Pests of Specific Crops

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Pest Description Leaf Gall (Exobasidium vaccinii): This fungus overwinters on azalea bark and bud scales, infecting opening buds in spring. Leaves become fleshy, thickened, and covered in a white bloom of spores. Leaf Spots (Phyllosticta, Colletotrichum spp. and other fungi): These fungi are usually weak pathogens that infect winter or sun-damaged leaves. Spots and blotches are dark brown, zonate and may cover half the leaf area. Black fungal fruiting bodies are often present in the spots in humid weather. Lime-induced Chlorosis (Iron Deficiency): Leaves yellow between the veins, from margins inward. Veins remain green. Powdery Mildew (Microsphaera spp.): Large brown areas or faint yellow spots may appear on leaves in early spring. White powdery fungal growth may be on the underside of these areas. Root Rot, Wilt and Foliar Blight (Phytophthora spp.): Plants wilt and leaves curl and droop. Roots are brown and soft, sometimes only on one side of the plant. The rot may extend into the crown, where the advancing discolouration shows a distinct line with healthy tissue. Leaf and stem blight may occur without root rot. Symptoms are blackening of leaves, stems and petioles. Rust (Chrysomyxa spp.): Rust first appears as yellow spots on the upper leaf surface and brown to purple spots on the lower surface. Blisters form on the lower surface, which rupture to expose orange-red pustules. Several generations can occur in one growing season. It will overwinter on rhododendron and azalea and cause new infections each spring. Spruce may be an alternate host for some of these rust species. Tissue Proliferation (Genetic or Physiological Disorder): A large gall occurs at the base of rhododendron stems that resembles crown gall infection. Small shoots often develop from the gall. Galls may also be present on stems. Growth is not usually affected, but large galls may cause gradual decline of the plant and stems may break off at gall sites. Insects: Lace Bugs (Stephanitis pyrioides): Small white spots appear in a dense mass on leaves in early spring. Damage resembles mite injury. Tiny lace bug nymphs can be seen on the underside of damaged leaves. Chemical Control (rate per 100 L water; or per unit area if indicated) Commercial nurseries: Application of DACONIL 2787 for foliar Phytophthora blight (see below) should provide some control of these diseases also. (See Root Rot, Wilt and Foliar Blight, below.) Apply an iron chelate foliar fertilizer spray or soil application. Cultural Management Do not overhead irrigate where leaf gall has been a problem. Remove and destroy leaves with galls as they appear. Reduce greenhouse humidity. Collect and compost, bury or burn affected leaves and fallen leaves. Provide good plant care and proper nutrition. Plant sun-sensitive varieties in shaded areas and protect frost-sensitive varieties from winter injury. If soil is high in lime, incorporate organic matter or a sulphur-containing fertilizer. Work soil shallowly to avoid damaging feeder roots close to surface. See General Disease Management: Powdery Mildew, Chapter 9. Foliar blight: DACONIL 2787F: 250 mL DACONIL Ultrex: 150 g May discolour blooms. Soil drench: TRUBAN 30WP: 0.6-0.9 kg/100 m 2 TRUBAN 25EC: 115-240 mL/40 m 2 SULPHUR (DOMESTIC): 0.4 - 0.9 % or other formulations. See label for rates and application. Use disease-free stock. Place containers on coarse, welldrained beds. Avoid heavy, wet soils for field growing. See Appendix H for a list of Rhododendron species and varieties that are resistant to root rot. Plants growing in crowded, damp or shady locations are more likely to become infected. Collect and destroy infected leaves. See General Disease Management: Rusts, Chapter 9. Provide good growing conditions. Rogue out affected plants if desired. See General Insect and Mite Management: Lace Bugs, Chapter 11. 6 • Pests of Specific Crops Nursery Production Guide
Pest Description Mealybugs: These scale-like insects have a soft scale that is covered in white, powdery wax. They feed on the sap of plants and produce honeydew. The honeydew attracts ants and often leads to the growth of sooty mold. Affected plants appear unthrifty and yellow. Root Weevils: Larvae girdle roots and crown tissue, and the adults notch leaf margins. BERBERIS – BARBERRY Diseases: Chemical Control (rate per 100 L water; or per Leaf Spot/Anthracnose (Phyllosticta spp./Gloeosporium berberidis): See Mahonia. BETULA – BIRCH Diseases: Leaf Blister (Taphrina spp.): This fungal disease related to peach leaf curl causes red blisters and curling of leaves. Insects: Apple & Thorn Skeletonizer and Other Caterpillars: Caterpillars are about 12 mm long, yellowish to greenish with many black dots. They begin feeding on underside of leaves, later moving to upper surfaces. Silken webs are formed, curling the leaves. The feeding “skeletonizes” leaves. Birch Leafminer (Fenusa pusilla): The adult is a black sawfly (3 mm long) that lays eggs in young leaves. The white larvae mine the leaves, which turn brown. There are 2 generations per season. Bronze Birch Borer (Agrilus anxius): Usually attacks weak or injured trees. The adult is a 13 mm long, olive-bronze beetle. Adults appear in May-June and lay eggs in bark crevices. Larvae (grubs) up to 15 mm long, chew tunnels under the bark, girdling twigs and branches and causing the upper part of the tree or branch to dieback. Chlorotic leaves and sparse upper branches are the first symptoms. Lumpy bark and half-moon-shaped beetle exit holes can be found. BUXUS – BOXWOOD Diseases: Boxwood Blight (Cylindrocladium buxicola): It was first detected in North America in 2011. The pathogen is spread by wind-driven rain and splashing water. Symptoms include brown leaf spots, black streaks on stems, and rapid defoliation. Clusters of spores are produced by the white fungal growth (mycelium) on the underside of leaves under warm and humid conditions. It does not infect roots. It overwinters in the plant and leaf debris. Cultural Management unit area if indicated) See General Insect and Mite Management: Mealybugs, Chapter 11. See General Insect and Mite Management: Root Weevils, Chapter 11. Prune out infected leaves and twigs if practical and rake fallen leaves. See General Insect and Mite Management: Tent Caterpillars and Skeletonizers, Chapter 11. See General Insect and Mite Management: Leafminer/Needle Miners, Chapter 11. DURSBAN WSP: 44.8 g PRO DURSBAN TURF: 50 mL If insecticide treatment is necessary, make three applications at 2-3 week intervals during June and July to control adults before they lay eggs. Thorough coverage is important. Insecticides will not kill grubs under the bark. DACONIL 2787: 250 mL SWITCH 62.5: 100 g NOTE: These are emergency registrations that expire on December 31, 2013. Drought-stressed trees are more susceptible. Keep trees healthy to prevent borer invasion (e.g. provide with optimum fertilizer and water). Prune, burn or chip wilted/dead branches to destroy larvae in the wood. Appendix A ranks susceptibility of white-barked birch to birch borer. Inspect incoming plants for symptoms and isolate from existing boxwood stock for at least 3 weeks. Sanitize pruning tools and collect leaf debris. Do not plant new boxwoods into landscapes with mature boxwoods. Nursery Production Guide Pests of Specific Crops • 7
Page 1 and 2: Pests of Specific Crops 14 (updated
Page 3 and 4: Pest Description Bacterial Blight (
Page 5: Pest Description Rusts: Fungal frui
Page 9 and 10: Pest Description Insects: Mealybugs
Page 11 and 12: Pest Description CORNUS - DOGWOOD D
Page 13 and 14: Pest Description Insects: Cotoneast
Page 15 and 16: Pest Description Leaf Spot (Cercosp
Page 17 and 18: Pest Description Web Blight (Rhizoc
Page 19 and 20: Pest Description Juniper Webworm (D
Page 21 and 22: Pest Description Blister Spot (Pseu
Page 23 and 24: Pest Description Insects and Mites:
Page 25 and 26: Pest Description Sydowia Blight/Tip
Page 27 and 28: Pest Description Needle Cast (Cycla
Page 29 and 30: Pest Description Sooty Mould: Black
Page 31 and 32: Pest Description Coryneum Blight, S
Page 33 and 34: Pest Description PSEUDOTSUGA - DOUG
Page 35 and 36: Pest Description Pear Trellis Rust
Page 37 and 38: Pest Description ROBINIA Diseases:
Page 39 and 40: Pest Description SALIX - WILLOW Dis
Page 41 and 42: Pest Description Berckmann’s Blig
Page 43 and 44: Pest Description ULMUS - ELM Diseas

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