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