The Online Gardener's Handbook 2010
Chapter 6: Ornamental Plants
Problem Areas on Ornamental Plants

Table of Contents

  1. Introduction
  2. Seedlings and Transplants
  3. Leaves or Needles
  4. Stem, Trunk or Branches
  5. Throughout Plant
  6. Roots or Tubers
  7. Buds and Young Shoots
  8. Flowers
  9. Learn More

Introduction

Use the following information as a guide when identifying the cause of your plant problems. Examine the damage on the plant and then refer to the corresponding section. Remember, however, that similar symptoms can result from different problems. When in doubt, consult a qualified specialist.

Seedlings and Transplants

Seedlings don't emerge, are stunted or wilt early

  • seed has lost viability
  • unfavourable soil conditions: too cold, too wet, too dry, compacted or with surface crusting
  • improper planting depth
  • damping-off disease, seed-borne fungal disease, bacterial disease
  • seed corn maggots, wireworms or similar insects
  • exposure to pre-emergence herbicides or to excessive fertilizer salts

Seedlings are cut off near the ground, or are badly chewed

  • insect and pest damage: cutworms or earwigs; slugs or snails; sowbugs or pill bugs
  • animal damage: birds feeding on seeds or seedlings; meadow mice, chipmunks, groundhogs, rabbits

Transplants wilt, develop dead areas on leaves or die

  • stems or roots damaged during transplanting; transplant shock
  • transplants diseased at the start
  • abiotic causes: over-fertilization; soil too wet or too dry; cold temperature or frost; transplants planted too deeply
  • damping-off and root rot fungi
  • insects such as white grubs or wireworms

Leaves or Needles

Dead spots on leaves

  • fungus leaf spot, blight, anthracnose, Botrytis, white mould, black spot (roses)
  • bacterial leaf spot or blight
  • injury from contact-type weed killers (paraquat) applied nearby

Scorched or browned leaf margins or interveinal areas

  • abiotic causes: severe temperature changes; soil too wet or too dry; over-fertilization; herbicide damage; salt injury; mechanical injury to root or stem
  • root rot
  • insect or nematode damage
  • feeding damage by mites or insects such as leafhoppers or thrips

Deformed leaves

  • herbicide injury, most often from lawn weed-killers
  • viral disease
  • frost or severe wind injury
  • infestation of aphids, leafhoppers or plant bugs

Abnormal growths on leaves

  • leaf curl or blister fungi
  • gall-forming insects, mites, or other organisms
  • edema or tan blistering

Grainy material or insect larva found in dead, hollowed out areas on leaves

  • leafmining insects; birch cedar leafminer

Small notches at leaf margins or lace-like skeleton leaves

  • leaf skeletonizer insects: pear or rose slug; elm or willow leaf beetle
  • young or small insects such as caterpillars and beetles
  • black-vine weevil; Taxus weevil

Sections of leaf completely missing, with ragged or clean-cut edges

  • caterpillars, cutworms, grasshoppers, leaf beetle, leaf cutter bees or ants
  • slugs or snails
  • groundhogs, rabbits, deer, etc.
  • severe wind injury or hail

Sticky deposit on leaves, can be sooty and black

  • sucking insects: aphids, mealybug, scale and whitefly

Yellowed leaves

  • abiotic causes: improper pH, nutrient deficiency, too wet or too dry, over-fertilization, herbicide injury from residues in soil
  • root rot
  • nematode infestation of roots
  • wilt disease, either bacterial or fungal
  • autumn shed of conifers

Bleached, bronzed or glazed leaves

  • abiotic causes: chilling injury, sun scald, desiccation by strong winds, air pollution, damage by dogs
  • mites, thrips or lacebugs

Red or purple leaves

  • abiotic causes: nutrient deficiency in soil (usually phosphorus) or high pH (alkaline), cold
  • temperature stress
  • poor root growth
  • needle cast of spruce

Mottled yellow and green leaves

  • virus, fungus or mycoplasma-like organism
  • plant bugs, leafhoppers or other leaf insects
  • Premature fall colouring
  • unfavourable soil conditions
  • damaged root systems
  • trees in state of decline

Mould on leaves

  • olive-green, black or dark brown: scab
  • sticky black: sooty mould
  • greyish-brown: Botrytis
  • white and fluffy: white mould
  • white and powdery: powdery mildew
  • rusty red or orange blisters: rust
  • shiny black: tar spot

Fine webbing on leaves

  • mites

Leaves rolled up or covered with silk webbing containing frass

  • tent caterpillars, fall webworm, ugly nest caterpillar, leafroller caterpillars, web spinning sawflies

Stem, Trunk or Branches

Sunken areas of dead bark; bark missing or cracking

  • cankers caused by fungi or bacteria
  • cankers caused by abiotic injury: winter injury, lightning, vandalism, power tools
  • animal damage: squirrels, porcupines, meadow mice, rabbits

Gum, resin, or sawdust-like frass on bark; ridging on bark

  • wood-boring insects
  • canker fungi or bacteria
  • mechanical wound
  • winter injury

Swellings on bark

  • crown gall
  • cedar apple or quince rust on juniper
  • fungus gall (Black Knot)
  • feeding or egg-laying by insects

Branches, twigs, or leaves with bumps that easily scrape off

  • scale

Branches and leaves rolled up or covered with silk webbing containing frass

  • scale insects, tent caterpillars, fall webworm, ugly nest caterpillar, leafroller caterpillars, web
  • spinning sawflies

Inner tissues of branch, stem, or trunk show discoloration or decay

  • outer wood (sapwood) discoloured: fungal wilt disease, fire blight, bacterial blight, wood decay
  • fungus
  • inner wood discoloured (fungi or mushrooms may be on bark or on ground nearby): winter injury or Armillaria root rot
  • discoloured stems on herbaceous plants: bacterial or fungal wilt disease

Branches die back from tips

  • shoot-boring insects
  • tip blight fungus or bacterial blight
  • winter injury

Throughout Plant

Plants wilt or die suddenly

  • abiotic causes: over-fertilization, exposure to high soluble salts, severe drought, root girdling,
  • winter injury
  • black walnut trees nearby
  • insects boring or tunnelling in stem
  • wilt or canker fungi or bacteria attacking roots and stem
  • root rot disease

Slow growth; sections die back; discoloration; premature fall colour

  • abiotic causes: winter injury, improper soil moisture, exposure to herbicides, salt injury, root
  • girdling
  • root gall disease
  • birch dieback, ash and maple decline
  • root rot disease
  • cankers or borers girdling trunk or stem
  • nematode infestation

Roots or Tubers

Plant pulls out easily; discolored roots; outer root pulls away from inner

  • root rot
  • soil too moist
  • root-feeding insects
  • nematode infestation

Swellings on roots

  • crown gall
  • root knot or cyst nematodes
  • normal root nodules on plants of the legume (pea) family

Tunnels in or on root

  • black vine or Taxus weevil, white grubs
  • rodents

Soft, smelly roots or rhizomes

  • bacterial soft rot

Buds and Young Shoots

Buds are dead, dry, or discoloured

  • abiotic causes: winter injury, stress during previous year caused poor bud set, salt spray from nearby road

Misshapen or swollen buds

  • insect or mite injury
  • virus or mycoplasma disease
  • herbicide injury

New shoots wilt and die

  • winter kill or frost injury (delayed effect)
  • fungal or bacterial blight
  • shoot-boring insects
  • girdling by rabbits and rodents

Flowers

Flowers do not appear

  • flower buds not produced the previous year
  • flower buds removed by pruning
  • winter kill or frost injury to buds

Flowers die without producing fruit

  • winter or frost injury
  • fungal or bacterial disease such as Botrytis, leaf spots and fire blight
  • poor pollination

Misshapen flowers

  • aphids, plant bugs or thrips
  • virus disease
  • aster yellows

Flowers eaten inside or on petals

  • aphids, corn rootworm beetles, earwigs, grasshoppers, rose chafer, Japanese beetle, thrips
  • slugs or snails

Learn More


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 25 July 2005
Last Reviewed: 28 June 2010