1. Sustainable Management of Common Plant Diseases in the Landscape Dr. Elizabeth Little Department of Plant Pathology University of Georgia

2. Plant Disease Triangle HostPathogen Environment Disease Stressed or injured plant Capable of causing disease (many are host specific) WATER! (wet foliage or soils, high humidity, poor air circulation)

3. Types of Plant Diseases Root and crown problems –Root rots, crown rots, nematodes, galls, drought, overwatering, poor planting, poor soil, inappropriate site Foliage and stem diseases –Leaf spots, cankers, herbicide damage Systemic diseases –Viruses, bacterial scorch, aster yellows

4. Soil and Fertility Management Healthy plants resist disease Proper site preparation will avoid many problems. Right plant/right place Promote healthy plants and healthy soils with: –Compost amendments –Mulching –Nutrient additions

5. Most plant health problems in the landscape are due to a problem with the roots or soil, but diagnosis of root problems can be confusingMost plant health problems in the landscape are due to a problem with the roots or soil, but diagnosis of root problems can be confusing The above ground symptoms of any root stress will look the same, even though root stress can have different causes: poor nutrition, drought, soil compaction, or root diseaseThe above ground symptoms of any root stress will look the same, even though root stress can have different causes: poor nutrition, drought, soil compaction, or root disease

6. Root Disease Symptoms WiltingWilting StuntingStunting Leaf yellowing and dropLeaf yellowing and drop Softening and discoloration of roots and stems,Softening and discoloration of roots and stems, Branch diebackBranch dieback Plant deathPlant death

7. Pythium root rot Most plants you buy already have some root rot Prevent root rot: –Plant high –Improve soil drainage –Redirect water –Do not over-water –Do not over- fertilize –Right plant/right place Armillaria

8. Root rot diseases in the landscape are often associated with improper planting, irrigation, or site preparationRoot rot diseases in the landscape are often associated with improper planting, irrigation, or site preparation

9. Juniper Dieback Junipers like dry, sunny conditions, and do not like poorly drained sites

10. Oak leaf blister Oak leaf blister Spot anthracnose Spot anthracnose Phyllosticta leaf spotPhyllosticta leaf spot Discula leaf spot (birch)Discula leaf spot (birch) Most fungal leaf spots are mostly an aesthetic problem

11. Cercospora leaf spot on Hydrangea

12. Black spot of rose Leaf Symptoms

13. Management of Black Spot Sanitation (destroying leaves, cutting back diseased canes) Mulching each year Resistant cultivars!! Increase air flow, plant in full sun Keep leaves dry when irrigating Fungicide Sprays (protectants every 7 to 12 days or systemics)

14. Seiridium canker on Leyland Cyprus Very commonVery common Drought-stressed and wounded treesDrought-stressed and wounded trees Irrigate trees during periods of droughtIrrigate trees during periods of drought

15. Mycosphaerella leaf spot on iris Entomosporium leaf spot on red-tip (Photinia) Prolonged leaf wetness, high humidity and poor air circulation increases foliar diseases

16. Defoliation on Photinia due to Entomosporium leaf spot disease, overcrowding, and poor air circulation

17. Entomosporium on Indian Hawthorne Resistant Cultivars Available

18. Powdery Mildew Reduces yield and weakens plants Surface mycelium – easy to diagnose Some survive as spores in debris, others blow in each year (cucurbit powdery mildew) Management: –Damage is minimal in most plants –Some cultivars with resistance –Increase air circulation –Sulfur - oldest fungicide, not very efficacious –Sodium and Potassium Bicarbonate –Ultrafine oils interfere with infection –Biologicals

19. Powdery mildew

20. Rust diseases Very complex lifecycles –Autoecious: one host (geranium rust) –Heteroecious: two hosts (daylily rust, cedar-apple rust, fusiform rust) Spores are spread by wind and water-splashing Fungicides usually not needed for landscape plantings. Resistant cultivars are better options in crop plants.

21. Daylily rust Yellow spots on upper side of leaf Orange spores directly beneath on leaf underside Destroy infected leaves Resistant cultivars Fungicides

22. Cedar-apple rust Orange telial horns disperse spores to apples, crabapples in spring Leaf spots and fruit distortion occur on apple/crabapple Spores then spread back to cedar in summer

23. Cedar apple rust on crabapple

24. Cedar Quince Rust

25. Fire blight of apple, pear, crabapple, pyracantha, cotoneaster, photinia Occurs in warmer, wet springs Secondary summer infections can occur during wet years Prune affected branches to reduce spread

26. “We” cause the majority of tree decline problems“We” cause the majority of tree decline problems Construction damage, mechanical injury, improper planting, girdling roots, and compacted soils all stress treesConstruction damage, mechanical injury, improper planting, girdling roots, and compacted soils all stress trees Natural events also contribute, i.e. drought, lightning, fire, etc.Natural events also contribute, i.e. drought, lightning, fire, etc. Disease and insectsDisease and insects What’s wrong with my tree?

27. Red Maple with Gradual Dieback Can you spot the cause of this decline?

28. Bacterial Scorch of Sycamore – many tree species are susceptible, no cure

29. Phytoplasma Disease – Aster Yellows Cause stunting and color deformities Systemic bacteria in phloem Interfere with growth and development

30. Viruses – no cure, inspect planting material

31. Ring spot symptom – always a virus disease

32. Herbicide Damage

33. Root-knot nematodes are common Plants are stunted, roots galled Healthy plants can resist infections Some plant species more resistant Root-knot nematodes are common Plants are stunted, roots galled Healthy plants can resist infections Some plant species more resistant

34. When a disease problem is suspected, obtain background information: Pattern in landscape Number of plants affected Part of plant affected Irrigation time/frequency/areas Recent weather conditions Chemicals used on or near the site, rates Fertilizer applied (rate, form of application) Insects present