TL;DR : There are many pests that may cause holes in your plants’ leaves. These include gastropods, animals and insects and there are many ways to get rid of them so please don’t resort to chemical warfare for your own sake and for your pets’.
Welcome to the “What is eating my plant?” series.
You are about to read the second part of a series. This part concerns insects. If you think you plants are (also) under attack by gastropods or insects please read our article on animal threats in the garden and for the best solutions to control your insect population head to our blog post on the best ways to get rid of these insect threats.
Many insects, like caterpillars and leaf beetles, get most of their nutrition from our leafy greens or from other plants (or from other insects which feed on the these). We call these type of insects phytophagous. Some phytophagous insects eat a variety of plant species, while others specialize in eating only one, or just a few. This is why when your garden is suddenly infected a few of your plants may continue thriving as other are completely depleted of their leaves. This may help you identify the type of pest that has set up shop in your backyard.
New leaves and sprouts are usually the parts that will suffer the most damage from an insect invasion. Not only are they more sensitive to these types of attacks but they are also the part that tastes the best to the invaders.
Some insects’ larva will also attack the root system of a plant, which may make the plant more susceptible to other pests and diseases that will kill it. This is an issue you should also turn some of your attention to.
Once insects have infested a bed or one of your plant pots, it is rather difficult (or sometimes just time consuming) to get rid of them for the current season (even with chemical controls), but steps can be taken to reduce the infestation and then eliminate it for next year if you really want to.
Some pests in the garden are more annoying than harmful and some may nibble on your leaves causing no permanent damage. These same “pests” may prove very useful at other things. Caterpillars are some of the biggest nibblers I know, and if you love seeing butterflies flutter about in spring and summer you may not want to dispose of all the caterpillars that are chewing away at some of your leaves if they are not too much of a nuisance.
Identifying the insects
Here is a list of the insects that can potentially harm your plants that you are most likely to meet.
Various caterpillars (cabbage loopers, corn earworms, cutworms, …) feast on vegetable foliage, chewing large holes in leaves or devouring leaves completely. On the plus side, sometimes you get beautiful butterflies (or if you’re unlucky, pretty ugly moths). You might want to check what type of caterpillar the one you’ve just picked is, before stomping on it. It might be a Monarch Butterfly! Don’t forget that butterflies and insects also help pollinate your flowers. They are essential if you want fruit, vegetables or seeds for example.
You can find all types of caterpillars (some prettier than other) chewing on your plants, though each type usually has its preferences.
If you see 6.3 mm-long (yes exactly this size – actually you better look at the picture bellow) yellow and black beetles (spotted or not, kinda depends on where you live, too bad if you only like stripes) cucumber beetles are eating your veggies. Both feed on a wide variety of vegetables, and both carry various diseases that can cause plants to wilt and die suddenly if your plant is weakened.
Predators that feed on cucumber beetles include wolf spiders and ground beetles. There seems to be an incredible array of different predator species eating the beetles, including harvestmen commonly known as “daddy long legs” (ok this here is subject to long disputes in our relationship, apparently Daddy-Long-Legs are not spiders, but crane flies. Wikipedia does not seem to know the answer to this one either: https://en.wikipedia.org/wiki/Daddy_longlegs, so we just agree to keep on disagreeing until some-one more knowledgeable will solve our disagreement once and for all. We have several other ones like these in French if you want to give us your opinion : Chocolatine or Pain au Chocolat, and is Galette des Rois a crown or an almond paste cake? Oooook I got totally side-tracked here, let’s go back to our main point), ground and rove beetles, spiders of several kinds, and predatory mites. It is also believed that radishes repel cucumber beetles. We don’t get a lot of them, and we do plant radishes, but that’s the most we can say about this.
Cucumber beetles often overwinter and lay their eggs near to the previous years’ cucurbit (hence their name, wow, you’re surprised aren’t you, they eat cucumbers :3) crop. So, one way to reduce pest problems the next year is to plant cucurbits as far away from last year’s crop as possible. You can also try to hinder their progress with any sort of barriers you like : hedgerows, plastic, mulch or floating row covers (until the plants are ready for pollination) might prove useful for example.
So, as you can guess these beetles are called flea beetles because they move around by jumping. These are pretty voracious pests, they will harm your plants by chewing tiny holes all over the leaves.
The patterns they use makes it easy to identify them, you’ll easily recognise these small holes peppered on your leaves. When populations are high, flea beetles can quickly defoliate and kill entire plants. They do the most damage on hot sunny days in order to get as much water as possible.
Flea beetles will attack a wide variety of plants including beans, cabbage, corn, eggplant, potatoes, peppers, tomatoes, lettuce and most seedlings (all the best stuff right?).
Adults are small (only around 20 millimeters), shiny, dark brown or black beetles with long and robust hind legs that allow them to get away by jumping when disturbed. Larvae are a little larger, cream-colored worms. They live underground and feed on the roots of young plants as well as on germinating seeds. You should watch out for these as they can do a lot of damage in your garden.
There is so much to say about aphids. They are definitely one of my worst rated very annoying pests. They just keep coming back (and I can thank ants for them most of the time). There are approximately four thousand aphid species found throughout the world, which usually means several hundred different species of aphids in the country where you live.
Luckily, low to moderate numbers are usually not harmful to plants and rarely require aphid control, but you should definitely always keep an eye on them and get rid of them every time you see a few.
On the other hand heavy infestations will cause leaves to curl, wilt or yellow and will also result in stunted plant growth. The worst problem is that they attack new growth on plants (because those are the best and softest bits) and this will stunt or completely stop your plant’s growth. They will also make your plants weaker (they are basically slowly draining their “blood” after all) , more vulnerable to disease (they pass on disease and viruses through feeding) and may eventually kill them by decreasing their overall health. As they feed, aphids secrete large amounts of a sticky fluid known as honeydew. These secretions drip onto plants, attracting ants and promoting a black sooty mold growth on leaves.
Generally adults are wingless, but some females can grow wings, especially if populations are high. Once they grow wings (every few generations) they may fly to another plant and infect this one too. This is one of the reasons you should always keep the population in check.
Grasshoppers are voracious feeders, they aren’t that much of a problem in France (at least that I know of) but they can be a very destructive species (I mean have you seen A Bug’s Life?: www.imdb.com/title/tt0120623/). They can consume approximately one-half of their body weight (an average weight of 0.54 grams about half a gram basically) per day.
Both adults and nymphs cause damage by chewing on the leaves and stems of plants, and if infestations are severe, may defoliate entire fields (you at least know about the locust plague, I know I know, locusts, not grasshoppers, but it’s pretty much the same thing isn’t it?!). They usually die during the winter, so you just have to get rid of the eggs for the following year.
You’ll get some insects that only specialize in a few plants like lavender or rosemary. You know the ones that make cocoons composed of little bubbles on lavender branches. They’re from a family called leafhoppers (a really big family, so they get to specialize). These aren’t easy to get rid of when they are adults but if you see some of these cocoon just wash them away with water.
Leafhopper damage on plants can be extensive, if your population is too important. You might know these from the little white bubbles (that are actually cocoons, like the picture below) on your rosemary or your lavender. They chew holes but seem more interested in some plants than others. They each specialize in a few plants. They suck plant sap from grass, shrubs, or trees.
There are at least 20000 species of leafhoppers and they are rather common so we believe you have definitely already encountered these. Adults will spend the winter in your garden debris or non-cultivated areas adjacent to gardens. In late spring females deposit 1-6 eggs daily within the stems and larger veins of the leaves. Hatching happens around 6 days later and the young nymphs will have to molt 5 times before they become fully grown adults. You can imagine that from this point on they reproduce fairly quickly since the period from egg to adult is about three weeks.
Personally I must admit I was always had a horrible fear of all things earwig, they used to get in our bathroom when I was young and they scared the sh*t out of me as a child. My parents would tell me they would crawl into my ears while I slept or would pierce my ears. Earwigs are called Perce-oreilles in french, which literally translates into “Will pierce your ears”. The species we had emitted a foul smelling liquid that they use for defense. At least I’m enough over it that I can add a picture of one on the blog and not die of fear.
They feed on things like clover, dahlia, zinnia, lettuce, cauliflower, strawberry, blackberry, sunflower, celery, peach, plum, grape, potato, rose, seedling bean and beet, and tender grass shoots and roots. Females lay between 30 and 50 eggs depending on the species. After hatching, the nymphs undergo four to five molts until they become adults. As usual the most important things about these insects is not to exterminate them (even if you are really disgusted by them), but rather to control the population you are harbouring in your garden.
Other small insects
There are many more like the potato beetle or the asparagus beetle or even spider mites (these love the dry weather), but you get the point don’t you.
Here are the pests we encountered and had issues with so far:
- Aphids : Of course, can you name anyone who hasn’t had the burden to have ants farming aphids in your flower pots? They seem to love the new shoots from my peach tree…
- Cochineal : On avocado trees, blueberry bushes and especially citrus trees. We get rid of these with black soap (made from olive oil) and by cleaning with alcohol the leaves on which they start popping-up.
- Leafhoppers : On rosemary and lavender. They haven’t done any “real” damage to any of our plants except make them less awesome to look at.
We do have the other insects in our garden of course, but they aren’t any hassle.
If you want to read about how to effectively control these insect populations then you should continue to the nest and last part of our series on garden pests : how to get rid of these little creatures.
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