If you’ve ever walked outside to check on your garden or greenhouse in the spring, only to discover that something—or several somethings—have munched on them, then you have experienced what I like to call “gardener’s wrath.” Standing by helplessly as unseen villains destroy your seedlings before they get a chance to thrive is heartbreaking. It is also frustrating, and a waste of your garden budget.
Here are the tools you need to identify and prevent common garden pests from putting an end to your seedlings.
What Are These Pests and Why Are They Here?
Seedlings are young, tender, and vulnerable. They have not fully developed their immune systems and their roots are shallow, limiting the nutrients they can access. Like human infants, most varieties of seedlings depend on us for most of their needs, save a hardy few.
To pests, these seedlings are an all-you-can-eat buffet. Whether you grow your seedlings in the greenhouse, in your house, or in the field, there are few common pests you need to watch out for.
My least favorite pests are mammals. These are harder to get rid of than other pests, and they have the disadvantage of occasionally being either cute or majestic, depending on the species. I personally have no qualms about killing insects, but deer, mice, raccoons, voles, and groundhogs give me pause.
Mice are particularly problematic in greenhouses, where they eat seeds before they have a chance to sprout. If you are having germination failures, especially in tasty crops like corn, squash, and melons, check for mouse droppings.
Deer and groundhogs are a bigger problem in the field. Deer especially love to graze and will take a nibble out of your tender seedlings, causing your lettuce to grow with a big, old, bite taken right out of it.
Dealing with mammals is tricky and requires ingenuity and a certain degree of heartlessness. Have-a-heart traps are great for animal lovers, and deer fencing can keep out deer and some other mammals. Voles, which damage plants by burrowing beneath the roots, may require buried fencing, and mice are best trapped and removed.
2. Flea Beetles
The brassica family is particularly susceptible to flea beetles. These tiny beetles jump around, rather like fleas, and are equally irritating. They can decimate brassica seedlings, weakening the plants and opening them up to disease. Flea beetles are often found in areas with wild mustard, which is also a member of this same family.
If you don’t want to use pesticides, row cover is a great option. Keep your endangered plants under row cover for as long as possible to help them reach maturity without damage.
3. Leaf Miners
Your seedlings' healthy young leaves are very appealing to a variety of insects as the perfect nursery for their larvae. These larvae, called leaf miners, burrow into the leaves of the plant, consuming foliage as they go. They leave behind discolored trails, which is how they’ve earned their name, but the good news is that these pests don’t typically leave lasting damage. The trails can simply be problematic for commercial growers selling greens.
Aphids are not only unsightly, but they also transmit diseases to your seedlings. These sap suckers affect a wide variety of vegetables and flowers, and there are hundreds of species of them. They stunt plant growth, promote the growth of black sooty mold, and can ruin crops.
You can remove aphids by hand, which is time-consuming, or import natural aphid enemies, like parasitic wasps and ladybirds. Aphids are particularly prevalent in the spring, posing a threat to seedlings, but there is a wide range of pesticides available—including my personal favorite, neem oil—and insecticidal soaps.
Starting seeds in a greenhouse has many advantages. Your plants get a head start and are protected from the elements and even some pests and diseases. However, whiteflies are one of the disadvantages. These insects thrive in greenhouses and are particularly fond of tomatoes, cucumbers, and spring crops. Whiteflies are sap suckers, which means they remove sap from plants, weakening them and transmitting diseases. Sap suckers are ticks of the plant world, and whiteflies are particularly insidious.
The best way to get rid of whiteflies is to discard infected plants and use predatory insects. From a chemical perspective, you can also turn to whitefly specific pesticides, but make sure you decide whether or not you want to use beneficial insects or pesticides before you spray, as the pesticides could take out your helpers, too.
6. Cabbage White Caterpillars
Out in the field, flea beetles aren’t the only threat your brassicas face. Cabbage white caterpillars can decimate brassica seedlings and crops with their voracious appetites. Row cover can help keep them at bay, but if that fails, try removing them by hand.
The best way to prevent pests on seedlings is to keep them healthy. Starting them off with enough light, proper nutrition, and adequate watering will help them deter pests all on their own, saving you the trouble later.