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

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

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

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

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

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

Daylily Rust

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

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

Aster yellows –Purple coneflower

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

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

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

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

Cercospora leaf spot of bottle brush buckeye

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

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

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

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

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

Dogwood Anthracnose

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

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

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

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

Hypoxylon canker Thyronectria canker

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

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

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

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

Camellia leaf gall

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

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

Rhizoctonia stem rot Oak leaf hydrangea

Southern blight Crabapple Dec. Magnolia Sclerotia at base of tree

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

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

Lesion Nematode/Crabapple liners

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

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

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

Phytophthora root rot/Boxwood

Black root rot/Japanese holly

Black root rot - pansy