Holes In Cucumber Leaves – What’s The Cause?

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We’re protective of our garden veggies and other things we care for. Cucumbers are delicious in salads, on their own, as a vessel for your favorite dip, and especially when pickled. You go through a lot of work to grow these juicy veggies, so when something starts disturbing them you want to fix it quickly.

Most of the time, striped or spotted cucumber beetles are the cause of holes in your cucumber leaves. These insects can cause damage to the plant, and introduce microbial infection. Other causes include anthracnose, scab, or another fungal or viral infection.

One of the most disturbing things is to go out, check your garden and find ragged, holey leaves. This usually means something small with a lot of legs is feeding on your precious plants. While a few holes won’t cause the plant much harm, too many bugs can stunt the growth, or ruin the plant altogether.

Depending on the types of holes in your cucumber plants it could be insects such as the cucumber beetle, Japanese beetles, or a fungal or viral infection in the plant. Each has a different treatment, so identifying the culprit is essential.

Holes in Cucumber Leaves

Could It Be The Dreaded Cucumber Beetle?

When you start seeing holes in the leaves of your cucumber plants, the first thing you should do is check for this destructive beetle. A big majority of the time, these beetles are the main culprit. 

Only a few cucumber beetles won’t do enough damage to your cucumber plants to bother it, but if they continue to feed, and multiply, they could completely defoliate your plants. Cucumber beetles also feed on the flowers which prevent veggie production, they can feed on the cucumbers themselves leaving behind ugly scabs, and they can eat the stems. 

Recognizing the Cucumber Beetle

Your first line of defense against these beetles is being able to identify them. They are very small, but bright beetles. There are two main types, the striped, and the spotted cucumber beetle. 

Both are yellow, to yellow green with black markings. The striped version has three black stripes running from the tiny head, down the elongated, domed back. They are only about ¼ of an inch long and have a black head and small black antennae. 

The spotted cucumber beetle is the same size, usually a little brighter yellowish, and has about 12 black spots on its hard shell. Both types are most active from June through September. Coincidentally this timeline tends to line up with cucumber growing months. 

Cucumber Beetle Life Cycle

Fortunately, it takes nearly 2 months for the eggs of these beetles to hatch and grow into adulthood, so you’ll likely only have to deal with one generation. The problem is, they can lay hundreds of eggs, and the larvae also feed on cucumber plants.

The adult beetles will lay their eggs in the dirt next to the host plant. When the egg hatches, the little grubs feed on the roots and underground parts of the stem. Once they pupate and emerge as adults, they crawl out of the ground and start feeding on the flowers and leaves.

With large enough numbers, the beetles can defoliate an entire plant. If that happens, they will move on to other plants such as squash, melons, corn, asparagus, and eggplant. They prefer cucurbits, but when that food source is gone, they aren’t terribly picky. 

How Do You Get Rid of Cucumber Beetles?

Fortunately, it’s not super difficult to get rid of these beetles, you just have to be diligent. The first thing you can do is pick them right off the plants. You can do this with your hands, or with a small handheld vacuum. 

Pick Them Off

If you’re plucking them off with your fingers, have a container of soapy water with you. Just some warm water and a few drops of dish detergent stirred in works wonders. When you plop the beetles in the soapy water, the soap breaks the surface tension of the water and the bug sinks and drowns.

When using the vacuum cleaner method, be sure to empty the bugs into an airtight container, or thick, sealing plastic bag and dispose of them. 

Insecticidal Sprays

Sprays can be effective at getting rid of cucumber beetles too. Neem oil and insecticidal soaps are great, food safe alternatives to harsh pesticides. You’ll probably have to apply these sprays several times—especially if the adults have laid eggs in your garden—to get rid of them all. 

Neem oil and insecticidal soaps only work if you spray the bugs directly, they are not long lasting, residual bug killers. This helps from accidentally targeting beneficial insects. 

You can make your own insecticidal soap by mixing water and an all natural detergent such as castile soap. These won’t harm your plants or douse them with harmful chemicals. 

Sticky Traps

Another way to prevent and get rid of cucumber beetles is to use yellow sticky traps. These Gideal 20-Pack Dual-Sided Yellow Sticky Traps for Flying Plant Insects attract cucumber beetles and many more pests. The bugs get stuck to the glue and cannot extract themselves. All you have to do is throw away the pads when it gets coated in bugs. 

Ways to Prevent Cucumber Beetles

There are also a few ways you can help prevent these pests. One of the most effective ways of preventing an infestation is to apply a thick bed of mulch or place row covers around your cucumber plants. 

Row covers or mulch won’t prevent wandering cucumber beetles, but it will stop them from laying eggs, which could help reduce their numbers. A thick bed of mulch will keep adults from burrowing into the soil and laying their eggs. 

The same goes for row covers. Just be sure to bury the edges so the beetles don’t crawl underneath them and lay their eggs. 

Crop Rotation

By implementing proper crop rotation, you can also help prevent cucumber beetles from becoming a big problem. When their host plants are moved or planted on rotating years, it’s harder for overwintering grubs to feed and grow into adults. 

Keep Your Garden Clean and Neat

Removing debris, and spent plants, and keeping weeds down will make the area less inviting and hospitable for cucumber beetles. These bugs like to hide in weeds and under leaf cover. By keeping your garden neat and clean, there aren’t many places for them to hide. 

Either the bugs will get eaten by birds or other predators, or they will seek out areas with more shelter and hiding places. 

Cucumber Beetle Resistant Plants

If despite your best efforts you are still being plagued by cucumber beetles, instead of giving up on planting these salad staples again, try planting resistant varieties. Look for cucumber varieties such as Marketmore 76, Dasher II, or Saladin if you want cucumbers that are great for slicing or just eating raw. If pickles are your favorite, look for Fanfare and Liberty varieties. 

All of these plants are resistant to cucumber beetles. You may still have an occasional beetle, but it’s very unlikely that you’ll have a full blown invasion. 

Slugs Could Be Chewing Holes In Cucumber Leaves

You’d think such a slow moving, slimy, unprotected creature wouldn’t be able to cause much damage, but in one night, an army of slugs can destroy a garden. Slugs usually only come out at night when it’s cool and humid. 

Hot sun and dry weather are extremely hazardous to these slimy creatures. They like to hide under leaves, rocks, in the soil, and other cool, moist places. 

When they come out at night, they are voracious feeders. They use rasping mouthparts to scrape away leaves and other plant parts. Slugs can cause holes in your cucumber leaves, or even eat them down to the stem if they are small young leaves.

You’ll be able to recognize slug damage by the iridescent slime trails they leave behind. Everywhere they crawl, they leave a thin film of mucus that dries and looks almost like see through streaks of mixed rainbow paint. 

Treating Slugs

Luckily it’s easy to prevent future slug damage. There are tons of ways to prevent or get rid of slugs. You can use something to make a barrier that will prevent them from getting to your veggies, you can make a beer trap, create a lure, pick them off by hand, or attract slug predators to get rid of them. 

Put Up a Barrier

Being such soft bodied mollusks, and having a mucus covered body means there are a lot of surfaces they can’t traverse. By creating a barrier around your garden, your pots, or individual plants, you will keep slugs away. 

You can use a barrier of crushed eggshells, diatomaceous earth, sharp rocks or gravel, salt, or even copper to keep slugs out. Eggshells, diatomaceous earth, and gravel keep the slugs away because their soft bodies can’t cross these barriers without causing severe damage. 

Salt will kill slugs, but too much salt will also damage plants. Epsom salts will do the same thing, and in smaller doses is a good source of minerals for plants. Unfortunately, too much Epsom salt can be damaging to plants so be careful with these methods. 

Copper will keep slugs away because it’s thought that when a slug touches anything copper, the mucus layer on the slug creates an electric current preventing passage. Vaincre Copper Tape Conductive Adhesive can be placed on the ground, around pots, or around raised beds to prevent slugs. 

Make a Beer Trap

Slugs love beer, unfortunately, they don’t know when to stop. You can use this to your advantage and trap these slimy mollusks. Save a few short cans such as cat food tins, tuna, or soup cans.

In the garden place these cans in the dirt with about an inch of the lip above ground, and fill the can about halfway full of beer. (Use that nasty, cheap stuff that you just can’t seem to drink. Don’t waste your craft beer on slugs.)

The slugs are attracted to the smell, they fall into the beer and then drown in their sorrows. In the morning, empty the cans of the pickled slugs and the ruined beer, and do it all over again the following night until you no longer have a slug problem.

Create a Slug Lure

Use a handful of lettuce leaves or some cat food and pile it up in a shady corner of your garden. This should attract the slugs. At night, when the temps cool, go out with a flashlight and dispose of all the banquet feeders. While you’re out there, search your garden and surrounding areas for more of these mollusks.

If you have insect eating pets or chickens, you have free food and snacks for them. Most insect eaters love slugs and snails.

While we are on this topic, you can simply pick the slugs off plants, garden walls, or out of the ground and dispose of them. They won’t hurt you, and they can’t move fast at all so it’s easy to pluck them by hand.

You may not want to have that slimy texture all over your hands, so if you have some surgical or rubber coated gardening gloves, now might be a time to put them on.

Attract Natural Slug Predators

Birds, toads, frogs, predatory beetles, and lizards feed on slugs, so make your garden inviting to these natural slug eaters. You can purchase toad houses, or make your own with large pots.

Cut a pair of small holes in a pot and turn it upside down. This is a simple way to attract toads and lizards. If you have a small water source, add some water plants to attract frogs. It may take some time, but nature will help keep these pests away.

Are Japanese Beetles Chewing Holes In Cucumber Leaves?

Another major pest in many areas of the United States is the Japanese Beetle. These green and golden brown colored small beetles show up in the heat of the summer and can decimate certain plants. Cucumber plants are definitely on their menus.

Japanese beetle damage will skeletonize leaves. They feed on the soft green tissue between the larger veins of the leaves. You’ll often see these beetles on the plant as well.

You’ll recognize Japanese beetles by their bright, iridescent colors. Their wing covers are ridged and shiny brown and their head and thorax are covered with a shimmering dark green shell. They have black and white stripes on their abdomen, underneath the wing covers.

How to Treat Japanese Beetles

Diatomaceous earth, planting trap crops, or putting up a barrier can help you get rid of Japanese beetles. There are Japanese beetle traps that you can hang up to remove these insects, but they work so well, you may end up with all the beetles in the entire neighborhood.

I’ve seen these bags get so full of Japanese beetles that they have fallen out of the tree. Unless you want to be a neighborhood hero and remove all the Japanese beetles within a square mile, steer clear of these beetle traps. They may work too well.

Diatomaceous Earth

DE is a white powder made of microscopic, fossilized sea creatures. It’s a non-toxic powder that kills insects by contact. When DE contacts insects, or they walk through it, the grit creates tiny cuts in the carapace of the bugs.

These cuts can’t heal, so the bug eventually dehydrates. It can take a few days to work, but it will get rid of any insects on your plants. Just be sure to follow the instructions and wear a mask. If you breathe the dust, it can cause respiratory irritation.

Plant A Trap Crop

Japanese beetles love geraniums! You can plant them near your garden, or place them in hanging baskets. The Japanese beetles will feed on these flowers, and then become “drunk.” There is a chemical in geraniums that makes Japanese beetles become slow, lethargic, and unable to fly.

They will fall to the ground in a self-induced stupor where you can either vacuum them up, or let birds, chickens, or other predators take care of them for you.

The Early Gardener Gets The Japanese Beetle

In the early morning, insects are usually slow and sluggish. They don’t typically get moving around much until the sun comes out and starts to warm the world up. This is the perfect time to go out and pick the bugs off your garden.

Using the soapy water method, pluck the beetles off your cucumber plants and drop them into the bath. They will sink and drown, never to bother your cucumber plants again.

Put Up Fine Mesh Netting

Putting up a barrier is another way to keep Japanese beetles and other flying insects off your plants. This 10 * 50FT Garden Mesh Netting Barrier keeps bugs off your plants while still allowing airflow, water, and sunlight to filter through.

Anthracnose Could Be Causing Holes In Cucumber Leaves

This is a fungal disease that actually starts off as brown, round, spots that can lead to holes in the leaves. When you don’t see any insect activity, but still see holes in your cucumber’s leaves, most likely you have some kind of fungal, viral, or bacterial infection affecting your plants.

Anthracnose is spread during the rain, especially during hot, and wet seasons. Infected plant debris settles on the ground, and when rain splashes around this debris, the spores fly up and attach to other plants.

If anthracnose is not treated, the leaves will curl up, dry out, and fall off, helping spread the spores. It can affect the production, stunt the plants, and eventually kill the plant.

During periods of high humidity, this fungal infection can really be spread by contaminated soil, plant debris, or even garden tools.

Prevention is the best way to fight anthracnose. This includes crop rotation, proper watering techniques—water at the ground level and don’t get the leaves wet—and not over watering. Getting rid of infected plants and plant material also helps in reducing the spread.

Use a Fungicide

When anthracnose is caught early, a fungicide can help treat it. Follow the manufacturer’s directions, and remove and properly dispose of any infected leaves or plants to keep it from spreading throughout your garden.

Increase Airflow

Planting with plenty of space between your vegetables will help prevent this fungal infection. When you’re trellising your cucumber plants (assuming you are growing the vining types) keep them spread out enough for good airflow.

This helps reduce humidity between the leaves which is what fungal infections like anthracnose need to become established. This can infect your trees as well as your garden, so if you have a lot of trees on your property, keeping them properly trimmed will also help prevent anthracnose.

Plant Anthracnose Resistant Cucumbers

The following cucumber varieties are bred to be resistant to fungal infections such as anthracnose. If you are having an issue with this fungus, or just would like to avoid it altogether, try these out:

• Straight Eight
• Marketmore 76
• Dasher II
• Sweet Success
• Salad Bush
• Bush Whopper

Holes In Cucumber Plants Caused By Angular Leaf Spot

Angular leaf spot is caused by a bacteria and it causes angular, brown spots that are surrounded by yellow. As the disease progresses, holes can be formed in the leaves, defoliation can happen, and you’ll get fewer and smaller cucumbers. 

Angular leaf spot is spread through the soil, or from contaminated seeds, and to a lesser degree, contaminated water. It’s not often encountered in cucumbers as most plants are resistant to it, but it warrants a mention. 

Treating Angular Leaf Spot

It can be treated with a copper based fungicide, but prevention is the best way to treat this bacterial infection. If you notice it starting, remove any infected leaves and dispose of them in the trash so that it doesn’t spread. 

Crop rotation, not overwatering, and avoiding overhead watering practices will go a long way in preventing angular leaf spot. Providing good air circulation is another way to help prevent this infection. 

Scab Can Cause Holes In Cucumber Leaves

One more fungal disease that can cause holes to appear is scab. First, you may notice small circle spots on your cucumber leaves, that can turn into black lesions, and eventually holes. 

When scab spreads throughout the plant—this can happen quickly during warm humid days—the leaves can turn yellow and lead to defoliation. Scab can also affect the fruits. The cucumbers will turn colors, and become rough, bumpy, and be unfit for consumption. 

Treating Scab

Since this is a fungal infection, it can be treated with a fungicide that is labeled safe for cucumber plants. You’ll need to remove any infected leaves and dispose of them properly. Place them in a sealable plastic bag and throw them away. 

You don’t want to put infected plants in your compost bin because the heat may not get hot enough to destroy the microbes. When you spread your compost among your plants, you could inadvertently infect them all. 

Prevention is Best

With most fungal infections, prevention is the best way to treat scab. Be sure to water your plants from the ground, don’t get the leaves wet. If you can afford a soaker hose and a timer, this will help keep your garden healthy, and free up a lot of time for you. 

Water in the morning if at all possible. Watering in the evening will leave the ground damp and cool longer, possibly allowing fungal and bacterial infections to grow in the soil. Watering during the heat of the day will cause a lot of the water to evaporate. If water hits the leaves, this can cause scalding or scorching of the leaves. 

Allowing for ample airflow is another great way to prevent scab. Prue old leaves, plant your cucumbers with plenty of space between them and be sure to remove weeds promptly. Keeping your soil clean and removing spent plants will help prevent most plant infections.  

How To Keep Cucumber Plants Healthy

A healthy plant is a happy plant. It also helps them stay strong and able to shrug off bug damage and most infections. So how do you make sure your cucumbers are as healthy as they can be? 

Pick The Best Location

Cucumbers like warmer weather and need plenty of sunlight. At least 8 hours of sunlight a day is essential to cucumber health. Make sure you plant them well after any threat of frost is possible, because cold temperatures will stunt their growth, and could kill them outright. 

Secondly, don’t plant cucumbers in the same spot every year. For one, cucumbers are heavy feeders and will deplete an area of certain nutrients, plus, if there is a microbe in the soil that affects cucumbers, chances are, your plants this season will become afflicted with it. 

Provide Well Draining Soil

Cucumbers need plenty of water, but they don’t like to have wet roots. Be sure your soil has plenty of drainage and isn’t a heavy clay type of soil. If you do have thick, heavy dirt, add some peat moss, clay breaker, compost, or other organic material that will allow the cucumber roots to “breathe.”

Water And Fertilize

Once your cucumbers are established, you’ll probably need to water them throughout the week. Cucumbers typically need 1 to 2 inches of water a week, but that number may need to be adjusted depending on several factors. 

One way to tell if you need to water your cucumbers is to stick your finger in the dirt. If it’s dry up to the first joint on your finger, you need to give them some water. 

You’ll also need to provide some fertilizer throughout the growing season. You can do this by adding compost to the soil periodically, or by adding a supplemental fertilizer. Follow the instructions because too much fertilizer can be worse than not enough. 

Proper Spacing

Airflow throughout your garden is just as important as sunlight, water, and fertilizer. Be sure to space your cucumbers accordingly. If you plant them in rows, it’s okay to space them about 12 to 18 inches apart. When you plant cucumbers in a hill, you’ll need to space them out considerably more, between 36 to 60 inches apart. 

Other Considerations

Providing a thick layer of mulch can help reduce certain insects and weeds, and prevent the spread of fungal infections in the soil. It creates a barrier that can make it too difficult for bugs and weeds to penetrate, and it keeps dirt from splashing up onto low lying leaves. 

Mulching also slowly adds nutrients to the soil, and keeps more moisture in the ground which can reduce your need to water. You can mulch with shredded wood or bark, or straw. Each has its own benefits. 

FAQs

Conclusion

When holes show up on your cucumber leaves take a little bit of time to try and identify what the cause is. Are there Japanese beetles, cucumber beetles, or some type of infection causing them? Once you have identified the cause you can go about treating it.

For insects and pests, some things you can do include using diatomaceous earth, neem oil, insecticidal soap, putting up barriers, or covering your plants with a mesh. When your plants have a fungal or bacterial infection, antifungals may help, or you may need to remove infected leaves and alter your watering behaviors.

We hope this has helped you figure out, and come up with a treatment plan for holes in your cucumber plant leaves.

More cucumber stuff

• Types of cucumbers
• Companion plants for cucumbers
• Why your cucumber leaves are turning yellow