The California spinach industry has grown dramatically over the past few decades; it now supplies well over 100,000 tons of various high-quality products to consumers. But a new foliar disease. Stemphylium leaf spot, can reduce spinach quality. After identifying this disease, we determined that the pathogen may also be a new, distinct strain of the fungus that is specific to spinach. Inoculation experiments demonstrated that numerous spinach lines are susceptible, including new downy mildew-resistant cultivars. Diagnosing this disease can be difficult because its symptoms often resemble damage from agrochemicals. Growers and pest control advisors should become familiar with the symptoms of the various foliar spinach diseases that occur in California because consumers of this crop tolerate only a small level of leaf spots and defects.
In 1998, following the very wet EI Niño weather event, a devastating outbreak of rust disease severely damaged the garlic crop in California. The disease also occurred in 1999 and 2000, indicating that rust may have developed into an annual problem. We identified the pathogen as Puccinia allii. In our study, it infected allium crops such as garlic, onion and chives, but not leek, elephant garlic or shallot. Currently registered materials did not control the disease, but tebuconazole (Folicur) and azoxystrobin (Quadris) provided good protection against garlic rust. Based on our work, a Section 18 emergency exomption for tebuconazole was approved by state pesticide regulators. We tested 34 UC and industry garlic varieties and found that none were completely resistant to garlic rust.