Before attempting a pest control method that may prove to be unnecessary, ineffective or complete overkill, the first step a gardener should take is to correctly identify the problem. Positive identification of garden pests paired with the appropriate intervention will yield the best results while minimizing or eliminating negative impacts. My guest this week, Susan Mulvihill, has penned a new book on solving common pest problems that will arm you with all the information you need to make the right control decisions.
Susan is a Master Gardener who gardens on her five acres in Washington State. She writes the blog Susan’s in the Garden as well as a newspaper column for The Spokesman-Review in Spokane, Washington, and is a member of the Garden Communicators International.
Susan and I are old friends, and I am a big fan of her gardening techniques. I was excited to hear about her upcoming book, “The Vegetable Garden Pest Handbook.” This is the book that many gardeners have been waiting a long, long time for, and it’s the most practical handbook for organic pest control that I’ve ever seen. There are a lot of gardening books that are good to have, but Susan’s book is a must-have.
This week’s podcast is an excellent primer on garden pests and how to manage them. If you are interested in comprehensive lessons on how to organically manage not just pests, but plant diseases and weeds in the garden as well, my joegardener Online Gardening Academy™ course Master Pests, Diseases & Weeds is for you.
How ‘The Vegetable Garden Pest Handbook’ Came to Be
Susan had contemplated writing an organic gardening book for the past few years and wanted it to have a heavy emphasis on organic pest control. “I worry about the amount of pesticides that are being used and their impact on the balance that should be out in our gardens,” she explains. “While it’s easy to buy something to kill bugs with, there’s so many negative ramifications.”
Susan has grown an annual vegetable garden since she was 16 years old and has been a Master Gardener for nearly 20 years now. In that time, she’s gotten many questions about a variety of bugs. During her winters off from writing her newspaper column, she set out to write a book that answers all those questions and is research based — but without getting too sciencey. “I didn’t want people’s eyes to glaze over,” she says. “I didn’t want to make it so technical.”
At the 2019 Garden Communicators International conference, Susan pitched her book to Jessica Walliser of Cool Springs Press. (Podcast listeners will recognize Jessica’s name as a repeat guest who was most recently on the show to discuss companion planting.) Jessica enjoyed the proposal and suggested that Susan focus even more on organic pest control and how it leads to a more successful vegetable garden overall. Susan followed up with an outline, and the publisher loved it.
The result is a book geared toward gardeners of all experience levels, from novices to her fellow Master Gardeners.
One of the principles that she underscores in the book is the importance of bug identification, so gardeners will know what bug they are dealing with before deciding its fate. A diagnostic chart helps gardeners learn what unseen pests are causing damage to plants, and pest profiles show what different bugs look like, how many generations they have, what their life cycle is, what they do to plants, and how to control them organically.
Susan didn’t stop at profiling pests. The book also profiles the beneficial insects, explaining what makes them beneficial and how to attract them to a garden.
Susan’s Take on Integrated Pest Management
Integrated Pest Management, or IPM, is a systematic approach to dealing with plant damage when it arises in your garden. As an organic gardener, Susan’s take on IPM may differ from what you’ve heard before. Here are Susan’s steps:
Monitor — Monitor your garden regularly so you can spot problems early on. Keep an eye out for pests, but also for signs of damage. “It doesn’t cost you a cent,” Susan notes, and all it takes is a pleasant stroll through your garden to see how things are doing.
Identify — If you do notice an insect, take the time to identify and research it to find out if it is a beneficial insect or a damaging pest. If it is the latter, figure out what kind of damage that pest might inflict on plants, and monitor closely.
Insects can often be unrecognizable from one life stage to the next. For example, the larva of the beneficial, aphid-eating lady beetle looks like a little scary crocodile, and it might be mistaken for a bad bug. “The Vegetable Garden Pest Handbook” is particularly handy at identifying pests because it includes images of insects at each phase of their life cycle. Susan said she thought a “mug shot gallery” of both “the good guys and the bad guys” would help gardeners who are unsure about what they’ve found.
Other times, you may notice damage without ever seeing the bug causing it. Susan’s book includes descriptions of damage to match the problem to the potential culprits.
Choose a Course — If a pest infestation or pest damage gets worse, choose a course of action to control it, starting with the least impactful methods.
Handpick — Picking bugs off plants by hand and disposing of them (like in a cup of soapy water) can be effective in controlling bugs that are easy to spot. Some bugs are slower-moving early in the morning and easier to pick up then, and others, like slugs and snails, come out at night. Handpicking can also be effective for removing pest eggs before they hatch.
Use a barrier — A physical barrier over or around a crop can keep bugs off. Floating row cover can stop many flying insects from landing on plants, where they will eat leaves and fruit or lay their eggs. A plant collar can protect stems from cutworms and cabbage root maggots.
Set a trap — Susan’s book provides DIY instructions for a number of different simple traps for pests. Depending on which bug is causing trouble, the right attractant in a trap can lure it in.
Use an organic spray — There are organic pest control sprays that can be used to target certain pests. Susan’s book describes the differences between sprays to help gardeners choose the best one for their situation with the least impact on non-target insects. “Even though a product might say that it’s organic, you really need to read the label, follow the directions to the letter and use it just the way it’s intended,” she advises.
Plant trap crops — Strategically siting plants that pests are attracted to can lure them away from a vegetable garden.
Strategize — When a pest problem is not brought under control, it will likely come back and spread in subsequent years. Susan suggests coming up with a strategy to prevent a recurrence. This could mean practicing crop rotation or using a barrier next growing season before a pest problem arises.
Document — What was effective and what could have worked better? Jot down what methods you used and the results they yielded. It will help you find what works next time.
Susan says that, no matter what, a gardener always wants to choose the solution that has the least impact on the environment. The final control recommendation of traditional Integrated Pest Management is to use a synthetic insecticide after all else fails. However, Susan says she can’t bring herself to do that because she knows insecticides cause more problems than they solve. She skips that step entirely and calls her approach “organic IPM.”
The Big Bad of Tomato Pests: The Hornworm
Both the tomato hornworm and the tobacco hornworm eat tomato plants, quickly devouring the leaves and branches. The green caterpillars with namesake horns on their rear ends both grow to be between 2 and 4 inches long, so they can be difficult to tell apart, but their damage is the same.
Because of their green color, hornworms stay camouflaged. If you see unexplained damage to your tomato plants, Susan recommends checking the ground directly below the damage for hornworm droppings — which look like little green or brown soccer balls.
Spotting the hornworms themselves is much more difficult because they really do blend in that well. It was Jessica Walliser who turned me on to a tip: Use a UV flashlight at night on tomato plants to easily spot hornworms. They will shine under the light and be easy to spot and pick off.
The Three Big Bads of Brassica Pests: Cabbage Worm, Cabbage Looper, Diamondback Moth
There are quite a few pests that prey on brassicas, the members of the cabbage family. In addition to cabbage, this includes broccoli, cauliflower, kohlrabi, kale, Brussels sprouts and collard greens.
Susan identifies the biggest concerns as the imported cabbage worm, the cabbage looper, and the diamondback moth caterpillar. Each is a small green caterpillar, and each causes similar damage and calls for the same kind of treatment.
These cabbage pests chew near the ribs of the leaves and make lots of holes. Before it gets that point, however, an early sign of trouble to look for is little white butterflies fluttering around brassica crops. This is known as the cabbage white or cabbage butterfly, and it is the adult of the imported cabbage worm. When you see them flying over crops, it’s because they are scouting locations to lay their eggs.
Susan notes that the cabbage white is active during the day, while diamondback moths and cabbage looper moths are active at night.
The Big Bad of Squash Pests: Squash Vine Borer
The squash vine borer moth is actually quite an interesting looking black and red moth, and Susan notes that it is active during the day.
The moth lays eggs at the base of a squash plant. When the eggs hatch, the larvae burrow into the main stem and eventually out into the vines. The damage restricts the flow of moisture and nutrients throughout the plant, so the vines begin to wilt or die.
Pests That Are Less Discriminating
Some pests are unique to a plant family, like cabbage worms are to the cabbage (brassica) family, but some pests have names that don’t tell the whole story. For example, Susan says, the corn earworm affects more than just corn. It preys on beans, lettuce, peppers and tomatoes. Likewise, the cucumber beetle is often found on asparagus, beans, beets, corn, potatoes and tomatoes.
Bugs that are specific to a certain type of crop are easier to identify than less discriminating pests. To give gardeners a better idea of what groups of vegetables are vulnerable to the same pests, Susan’s book includes a chart that lists the plant families and all the different members of each family.
Mystery Bugs Are Often Friends, Not Foes
Roughly 97 percent of the insects out there are beneficial or neutral — which is one of the reasons why reaching for a spray any time you see an insect is a bad idea.
Susan shares that as she became more aware of the insects in her garden while researching for her book, she noticed a green metallic fly that she couldn’t identify initially. Following the steps of Organic IPM, she sought to find out what it was before considering any control options. Well, Susan discovered that it’s called the long-legged fly, and it eats aphids, which makes it a very beneficial insect to have in the garden.
Common Organic Control Products
Attracting beneficial bugs, such as aphid-eating predatory insects, is just one of the organic control options for garden pests. Susan’s book includes an entire section on the organic controls that are available.
“I created this chapter because I want gardeners to better understand their options so that they could make the right decision about what to use,” Susan says.
Bacillus thuringiensis kurstaki – This soil bacteria often referred to as Bt or Btk is a control for caterpillars, such as armyworms, cabbage worms, cabbage loopers, corn earworms and tomato fruit worms. Because it is specific to the larvae of moths and butterflies, it is a targeted control. It also won’t harm humans and pets. There is a caveat, however. Bt should never be sprayed on or near butterfly host plants, such as milkweed and parsley, where butterflies lay their eggs and where their larvae eat. Bt is sensitive to sunlight, so to be the most effective and last longer, it should be applied late in the day.
Pyrethrin – Derived from chrysanthemum flowers, pyrethrin is a broad-spectrum organic pesticide, which means that it does not discriminate between good and bad insects.
Beneficial nematodes – Nematodes are tiny worms, many species of which are microscopic. There are pest nematodes (root-knot nematode, for example) but there are beneficial parasitic nematodes that can be applied in the garden to eliminate pests. Nematodes are specialists, such as Heterorhabditis bacteriophora for controlling rootzone weevils and Japanese beetles. (To learn more about beneficial nematodes, you can listen to my conversation with Dr. William Crowe of the University of Florida.)
Diatomaceous earth – Often called DE, diatomaceous earth is one of Susan’s favorite organic pest controls. It is the ground-up remains of algae fossils and looks like flour. DE has tiny sharp edges that make it a barrier to certain types of pests, such as soft-bodied bugs. Susan uses DE around broccoli seedlings, and then when slugs come in contact with the circle of DE, the sharp edges cut into their skin, causing them to dehydrate and die. She’s also found success using DE to protect cucurbit seedlings from pillbugs and sowbugs.
Kaolin clay – This naturally occurring mineral is ground into a fine powder for orchard applications. Sprayed onto the developing fruits and leaves of fruit trees, kaolin clay forms a film that confuses apple maggot fly, apple codling moth and other pests, so they don’t lay their eggs.
The Beauty of Barriers
After planting crops that are “bug magnets,” like vegetables in the cabbage family, Susan immediately covers her garden beds with a barrier, such as floating row cover.
A physical barrier prevents adult insects from landing on crops and laying their eggs, while still allowing light and water to get through. No eggs means no hatching larvae or nymphs eating the plants. And that means no pest control spray or other product will be needed.
Another benefit of row cover, Susan says, is that — being in a colder zone like she is — the cover holds heat and gives warm-season crops such as melons, winter, squash, cucumbers, tomatoes, eggplants and peppers a nice, warm start. Just be sure to remove the row cover when the plants flower, so they can be pollinated and set fruit.
The Trouble with Spinosad
Spinosad is a pesticide spray with an interesting backstory. Susan explains it is a fermented soil bacteria first discovered by a scientist in an abandoned Caribbean rum distillery in the early 1980s. Spinosad attacks bugs’ nervous systems. It kills by contact or when insects ingest it.
Spinosad controls an amazing diversity of garden pests, according to Susan, from moths and flies to thrips. Off the top of her head, she can rattle off asparagus beetles, armyworms, cabbage, loopers, cabbage worms, Colorado potato beetles, cucumber beetles, diamondback moths, flea beetles, harlequin bugs, leaf miners, Mexican bean beetles, pill bugs, sow bugs, spider mites, tomato fruit worms, and tomato hornworms. Spinosad controls them all.
Susan says Spinosad may sound like the answer to a gardener’s prayers. But there are also problems, she notes. If Spinosad is used repeatedly, certain insects can develop a resistance to it, which can lead to more challenging pest problems. It can be used in rotation with other controls to avoid creating a resistant pest population.
Spinosad raises other concerns as well. Most importantly, it is highly toxic to bees and other pollinators and should never be used near flowers. If Spinosad is used at all, it should be sprayed super early in the morning or very late in the day, when pollinators are inactive, Susan says.
If you haven’t already listened to my conversation with Susan Mulvihill on identifying garden pests and solving common pest problems, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
What is your approach to controlling garden pests? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
joegardener Online Gardening Academy™: Three popular courses on gardening fundamentals; managing pests, diseases & weeds; and seed starting.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Master Seed Starting: Everything you need to know to start your own plants from seed — indoors and out.
Susansinthegarden.com – Susan Mulvihill’s website
“The Vegetable Garden Pest Handbook” by Susan Mulvihill – Publishing April 13, 2021. Be sure to let Susan know if you pre-order her book so she can send you her bonus material, “Susan’s Top Tips for the Vegetables Everybody Loves to Grow!” Just send your order confirmation to email@example.com and she will send you a link to it.
Wild Alaskan Seafood Box – Our podcast episode sponsor and Brand Partner of joegardener.com – Enter code JOE at checkout for two special bonuses just for our podcast listeners – 2 pounds of Dungeness crab with your first order and free scallops for the life of your subscription.
Disclosure: Some product links in this guide are affiliate links, which means we would get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us. None of the items included in this list have any bearing on any compensation being an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, and Wild Alaskan Seafood Box. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.