Common Plant Diseases & Pests: How to Recognize and Treat Them

The wet winter season is upon us, with spring just around the corner! While spring brings back flowers, birds, and bees, it also means that it is almost pest and disease season for your plants and trees. If you want to avoid your plants being taken over by pests and diseases, continue reading for our list of the most common plant diseases and pests, and how to recognize and treat them.

Before we begin with the list, there are two extremely important things to do when you are treating your plants from infections. The first is, when you are purchasing chemicals for your plants, always read the label. Only purchase chemicals that are made specifically for your plant and for the disease you are treating; if not, you could risk killing your plant rather than helping it. Always remember that they best way to chemically treat your plants is by having a professional do it. The second piece of advice is to clean your pruning shears after each use. This helps stop the spread of bacteria from plant to plant. Clean, dry, and oil your tools after each use. If you are pruning infected plants, use rubbing alcohol to rid your pruners of any pathogens.


Our first common pest is the well-known aphid. Aphids are small insects that are attracted to your plants because they suck the sap out of them. Typically, aphids do not harm your plants when they suck their sap; the little bite marks and the dry places in the plants tend to make it look unhealthy, and lose moisture.

To recognize an aphid infestation, check the leaves on your plant. The aphids will live on the underside of them, and when they suck on their sap, the leaves will turn yellow and wilt. Aphids are hard to miss, as they exist in colonies, so there will be many tiny insects living under your plant’s leaves.

To get rid of aphids, wipe the affected leaves with a mixture of dish soap and water. To prevent aphids form being attracted to your plant, bury banana and orange peels around 1-2 inches under the soil surrounding your plant.

Japanese Beetles

These beetles are highly recognizable, as you have probably had them in your garden before! This invasive species is related to the scarab beetle, and so is not native to North America. Japanese beetles are attracted to the tissues in between the veins of the leaves; when they are eaten, only the brown skeleton of the leaf remains.

You can recognize a Japanese beetle infestation just like an aphid infestation. The leaves of your plant will be brown, and pieces inside will be nibbled away. You will also spot Japanese beetles nearby, as they like to feed on the upward side of the leaves in groups. Their coppery wings and green bodies are easy to recognize!

Japanese beetles are most active in the early morning, and so a natural way to deter them is to cover your plants with a drop cloth at night, and remove it in the morning. It should be full of Japanese beetles, which you can dump in soapy water. For a less natural but more effective way of ridding your plants of these pests, spray your plants with neem oil. We suggest not using beetle traps, as these will just draw more beetles to your plants.


Bagworms are a type of moth which are known to wrap their silk around the twigs of trees to build bags. They use these bags to hide in when they are upset, as well as to camouflage themselves against the tree. The larvae will feed on the tree’s leaves, causing defoliation of your tree.

To recognize if you have a bagworm infestation, inspect your tree to find any silk bags hanging in the branches. If your tree’s leaves are chewed through, and there is not a noticeable presence of Japanese beetles or aphids, then you have a bagworm infestation.

With a small infestation, you can clip each silk bag off of your tree and into a bucket of soapy water. With a larger infestation, contact a specialist to treat your tree with an insecticide.

Fungus or Fungal Spores

Fungi are the most common type of plant disease, as there are thousands of types of fungi that can spread bacteria and pathogens. When fungi comes into contact with a plant, it germinates, and begins to grow.

There are quite a few types of fungi that can spread disease, but there are also some fungi that are not necessarily bad for the plant, and some that are good for the plant. The bad fungi will cause canker, discoloration, wilting, and defoliation. The in-between fungi will neither help nor harm the plant, and the good fungi will actually become a food source for the plant.

Fungi is the hardest of the plant diseases to recognize, as it comes in many different forms. Typically, once a plant is infected with a fungus, it cannot be cured. For this reason, it is so important to spray your plants with specific fungicides to prevent fungi from growing around your plant.


A canker is simply an area on the bark of the tree that is dying, or is dead. This can by caused by something hitting the tree, like a lawn mower, or by a bacterial fungus.

To treat canker, any open wounds on the bark of the tree should be trimmed back to prevent the spread of pathogens, bacteria, or fungi. Prune all branches below the canker, and remember to clean your pruning shears! One tip for when you are pruning or trimming cankers, is to avoid doing so in early spring, as this is when bacteria is easiest to spread.


Gall is the name for abnormal growths or balls that occur on roots, stems, or branches of plants and trees. These growths are caused by many different types of bacteria, as it spreads through soil, water, and wind, and can cause leaf drop or death of plants.

Gall is one of the most easily recognizable of plant diseases, as the tumors that grow due to gall are usually large, and can expand without treatment. The only way to rid gall from your plant is to trim all of the gall into soapy water, and to clean up surrounding twigs, leaves, and petals surrounding your plant. Typically, if gall is found in orchards or vineyards, the crops will spread them around, most likely killing the produce.

Powdery Mildew

Powdery mildew is a common fungal disease that mostly affects crops and woody ornamentals. This type of fungus can affect plant growth and fruit development, but will most likely not kill the plant.

Powdery mildew grows on the surfaces of leaves, and is easily recognizable because of its white or gray powdery appearance. This fungus may start off in one isolated spot, but can grow to cover the entire surface of the plant. Prevent powdery mildew by pruning back plants during the winter months, which will increase light and air flow for the plant. Watering the infected leaves prevents the fungus from moving to the other leaves, but a fungicide will be the most effective way to rid your plant of powdery mildew.

Fire Blight

Fire blight is a common disease that affects many fruit trees, the most common being apple and pear. This bacteria grows in hotter air temperatures, thriving in 70 degree weather and killing trees in 90 degree weather. Fire blight is caused by a disease that grows in cankers of trees, which multiplies to spread to other trees.

Fire blight is recognizable because of the affect that it has on the tree’s leaves, which is that it causes them to look as though they were burnt in a fire. To treat, cut out cankers in the winter, when the bacteria is dormant. Apply a nitrogen-heavy fertilizer, and only prune infected branches to avoid spreading the disease any further. Apply biologicals during early bloom, and if the disease persists, consult a professional for chemical treatments.

Leaf Rust

Leaf rust is a disease that can affect plants in mild and humid conditions. These fungal spores are transferred from one infected plant to one healthy plant by wind and water, and feed on the plant to survive.

Rust on plants can by identified by looking closely at your plant’s leaves. If there are small, circular, copper-colored spots on the leaves without the presence of bugs, then your plant is infected with rust. Leaf rust also causes defoliation, and distortion on the surface of leaves. To treat, prune the infected leaves and destroy all leaves that have dropped from the plant. If leaf rust persists, use a chemical treatment only on the infected plants.

Botrytis Blight

Botrytis blight, also called gray mold, is a type of fungus that grows in humid conditions. This common disease is found mostly among bedding plants, and can affect the entire plant, rather than just the leaves or stem. Botrytis blight attacks your plants and feeds off of them, harming them and in some cases killing them.

Water-soaked spots will form on the leaves, eventually causing the leaves to wilt. Without treatment, fuzzy gray spores will form on the plant, which can spread through air or water. The best way to avoid botrytis blight is to trim back your plants, and the best way to rid your garden of this fungus is by completely removing any infected plants and destroying all debris. If your gray mold continues spreading, use a fungicide specific to your plant to cease the spread to any healthy plants.

Pest and disease season is almost upon us, and that is why it is so important to always check on your plants to ensure they are healthy. Failing to check on your plants means there is no way of knowing if you have Japanese beetles, or if powdery mildew is spreading in your garden! When in doubt of whether a plant is infected or not, always consult a professional before you spray a chemical on your plant that it does not need. Pruning your plants is the best way to prevent the spread of disease and bacteria in your garden, as long as you remember to clean your shears!


8826 Santa Fe Drive Suite 300,

Overland Park, KS 66212

Tel: 913-362-0089

© 2017 Principal Landscape Group, LLC

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