Sustainable Management of Common Plant Diseases in the Landscape Dr. Elizabeth Little Department of Plant Pathology University of Georgia
Dec 17, 2015
Sustainable Management of Common Plant Diseases in the
LandscapeDr. Elizabeth Little
Department of Plant Pathology
University of Georgia
Plant Disease TrianglePlant Disease Triangle
Host Pathogen
Environment
Disease
Stressed or injured plant
Capable of causing disease (many are host specific)
WATER! (wet foliage or soils, high humidity, poor air circulation)
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
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
• Most plant health Most plant health problems in the problems in the landscape are due to a landscape are due to a problem with the roots problem with the roots or soil, but diagnosis of or soil, but diagnosis of root problems can be root problems can be confusingconfusing
• The above ground The above ground symptoms of any root symptoms of any root stress will look the stress will look the same, even though root same, even though root stress can have stress can have different causes: poor different causes: poor nutrition, drought, soil nutrition, drought, soil compaction, or root compaction, or root diseasedisease
Root Disease Root Disease SymptomsSymptoms
• WiltingWilting• StuntingStunting• Leaf yellowing and Leaf yellowing and
dropdrop• Softening and Softening and
discoloration of discoloration of roots and stems, roots and stems,
• Branch dieback Branch dieback • Plant deathPlant death
Pythium root rotPythium 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
placeArmillaria
• Root rot diseases in the landscape are often Root rot diseases in the landscape are often associated with improper planting, irrigation, associated with improper planting, irrigation, or site preparationor site preparation
Oak leaf blisterOak leaf blister
Spot Spot anthracnoseanthracnose
• Phyllosticta leaf spot Phyllosticta leaf spot
• Discula leaf spot (birch)Discula leaf spot (birch)
Most fungal leaf spots are mostly an Most fungal leaf spots are mostly an aesthetic problemaesthetic problem
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)
Seiridium canker on Leyland CyprusSeiridium 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
Mycosphaerella leaf spot on iris
Entomosporium leaf spot on red-tip (Photinia)
Prolonged leaf wetness, high humidity and poor Prolonged leaf wetness, high humidity and poor air circulation increases foliar diseasesair circulation increases foliar diseases
Defoliation on Photinia due to Entomosporium leaf Defoliation on Photinia due to Entomosporium leaf spot disease, overcrowding, and poor air circulationspot disease, overcrowding, and poor air circulation
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
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.
Daylily rust
• Yellow spots on upper side of leaf
• Orange spores directly beneath on leaf underside
• Destroy infected leaves
• Resistant cultivars
• Fungicides
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
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
• ““We” cause the majority We” cause the majority of tree decline problemsof tree decline problems
• Construction damage, Construction damage, mechanical injury, mechanical injury, improper planting, improper planting, girdling roots, and girdling roots, and compacted soils all compacted soils all stress treesstress trees
• Natural events also Natural events also contribute, i.e. drought, contribute, i.e. drought, lightning, fire, etc.lightning, fire, etc.
• Disease and insects Disease and insects
What’s wrong with my tree?
Phytoplasma Disease – Aster Yellows
• Cause stunting and color deformities
• Systemic bacteria in phloem• Interfere with growth and
development
• 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
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