- Author: Steven T. Koike
- Author: Carolee Bull
Since 2002, a severe leaf spot disease on parsley has occurred throughout central coastal California and particularly in Monterey County. Three different bacterial pathogens (Pseudomonas syringae pv. apii, P. syringae pv. coriandricola and an organism very closely related to P. viridiflava) have been associated with these outbreaks on parsley. Of interest to researchers and of potential importance to growers is the fact that two of these bacteria were already causing problems in coastal crops. Pseudomonas syringae pv. apii is the causal agent of northern bacterial blight of celery and P. syringae pv. coriandricola causes bacterial leaf spot of cilantro. Symptoms of all three diseases are similar and consist of small (usually less than ¼ inch in diameter) leaf spots that are noticeably angular in shape, with the edges of the spot restricted by leaf veins. The color of the leaf spots can vary from light tan to brown to dark brown. These bacterial leaf spots penetrate the entire leaf, so that the spot will be visible from both the top and bottom sides of the infected tissue (in contrast to chemical damage or abrasion in which the symptom is usually only seen from the top side of the leaf). See photos below.
Our research team is also investigating a possible new bacterial disease on fennel, as well. Because of these developments on commercially grown plants in the Apiaceae, we are seeking additional samples of foliar problems from any member of the Apiaceae crop group: celery, cilantro, dill, fennel, parsley, and others. Further clarification of the relationship between these various bacterial pathogens, determination of which hosts are susceptible to which pathogen, and other aspects may assist industry in managing these diseases.
The best samples will consist of diseased plants collected from several different locations of a field. Send samples to the UC Cooperative Extension diagnostic laboratory in Salinas: 1432 Abbott Street, Salinas CA, 93901 (phone 831-759-7550), attention Steve Koike.
Bacterial leaf spot of celery.
Bacterial leaf spot of cilantro.
Bacterial leaf spot of parsley.
- Author: Steven T. Koike
- Author: Jian Long Bi
The spring growing conditions have been responsible for several problems that affected head lettuce in coastal California. Rain and cold temperatures have allowed significant development of bacterial leaf spot (Xanthomonas campestris pv. vitians) and a physiological disorder possibly related to tipburn. In addition, recent samples, received by UC Cooperative Extension, have been infested by an insect. Field personnel and pest control advisors have also been detecting this problem.
Underneath the wrapper leaves, inner layers are being fed upon by the larval stage (maggot) of a fly insect. Damage consists of holes and breaks in the leaves where the maggot has been feeding (photos 1, 2, 3).
Photo 1 |
Photo 2 |
Photo 3 |
Edges of the damaged areas turn tan to brown. Such feeding damage can occur anywhere along the leaf and midrib tissue. Careful examination of the inner leaves will likely reveal the presence of the maggot (photo 4) and/or the pupa (photo 5). Maggots are small (approximately 7 mm (1/10th inch) long) and pale in color.
Photo 4 |
Photo 5 |
The insect damage, which consists of actual holes in the tissue, is distinct from the physiological problem that typically does not result in breaks in the leaf and which is usually restricted to the leaf margins. The bacterial leaf spot disease affects mostly outer leaves and results in characteristically black lesions.
Identification of the fly is pending and Entomology Farm Advisor Jianlong Bi will be investigating this further.