🐛 Biological Pest & Disease Control

Prevention: The First Line of Defense

The most effective pest control is preventing problems before they start. Healthy, vigorous plants in balanced ecosystems naturally resist most pest and disease problems.

Cultural Prevention Methods

• Build healthy soil: Plants growing in nutrient-rich, biologically active soil are more resistant to pests and diseases
• Choose resistant varieties: Many modern cultivars are bred for disease resistance
• Proper spacing: Good air circulation prevents fungal diseases and makes it harder for pests to move between plants
• Crop rotation: Move plant families to different beds annually to break pest and disease cycles
• Timing: Plant when pests are less active or after peak infestation periods
• Water properly: Water at soil level in morning so foliage dries quickly
• Sanitation: Remove diseased plant material promptly, clean tools between plants
• Mulch: Prevents soil-borne diseases from splashing onto leaves

Common Garden Pests: Identification & Control

Aphids

Identification: Small (1-3mm), soft-bodied insects in green, black, yellow, or pink. Cluster on new growth and undersides of leaves. Excrete sticky honeydew.

Damage: Stunted growth, curled leaves, sooty mold on honeydew

Biological Controls:

• Water spray: Strong jet dislodges aphids. Repeat every 2-3 days
• Beneficial insects: Ladybugs, lacewings, hoverflies eat aphids voraciously
• Insecticidal soap: Spray directly on aphids. Safe for beneficials once dry
• Companion plants: Nasturtiums attract aphids away from other plants
• Neem oil: Disrupts aphid reproduction and feeding

Caterpillars & Cabbage Worms

Identification: Green or brown larvae of various moths and butterflies. Chew holes in leaves, often leaving dark frass (droppings)

Damage: Large holes in leaves, can defoliate plants rapidly

Biological Controls:

• Hand-picking: Check plants daily, especially undersides of leaves for eggs
• Bt (Bacillus thuringiensis): Biological pesticide specific to caterpillars. Harmless to other insects, humans, and pets
• Row covers: Exclude adult moths and butterflies from laying eggs
• Birds: Encourage chickadees, wrens, and other insect-eating birds
• Parasitic wasps: Trichogramma wasps parasitize caterpillar eggs

Slugs & Snails

Identification: Soft-bodied mollusks, leave silver slime trails. Feed at night on leaves and seedlings

Damage: Irregular holes in leaves, entire seedlings consumed, slime trails visible

Biological Controls:

• Beer traps: Bury containers level with soil, fill with beer. Slugs drown
• Copper barriers: Copper tape or mesh around beds - slugs won't cross
• Iron phosphate bait: Organic bait (Sluggo) - safe for pets, wildlife, and soil organisms
• Hand-picking: Go out at night with flashlight, drop slugs in soapy water
• Diatomaceous earth: Sharp particles cut slug bodies. Reapply after rain
• Habitat modification: Remove hiding places (boards, dense mulch near plants)
• Predators: Encourage ground beetles, toads, birds, ducks

Whiteflies

Identification: Tiny white flying insects (1-2mm). Cloud of flies when plant disturbed. Nymphs on leaf undersides

Damage: Yellowing leaves, stunted growth, honeydew and sooty mold

Biological Controls:

• Yellow sticky traps: Attract and trap adult whiteflies
• Vacuum: Use handheld vacuum in early morning when flies are sluggish
• Insecticidal soap: Spray undersides of leaves thoroughly
• Neem oil: Disrupts whitefly lifecycle
• Encarsia formosa: Parasitic wasp for greenhouse whitefly control
• Reflective mulch: Confuses whiteflies, reduces landing on plants

Spider Mites

Identification: Microscopic arachnids (not insects). Fine webbing on leaves, stippled yellow leaves

Damage: Leaf stippling, bronzing, eventually leaf drop. Worse in hot, dry conditions

Biological Controls:

• Water spray: Strong spray dislodges mites and increases humidity
• Predatory mites: Phytoseiulus persimilis eats spider mites
• Ladybugs: Some species specialize in mites
• Neem oil: Spray all leaf surfaces including undersides
• Increase humidity: Mites thrive in dry conditions
• Remove heavily infested leaves: Dispose in trash, not compost

Japanese Beetles

Identification: Metallic green and copper beetles (1cm). Skeletonize leaves, leaving only veins

Damage: Rapid defoliation of roses, fruit trees, vegetables

Biological Controls:

• Hand-picking: Drop into soapy water in early morning when sluggish
• Milky spore: Biological control for grubs in lawn (takes 2-3 years to establish)
• Beneficial nematodes: Apply to soil to kill grubs
• Row covers: Exclude beetles during peak season (late June-July)
• Trap crops: Plant preferred hosts (roses, grapes) away from main garden
• **Avoid pheromone traps**: Actually attract more beetles to your yard

Squash Bugs

Identification: Brown or gray shield-shaped bugs (1.5cm). Eggs in neat rows on leaf undersides

Damage: Wilting leaves, stunted plants, eventual plant death

Biological Controls:

• Egg removal: Check plants daily, scrape off egg clusters
• Hand-picking: Adults are slow-moving, easy to catch
• Trap boards: Place boards near plants. Bugs hide underneath at night, collect in morning
• Row covers: Cover plants until flowering, then hand-pollinate
• Companion plants: Nasturtiums, tansy, catnip may repel
• Tachinid flies: Parasitize squash bugs (plant flowers to attract)

Beneficial Insects: Your Garden Allies

Encouraging beneficial insects is one of the most effective biological control strategies. These natural predators and parasitoids keep pest populations in check.

Key Beneficial Insects

How to Attract Beneficial Insects

• Plant diverse flowers: Include plants that bloom throughout the season
• Small flowers matter: Many beneficials prefer tiny flowers (herbs, umbellifers)
• Avoid pesticides: Even organic sprays can harm beneficials
• Provide water: Shallow dishes with pebbles for landing
• Create habitat: Leave some areas undisturbed, provide shelter
• Tolerate some pests: Beneficials need pests to survive - aim for balance, not elimination
• Plant native species: Native plants support native beneficial insects

Common Plant Diseases

Powdery Mildew

Symptoms: White powdery coating on leaves, stems, buds. Leaves may curl and yellow

Prevention:

• Choose resistant varieties
• Ensure good air circulation (proper spacing, pruning)
• Water at soil level, not foliage
• Avoid excessive nitrogen fertilization

Biological Controls:

• Baking soda spray: 1 tbsp baking soda + 1 tsp horticultural oil per quart water
• Milk spray: 1 part milk to 9 parts water, spray weekly
• Sulfur: Preventive fungicide (don't apply in hot weather)
• Neem oil: Both preventive and curative
• Remove affected leaves: Dispose in trash, not compost

Early & Late Blight (Tomatoes, Potatoes)

Symptoms: Brown spots on leaves, often with yellow halo. Can spread to fruit

Prevention:

• Crop rotation (3-4 year minimum)
• Mulch to prevent soil splash
• Water at soil level only
• Space plants for air circulation
• Remove lower leaves that touch ground
• Choose resistant varieties

Biological Controls:

• Copper fungicide: Apply preventively or at first sign
• Compost tea: Spray foliage weekly with actively aerated tea
• Remove infected leaves: Dispose immediately, sterilize tools
• Baking soda spray: Can slow progression

Damping Off (Seedlings)

Symptoms: Seedlings collapse at soil line, stems appear water-soaked

Prevention:

• Use sterile seed-starting mix
• Don't overwater
• Provide good air circulation (fan on low)
• Don't sow seeds too deeply or densely
• Maintain proper temperature

Biological Controls:

• Chamomile tea: Spray seedlings and soil surface
• Cinnamon: Dust soil surface (natural fungicide)
• Compost tea: Drench soil with beneficial microbes
• Improve conditions: More light, less water, better air flow

Fusarium & Verticillium Wilt

Symptoms: Yellowing and wilting of leaves, often one side of plant first. Vascular browning visible in stems

Prevention:

• Choose resistant varieties (VF, VFN notation)
• Long crop rotation (5+ years)
• Solarize soil before planting
• Don't plant tomatoes/peppers where previous crop had wilt

Biological Controls:

• No cure once infected: Remove and destroy plants
• Beneficial fungi: Trichoderma species compete with pathogens
• Compost: Beneficial microbes suppress disease organisms
• Soil solarization: Clear plastic in summer, 4-6 weeks

Physical & Mechanical Controls

Row Covers & Netting

Lightweight fabric excludes pests while allowing light and water through:

• Floating row covers: Exclude cabbage moths, flea beetles, squash bugs
• Insect netting: Finer mesh for tiny pests like thrips
• Bird netting: Protects fruit from birds
• Remove for pollination: Uncover when plants flower or hand-pollinate

Barriers & Traps

• Cutworm collars: Cardboard tubes or plastic cups around seedlings
• Copper tape: Around pots and beds to repel slugs
• Sticky traps: Yellow for whiteflies/aphids, blue for thrips
• Pheromone traps: Monitor pest populations (not always good for control)
• Tree bands: Sticky bands prevent crawling insects from reaching fruit

Timing & Plant Selection

• Early planting: Harvest before peak pest season
• Late planting: Miss first generation of pests
• Succession planting: If one crop fails, another is coming
• Resistant varieties: Check seed catalogs for disease codes

Biological Sprays & Treatments

When to Use Biological Pesticides

Even biological controls should be used judiciously as a last resort. Many can harm beneficial insects along with pests. Always try prevention, physical controls, and attracting natural predators first.

Least-Toxic Options

• Bacillus thuringiensis (Bt): Specific to caterpillars, safe for everything else
• Insecticidal soap: Fatty acids kill soft-bodied insects, safe once dry
• Horticultural oil: Smothers pests, use dormant oil in winter
• Neem oil: Disrupts insect feeding and reproduction, use carefully
• Diatomaceous earth: Physical barrier, food-grade only
• Spinosad: Bacterial fermentation product, broad-spectrum but organic
• Pyrethrin: Botanical insecticide from chrysanthemums, kills beneficials too

Application Best Practices

• Spray in evening to minimize harm to pollinators
• Target undersides of leaves where pests hide
• Spray to point of runoff for good coverage
• Reapply after rain or as directed on label
• Rotate products to prevent pest resistance
• Wear protective equipment even for organic sprays
• Follow label directions precisely

Integrated Pest Management (IPM)

IPM is a comprehensive approach that combines multiple strategies to manage pests economically and with minimal environmental impact:

IPM Steps

1. Monitor regularly: Check plants 2-3 times per week
2. Identify correctly: Know what you're dealing with
3. Determine threshold: Decide what level of damage is acceptable
4. Prevent: Use cultural practices to prevent problems
5. Control if needed: Start with least-toxic methods
6. Evaluate: Assess what worked and adjust strategy