How to Protect Your San Diego Garden from Pests & Diseases Year-Round

The San Diego Pest Calendar: Seasonal Focus

San Diego's mild climate means we don't get a hard winter freeze that kills off pest populations. Instead, our pest and disease cycles shift seasonally and you need a year-round awareness. Here's when to focus on what:

Winter (December–February)

• Snails & slugs: Our rainy season wakes them up. Set out iron phosphate bait before each rain event. Full snail guide here.
• Scale insects: Dormant oil spray on deciduous fruit trees in January–February smothers overwintering scale and mite eggs. Do this before bud break.
• Powdery mildew on dormant roses: Prune out infected canes and apply sulfur fungicide at pruning time (Valentine's Day is the traditional San Diego rose pruning date).
• Citrus leafminer: Watch for the characteristic squiggling tunnels in new citrus growth as temperatures warm in late February.

Spring (March–May)

• Aphids: Population explosion as new plant growth emerges. Begin weekly plant inspections. Release ladybugs in the evening on wet foliage. Full aphid guide.
• Caterpillars: Cabbage loopers arrive with brassica planting. Pre-treat with Bt spray when you set out transplants.
• Whiteflies on tomatoes: Set yellow sticky traps at planting time before populations build.
• Powdery mildew on cucurbits: Begin preventive sulfur or potassium bicarbonate sprays when squash vines are 6–8 inches long.

Summer (June–September)

• Spider mites: Peak season July–September in hot inland areas. Check weekly — they double in population every 7 days in extreme heat. Full spider mite guide.
• Tomato hornworms: Scout daily during peak season (July–August). Battle plan here.
• Drought stress: The silent killer. Check irrigation systems monthly and inspect plants for stress signs. 5 drought stress signs.
• Root rot in overwatered containers: Summer heat + overwatering = rapid Phytophthora root rot. Reduce container watering frequency during heat spikes.

Fall (October–November)

• Pre-rain snail prep: Apply iron phosphate bait and reduce debris piles before the first rains arrive.
• Cleanup as pest prevention: Remove spent summer vegetables, cut back dead perennials, and haul out leaf piles to destroy overwintering pest habitat.
• Whitefly on cool-season crops: Cabbage, broccoli, and kale are magnets. Row cover fabric at planting prevents establishment.
• Citrus harvesting and feeding: Feed citrus after harvest to set up next year's crop. Watch for Asian citrus psyllid (lumpy new growth) — report suspected sightings to the county.

Monthly Checklist

1. Inspect weekly: Walk every bed and check undersides of leaves on susceptible plants (tomatoes, roses, citrus, squash).
2. Check irrigation: Run each zone manually and verify all emitters are firing correctly. Replace clogged drip emitters immediately.
3. Remove debris: Rake out leaf litter from under trees and shrubs monthly — this is #1 for snail and scale control.
4. Refresh mulch: Keep 3–4 inches of mulch over all beds; reapply when it thins below 2 inches.
5. Feed appropriately: Fertilize growing season plants monthly. Stop feeding most plants in November to avoid pushing tender growth before cool weather.
6. Pull weeds early: Weeds host pest populations and compete for water. Pull before they flower and set seed.

Landscape Upgrades That Build Resilience

Individual pest treatments address symptoms. Long-term resilience comes from landscape design decisions that reduce vulnerability in the first place:

• Drip irrigation over overhead: Wet foliage is the primary trigger for powdery mildew, botrytis, and rust. Drip systems eliminate this.
• Raised beds with quality soil: Removes the alkaline native soil problem that causes chronic nutrient deficiencies.
• Diverse plantings: Monocultures are pest and disease magnets. Intermixing plant families and including flowering companions supports beneficial insect populations.
• Right plant, right place: A Mediterranean plant in shade + overwatering is a disease setup. Matching plants to their actual needs is the most impactful change most homeowners can make.

Whether you're dealing with a specific pest today or want to build long-term garden resilience, we're here to help. Hablamos Español — reach out any time.