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.
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.
Botrytis blight and stem canker is caused by Botrytis cinera. Wilted branches and darkened, woody stem seen in this photo are common symptoms. This pathogen is ubiquitous in the environment, has an extremely wide host range, and prefers to attack senescent and/or injured tissue. Botrytis can be controlled by management of environmental conditions, sound cultural practices and fungicide applications. Control weeds and remove plant debris. Space plants to allow good air circulation, reduce humidity within the canopy, and minimize leaf wetness.
Damping off is a disease that affects seeds (pre-emergence) and young seedlings (post-emergence). When severe, it can cause significant crop loss for greenhouse growers.
Cloudy weather and cool nights provide ideal conditions for Botrytis blight. When temperatures drop during the night, the colder air cannot hold as much moisture, so it condenses on the foliage and flowers, which encourages Botrytis.
Cercospora leaf spot caused by Cercospora violae, can damage the overall appearance of pansies and reduce their marketability and value. The disease is favored by extended periods of high humidity with nighttime leaf-wetting and daytime drying. The disease can come in through infected seed or weeds of the Viola family. The fungus overwinters in seed, infected crop residues, or in weeds of viola family. A few infected plants can produce large amounts of inoculum causing a lot of plants in the house to be infected.
Starting with high quality disease and insect free plant material is a critical step in the management of diseases and insect pests in your greenhouse. The first step in ensuring disease and insect free plants in your greenhouse is to purchase high quality pest free plant material from reputable producers. When the new plant materials are brought into the greenhouse they should be inspected thoroughly for any symptoms of disease or insect pests. Inspect incoming plants for key insects, diseases, weeds and cultural problems.
2014 was the worst year for basil downy mildew in the Northeast since the disease was introduced to the US in 2007. This was, partially due to the distribution of infected transplants nationally and widespread planting of infected material leading to earlier than usual disease and high levels of inoculum in the environment. Here are some recommendations for reducing the impacts of this disease in 2015.
Growers who purchased unrooted cuttings this season received a pest alert indicating Ralstonia solanacearum had been found on cuttings originating from Guatemala. USDA test results confirmed this. It is important to note that there are different strains of Ralstonia solanacearum.
Planning to clean and reuse pots and carrier trays this spring? Reused pots and trays may harbor Thielaviopsis basicola root and stem rot, often call Black rot.