If you’re a basil lover like me, few things are more disappointing than going out to your garden to harvest some fresh basil for your caprese salad or basil pesto only to find the leaves riddled with holes, coated in sticky residue, or wilting away.
As delicious as basil is for us humans, it’s also an incredibly appetizing meal for a number of hungry insects and other pests. But don’t reach for the pesticide just yet; many common basil pests can be managed through organic methods and prevention. Read on for tips on identifying and dealing with some of the most common basil plant pests.
Common Basil Plant Pests
Aphids
These tiny, pear-shaped bugs are probably the most common pest to plague basil plants. They come in a variety of colors like green, yellow, brown, red or black. Aphids congregate in clusters on stems and the undersides of leaves, using their long mouth parts to suck the sap out of the plant. This can leave the leaves looking discolored, wilted, curled, or stunted in growth.
Aphids also excrete a sticky, sugary substance called honeydew, which can coat the leaves and attract other pests like ants or lead to the growth of sooty mold fungus. While a few aphids here and there may not be the end of the world for your basil plant’s health, a large infestation can really do some damage.
How to Control Aphids:
- Use a strong spray of water from the hose to knock aphids off plants.
- Encourage natural predators like ladybugs, lacewings, and parasitic wasps by planting flowers they’re attracted to.
- Make an insecticidal spray by mixing 1 teaspoon of mild soap with 1 liter of water.
- As a last resort, use an insecticidal soap or neem oil spray, following instructions carefully.
Japanese Beetles
With their shiny, metallic blue-green shells, Japanese beetles sure are pretty—until you see them devouring your basil plants’ leaves, that is. The adults emerge in early summer to lay eggs in the soil, and the resulting grubs feed on grass roots through fall and winter. But it’s the adult beetles that wreak most of the havoc on basil leaves, chowing down on the tissue between the veins and leaving behind a lacy, skeletonized leaf.
How to Control Japanese Beetles:
- Hand pick beetles off plants and dispose of them.
- Set out Japanese beetle traps away from your garden to lure them away.
- Treat the soil with milky spore disease to kill grubs.
- Spray plants with neem oil to make them less appetizing.
- As a last resort, use an insecticide containing pyrethrins.
Slugs and Snails
These slimy subterranean creatures tend to come out at night to feed, leaving behind large, irregularly-shaped holes in basil leaves as well as a shiny trail of slime—not exactly appetizing. Slugs and snails thrive in cool, moist environments, so a wet spring or well-irrigated garden can be the perfect breeding ground.
How to Control Slugs and Snails:
- Handpick them off at night and dispose of them.
- Use diatomaceous earth, sharp sand, or crushed eggshells to create a barrier they don’t want to cross.
- Set out beer traps made from buried cups filled with a bit of beer to attract and drown them.
- Remove any boards or debris that give them hiding spots.
- Apply an iron-phosphate slug bait around plants.
Leafminers
The name says it all: leafminers are the larvae (immature stage) of certain flies and moths that tunnel between the upper and lower leaf surfaces, leaving winding tunnels filled with frass (excrement). The trails start out thin and eventually grow into wide, irregular tunnels. While leafminers rarely kill plants outright, the tunnels can significantly reduce the plant’s ability to photosynthesize, and the leaves often dry out and turn brown.
How to Control Leafminers:
- Remove any infested leaves and destroy them to prevent reproduction.
- Release parasitic wasps like Diglyphus isaea that feed on leafminer larvae.
- Spray plants with neem oil or spinosad (an organic pesticide).
- As a last resort, use an insecticide containing cyromazine or abamectin.
Spider Mites
Related to spiders, these tiny (1/50th of an inch) arachnids tend to cause the most problems during hot, dry weather. They pierce individual plant cells and suck out the contents, causing speckled, yellowing leaves that eventually turn crispy brown. Heavy infestations can also leave behind telltale webbing on leaves and stems. Spider mites thrive in dry conditions so a nice rainfall can temporarily knock back populations.
How to Control Spider Mites:
- Wash plants off with a strong spray from the hose every few days.
- Insecticidal soaps and oils like neem can help dislodge and kill spider mites.
- Introduce natural predators like ladybugs and predatory mites like Phytoseiulus persimilis.
- As a last resort, use an insecticide containing bifenazate or abamectin.
Basil Downy Mildew
Not technically an insect pest, but one that’s worth mentioning: downy mildew is a fungal disease that can wreak havoc on sweet basil in particular. It causes small yellowing areas on the topside of leaves with fuzzy gray growth underneath. Eventually the entire leaf turns yellow and dies back. The disease spreads quickly in warm, humid conditions and can completely defoliate plants.
How to Control Basil Downy Mildew:
- Remove any affected leaves to prevent spread.
- Improve air circulation by pruning overcrowded plants and rows.
- Switch to disease-resistant basil varieties like blue spice basil.
- Apply a fungicide containing copper, phosphorus acid, or hydrogen peroxide.
The best way to avoid pest problems on basil is to be proactive.
- Monitor plants regularly and take action at the first sign of pests.
- Attract beneficial insects by planting flowers like dill, yarrow, and alyssum nearby.
- Keep plants properly spaced and pruned for good air circulation.
- Fertilize plants adequately, but don’t over-fertilize with nitrogen.
- Rotate where you plant basil each year.
- Use row covers or floating row covers to physically exclude pests.
- Maintain cleanliness by removing plant debris and weeds.
With some diligent scouting, proper cultural practices, and occasionally deploying an organic spray or two, you can keep most basil pests at bay. Losing some leaves here and there is to be expected, but with the right arsenal of control methods, you’ll have plenty of fresh, delicious basil to harvest all season for your favorite recipes. The pest is worth protecting!