Fall Garden Pests & Diseases: Keep Your Garden Healthy Through Fall

Fall Garden Pests & Diseases: Keep Your Garden Healthy Through Fall

After all that hard gardening work during the spring and summer, it’s time to sit back and reap the rewards in the fall. But that doesn’t mean you can let your guard down. Many pests and diseases are just ramping up in the fall.

As autumn arrives, the garden slows down, but there is still plenty of growth and fruiting happening. At the same time, pests and diseases continue their destruction, which can ruin the harvest you worked so hard for!

Here’s what you need to know to keep your plants healthy.

Fall Garden Plants

Not only can a fall disease ruin your harvest, but it can stick around and harm plants next year, so you definitely want to address the problem.

To determine what pests and diseases you need to watch for in the fall, it helps to look at the types of plants growing at this time. The pests and diseases you’ll experience will be the ones that affect those plants.

Here are some of the most common fall veggies:

  • Root vegetables such as carrots, parsnips, rutabagas, kohlrabi, beets, radishes
  • Allium vegetables like onions, leeks, garlic
  • Edible leaf vegetables like lettuce, arugula, collards, swiss chard, kale
  • Broccoli
  • Cabbage
  • Cauliflower
  • Endive
  • Brussels sprouts

Complete list of fall plants here.

Obviously, there is a whole range of other ornamentals, trees, or other veggies that you could be growing. Most of the pests and diseases on this list can harm those, as well.

We’ll cover the most common pests and diseases that attack these types of plants in your garden during the fall, but you might encounter something different if you’re growing plants that aren’t on this list. Be sure to do your research.

Common Fall Pests

While many of these pests can attack at any time of year, they are particularly bothersome in the garden during the fall.

Cabbage Loopers

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Cabbage loopers (Trichoplusia ni) overwinter in your garden and emerge in spring to eat their way through many of your vegetables. They’re often still going strong in fall.

These are fat, green caterpillars, growing up to 2 inches in length. Usually, they’re about an inch long. Loopers can be distinguished from other green caterpillars by the way they raise their middle segment as they inch along.

They’re enthusiastic eaters, and love those fall vegetables like cabbage, cauliflower, broccoli, and brussels sprouts, along with lettuce, potato, and tomatoes. They also nibble on flowers like carnations and nasturtiums.

They have a voracious appetite and can do a lot of damage in just a little time.

To control them:

  • Handpick them off plants.
  • Use row covers in the spring and summer.
  • Apply neem oil every few days if you spot them.
  • Use an organic insecticide such as Bacillus thuringiensis.

Fall Armyworm

Technically, the fall armyworm (Spodoptera frugiperda) is a type of cutworm, but they behave like an armyworm.

If you find one fall armyworm, there are many, many more lurking in the garden. As their name suggests, they decimate gardens and move from plant to plant in large numbers like a little insect army, typically moving around at night.

These pests love fall vegetables like cabbage, collards, and carrots. They also enjoy citrus, avocado, and various flowers. The bertha armyworm is particularly fond of cabbage and broccoli.

Go out with a bucket of hot water, mixed with a tablespoon of dish soap. Pick the armyworms off the plants and drop them in the water. Leave them in there overnight.

Homemade pesticides that contain pepper or garlic are effective. You can also use neem oil if you spray early enough and regularly throughout the fall.

Fall Webworm

Not to be confused with tent worms, (these come out in spring), fall webworms (Hyphantria cunea) appear in trees, shrubs, and veggies and cause serious leaf damage. They’re a worldwide problem and can be hard to control.

After flitting around all summer, the small white moths lay eggs that hatch into the larvae that cause all the damage.

Webworms weave webs around plant foliage to create little protective homes. This web can cover small areas or entire branches. At the same time, they eat the leaves of your plants.

Go out with a broom or rake and pull down the webs to prevent the pests from reproducing. Insecticides are rarely necessary.


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Cutworm is the name for the larvae of several nocturnal moths. Many of them lay eggs that hatch in the fall. These pests normally live in the soil and emerge to eat the stem of the plant.

Cutworms also eat the roots and most lower parts of young plants. Because they cut plants off at the base, they usually die due to the damage.

I’ve found the best way to prevent cutworms is twofold. Mow the lawns around your garden and keep all grass two feet away from your garden. There should be a two foot barrier of open dirt.

Then, be sure to clear all weeds and debris away to deny these pests a place to hide.

Use diatomaceous earth around plants as another layer of defense. You can also place a cardboard collar around your plants to prevent cutworms from nibbling.


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Aphids are as much of a pest in the fall as they are in spring and summer. They’re sap suckers who cause damage and grow in numbers quickly. Like most sapsuckers, they excrete honeydew, which attracts ants, wasps, and causes issues like sooty mold.

Use organic sprays like neem oil and pyrethrum. Aphids are tricky little pests, so a number of sprays may be required. If you like using neem oil, it needs to be regularly. For that extra knockdown effect, add the pyrethrum for the first couple of sprays.

Fall Garden Diseases to Watch For

Some garden diseases thrive in the fall climate, so you’ll want to keep an eye out for them as the summer winds down.

Many diseases continue through fall, right up to winter.

Sooty Mold

Do your plants look like they are covered in black fuzz? You could have sooty mold.

This often goes hand-in-hand with aphids, because the spores land in the sticky honeydew and reproduce rapidly.

The first step is to get rid of those aphids. Next, carefully wash the mold off with warm, soapy water.

You’ll need to do this repeatedly until the mold is gone and stays away.

Powdery Mildew

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Powdery mildew makes it look like your plant is covered in flour. This disease starts out as little yellow spots which eventually develop a white, fuzzy coating.

Over time, the foliage yellows and dies off.

This fungus is spread by the wind, so once it’s present, it will go from plant to plant in your garden.

There are a lot of homemade recipes. Some are as simple as baking powder, water, and dishwashing liquid. You can also combine water and milk in equal parts to spray as a preventative.

Once powdery mildew starts, it spreads rapidly, so keep an eye out for it and treat it straight away.

Leaf Spot

As you may have guessed, leaf spot causes yellow and brown spotting to form on leaves. It can attack a range of veggies and trees in the garden.

It helps to keep your garden clean and to give your plants plenty of good air circulation. That means raking up the leaves in the fall and keeping up on pruning.

You should also water at the soil rather than on the foliage. Prune away infected leaves.


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If you have ever seen the orange rust on a piece of scrap metal, then you know what rust on plants looks like. It typically shows up as orange spots and can cause leaves to die off.

You can prevent it much the same way that you prevent leaf spot, with plenty of air circulation and keeping water off the leaves by watering at the soil level. Trim away infected leaves.

You can also create a treatment spray using a tablespoon of baking soda, 3 tablespoons of vegetable oil, a teaspoon of dish soap, and a gallon of water.

Fall Gardening Tips to Help Avoid Pests and Diseases

No matter what you’re facing, there are a few good practices that you can use to keep your plants in good shape.

  • Keep gardens clear of debris, weeds, and sick plants. Many pests overwinter in long grass and areas with debris and garden waste.
  • Plant a cover crop. This keeps the soil healthy and future plants strong.
  • Gather all fruit up as it drops to the ground. Allowing it to rot where it falls gives many pests and diseases the opportunity to start.
  • Mulch your fall garden well. Mulching protects the plants, keeps the soil warm, and feeds the soil with nutrients as it rots down. Gather all of those fallen leaves and make leaf mulch. This is highly nutritious and will eventually keep your soil in top condition.

Stay Diligent Even As the Season Winds Down

Fall is a wonderful season in the garden. Many gardeners focus on the highly active seasons of spring and summer, but fall has a lot to offer the avid grower beyond the much-awaited harvest.

Unfortunately, the fall garden also has a lot to offer in terms of pests and diseases as well, so don’t let your guard down. Keep an eye on your plants to see if anything is forming, and take action straight away.

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