Physical controls stop pests by blocking, trapping or removing them by hand, and they work best when matched to the pest’s habits: row cover over brassicas and squash with its edges sealed to the ground, collars around transplant stems against cutworms, shallow traps for slugs, and daily handpicking of large pests. Cover only on ground that did not hold the same crop last year, or you seal overwintering pests in with the plants.
Physical pest controls use barriers, traps and manual removal to keep pests off crops without chemicals.
Handpicking Works When Someone Is Assigned
Handpicking is the simplest control and, for pests you can see, often the most effective. It fails when it is nobody’s job. The carrier recommends a daily patrol by children and older adults (Children and Elderly Roles). Targets and timing:
- Colorado potato beetles: adults, and the orange egg masses on leaf undersides.
- Tomato hornworm: large green caterpillars; easy to find by their droppings.
- Squash bug: adults, and egg masses on leaves.
- Japanese beetles: shake into a bucket of soapy water in the early morning, when they are sluggish.
- Slugs: go out at dusk or after rain with a light.
Barriers
Row cover. Light spunbond or other fabric draped over a crop keeps flying insects from laying eggs. The carrier recommends it for brassicas against cabbage moth and for cucurbits against squash vine borer.
- Seal the edges completely with soil or boards; a gap is an entrance.
- Cover only ground that did not carry the same crop family last year. Pests that overwinter in the soil emerge under the cover and have the plants to themselves (Crop Rotation for Disease Break).
- Remove the cover at flowering when the crop needs insect pollination (squash, cucumber).
- Allow for heat and for the plants’ growth; slack material leaves room.
Cardboard collars. Wrap a collar of about 3 inches around a transplant stem at the soil line to stop cutworms. Press it a little into the soil.
Copper tape. The carrier says copper strips around beds repel slugs. The cause it gives, an electric reaction, is disputed, and field results are mixed; a continuous clean band, kept free of soil and bridging leaves, is the condition for any effect. Treat it as a minor tool.
Fine mesh for seedlings. For stored food barriers see Physical Barriers.
Traps
- Beer trap for slugs. Bury a cup with its rim at soil level, half filled with beer. Slugs fall in and drown. Empty and refill every few days; traps attract slugs from neighbouring beds, so place them at the edge of the crop, not in the middle.
- Board trap. A board laid on the soil between rows shelters slugs, earwigs and pill bugs by day. Lift it each morning and collect them.
- Sticky boards. Yellow boards coated in resin or fat catch whitefly, aphids and flea beetles. Use them to monitor (Monitoring and Identification) and sparingly to control, because they also catch hoverflies and parasitic wasps.
A Daily Patrol Costs Two Person-Hours And Pays Only Above The Threshold
A patrol of two people for one hour a day over a 100 m² potato patch costs 2 person-hours per day. The threshold arithmetic (Action Thresholds) tells you when the cost is justified: if larvae are below the action level, reduce the patrol to two or three times a week; if above, patrol daily.
Netting And Wildlife
Loose netting can entangle birds, snakes and bats. Use taut netting on a frame, with a mesh that cannot trap limbs, and check it daily. Remove it when the danger has passed.
Common Mistakes
- Covering infested ground. The cover seals the pest in.
- Leaving gaps at the edges. One hole lets in every moth.
- Placing beer traps among the crop. They draw slugs to the plants.
- Forgetting to remove the cover at flowering. No pollination, no squash.
- Handpicking without disposing. Drop pests in soapy water, or feed them to poultry.
What’s Next
- Learn next: Trap Cropping Strategies — a living trap
- Combine with: Duck Patrols for Slugs and Snails — animals that do the picking