How to Manage Summer Plant Diseases in Vancouver Gardens

Summer in Vancouver means long days, vibrant growth—and, unfortunately, ideal conditions for fungal diseases. Humid air, cool nights, and dense foliage provide the perfect environment for common outdoor fungal issues like powdery mildew, rust, and leaf spot.

These fungal diseases can spread quickly on flowers, vegetables, and shrubs. But with the right approach, you can prevent many infections—or catch them early and manage them effectively. Here’s your guide to identifying and managing summer fungal diseases in Vancouver’s coastal climate.

Common summer plant diseases in Vancouver

Powdery mildew often appears on the tops of leaves like a dusting of flour.

Powdery mildew

Symptoms: A white or grey powder-like coating on leaves, stems, or buds.

Common hosts: Squash, cucumbers, roses, bee balm, phlox, and other ornamentals.

Risks: Can weaken plants over time, reduce flowering, and lead to poor vegetable yields—especially in squash and cucumbers.

Prevention and control:

• Improve air circulation by spacing plants appropriately, and if needed, thinning out overcrowded plants.
• Avoid getting water on the leaves of plants. Water the soil, not the leaves, ideally in the morning so foliage has time to dry before nightfall.
• Remove affected leaves early to limit spread.
• Treat affected plants with a sulphur or potassium bicarbonate spray such as Safer’s Defender Garden Fungicide.

Rust is a fungal disease that looks like it sounds!

Rust

Symptoms: Raised orange, yellow, or reddish spots on leaves.

Common hosts: Hollyhocks, garlic, fuchsias, and snapdragons.

Risks: Severe infections can cause premature leaf drop, weaken perennials, and reduce the energy available for blooming or bulbing.

Prevention and control:

• Avoid overhead watering and prune for airflow.
• Remove and dispose of infected foliage (don’t compost).
• Mulch soil to reduce spore splash-back.
• Apply a copper-based fungicide preventatively.
• Don’t replant susceptible plants in the same spot for several years.

Some leaf spot diseases can cause leaf curl.

Leaf Spot (e.g. Septoria, Anthracnose, Diplocarpon)

Symptoms: Tan, black, or brown spots—sometimes with yellow halos.

Common Hosts: Tomatoes, hydrangeas, peonies, roses, and leafy vegetables.

Risks: Can rapidly defoliate plants, reduce photosynthesis, and impact fruit production or ornamental appearance.

Prevention and Control:

• Water only at soil level.
• Clean up fallen leaves and debris promptly.
• Improve spacing and airflow.
• Use sulphur or copper-based fungicides as needed.
• For perennials such as roses, spray with a dormant oil to smother overwintering spores.

Botrytis, also called simply grey mold, can impact a range of plants.

Botrytis (Grey Mold)

Symptoms: Fuzzy grey mold, especially on damaged or fading flowers and fruit.

Common Hosts: Strawberries, peonies, lettuces, and other soft tissue plants.

Risks: Can cause rot on blossoms, fruits, and stems—potentially ruining harvests or key ornamental displays. Spreads quickly in cool, damp weather.

Prevention and Control:

• Remove spent flowers and rotting foliage.
• Avoid overcrowding and overwatering.
• Treat early with organic fungicides.

Preventing summer plant diseases in Vancouver

Even in Vancouver’s humid climate, you can reduce the risk of fungal outbreaks with these simple practices:

• Water early and low: Morning is best. Water directly at the base of plants to avoid wet leaves, or install drip irrigation that targets root zones without spraying leaves.
• Thin and prune regularly: Good air circulation is your first line of defence.
• Mulch wisely: Use organic mulch to suppress spores—but keep it from touching plant stems.
• Sanitize tools and clean up debris: Fungi can spread via tools, hands, and fallen plant matter.
• Plant with airflow in mind: Leave space between plants and avoid overcrowding, especially in raised beds or containers.
• Rotate vegetable crops annually: Practicing crop rotation helps prevent soil-borne fungi from gaining a foothold.

Safer’s garden fungicides help to control powdery mildew, black spot and rust.

When to use organic fungicides

Fungicides work best preventatively or at the very first sign of infection. In our pollinator-rich gardens, organic options like sulphur, copper, and potassium bicarbonate are generally safe when used correctly. Always follow label directions and avoid applying in full sun or during extreme heat.

Need help identifying a problem?

Send a photo or bring bagged leaf sample to Figaro’s Garden and our knowledgeable team will help you diagnose the issue and recommend the best treatment—whether it’s a pruning tip or an organic spray.

Outdoor fungal diseases are common in Vancouver’s summer gardens, but they don’t have to take over. With smart watering, good airflow, and early intervention, you can keep powdery mildew, rust, leaf spot, and other fungal foes under control—and enjoy a thriving garden all season long.