PLANT HEALTH Figure 2. Xanthomonas leaf spot on strelitzia showing intervienal striping. geranium is relatively specific to geranium while the Xanthomonas on dieffenbachia can attack anthurium, philodendron and really most members of the Aroid family. The Xanthomonas from zinnia is known to attack zinnia only. They used to be called pathogens of X. campestris but with the renaming frenzy, keeping up with what they are called now is challenging. Pseudomonas diseases can be caused by a broad-host range species like P. cichorii, which attacks many tropicals, vegetables and other ornamentals. In the case of P. syringae pathovars, they can be broad-spectrum or narrow. Acidovorax species are somewhat specific on ornamentals often causing disease on a single genus. DIAGNOSIS Bacterial diseases remain the hardest to identify since fungi can be recognized by spores and selective media and viruses can be identified through antibody and related methods. Different labs utilize different methods to identify bacterial pathogens. Some use symptoms and research reports and other use bacterial steaming under a microscope and growth on bacterial media. Still others have access to sophisticated genetic fingerprinting technology. The most important thing to know is whether a foliar symptom is caused by Continued on page 22 ... fl oricultura.com Characteristic Water-soaked Color Colorful margins Disintegration Between veins Edges One size Concentric rings Sharp margins Figure 3. Xanthomonas on lavender cuttings. Phytotoxicity No Tan/white No No No Sometimes Yes No Yes Fungi Rare Tan/brown/black Yes Rare Bacteria Yes Brown/black No Yes No (except downy mildew) Yes No No Yes Sometimes Yes No No (except Erwinia) Sometimes Table 1. Typical symptoms for leaf spots caused by phytotoxicity, fungal or bacterial pathogens. BREEDING YOUR π SHIPPING SUPPLY SPECIALISTS SUCCESS CHAMPION SELECTION ORDER BY 6 PM FOR SAME DAY SHIPPING COMPLETE CATALOG 1-800-295-5510 uline.com GREENHOUSE PRODUCT NEWS 19http://www.oricultura.com http://www.uline.com