Garden Pests and Diseases:
The Culprits and What to Do About Them

Garden Pests and diseases have to be addressed. But there's good news to note. Container gardens are not quite as susceptible to their ravages as are flowers, herbs, and vegetables in your garden beds.

But as we've discussed elsewhere, good plant culture is your best defense. Garden pests and diseases may be less prevalent in pots than elsewhere, but they do still attack our plants from time to time.

So we'll deal with the most likely culprits here.

And more good news . . . As you know, our culture has moved toward more awareness of the danger of toxic chemicals. For us gardeners, this means a move from the idea of eradicating all garden pests to a more nuanced approach—using beneficial insects, planting to attract birds and insects that eat the bad guys, using non-toxic sprays, and deciding how much plant damage is too much.

In other words, growing flowers, herbs, and veggies in containers means you’ll need to determine how many bugs you can take and still enjoy your container garden.

This idea is gone into thoroughly—it’s called Integrated Pest Management—in Master Gardener classes. If you want a lot more information on garden pests and IPM than I provide here, try the EPA

There’s a map on that site where you can find the U.S. extension service office for your neck of the woods. There's also information on this site about natural pest control.

For our purposes here, let’s stick to some general guidelines, and a few likely garden pest culprits you might run into. Or at least keep an eye out for.

First, some insects, as I noted elsewhere about ladybugs and lacewings, are actually beneficial.

They eat the bad guys, so you want to encourage them. Praying mantis, too, is a really great insect to have around and you can purchase them for your garden—they’re pretty cool to watch, actually, and I’m not what you’d call a “bug person” by any stretch of the imagination.

The point is—some bugs are not garden pests. Some of them you actually want hanging around. And you can even buy them online atGardens Alive, The Beneficial Insect Company, and Ladies in Red.

As for which garden pests you don’t want hanging about, I've listed some of the more typical you might encounter below. Please note, when you click on the name of the insect, you'll see a picture courtesy of the Missouri Botanical Gardens.

The Pesky Little Critters:

Aphids
The Problem: These are pretty common, but very hard to see. 3 millimeters and green, they love the undersides of leaves where they suck until the leaf becomes rolled and sticky.
The Solution: You can spray the plant leaves to knock off the offenders and use a spray of water and soap (best to use insecticidal soap from the nursery). Repeat every few days until they’re gone.

Spider Mites
The Problem: Too little to see with the human eye, these guys also hang out on the underside of leaves. You’ll know they’re there if your leaves turn yellow and wither. At the worst, there’s a white web on the leaves.
The Solution: Rinse the leaves as with aphids and spray. You can also move the plants to a cool spot as you do this. Spider mites like it hot.

Whiteflies
The Problem: Little white flies. Usually a whole lot of them, and they fly up disgustingly when you touch a leaf (they like the underside) or water. The leaves wither.
The Solution: Use an insecticidal soap on them, and they’ll bite the dust pretty quickly.

Mealybugs
The Problem: 3 millimeter yellow-brown nasties that hold onto the stems and leaves. They leave behind little white fluffs and the leaves get sticky.
The Solution: You can squish the bugs between your fingers if you’re not like me and have a bug phobia. Otherwise, clean off the critters with a hose or hard spray with insecticidal soap and treat with horticultural oil you can buy online or at the nursery.

The Bigger Critters:

Caterpillars
The Problem: You’ll see hanging larvae and caterpillars—not too hard to spot. The thing about these garden pests is you need to decide if the harm is less than the pleasure of the butterfly that might come out. Sometimes letting them hang around, literally, can bring quite a lot of pleasure.
The Solution: Just pick off and discard. Enough said.

Japanese Beetles
The Problem: Big beetles with a shiny brown carapace and black head that reduce ornamental leaves to skeletons.
The Solution: Pick off and discard. You can drop them in a soapy solution if you get no pleasure from the squish option.

Snails and Slugs
The Problem: Little slow-moving, shelled creatures that love, love, love hostas.
The Solution: I’ve heard of lots of solutions, none of which have worked very well for me—these include setting out jar tops filled with beer (Really). Putting sticky boards at the base of plants—you have to get rid of them in the morning. Pick them up and dispose of them. In a manner of your choosing.

On to the DISEASES

The most prevalent diseases to be alert to are caused by viruses and fungi. Of these, the most usual fungi is powdery and downy mildew.

In general, the easiest way to prevent diseases is by being scrupulous in your gardening routine—clean pots, clean soil, good air circulation, appropriate feeding and watering. Just take care with each of the planting steps and you should be fine.

Except maybe for the zinnia fungus—no matter how hard I try, my zinnia always get this—it’s not deadly and I do live in a humid climate. What I’m trying to say is—sometimes stuff happens. You can deal with it.

Powdery Mildew
The Problem: Whitish deposits on leaves. Zinnias are very prone to this after blooming, as are begonia, roses, and chrysanthemums. It’s a fungus and is usually associated with damp conditions.
The Solution: Make sure your plants have plenty of air circulation and that you don’t over water. In humid, rainy climates, you might have more problem with this fungus. Horticultural oil spray works ok. This fungus usually is just disfiguring and not fatal. Of course, it can be, so attempt to avoid it by drier conditions, especially for the plants mentioned. Also, avoid high nitrogen levels in the soil.

Mosaic viruses
The Problem: The leaves are covered with yellowy mosaic patterns. They can also curl.
Solution: There really isn’t a way to control this. You can try to avoid the little critters in the insect section since they tend to transmit viruses of all sorts. You’ll need to discard a plant if you find these symptoms.

Get more information about identifying and destroying the most common garden pests.