How to Get Rid of Broccoli Worms
Broccoli worms, oh no! If your broccoli florets or leaves—or other brassica crops—become infested with worms, you are unlikely to harvest any edible broccoli heads.
Observe your plants regularly and act fast if you see any evidence of caterpillars on your broccoli (Brassica oleracea var. italica).
Common Broccoli Pests
Unfortunately, multiple garden pests find broccoli enticing. Those that are in “worm” form or go through a caterpillar stage include the cabbage looper, the cabbage worm and the diamondback moth.
Imported Cabbage Worm
If you see white butterflies fluttering around your plants, they are likely cabbage worm (Pieris rapae) butterflies. They have small black spots on their wings.
You might notice tiny yellow eggs on both the underside and upper side of the plant leaves. The eggs hatch into larvae or caterpillars that are about 1 inch long and velvety green when mature.
You are unlikely to notice the moths that result in a cabbage looper (Trichoplusia ni), because they are nocturnal—but their eggs are a creamy white color laid only on the undersides of leaves.
The caterpillar itself is quite large, so it is easily visible, reaching 1.25 to 1.5 inches in length.
Like the cabbage looper, diamondback moths (Plutella xylostella) are nocturnal. They lay their creamy white eggs near the leaf veins. The caterpillars are light green and very small, only about 1/3 inch long.
Broccoli Pest Control
Experts caution that eradicating all pests is generally unnecessary and overkill, because it would require intense and frequent pesticide applications. Instead, your goal should be to control pests, knowing that some damage to a cole crop will not necessarily affect the harvest.
The strategy behind this goal is called Integrated Pest Management, or IPM, which just means: use multiple tactics to control pests while avoiding the overuse of potentially damaging chemicals. These tactics include cultural, mechanical, biological and chemical strategies.
Weeds are unsightly, and they grab nutrients from the soil, depriving your broccoli plants of necessary fuel. In addition, when it comes to pests, they are heaven. They provide excellent overwintering and nesting sites for pests of all kinds.
To make your garden less attractive to pests, remove crop residue after the harvest and keep the area weed free.
During the growing season, monitor the plants at least once weekly, peering at both the undersides and tops of the leaves. If you see caterpillars, it’s easy to handpick them off and drop them in a container of soapy water.
Other manual types of control could include protecting broccoli and other plants with lightweight row covers that prevent adult moths from laying eggs.
You can make use of natural predators of common pests that target broccoli. These beneficial insects include the ubiquitous ladybug and predatory wasps.
- Paper wasps: You might notice these wasps' nests, which resemble a papery honeycomb. They are usually found under horizontal surfaces such as limbs, eaves or roof overhangs. If you see these, let them be unless they are located close to a living area.
- Ladybugs: Also called lady beetles, everyone knows them by their red, rounded body and black spots. Most gardeners know that ladybugs devour whiteflies, but they also enjoy the eggs of caterpillars.
- Parasitoid wasps: There are many species of this type of wasp, but you are unlikely to be able to identify them because they are tiny. If you have them, you might see caterpillars that appear to have grains of rice on them. These wasps lay their eggs and feed on other insects. To encourage them in your garden, ensure that you have a consistent supply of flowering plants and allow some pests; otherwise, these wasps will not find hosts.
The last strategy to use is chemical control. Avoid broad-spectrum pesticides because they act on multiple species and kill beneficial insects as well as true pests. Instead, opt for lower-risk, organic pesticides that target specific insects. These include:
- Pyrethrins: Derived from the flowers of a species of chrysanthemum, pyrethrin helps control a range of pests, including caterpillars. Products that include pyrethrin must be applied directly to the insect. Some neem oil products contain this chemical, and multiple other commercially available insecticides are based on it.
- Bt: Bacillus thuringiensis is a bacteria that produces strains of proteins toxic to specific insects. Look for Btk (Bacillus thuringiensis subsp. kurstaki), which is pest-specific to caterpillars and not other types of pests. Spray it directly on the leaves, because caterpillars must eat it for it to be effective.
- Spinosad: Also a bacterium that is toxic to insects, this substance is available in multiple commercial pesticide products. When insects ingest it, it affects their nervous system and causes paralysis.
- Clemson Cooperative Extension: Cabbage, Broccoli, and Other Cole Crop Insect Pests
- University of Florida IFAS Extension: Broccoli—Brassica Oleracea L. (Italica Group)
- University of Minnesota Extension: Caterpillars on Cole Crops
- University of Minnesota Extension: Parasitoid Wasps
- Iowa State University: Don't Let Your Guard Down: Fall Insect Pests of Cole Crops
- Oregon State University: Bacillus thuringiensis (Bt)
I garden in the Pacific North west, previously Hawaii where I had an avocado orchard. I have a Master Gardeners certificate here in Eugene, Oregon.