SPRING & AUTUMN · DAMP NIGHTS
Slugs
Ragged holes and silvery slime trails overnight. Seedlings and young transplants are most at risk.
Crop hub · Garden · Home garden
Basil & herbs
Ragged holes that appear overnight, with nothing to be seen by day, are usually slugs or snails. Clemson notes that slugs climb basil plants to feed, and UC IPM lists basil among the plants they damage. Leaves eaten to a lace of veins in summer are Japanese beetles. Clemson says they are around for about a month, and hand-picking them into soapy water works.
Stippled, sticky or yellowing leaves point to the sap feeders underneath: aphids, whiteflies and spider mites. Because you eat the leaves, stick to what Clemson recommends for basil: insecticidal soap sprayed in the early evening onto the undersides, or azadirachtin from neem. Basil in pots indoors brings fungus gnats, whose larvae live in wet compost; letting the surface dry between waterings is the long-term fix.
If the leaves yellow in patches bounded by the veins and a purplish-grey growth appears underneath, no insect is involved. That is basil downy mildew, which the University of Minnesota calls the most common basil problem in the state; it advises growing a resistant variety.
crop context · sweet basil in a raised bed
What eats basil and other herbs
SPRING & AUTUMN · DAMP NIGHTS
Snails
The same ragged holes as slugs, by night. In California gardens the brown garden snail is the usual one.
JUNE–SEPTEMBER
Two-spotted spider mite
Fine pale stippling, then webbing under the leaves. Worst in hot, dusty weather and on drought-stressed plants.
SUMMER OUTDOORS · ALL YEAR UNDER GLASS
Greenhouse whitefly
Tiny white adults lift in a cloud; sticky honeydew and sooty mould below. The parasitic wasp is for herbs under glass.
WHEREVER COMPOST STAYS WET
Fungus gnat
Small dark flies round potted herbs. The adults are a nuisance; the larvae hurt seedlings and young plants.
JUNE–SEPTEMBER
Leafhoppers
Pale mottling from small wedge-shaped hoppers that jump when disturbed. Cosmetic on herbs.
ReleaseNothing to releaseTolerate — no control needed
Season calendar
US GARDENS · QUALITATIVE READING OF EXTENSION SOURCES| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Slugs | Jan: Quiet | Feb: Quiet | Mar: Building | Apr: Pest pressure high | May: Pest pressure high | Jun: Pest pressure high | Jul: Building | Aug: Building | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Building | Dec: Quiet |
| Snails | Jan: Building | Feb: Building | Mar: Building | Apr: Pest pressure high | May: Pest pressure high | Jun: Building | Jul: Building | Aug: Building | Sep: Building | Oct: Pest pressure high | Nov: Building | Dec: Building |
| Japanese beetle | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Quiet | May: Quiet | Jun: Building | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Building | Oct: Quiet | Nov: Quiet | Dec: Quiet |
| Spider mites | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Building | May: Building | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Building | Nov: Quiet | Dec: Quiet |
| Whitefly (all year under glass) | Jan: Building | Feb: Building | Mar: Building | Apr: Building | May: Pest pressure high | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Building | Dec: Building |
| Leafhoppers | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Quiet | May: Quiet | Jun: Building | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Building | Oct: Quiet | Nov: Quiet | Dec: Quiet |
- Pest pressure high
- Building
- Release window
- Quiet
- Slugs · high pressure Apr–Jun, Sep–Oct
- Snails · high pressure Apr–May, Oct
- Japanese beetle · high pressure Jul–Aug
- Spider mites · high pressure Jun–Sep
- Whitefly (all year under glass) · high pressure May–Oct
- Leafhoppers · high pressure Jul–Aug
Starter program
Basil needs no release program outdoors. These are the jobs, in the order they come up, for a bed or pots you harvest from.
- AT PLANTINGClear slug shelterRemove boards, stones and debris near the bed, and water in the morning so the soil is dry by nightfall
- DAMP EVENINGSHand-pick by torchlightOr iron phosphate bait in the late afternoon; never metaldehyde where pets roam
- MIDSUMMERShake Japanese beetles into soapy waterClemson says they are around for about a month and can be hand-picked into soapy water
- ON FINDING MITES, APHIDS OR WHITEFLYInsecticidal soapIn the early evening, onto the leaf undersides; azadirachtin (neem) is the alternative
- POTS INDOORSSteinernema feltiaeDrench the compost for fungus gnats, and let the surface dry between waterings
Setting up the garden
Herbs are grown to be eaten, so the rules are about what goes on the leaves and what the plant is up against.
Spray soap in the evening, underneath
Clemson recommends insecticidal soap for soft-bodied pests on basil, sprayed in the early evening onto the lower leaf surfaces where they gather.
Water in the morning
A surface that is dry by nightfall gives slugs less to work with, and UC IPM recommends it.
Grow resistant basil
Downy mildew is the commonest basil problem in Minnesota, and UMN advises a resistant variety. For Fusarium wilt, Clemson lists resistant cultivars including ‘Nufar’, ‘Aroma 2’ and ‘Prospera’.
Tolerate the stippling
Leafhoppers and spittlebugs look worse than they are. Neither needs control on herbs.