1. Common Diseases of Landscape Plants found in Tennessee
Alan Windham
Entomology and Plant Pathology

2. 1. Powdery Mildews Easily identified by white mycelium
May distort infected leaves
Common hosts include: euonymus, crape myrtle, dogwood, rose, phlox, zinnia

3. 2. Downy mildews
Symptoms- angular leaf spots to severely burned foliage
Mycelium on the undersides of the leaves
Hosts – rose, snap dragon, pansy

4. 3. Gray mold (Botrytis blight)
Look for grayish-brown mold on leaves, stems, flowers
Favored by cool, moist weather
Numerous woody and herbaceous hosts

5. 4. Rusts Yellow leaf spots and rust colored pustules
Numerous hosts including conifers, broadleaf plants
May cause galls, twig dieback
Cedar-Apple Rust/on cedar

6. Cedar Hawthorne Rust Rust infects leaves, stems and hawthorne fruit
Rust spores emerge from
cankered cedar branch

7. Daylily Rust

8. 5. Virus diseases
Variety of symptoms including: mosaic, ringspots, rosette, oakleaf pattern, stunting and flower break
Impatiens necrotic spot has over 350 hosts

9. Rose rosette/landscape roses
Found on multiflora rose
Increasing common on landscape roses
Transmitted by eriophyid mites
Kills infected plants within two years

10. Aster yellows –Purple coneflower

11. 6. Fungal Leaf spot diseases
The most common plant diseases
Favored by wet weather, high humidity, overhead irrigation
Many cause premature defoliation

12. Apple Scab Common on older crabapple cultivars not resistant to scab
Causes premature leaf drop which leads to sucker growth
Many new cultivars are resistant to scab

13. Entomosporium leaf spot/Photinia
Generally there are two types of photinia: those that have this disease and those that are going to have this disease
Avoid this plant until resistant cultivars are available

14. Tar spot
Although not aesthetically pleasing generally harmless to maple
The black “tar spots” are the fungus Rhytisma
Speckled tar spot is a similar disease caused by a different pathogen

15. Cercospora leaf spot of bottle brush buckeye

16. 7. Shot hole diseases Fungal or bacterial shot hole diseases
Affecting plants in Prunus genus only
May be mistaken for insect feeding

17. Bacterial shot hole/cherry laurel
Worse in container nurseries or landscapes with overhead irrigation
Usually present at low levels in most landscapes
Chemical control is usually not needed in landscape beds

18. Needle Cast Diseases Essentially a leaf spot disease of conifers
Attack older needles in interior of trees
Disease of pine, spruce, fir
May make affected tree’s canopy look thin
Needlecast/Eastern white pine

19. Kabatina Tip Blight Common tip blight of juniper
Weak pathogen that invades wounds from insects/ice
Attacks last years growth
Symptoms visible in late winter/spring

20. 8. Anthracnose Diseases
Fungal leaf spot, twig blight and/or canker disease
Favored by cool, wet weather
Hosts: ash, dogwood, maple, oak, sycamore

21. Dogwood Anthracnose

22. 9. Canker Diseases Leaf, needle and twig dieback are early symptoms
Sunken, swollen or resinous cankers
Usually fungal but may be bacterial
Girdle and kill large branches

23. Botryosphaeria canker/Cherry
Young trees stressed by drought are most susceptible to this disease
Prune out diseased branches
Trunk cankers often lead to death of the entire tree

24. Seiridium canker/Leyland cypress
Fairly easy to find on Leyland cypress in non-irrigated landscapes
Prune out diseased shoots
Severely infected plants will have to be replaced

25. Seiridium Canker - Arizona cypress
Similar symptoms on Leyland cypress
Resinous canker
Disfigures and may kill tree

26. Hypoxylon canker
Thyronectria canker

27. Nectria Canker A perennial canker of dogwood, linden, walnut
Callus tissue forms at margin of canker each year
Canker appears like a target with concentric rings
Nectria canker of dogwood

28. Black knot/Purple leaf plum
Very common on flowering plum
Knots should be pruned out
Re-infection may come from nearby infected trees

29. Fire Blight ‘Shepherd’s crook’ symptom Bacterial disease
Control with dormant pruning, resistant cultivars, moderate nitrogen fertilization, antibiotic sprays

30. 10. Leaf Galls Fungal diseases of azalea, peach, oak
Most leaf galls are caused by mites or insects
Swollen or blistered leaves

31. Camellia leaf gall

32. 11. Crown gall Tumors/galls on stems/roots
Soft, spongy to wooden and corky with maturity
Bacteria enter through wounds
Inject genetic material into hosts cells

33. 12. Stem/Crown Rots
Fungal diseases that attack stem or crown of plants at soil-line
Damping off of seedlings
Southern blight
Sclerotinia stem rot
Rhizoctonia stem rot

34. Rhizoctonia stem rot Oak leaf hydrangea

35. Southern blight
Crabapple
Dec. Magnolia
Sclerotia at base of tree

36. 13. Nematode Diseases Root knot the most common disease
Foliar nematode on herbaceous plants
All plant parasitic nematodes have a stylet

37. Root Knot Nematodes Adult Root Knot Female Root knot juvenile
(Infective stage)

38. Lesion Nematode/Crabapple liners

39. 14. Wilt Diseases Restrict water flow to leaves
Soil-borne or insect vectored
Dutch elm disease,
Verticillium wilt
Bacterial leaf scorch

40. Dutch elm disease Transmitted by bark beetles
Sanitation is important for control
Injection can be used to protect valuable trees
Resistant cultivars are available

41. 15. Root rot diseases Affected plants may be stunted, wilted
Discolored, decayed roots
Poor drainage, standing water, excessive irrigation, favor disease development

42. Phytophthora root rot/Boxwood

43. Black root rot/Japanese holly

44. Black root rot - pansy