Late July marks the peak of tomato season in Quebec and across Canada. However, the combination of summer heat and humidity creates ideal conditions for fungal diseases to spread and pests to arrive. Inspect your vegetable garden regularly to act quickly and secure an abundant, delicious harvest right through to the fall.
To deepen your growing knowledge, explore our practical guides on growing tomatoes in pots or in the ground as well as the 5 pillars of tomato care.
Identify and Eliminate Fungal Diseases
Fungal spores spread rapidly through wind and splashing water. Adopt simple preventive steps today to stop disease in its tracks.
1. Late Blight
This destructive fungal disease ruins foliage and rots fruit in just a few days.
- Symptoms: Dark brown or black greasy-looking spots on leaves, followed by rapid drying of the foliage.
- Prevention: Space plants well to ensure maximum air circulation. Stake main stems securely and prune lower leaves that touch the soil. Always water directly at the base without wetting the foliage. Amend soil in spring with Botanix marine compost with peat and shrimp to promote healthy root development.
- Treatment: Immediately remove and destroy infected leaves and stems. Sterilize your pruners with rubbing alcohol between each cut. Apply a copper-based organic fungicide to protect healthy plant tissue.
2. Powdery Mildew
Powdery mildew often appears during hot days paired with humid nights.
- Symptoms: A distinct white, powdery coating on upper or lower leaf surfaces.
- Prevention: Prune suckers to open up the canopy and avoid high-nitrogen fertilizers.
- Treatment: Cut off affected leaves. Spray a natural fungicide or insecticidal soap as soon as white spots appear.
3. Early Blight (Alternaria)
Very common in local gardens, this fungal issue weakens plants if left unchecked.
- Symptoms: Circular brown spots with target-like concentric rings on older bottom leaves.
- Prevention: Apply organic mulch to stop soil-borne spores from splashing onto foliage during watering.
- Treatment: Remove damaged foliage and spray with a copper fungicide.
Stop Destructive Insect Attacks
Insects weaken plants and can transmit harmful viruses. Check under leaf surfaces and along main stems regularly.
4. Aphids
These tiny sap-sucking pests gather on young shoots and weaken plant growth.
- Symptoms: Curling leaves and a sticky honeydew residue on foliage.
- Prevention: Plant marigolds or lavender nearby to repel them, or grow nasturtiums as a trap crop.
- Treatment: Knock them off with a strong blast of water or spray natural insecticidal soap directly on the colony.
5. Tomato Hornworm
This large green caterpillar blends seamlessly into foliage and can strip a plant bare in days.
- Symptoms: Bare branches and dark, coarse droppings on leaves or near the base.
- Prevention: Inspect upper foliage daily for missing leaves.
- Treatment: Hand-pick the caterpillar and dispose of it. For severe infestations, apply an organic Bacillus thuringiensis (BT) spray.
6. Whiteflies
These tiny winged insects thrive in warm, sheltered garden beds.
- Symptoms: Clouds of small white flies rising whenever you disturb the plant.
- Prevention: Hang yellow sticky traps near tomato plants early in the summer.
- Treatment: Spray insecticidal soap on leaf undersides every 3 days for 2 to 3 weeks.
7. Leafminers
Leafminer larvae tunnel inside leaf tissue, leaving unsightly marks.
- Symptoms: Wavy, whitish trails visible across the leaf surface.
- Prevention: Cover young plants with floating row covers in spring and rotate crop locations yearly.
- Treatment: Pinch the leaf to squash the larva inside or remove damaged foliage manually.
Correct Common Physiological Disorders
Some symptoms stem from environmental stress and watering habits rather than pests or fungi.
8. Blossom End Rot
This issue occurs when plants cannot take up calcium properly, usually triggered by inconsistent watering or nutrient shortages in the soil.
- Symptoms: A flat, leathery black patch on the bottom of the tomato opposite the stem.
- Prevention: Water deeply and consistently, especially during summer heatwaves. Add a 5 to 7 cm layer of mulch around the base to keep soil moisture uniform. Apply Botanix Natur calcium-enriched natural vegetable fertilizer regularly to prevent calcium deficiency.
- Treatment: Remove damaged fruit so the plant directs energy into new tomatoes. Adjust your watering schedule immediately.
Protect Your Compost: The Golden Rule
Never put diseased leaves or pest-infested plants into your home compost bin. Fungal spores and larvae survive cold winter temperatures and will infect next year’s crops. Place infected material into regular household garbage or burn it where local regulations allow.
Follow these practical care steps today to keep your plants strong and harvest delicious tomatoes all summer long!
