COMMON DISEASES OF
GREENHOUSE FLOWER
CROPS
Greenhouse Floriculture Workshop
Feb 17, 2017
Sarah Jandricic
Common Foliage Diseases
Botrytis cinerea - Symptoms
• flower spotting, leaf blights, stem cankers, bulb rots
• Grows saprophytically on dead tissue (e.g. fallen flowers)
• Grows pathogenically (parasite) on healthy tissue
Bract blotches on
Poinsettia Sporulating grey mold
The Powdery mildews - Symptoms
• White fluffy powdery growth on leaves, stems and
flowers
• Begins as small discrete spots; spreads to cover entire
upper leaf surface
• Severe infections can cause leaf stunting, yellowing and
curling
The Downy Mildews - Symptoms
• Patches of leaf yellowing - initial infection (upper) – Angular yellow patches
– Some cause leaf drop
– Distortion of new growth/stunting
• Sporangia produced on under leaf surface
• Transmitted by air, water, seed (coleus)
Rose Hardy geranium
Plant Viruses - Symptoms
• Stunting of plant growth
• Mosaic or ring spot pattern on the leaves
• Yellow spotting or mottling on leaves
• Crinkling or curling of leaf margins
• Malformation of growing point
• NO CURE FOR VIRUSES!
– Purchase Virus-free plants for stock each year
– Weed control is essential
– Sanitation and disinfection equipment and benches critical
– Destroy infected plants!
Common Crown and Root
Diseases
Crown and Root Rots
Pythium, Rhizoctonia, Phytophthora,
Fusarium and Thielaviopsis (black root
rot)
• Occur any time during plant growth
phase
• Stressed plants are most at risk
– High/low temperatures
– Wet/dry moisture extremes
• Also spread by fungus gnats and
shoreflies
Fungus gnat larva
Begonia propagation with Rhizoctonia
Fusarium
• Sudden wilting
• Often one side of plant only
• Lower stem rot
Black Root Rot (Theilaviopsis)
• Stunting
• Yellowing of new foliage
• Sudden death
• Dark roots
• Often affects rooted plugs
• Yellowing of foliage
• Wilting/stunting
• Brown roots
- cortex sloughs off
Pythium
Phytopthora
• Attacks roots and crowns
• Older foliage turns reddish brown/grey
• Symptoms first appear on one branch then spreads
Crown and Root Rots
• Above Ground Symptoms:
– Stunting/poor leaf expansion
– Uneven or poor branching
– Foliage off colour; yellowing of older leaves
– Wilting when sunny yet not dry
– Destroys crop uniformity
Poinsettia crop with…
what?
Impatiens with Pythium
ROOT ROTS LOOK THE SAME!
- Why sending samples to Lab Services in Guelph is critical
- Misdiagnosis leads to using the wrong fungicide
- Waste of time, money, and may lead to loss of crop
1. Soil – Under benches, people’s feet, machinery
– E.g. Fusarium, Pythium, Thielaviopsis, Rhizoctonia
2. Debris from Previous Crops – Erwinia, Pythium, Botrytis
– Viruses
3. Plants kept all year – Pet Plants, Stock plants, Ignored weeds under benches
– E.g. powdery mildew, rusts
– viruses
4. Cuttings – Ralstonia, Verticillium, Fusarium wilts
– Viruses
5. Water – Pond Water: Phytopthora, Pythium
– City water: Fusarium
Sources of Disease
Disease Management
Managing Disease -Disease Triangle
(susceptible) (virulent)
(favourable to pathogen)
- Proper
Ventilation
- Temp. control
to avoid
condensation
- Plant spacing
- Don’t overwater
- Clean trays/pots
- Disinfection
- Eliminate
weeds
- Water treatment
- Microbials
- Fungicides
- Less susceptible
varieties
- Reduce stress
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