Symptoms of bacterial leaf spot caused by Pseudomonas cichorii on basil appear as brown and black spots on leaves and streaking on the stems. The leaf spots are angular or irregular or delineated by the small veins. The bacterium has a wide host range and infects chrysanthemum, geranium, and many other ornamental and foliage plants but is not known to be host specific. P. cichorii can be present on asymptomatic plants allowing long distance distribution of the bacterium via propagative material. On basil, seed and infected plugs are the most likely sources of infection.
Tospovirus is a genus that includes Impatiens Necrotic Spot Virus (INSV) and Tomato Spotted Wilt Virus (TSWV). Western flower thrips is the predominant insect vector. Thrips acquire the disease as a first instar larvae as they feed on virus-infected plants (including infected weeds showing few, if any symptoms). Once mature, the winged adult thrips are primarily responsible for viral spread. An infected thrips is able to transmit tospoviruses to at least one plant per day until its death. Adults do not transmit the virus to their young.
Powdery mildew was reported on rosemary this week.
In addition to rosemary, the characteristic white spots of powdery mildew usually first appear first on the upper surfaces of the lowermost leaves of many types of plants such as non-stop begonias, calibrachoas, dahlias, asters, phlox, monarda and other susceptible crops. Stems and flowers may also become infected.
It is that time of year for extreme temperatures and weather conditions. Monitor the weather forecast and avoid moving cold tolerant annuals and herbaceous perennials outdoors if a hard frost (colder than 28°F) is predicted at any point within at least three nights of when plants would be put outside. Avoid placing plants in low-lying areas because frost will more likely settle in these areas. Be prepared to cover plants if temperatures go below 28°F.
Intumescence is an abiotic disorder which produces small blisters on leaf surfaces. Severe cases can result in defoliation. Certain plants are especially susceptible to intumescence; these include members of the Solanaceae such as Ipomoea, peppers, and tomatoes, and Cuphea in the Lythraceae family. The symptoms resemble and are often mistaken for edema (or oedema), but their development is distinctly different. In addition to the genus of the afflicted plant, the location of the symptoms is also helpful in distinguishing intumescence from edema.