Insects and Diseases on plants

Insects and diseases on plants are a big problem for almost any part of the U.S. or in the world, and the southwest region has its share of pests and diseases.  Many folks have no idea why a plant looks magnificent one day then almost withers away a few days later.

It’s always best to consistently observe your plants.  If you find pests, insects, spots, yellowing or other substances that were not there a few days ago then this post is for you.

We have a few tips that will help you avoid common disease and insects on plants.

Use neem oil or horticulture oil early in the season to prevent insect eggs, borer larvae from hatching. It really works!

Common Disease and Insects on Plants

Witches Broom Disease

Will usually attack Ash, willow, pine, oleanders, privets, and a wide range of other trees.  What causes this disease? Mainly stressful conditions.  Not enough aeration and too many other insects attacking the plant will also cause witches broom.

Curing Witches Broom?

There is no real cure for this disease, however, you can remove the infected area by pruning out these clusters of small twigs.  (See photo below.) Sometimes removing the plant and replacing it with a new one might be your best course.   Remember, always clean your pruning tools before moving on to your next pruning job!

Rust can also cause witches broom and it is a viral fungus.  It would be a good idea to use a good fungus spray to help with this disease. Always spray after you have completed pruning.

Insects and Diseases on plants

Borer Damage on a tree trunk

Borer’s are a real pain in the neck for all gardeners.  Borer’s come from the larval stages of beetles and moths.  The most common in the U.S is the Emerald Ash Borer.  They basically lay their larvae eggs on the tree and this turns into a worm that digs a hole into your tree.

This female borer lays its eggs between the bark and crevices of the tree.  Eventually, this larvae becomes a worm and starts to eat away at your tree.  Thus producing medium to large holes on the trunk or lower large limbs of trees.  (see photo below).

For all ornamental type trees use a good systemic borer control.  This works by applying the borer control mixed with water on the ground.  The root system will take in the mixture thus killing any type of borer or insect that lives in your tree trunk, foliage or insects sucking on tree stems.

Go organic

Use beneficial nematodes.  Nematodes are small beneficial organisms that eat away at borers and insect larvae.  You can inject this substance directly into each hole to kill them.


Insects and Diseases on plants

Snail Damage Control

Snails are big problems for gardeners who keep a well-maintained garden.  Snails love cool, wet, well-composted soil. They thrive in it.  They eat the tender foliage of most herbs, vegetables, and other edible plants.  Slugs are snails without their hard shell.  Snail bait works well to kill these slimy creatures.

Go organic and place copper tape around your plants.  Yes, they do work but not as well as Sluggo. And as icky as it sounds you could just pick them out by hand!  Snails and slugs are active in early morning or late in the evenings that is the best time to find them and pick them out!

Snails love beer. Place a pan with about a cup of beer near your plants and the snails will dive in drink the beer and drown!

Insects and Diseases on plants


A photo of aphids on a rosebud and stems (see image below).  These insects are very small bugs about 1/8 inch long. They are green, red, black or brown in color. They usually attack new growth in masses.  Their reproduction cycle is fast and will secret a clear sticky substance on your plants and trees.  The yellow aphids attack only Oleanders.  The green type will attack the new shoots of roses and other early spring plants.  Use an insecticide at the first sign to kill these insects.

Use Neem oil for a more organic substitute.  Spray horticulture oil early in the spring season to suffocate aphid eggs.

Insects and Diseases on plants


White grubs (shown below) come from June and Japanese beetles larvae.  They feed on the root system of many plants including roses and lawns.  These worms are embedded in the soil so spraying will not do the trick.  Grubs will turn into adult beetles and come out from the soil to mate and lay eggs, which hatch into more grubs.  It’s best to use a systemic grub control.  Ask for it at your local Nursery.

A good organic substitute is beneficial nematodes.  These nematodes are tiny microscopic bugs that eat away at the insides of grubs and other invasive bugs.  Ask for it at your local nursery.

Insects and Diseases on plants
Image of grub worms in the human hand.

Spider Mites

Spider mites thrive in dry hot conditions.  In the southwest, mites are a big problem. They are small almost naked to the eye insect.  Pines, arborvitae, cypress, junipers and other conifers are susceptible to these pests.

Spider mite damage on Italian Cypress. Photo Below.

Insects and Diseases on plants

Spider mite damage on Mock Orange

Insects and Diseases on plants


Fire Blight

Is a bacterial disease that affects many types of plants.  Roses, apple trees, pears trees fruiting and ornamental, pyracantha, cotoneaster, and photinia.

The foliage of infected plants looks similar to sun scorch.  Red, mixed with black color on tips of leaves usually indicate fire blight.  It is usually spread by pruning tools, too much water, bees, and insects hoping from one plant to another.

Fire blight is a fungal virus.  Spraying with a fungicide will alleviate the problem but it will take 3-4 applications before it works.  Trimming off the infected limbs and leaves will also help.  Always clean your pruning tools with alcohol, soapy water, or about a tablespoon of Clorox mixed with about 1 ga. of water.

Trimming down your plant about 6 inches from the infected area is advisable.  Heavy lush growth from other plants nearby make your plants susceptible to infection.  Do not overwater your plants and avoid sprinkler watering from the top this could make ideal conditions for fire blight.

Insects and Diseases on plants
I, Paethon [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY-SA 2.5-2.0-1.0 , via Wikimedia Commons

Slime Flux disease

Is a wet wood bacteria. It usually affects trees and plants that are fast growing.  Willow trees and cottonwoods are susceptible.  It oozes out a slimy clear color that will eventually turn white.  There is no known remedy for this disease.  However, there are things you can do to slow or keep it from getting worse.

Wash off the slime by using a strong stream of water.  Make sure the overspray does not fall on other nearby trees or plants.  Use about a tablespoon of Clorox mixed with 1 ga. of water.  Mix both in a spray bottle container and spray the infected area.  Be sure to cover ground with plastic to keep it from infecting your lawn or other plants below the tree.

Extra watering and tree fertilizer will help keep the bacteria at bay.

Insects and Diseases on plants
Slime flux on elm tree bark. Close-up.

Mealybugs and White Scale

The photo below with large white cottony scale and mealy bugs.  These insects suck the juice on roses and other plant stems. They will feed on foliage, stems, fruit and even exposed roots.

First, the mealybugs are soft body insects that have a white waxy filament that resembles soft cotton.  If not treated quickly they will devour your plant.  They are also very prevalent in cactus, agave, and other desert type plants.

Use a good systemic insecticide to remove. Also, a spray insecticide will work however it will take several applications to kill these pests.

Sometimes your best course is to trim out heavily infested area place in plastic bag and place it in an outdoor trash bin.  Smaller plants that are completely covered should be trashed before they infect other nearby plants.

Insects and Diseases on plants

Powdery Mildew

Powdery Mildew on a Euonymus Plant.  Are a fungal disease and attacks many types of plant species.  The disease is a spore and usually caused by high humidity and overwatering.  White powdery spots will appear on foliage and will get larger if not treated asap.  Use a good fungicide to remove this fungus.  It will take several applications before the symptoms are eliminated.

Insects and Diseases on plants



Common Insects and Diseases on Plants.

There is a multitude of other insects and diseases that can prevail in your area.

You can always fill out the form here and describe your problem to the best of your ability.  Also please take a good close up photo of your infected plant and or tree and we will do our best to Diagnose plant problems. 

Common Insects and Diseases on Plants.
Photo Courtesy of Downtowngal [CC0], from Wikimedia Commons

The squash bug has a brown body, which is long and slender, and a very disagreeable odor when stepped on or “squashed”.   Spraying with a good insecticide will kill them quickly.  Malathion, diazinon, and carbaryl (Sevin) are good insecticides.  You can also spray with horticultural oil in early spring to keep the bug eggs from hatching.

Privet Mites

Privet mites will typically only infect privet evergreens.  These mites are small and hard to notice on most evergreen plants.   They thrive in dry hot conditions and are so small they are hard to see. They are similar to spider mites but they will not produce webbing.

Spray with a good insecticide to kill these pests.  You can go organic and spray with neem oil but it will take more applications as opposed to insecticides.

Insects and Diseases on plants


Insects and Diseases on plants





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    • josie perez
    • March 3, 2018

    what to buy some fruit tree cherry,,,,apple…..and other fruit tree can I plant them in a planter
    thank you

      • Paul Guzman
      • March 3, 2018

      Hello, Josie. You can plant fruit trees in a large planter. However, they will tend to produce smaller fruit and a smaller crop. There is a little more maintenance and care when they are in a container as opposed to having them on the ground.

        • josie perez
        • March 4, 2018

        thank you so much

          • Paul Guzman
          • March 6, 2018

          Your Welcomes Josie. We strive to give our subscribers and visitors the best possible gardening advice possible.

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