Category Archives: Quick Reference Guide

Plant Problems to Watch for in 2023

Lipstick Rust Lipstick Rust
Host:   Chinese juniper, apple, crabapple
Pathogen:   Gymnosporangium yamadae
Signs/Symptoms:   Brown blobs with orange gelatinous masses (juniper), red leaf spots (apple, crabapple)
Boxwood Blight Boxwood Blight
Host:   Boxwood
Pathogens:   Calonectria pseudonaviculata
Signs/Symptoms:   Circular, brown leaf spots followed by leaf drop and shrub death
For more information see:   UW Plant Disease Facts D0023
Late Blight Late Blight
Host:   Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:   Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:   UW Plant Disease Facts D0068
Septoria Leaf Spot and Early Blight Septoria Leaf Spot and Early Blight
Host:   Tomato
Pathogens:   Septoria lycopersici and Alternaria solani
Signs/Symptoms:   Spotting and eventual total collapse of leaves, working from the bottom of the plant up
For more information see:   UW Plant Disease Facts D0100/46
Septoria Leaf Spot of Lilac Septoria Leaf Spot of Lilac
Host:   Lilac
Pathogen:   Septoria sp.
Signs/Symptoms:   Dead spots on leaves, potentially leading to complete leaf browning
Verticillium Wilt Vascular Discoloration Verticillium Wilt
Hosts:   Woody and herbaceous ornamentals, vegetables
Pathogens:   Verticillium sp.
Signs/Symptoms:   Wilting, branch dieback, plant death
For more information see: UW Plant Disease Facts D0121/D0122
Powdery Mildew Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruit, vegetables, turf
Pathogens:   miscellaneous powdery mildew fungi
Signs/Symptoms:   Powdery white growth on leaves
For more information see:   UW Plant Disease Facts D0084/86/87
Rhizosphaera Needle Cast Rhizosphaera Needle Cast
Hosts:   Colorado blue spruce, other spruces
Pathogen:   Rhizosphaera kalkhoffii
Signs/Symptoms:   Browning/purpling of interior needles of lower branches, followed by needle drop
For more information see:   UW Plant Disease Facts D0093
Diplodia Shoot Blight and Canker Diplodia Shoot Blight and Canker
Hosts:   Austrian pine, other pines
Pathogen:   Diplodia spp.
Signs/Symptoms:   Dieback of brand tips with dead needles showing uneven lengths
For more information see:   UW Plant Disease Facts D0042
Chlorosis Chlorosis
Hosts:    Pin oak, red maple, birch, azalea, white pine, blueberry
Pathogen:   None
Signs/Symptoms:   Yellow leaves with dark green veins
For more information see:   UW Plant Disease Facts D0030
Improper Planting Improper Planting
Hosts:   Woody trees and shrubs
Pathogen:   None
Signs/Symptoms:   No root flare at the soil line, girdling roots, frost cracks, canopy thinning, early fall color, branch dieback, tree/shrub decline and death

For more information on plant problems to watch for:
See https://pddc.wisc.edu/ or contact your county Extension agent.

Plant Problems to Watch for in 2022

Boxwood Blight Boxwood Blight
Host:   Boxwood
Pathogens:   Calonectria pseudonaviculata
Signs/Symptoms:   Circular, brown leaf spots followed by leaf drop and shrub death
For more information see:   UW Plant Disease Facts D0023
Lipstick Rust Lipstick Rust
Host:   Chinese juniper, apple, crabapple
Pathogen:   Gymnosporangium yamadae
Signs/Symptoms:   Brown blobs with orange gelatinous masses (juniper), red leaf spots (apple, crabapple)
Late Blight Late Blight
Host:   Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:   Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:   UW Plant Disease Facts D0068
Septoria Leaf Spot and Early Blight Septoria Leaf Spot and Early Blight
Host:   Tomato
Pathogens:   Septoria lycopersici and Alternaria solani
Signs/Symptoms:   Spotting and eventual total collapse of leaves, working from the bottom of the plant up
For more information see:   UW Plant Disease Facts D0100/46
Septoria Leaf Spot of Lilac Septoria Leaf Spot of Lilac
Host:   Lilac
Pathogen:   Septoria sp.
Signs/Symptoms:   Dead spots on leaves, potentially leading to complete leaf browning
Wood Rots Wood Rots
Hosts:   Woody trees and shrubs
Pathogens:   Miscellaneous wood rot fungi
Signs/Symptoms:   Shelf-like growths on trunks and branches
Canker Diseases Canker Diseases
Hosts:    Woody trees and shrubs
Pathogens:   Miscellaneous canker fungi
Signs/Symptoms:   Sunken areas on trunks/branches
For more information see:   UW Plant Disease Facts D0027, D0037, D0042, D0055, D0074, D0114
Virus Diseases Virus Diseases
Hosts:   All plants, particularly herbaceous ornamentals
Pathogen:   Miscellaneous plant viruses
Signs/Symptoms:   Blotchy leaf color, growth distortions
For more information see:   UW Plant Disease Facts D0036, D0063, D0067, D0115, D0116, D0130
Rhizosphaera Needle Cast Rhizosphaera Needle Cast
Hosts:   Colorado blue spruce, other spruces
Pathogen:   Rhizosphaera kalkhoffii
Signs/Symptoms:   Browning/purpling of interior needles of lower branches, followed by needle drop
For more information see:   UW Plant Disease Facts D0093
Chlorosis Chlorosis
Hosts:    Pin oak, red maple, birch, azalea, white pine, blueberry
Pathogen:   None
Signs/Symptoms:   Yellow leaves with dark green veins
For more information see:   UW Plant Disease Facts D0084
Improper Planting Improper Planting
Hosts:   Woody trees and shrubs
Pathogen:   None
Signs/Symptoms:   No root flare at the soil line, girdling roots, frost cracks, canopy thinning, early fall color, branch dieback, tree/shrub decline and death

 

Vegetable Disease Quick Reference

Septoria Leaf Spot Septoria Leaf Spot and Early Blight
Host:   Tomato
Pathogens:   Septoria lycopersicia and Alternaria solani
Signs/Symptoms:  Spotting and eventual total collapse of leaves working from the bottom of the plant up
For more information see:        UW Garden Facts D0100/D0046
Late Blight Late Blight
Hosts:   Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:  Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:        UW Garden Facts D0068
Blossom End Rot Blossom End Rot
Host:   Tomato, pepper, eggplant, cucumber, squash
Cause:   Calcium deficiency
Signs/Symptoms:  Decayed areas on the bottom sides of vegetable fruits
For more information see:        UW Garden Facts D0022
Powdery Mildew Powdery Mildew
Hosts:    Any vegetable, particularly vine crops, peas
Pathogens:    Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:        UW Garden Facts D0086
Common Corn Smut Common Corn Smut
Hosts:   Corn
Pathogen:   Ustilago maydis
Signs/Symptoms:  Pasty white masses on corn ears eventually decomposing into a brown powder
For more information see:        UW Garden Facts D0031
Black Rot Black Rot
Hosts:   Crucifers (e.g., cabbage, broccoli, cauliflower)
Pathogen:   Xanthomonas campestris pv. campetris
Signs/Symptoms:  V-shaped yellow/dead areas on leaves progressing into plant deterioration and death
For more information see:        UW Garden Facts D0019
Potato Scab Potato Scab
Hosts:    Potato, carrot, beet, other root crops
Pathogen:  Streptomyces scabies
Signs/Symptoms:  Brown, rough, scab-like areas on tubers and roots
For more information see:        UW Garden Facts D0083
Verticillium Wilt Verticillium Wilt
Host:   Tomato, pepper, eggplant, potato, vine crops
Pathogen:  Verticillium spp.
Signs/Symptoms:  Leaf yellowing and wilting of plants followed by eventual plant death
For more information see:        UW Garden Facts D0122
Aster Yellows Aster Yellows
Hosts:    Carrot
Pathogens:    Aster yellows phytoplasma
Signs/Symptoms:  Yellow/orange/purple leaves, stunted roots with tufts of white hairy roots
For more information see:        UW Garden Facts D0007
Bacterial Wilt Bacterial Wilt
Hosts:   Vine crops
Pathogen:   Erwinia tracheiphila
Signs/Symptoms:  Sectional wilting and eventual death of plants after cucumber beetle feeding
For more information see:        UW Garden Facts D0014
Basil Downy Mildew Basil Downy Mildew
Host:   Basil
Pathogen:   Peronospora belbahrii
Signs/Symptoms:  Downward-cupped, yellow leaves with purple-gray fuzz on leaf undersurfaces
For more information see:        UW Garden Facts D0015

For more information on conifer diseases:  See https://pddc.wisc.edu/ or contact your county Extension agent.

Ten Common Plant Diseases/Disorders You Can Diagnose by Eye

Powdery Mildew Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruits, vegetables, turf
Pathogens:   Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:       UW Plant Disease Facts D0084/86/87
Tar Spot Tar Spot
Hosts:  Maples
Pathogen:   Rhytisma spp.
Signs/Symptoms:  Tarry areas (either solid spots or clusters of small spots) on leaves
For more information see:       UW Plant Disease Facts D0110
Peach Leaf Curl Peach Leaf Curl
Hosts:  Peach
Pathogen:   Taphrina deformans
Signs/Symptoms:  Light-green, yellow or purplish-red puckered areas on leaves
For more information see:       UW Plant Disease Facts D0076
Sooty Mold Sooty Mold
Hosts:  Any plant
Pathogen:   Miscellaneous sooty mold fungi
Signs/Symptoms:  Powdery black growth on leaves or needles
For more information see:       UW Bulletin A2637
Chlorosis Chlorosis
Hosts:  Oak, red maple
Cause:   Iron or manganese deficiency, often induced by high soil pH
Signs/Symptoms:  Yellow leaves with dark green veins
For more information see:       UW Plant Disease Facts D0030
Gymnosporangium Rusts Gymnosporangium Rusts
Hosts:  Juniper, apple, crabapple, hawthorn, quince
Pathogen:   Gymnosporangium spp.
Signs/Symptoms:  Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts)
For more information see:       UW Plant Disease Facts D0058
Black Knot Black Knot
Hosts:  Prunus spp. (plum and cherry)
Pathogen:   Apiosporina morbosa
Signs/Symptoms:  Black poop-like growths on branches
For more information see:       UW Plant Disease Facts D0018
Elderberry Rust Elderberry Rust
Hosts:  Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
For more information see:       UW Plant Disease Facts D0049
Golden Canker Golden Canker
Hosts:  Pagoda dogwood
Pathogen:   Cryptodiaporthe corni
Signs/Symptoms:  Gold-colored branches with orange spots
For more information see:       UW Plant Disease Facts D0055
Dog Vomit Slime Mold Dog Vomit Slime Mold
Hosts:  Any plant and on mulch
Cause:   Fuligo septica
Signs/Symptoms:  Scrambled egg-like masses on mulch or at the base of plants
For more information see:       UW Plant Disease Facts D0102

For more information on common plant diseases:  See https://pddc.wisc.edu/ or contact your county Extension agent.

Deciduous Tree Leaf Disease Quick Reference

Anthracnose Anthracnose
Hosts:  Most trees, commonly ash, maple and oak
Pathogens:  Gloeosporium spp. as well as other fungi
Signs/Symptoms:  Blotchy dead areas on leaves
For more information see:  UW Plant Disease Facts D0002
Purple-bordered Leaf Spot Purple-Bordered Leaf Spot
Host:  Amur, Japanese, red, silver and sugar maple
Pathogen:  Phyllosticta minima
Signs/Symptoms:  Discrete, circular leaf spots with purple borders
For more information see:  UW Plant Disease Facts D0089
 Tubakia Leaf Spot Tubakia (Actinopelte) Leaf Spot
Hosts:  Oak
Pathogen:  Tubakia spp. (Actinopelte spp.)
Signs/Symptoms:  Discrete circular, or irregular blotchy dead areas on leaves
For more information see:  UW Plant Disease Facts D0118
 Apple Scab Apple Scab
Hosts:  Apple, crabapple, pear, mountain-ash
Pathogen:  Venturia inaequalis, V. pirina
Signs/Symptoms:  Circular, black leaf spots with feathery edges; eventual leaf loss
For more information see:  UW Plant Disease Facts D0004
 Gymnosporangium Rusts Gymnosporangium Rusts
Hosts:  Apple, crabapple, hawthorn
Pathogens:  Gymnosporangium spp.
Signs/Symptoms:  Bright yellow-orange, circular leaf spots
For more information see:  UW Plant Disease Facts D0058
 Powdery Mildew Powdery Mildew
Hosts:  Most deciduous trees
Pathogens:  Several genera of powdery mildew fungi
Signs/Symptoms:  Uniform/blotchy powdery white areas on upper and lower leaf surfaces
For more information see:  UW Plant Disease Facts D0087
 Downy Leaf Spot Downy Leaf Spot
Hosts:  Hickory, walnut
Pathogen:  Microstroma juglandis
Signs/Symptoms:  Discrete powdery white areas on lower leaf surfaces
 Clorosis Chlorosis
Hosts:  Oak, red maple
Cause:   Iron or manganese deficiency, often induced by high soil pH
Signs/Symptoms:  Yellow leaves with dark green veins
For more information see:  UW Plant Disease Facts D0030
 Scorch Scorch
Hosts:  Most deciduous trees
Cause:   Water stress induced by drought, high soil salt content, or other water-limiting factors
Signs/Symptoms:  Dead tissue on leaf margins
 Tatters Tatters
Hosts:  Most deciduous trees, but commonly oak
Cause:  Possible early season cold injury
Signs/Symptoms:  Lacy, tattered-looking leaves
For more information see:  UW Plant Disease Facts D0111

For more information on deciduous tree leaf diseases:  See https://pddc.wisc.edu/ or contact your County Extension agent.

Conifer Disease Quick Reference

Root and Crown Rot Root and Crown Rots
Hosts:  All conifers
Pathogens:   Assorted root rot fungi/water molds
Signs/Symptoms:  Poor growth, branch dieback, discolored and deteriorated roots
For more information see:       UW Plant Disease Facts D0094
Rhizosphaera Needle Cast Rhizosphaera Needle Cast
Hosts:  Colorado blue spruce, other spruces
Pathogen:   Rhizosphaera kalkhoffii
Signs/Symptoms:  Browning/purpling of interior needles of lower branches, followed by needle drop
For more information see:       UW Plant Disease Facts D0093
Cytospora Canker Cytospora Canker
Hosts:  Colorado blue spruce, other spruces
Pathogen:   Cytospora kunzei
Signs/Symptoms:  Branch dieback with milky-white patches of dried sap on affected branches
For more information see:       UW Plant Disease Facts D0037
Spruce Needle Drop Spruce Needle Drop
Hosts:  Spruces
Pathogen:   Unknown (possibly Setomelannoma holmii)
Signs/Symptoms:  Needle loss and dieback at or near branch tips
Gymnosporangium Rust Gymnosporangium Rusts
Hosts:  Juniper, apple, crabapple, hawthorn, quince
Pathogen:   Gymnosporangium spp.
Signs/Symptoms:  Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts)
For more information see:       UW Plant Disease Facts D0058
Phomopsis Tip Blight Phomopsis Tip Blight
Hosts:  Junipers
Pathogen:   Phomopsis juniperovora
Signs/Symptoms:  Browning and dieback of branch tips  in spring and early summer as new growth emerges
For more information see:       UW Plant Disease Facts D0077
Diplodia Shoot Blight and Canker Diplodia Shoot Blight and Canker
Hosts:  Austrian pine, other pines
Pathogen:   Diplodia spp.
Signs/Symptoms:  Dieback of branch tips with dead needles showing uneven lengths
For more information see:       UW Plant Disease Facts D0042
Dothistroma Needle Blight Dothistroma Needle Blight
Hosts:  Austrian pine, other pines
Pathogen:   Dothistroma pini
Signs/Symptoms:  Needle tip browning and death with a distinct break between live and dead tissue
For more information see:       UW Plant Disease Facts D0043
Drought Stress Drought Stress
Hosts:  All conifers
Cause:   Insufficient water
Signs/Symptoms:  Purpling/browning of needles near branch tips or higher up in plants during the summer
Winter Injury Winter Injury/Winter Burn
Hosts:  All conifers, particularly yew and juniper
Cause:   Insufficient water
Signs/Symptoms:  Needle browning/bleaching over winter or in spring as plants come out of dormancy
For more information see:       UW Plant Disease Facts D0127
Herbicide Damage Herbicide Damage
Hosts:  All conifers
Cause:   Exposure to herbicides
Signs/Symptoms:  Twisted or otherwise distorted growth, needle yellowing or browning, plant death
For more information see:       UW Plant Disease Facts D0060

For more information on conifer diseases:  See https://pddc.wisc.edu/ or contact your county Extension agent.

Lawn Disease Quick Reference

Snow Mold
Snow Mold

Snow Molds
(Microdochium nivale and Typhula spp.)

Occurrence: Early to late spring
Favorable Conditions: Cold wet weather with periods of prolonged snow cover over unfrozen ground often leading to the most severe damage
Hosts: Kentucky bluegrass, tall fescue, perennial ryegrass
Symptoms: Circular, matted, gray to straw-colored patches ranging from a few inches to a foot or more in diameter
Management: Remove leaf litter from lawns. Mow lawns until dormant in the fall. Avoid heavy fertilizer applications (greater than 0.5 lb. N/1,000 sq. ft.) late in the year. Rake and lightly fertilize damaged areas in the spring to encourage recovery. Reseed lawns as needed.


Necrotic Ring Spot
Necrotic Ring Spot

Necrotic Ring Spot
(Ophiosphaerella korrae)

Occurrence: Spring, summer and fall
Favorable Conditions: Cool (soil temperatures of 55 to 65oF) and wet conditions for infection, followed by heat and drought stress for symptom development; most severe when soil compaction limits rooting
Host: Kentucky bluegrass
Symptoms: Circular, straw-colored patches usually less than 12 inches in diameter; regrowth often occurring in the center of patches, creating a “frog-eye” appearance; most common in newly sodded lawns, but also occurring in seeded lawns
Management: Reduce soil compaction and improve lawn drainage. Maintain proper fertility.


Fairy Ring
Fairy Ring

Fairy Rings
(many mushroom-forming fungi)

Occurrence: Anytime
Favorable conditions: Warm, wet weather; significant thatch accumulation
Hosts: All cool-season lawn grasses
Symptoms: Type I: a ring or arc (up to several feet in diameter) of lush, dark green grass bordered by a band of dead turf, with or without mushrooms; Type II: a ring or arc of lush dark green grass with no band of dead turf, with or without mushrooms; Type III: a ring or arc of mushrooms with no band of lush green turf or dead turf
Management: Lightly fertilize and routinely core aerate lawns.


Summer Patch
Summer Patch

Summer Patch
(Magnaporthiopsis poae)

Occurrence: Summer
Favorable conditions: Hot, moist conditions; alkaline (i.e., high) soil and thatch pH
Hosts: Kentucky bluegrass, fine fescues
Symptoms: Ring-like patches of wilted turf up to 3 inches in diameter, similar to those of necrotic ring spot (see above), and with rings often merging into larger irregular patches
Management: Avoid excessive watering during hot periods. Core aerate to promote root growth and reduce compaction. Use acidifying fertilizers to lower thatch pH to below 6.5.


Dollar Spot
Dollar Spot

Dollar Spot
(Clarireedia jacksonii)

Occurrence: Summer
Favorable conditions: High humidity; low nitrogen fertility
Hosts: Kentucky bluegrass, perennial ryegrass, fine fescues
Symptoms: Bleached patches ranging from a few inches to a foot in diameter, with leaf blades (inset) having bleached, hourglass-shaped areas
Management: Water deeply and infrequently early in the morning to minimize prolonged periods of leaf wetness. Apply nitrogen to alleviate symptoms.


Red Thread
Red Thread

Red Thread
(Laetisaria fuciformis)

Occurrence: Spring through fall
Favorable conditions: Wet, cool conditions
Hosts: Kentucky bluegrass, perennial ryegrass, fine fescues
Symptoms: Irregular beige patches ranging from a few inches to a few feet in diameter (oftentimes merging into irregular patterns) with red, thread-like filaments among the grass blades
Management: Collect clippings when disease is active. Maintain adequate nitrogen fertility.


Rust
Rust

Rust
(Puccinia spp., Uromyces spp.)

Occurrence: Summer and fall
Favorable conditions: High humidity, low soil moisture, low nitrogen fertility, shade
Hosts: Kentucky bluegrass, perennial ryegrass
Stand Symptoms: Reddish-brown, powdery areas (masses of fungal spores) that can discolor clothing and equipment
Management: Maximize light and airflow in lawns by pruning and thinning surrounding landscape plants. Water and lightly fertilize.

For more information on lawn diseases:  See UW Plant Disease Facts D0051, D0059, D0073 and D0092; UW Bulletin A3187 (available at http://learningstore.uwex.edu); contact the UW-Madison Turfgrass Diagnostic Lab (see https://tdl.wisc.edu/); or contact your county Extension agent.