What’s Wrong with My Garden? Part 1: How to Manage Common Insect Pests

Nearly everyone who’s gardened for a season or two has experienced that moment of shock when, upon entering the garden, one first lays eyes on a squadron of cucumber beetles happily chomping away on the squash plants. After the shock of seeing the carefully-tended plants in tatters, one moves on to the next phase of garden grief: denial. How could these creatures just lay claim to what is clearly yours? How could they? Finally denial gives way to acceptance and infuriation – with a smattering of bitter hatred – before settling on a deep need to fight back. So, to aid you in your battles with beetles, bugs, borers and slugs, I’ve put together a primer on pests and how to handle them. All is not lost! With all these tools to hand, you might even wind up missing your garden marauders (but I doubt it).

Organic Pest Control Basics

Personally I’m in favor of using simple tricks and homemade remedies when possible for garden problems. Certainly these aren’t appropriate in every instance, and may not be practical on a commercial farm. But a lot can be accomplished with soapy water, your hands, and a few good homemade and store-bought OMRI-listed formulations, without spending a fortune or using persistent chemicals on your hard-won produce.

Another important thing to consider is that plant pests are often vectors for diseases, especially fungal diseases—they walk on one plant that has a disease, then fly over to a healthy plant, where (like muddy dogs on a white carpet) they track spores all over, inoculating the surfaces they’re munching on. So by taking the time to stay on top of pest populations, you’re also helping prevent serious diseases from gaining a foothold in the garden (where they can remain for years to come).

The last key thing to keep in mind is that garden pests are people too. Ok, so they’re not actually people, but they are members (like us) of a vast, interconnected web we call the ecosystem. These creatures aren’t bad in their own right, they’re just bad when they’re out of balance and too many of them multiply in one place at one time. Often that imbalance is a response to monoculture (huge plantings of one crop). In balance, they provide nutritious food for birds and help keep other species in check. When attempts are made to eradicate pests altogether, cascades of negative impacts become evident on farms as well as on the ecosystem as a whole. By educating ourselves about pest life cycles and practicing good holistic management of our gardens through crop rotation, supporting beneficials, and interplanting or companion planting, we can avoid pest population explosions in the first place. Let’s learn to live together, shall we?

The Brassicas

This family includes the siblings broccoli, cabbage, cauliflower, kohlrabi, and kale, as well as more distant cousins like radishes and mustards. I like to discourage brassica pests by interplanting—the smell and mix of species confuses the pests.  I sow aromatic dill or cilantro thickly around the plants, where it eventually gets shaded by the brassicas, making it last longer before bolting. I also plant tall sun-lovers like sunflowers between them, which in turn prevents the brassicas from bolting in late summer heat. In this way pests are discouraged by diversity, weeds are shaded out, and I get three crops in the space of one. There are two main pests that love the brassica family and usually hang around in the springtime: flea beetles and cabbage worms.


Photo: Jeff Hahn, UMN Extension

-          Flea Beetles are tiny (like, pinhead-sized) shiny black beetles that will jump like fleas the moment you get close.  They chew miniscule round holes, eventually turning leaves to lace, and especially prefer radishes, arugula, mustards, and broccoli raab. The simplest method for dealing with flea beetles and many other pests which are too small and fast to remove by hand, is exclusion – the same day you plant, cover your beds with row covers and make sure all edges are tucked in (covered with soil). Leave the row cover on as long as possible, as smaller plants are much more vulnerable to flea beetles. If you already have flea beetles in your soil, the row cover won’t help much. Try planting an early trap crop of broccoli raab well away from your covered brassicas – the flea beetles would much rather go for the low-hanging fruit. As soon as the trap crop is infested, cover the plants with plastic bags, pull them out of the ground, seal tightly, and throw away. Garlic or kaolin clay sprays can also be used to repel the beetles, and sprays using Beauveria bassianaor or spinosad can be used in severe cases.


Photo: UMN Extension

-          Cabbage Worm (aka cabbage moth or cabbage looper) is a very common and insatiable pest on broccoli, cabbage, and kale. The worms start their lives as pretty white moths that will flutter unassumingly around your brassicas. Beware! The moths will then lay eggs that will grow into dusty green caterpillars precisely the same color as the ribs of cabbage leaves – and that is where they like to hang out. Check the tops and undersides of your brassica leaves, especially if you see any large holes in the leaves, and pick off and squish any worms that you find. I like to use the leaf itself to squish the worms and any eggs I find, as I think this sends a strong message to any other cabbage loopers that might try their luck. Keep the plants covered with row cover after planting to exclude the moths, and spray plants with Bt (Bacillus thuringiensis) or spinosad for serious infestations.

-          Cabbage Maggot is a little less common but more serious – ¼” gray flies lay white, tapering maggots that tunnel into cabbage family roots, killing the plants directly or by introducing diseases. Use floating row covers when the crop is planted, apply parasitic nematodes, and try mounding red pepper or wood ash around the stems. For severe cases, only plant brassicas as a fall crop to discourage early generations.

The Cucurbits

This family includes winter and summer squashes, zucchinis, cucumbers, and melons. Dipping transplants in a kaolin clay solution before planting really helps discourage cucumber beetles and squash bugs (even if it makes your plants look like they have powdery mildew!)


Photo: Jeff Hahn, UMN Extension

-          Squash Bugs are large, ½-3/4” long, shield-shaped brown bugs. They are pretty slow, so quite easy to pick off, but are smelly when squished. I bring a folded piece of cardboard out to the garden and squish them in that (yes, it’s still gross). You can also spray them and other hard-shelled insects with insecticidal soap, which causes paralysis and death. Get creative with mechanical control – some people shake them off the plants onto plastic in the morning when they’re still sluggish, or even vacuum them up before dumping them in soapy water to kill them. I’ve tried to get chickens to eat them, but no luck – even they seem to be intimidated by their significant size and smell. Always check under the leaves for clusters of metallic brownish eggs, and squish any that you find.


Photo: Jeff Hanh, UMN

-          Cucumber Beetles are about ¼-½” long and yellow with black spots or stripes. You can shake them off or vacuum them in the morning, but the rest of the time they’re too fast to hand-pick effectively. Re-applying kaolin clay solution to the top and bottom of the leaves every few weeks helps a lot, and try to keep the plants covered with row cover from planting until they start to flower (at which point they need access to bees for pollination). Always check under the leaves and around the base of the plant for their orange eggs, and squish away. For severe infestations, you can spray the beetles with insecticidal soap or a product containing pyrethrins (compounds made from chrysanthemum flowers). Use pyrethrin products sparingly, avoid ones containing the synergist compound piperonyl butoxide, and only apply in the evening or early morning as they are also toxic to bees and other pollinators. You can also try using sticky traps and/or planting Baby Blue Hubbard Squash as a trap crop. It is very attractive to the beetles, the seedlings are vigorous and it is tolerant of bacterial wilt, the most common disease they transmit.


Photo: Jeff Hanh, UMN

-          Squash Vine Borers are 1” long white larvae, but are hard to see because they bore into the hollow squash vines themselves and then eat them from the inside out. The damage from them, however, is obvious – a whole section of the plant will suddenly wilt while the rest of it looks fine. Follow the wilted section back to where it connects to the main stem, and you will probably see what looks like a tiny pile of sawdust where the borer has chewed its way into the vine. Now here’s the fun part where you get to play ‘Operation’ – take a razor blade and cut a slit lengthwise along the stem starting where you see the sawdust-like droppings. Keep going until you find the larval culprit and remove it. Then bury the slit stems with soil to help them recover and stimulate root formation.

The Nightshades

This glamorous family group includes tomatoes, potatoes, eggplants, peppers, tomatillos, and husk cherries. There are not too many pests of this family because the plants in it produce alkaloids that may be toxic or bad-tasting to most bugs…with a few exceptions, of course.


Photo: Jeff Hahn, UMN

-          Colorado Potato Beetle is by far the most common pest in this family. They start as bright orange eggs on the underside of potato leaves, then grow into gross shiny reddish larvae before finally becoming boxy black and orange striped beetles. They are voracious eaters starting in the larval stage and can defoliate potato plants very quickly. They are also now resistant to many insecticides and can fly long distances, so crop rotation may not make much difference. So what can you do? Timing is key with these buggers – they are most vulnerable in the young larval stage. Crush any eggs you find, and handpick larvae in the early morning before dropping into a bucket of soapy water. For serious infestations, you can spray the larvae and beetles early in the morning with Bt, neem oil or spinosad. (Spinosad is an aerobic fermentation product of the soil bacterium, Saccharopolyspora spinosa, and should be sprayed every few days when the larvae are hatching.) Lady bugs will also prey upon the eggs, so purchasing some and releasing them in the garden at night may help in extreme cases.


Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

-          Tomato Hornworms are giant (finger-sized) green caterpillars that are surprisingly good at staying camouflaged among tomato foliage. If you start seeing leaf damage, look for these guys – you can also trap them by planting dill, their favorite food, nearby. Simply hand-pick them and drown in soapy water, or spray Bt for serious infestations. If you see ones with what look like rice grains on their backs, leave them where they are! These caterpillars have been parasitized by beneficial wasps that will keep hornworm populations down in your garden.

Corn

There are many pests that will try to beat us to the sweet, starchy kernels of growing ears of corn. Raccoons in particular use a funny trick of climbing up the stalks until their weight pulls them over, then picking the ears off from the ground. The insect pests are even more clever and need to be stopped early to prevent destruction of the crop.


Earworm Photo: University of Kentucky Dept of Entomology

-          Corn Earworms start as moths that lay eggs on corn silks, from which point the yellow-headed larvae can easily crawl down into the ear, where they feed on the developing tips.  To prevent problems, use a spray bottle to apply a mixture of vegetable oil, Bt, water, and a few drops of dish soap to the tops of the ears just after the silks emerge. Corn earworms are cannibalistic, so you will generally only find one per ear.

-          European Corn Borers are 1” long tan worms that feed on foliage and ears. They can be managed if sprayed early (before boring into ears) with Bt or spinosad.

Flowers and More


Photo: Colorado State University Extension

-          Japanese Beetles are generalist iridescent bronze beetles that will completely defoliate everything from apples to zinnias. You can vacuum or shake them off early in the morning and dump into soapy water, place commercially available Japanese beetle traps around your property, or spray them with insecticidal soap.

-          Aphids are very common garden pests on everything from flowers to tomatoes. Look for ants on the plants, as ants actually “farm” these tiny green or red bugs like cows, eating the sweet sap they produce from your garden plants. The best way to deal with infestations is to


Aphid Photo: David Cappaert, Michigan State University, bugwood.org

spray a strong jet of water to knock them off. If need be, you can spray them with insecticidal soap. Lady bugs eat aphids, so purchasing some and releasing them in the garden at night may help as well.

-          Slugs and Snails have lots of mythology around them involving stale beer and spent yeast. I’ve only found these methods attract more, and don’t kill very many. Handpick as many as you can, and use a board laid down in the garden overnight to attract them to one spot where you can scoop them into a bucket of soapy water in the morning. You can also purchase diatomaceous earth and sprinkle it around your plants – it cuts them when they try to cross it and will keep them away as long as it is visible on the soil surface.

For more information about pests in your area, call or visit your local Cooperative Extension Service website.

You can also check out some of our other great articles on pest control:

Optimizing Your Backpack Sprayer

The Unique Challenge of Colorado Potato Beetles

Bloat Nematodes and You

Pest, Disease, and Weed Resources in the Information Age

Organic Control Measures for Striped Cucumber Beetles

Controlling Japanese Beetles in the Home Garden

This entry was posted in Beginner Gardeners' Guide, Growing Tips, Plant Pests, Uncategorized. Bookmark the permalink.

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