Spring and Summer: isolated, small INSV outbreaks were observed. These outbreaks were associated with adjacent, unmanaged weedy sites.Late Summer and early Fall: more…

Fungal diseases plague many different kinds of plants and their gardeners.  Fungal diseases tend to be persistent and can be difficult to manage.  Powdery mildew is one such disease.  It includes multiple fungal species and affects many different types of plants.  Powdery mildew…

If you have peach or nectarine trees, winter is the time to spray them to prevent peach leaf curl. Peach leaf curl is a fungal disease that attacks peaches and nectarines. It appears in spring, causing new leaves to become reddish, puckered and severely distorted. This disease is caused by the fungus…