What's Eating Your Potato?

Hand-pick eggs, larvae, and adults into soapy water

Spinosad spray when pressure is overwhelming

If hand-picking can't keep up, spray spinosad (Captain Jack's Deadbug Brew or Monterey Garden Insect Spray, ~$12 to $15) on leaf tops and undersides at dusk. Repeat every 7 days for 2 to 3 rounds. Spinosad still works on most populations even where the beetles have evolved resistance to older chemicals.

Rotate potatoes away from last year's bed

Adults overwinter in the soil under the previous potato or tomato patch and emerge in spring to feed on whatever is planted there. Move potatoes at least 30 feet from last year's solanaceous beds. The further the better, since the beetles walk before they fly.

Strong water blast every 2 to 3 days for 2 weeks

Hold a hose nozzle 12 inches from the affected new growth and spray at high pressure. Most aphids dislodge and don't make it back. Repeat every 2 to 3 days for 2 weeks. The fastest, cheapest fix and works without chemicals that would kill aphid predators.

Lay reflective mulch between rows at planting

Roll out silver reflective plastic mulch (about $20 for a 25-foot roll) between potato rows. Winged aphids use the sky as a navigation cue, and the reflection disorients them so they don't land. The mulch also keeps the soil cooler, which potatoes like.

Insecticidal soap on heavy clusters at dusk

Spray ready-to-use insecticidal soap (Safer Brand, ~$10) on the underside of affected leaves at dusk. Soap kills on contact but doesn't persist, so it spares ladybugs and lacewings that arrive after the spray dries. Repeat every 5 days for 2 rounds.

Avoid planting potatoes in recently grassed soil

Wireworm populations build up in sod and pasture. The single biggest prevention is to wait 2 to 3 years after breaking ground before planting potatoes there. If you must plant in newly turned grass, expect damage and plan for it.

Trap with potato slices 2 weeks before planting

Rotate to non-host crops for 2 years

After a wireworm-damaged harvest, plant beans, peas, or lettuce in that bed for the next 2 years. Wireworm populations crash without root crops to feed on. Avoid corn, carrots, and other potatoes during the rotation.

Floating row cover from emergence to 6 inches tall

Lay lightweight floating row cover (Agribon AG-15, ~$25 for a 50-foot length) over the bed as soon as shoots emerge. Bury the edges with soil. The cover blocks the beetles entirely until plants are big enough to outgrow damage. Pull it off when plants hit 6 inches.

Spinosad spray on seedlings every 7 days

If row cover isn't an option, spray spinosad (Captain Jack's Deadbug Brew, ~$12) on seedlings at dusk every 7 days for the first month. Once plants are taller than 6 inches and the canopy fills in, you can usually stop spraying.

Plant a sacrificial trap row of radish

Sow a row of radishes 3 to 5 days before planting potatoes. Flea beetles strongly prefer radish leaves and concentrate there. Spray or pull the radishes once damage is heavy, removing the bulk of the local beetle population before they hit the potatoes.

Hand-pick at dusk under a UV blacklight

Bt spray on leaf undersides at dusk

Mix 1 teaspoon Bt (Monterey or Safer Caterpillar Killer, ~$15) per quart of water. Spray the underside of every compound leaf at dusk because Bt breaks down in sunlight. Reapply after rain or every 7 days until you stop seeing droppings.

Leave wasp-cocooned hornworms alone

If you find a hornworm covered in white rice-grain cocoons on its back, leave it on the plant. Those are braconid wasp pupae, and the wasps that hatch will hunt down more hornworms in the bed. The parasitized hornworm has stopped feeding and won't do further damage.