Fireblight: Erwinia amylovora (Pears) | Wilt and collapse of blossoms. The bacteria causing fireblight are sucked back into the vascular tissues far below the visible symptoms. | Promptly cut 6 to 12 inches below the edge of discolored area, back to the closest lateral. |
Brown, blossom or twig blight: Monilinia spp. (Prunus spp.) | Collapse of young blossom spurs, leaves and shoot. | Remove infected twigs and branches in the winter. Prune the tree canopy to improve air movement. |
Eutypa Canker: Eutypa sp. (Grapes & Apricot) | Sudden limb collapse during summer heat. | Make a cut at least 6 inches below discoloration. Prune tree when there is minimal risk of rain and no fog. Treat wounds with thiophanate-methyl. |
Bacterial canker and blast: Pseudomonas syringae (Prunus spp.) | Blossom shoot blast. Cankers develop on branches, gum exudes from canker margins. | Cut 6 inches below stain. Remove symptomatic twigs in the summer. Sterilize pruning tools. |
Powdery mildew on apples: Podosphaera leucotrica (Apple) | White powdery growth on leaves and shoots. | Prune out diseased twigs. |
Silver leaf of prunes, pears or peaches: Chondrostereum purpureum (Prunus spp.) | Leaves on one or more branches have a silvery appearance. Branch dies. | Prune off the branch at the stem when symptoms are visible. THIS DISEASE ORGANISM IS TRANSMITTED THROUGH PRUNING WOUNDSI |
Olive knot: Pseudomonus savastonoi (Olive) | Rough galls or swellings | Remove heavily infected branches in July or August to prevent wound infection. |
Leaf gall in azaleas: Exobasidium vaccinii (Azalea) | Thickened, distorted and crisp leaves. | Remove galls in the late summer. |
Dutch elm disease: Ceratocystis ulmi (Ulmus spp.) | Wilted, yellow and brown foliage. | PROMPTLY prune infected branch 10 FEET below the discolored tissue. Sterilize pruning tools. |
Chinese elm anthracnose: Gleosporium sp. (Ulmus parvifolia) | Irregular, black, tar-like spots on the leaves. Cankers on branches and limbs. | Prune infected branches to the next healthy lateral. Excise bole cankers. |
Cypress canker: Seridium cardinale (Cupressus spp.) | Girdling cankers with resin drip on branches. | Prune out diseased branches, below visible infection (6 inches) in the hot, dry summer. SPRAY WOUNDS with Thiophanate-methyl or Chlorothalonil. |
Branch dieback of coast and giant Sequoias and canker of madrone: Botryosphaeria dothidea | Death and dieback of branches. Cankers on branches. | Prune out dead and diseased branches. SPRAY WOUNDS with Thiophanate-methyl. |
Sycamore anthracnose: Apiognomonia platanil (Platanus spp.) | Irregular, dead areas along the veins of a tree’s leaves. Cankers on twigs. | Prune out and destroy infected twigs on young trees. Make cuts into previous years growth. |
Pitch canker of pines: Fusarium subglutinans f. sp. pini (Pinus spp) | Fading of shoots to yellow, then red at the early stage. Needles fall later. Bole and branch cankers. | Prune off infected shoots down to the 2nd whorl from the canker between November to February. Sterilize pruning tools. Chip and dispose of infested branches. |
Leafy mistletoes: Phoradendron sp. (Many deciduous trees) | Clusters of evergreen mistletoe appear on the trunk and branches of many susceptible deciduous trees. | Prune off branches infected with mistletoe at least one foot below the haustorium. |
Western gall rust: Peridermium harknsssil (Pinus spp. two- and three-needle pines in the western United States) | Galls on the branches. Stunted growth — witches’ brooms. | Prune off branches with galls from October to January. Wrap galls with plastic on the main trunk in January to prevent dispersal of spores. Chip and dispose of infested branches. |