What's Wrong with my Plant?
How to tell the difference between Pests, Disease, Herbicide, or Environmental damage
Damage to plants can occur from many different sources
Animal: Deer, Rabbit, Javelina, and Gophers
Insect: Aphids, Thrips, Spidermites, and Grasshoppers
Chemical: Herbicide applications, even if you haven't applied any you can still end up with damage
Environmental: Sun damage, wind events, drought stress
Treatment options vary depending on the source of the damage
Animal Damage: Gophers
One day that beautiful plant you had is laying over and dying
One day that beautiful plant you had is laying over and dying
One day that beautiful plant you had is laying over and dying
the roots have been completely eaten away
One day that beautiful plant you had is laying over and dying
One day that beautiful plant you had is laying over and dying
And there is a hole leading into the ground!
One day that beautiful plant you had is laying over and dying
And there is a hole leading into the ground!
Unfortunately there isn't much you can do about gophers. If you see dirt mounds in your yard it's time to set traps.
Insect Damage
"Sudden Agave Death" is caused by Agave Weevil that slowley devour the roots
Leaves on your agave will begin to yellow, and the plant will be loose in the ground.
If you're plant has declined this much, it's already too late to save it.
Agave Weevil are a native insect that are always present in the environment, but you can pretreat your Agave to protect them.
Chemical Treatment: Fertilome Systemic Insecticide. Apply the diluted mixture once a year to keep your Agave safe from Weevil predation
Agave Weevil Larval State
A native and natural species in Arizona, but a nuisance in the landscape.
By the time you notice damage to your Agave it is already too late. Pre-treat other Agave before they start to show damage.
Insect Damage
Leafcutter Bees
Round holes in the leaf about 1-2cm across.
They really like Redbuds and Lilacs but will also cut holes in other plants.
Chemical Treatment: None! These are a beneficial, native pollinator.
They use the cut a piece of leaf to wrap up their baby larvae, the leaf piece will be eaten by the baby when it hatches.
Insect Damage
Spider Mites vs Spiders
Very very fine webbing that encompasses the leaves, and microscopic orangish red mites.
There will also be a discoloration to the leaves that makes the leaves mottled with thousands of tiny dots where the nutrients have been sucked out.
Can be found on all different types of plants from leafy shrubs to conifers.
Spider Mites are super small, several of them would fit on the end of a ballpoint pen.
Chemical Control: Systemic insecticide is your best bet, and usually this is fine because they typically bother plants that you won't be eating.
Spider Mite Webbing Up Close
The webbing is difficult to see unless you're up close or it is backlit.
You can also see the mottled discoloration of the leaf.
Insect Damage
Aphids
Tightly curled leaves, if you unwrap these leaves you will find them full of tiny aphids sucking the nutrients out of your plants.
Commonly found on new growth at the edge of the branches.
They love fruit trees and roses.
You will also notice shiny and sticky leaves, this the sugary excrement from the aphids.
Fun fact, Ants will "farm" this sugary mess, and sometimes Ants even bring aphids to your plants to set up a farm.
Other fun fact, where there are Aphids there will be Ladybugs!
Chemical Treatment: If the plant is ornamental and you won't be eating from it then you can use a systemic insecticide.
If the plant is going to be producing food then you should use organic topical sprays.
One more fun fact, when Aphids are on toxic plants like Oleander or Milkweed, they tend to be bright orange in color.
Typical Aphid Colors: Green, Black, Orange, and a fuzzy White (woolly aphid)
Insect Damage
Thrips
Contorted new growth on leaves, flower buds that turn brown and don't open well.
Commonly found on new growth and they LOVE rosebuds.
Nearly microscopic, they will be a thin and long, tan to brown colored insect.
Chemical Treatment: If the plant is ornamental and you won't be eating from it then you can use a systemic insecticide.
If the plant is going to be producing food then you should use organic topical sprays.
Thrips (More images)
Damage shows up most clearly on white or light colored roses.
They suck moisture and nutrients out of the plants.
Thrips (More images)
Thrips (More images)
Thrips are super small and difficult to see with the naked eye.
They cause damage to many blooming plants, like fruit trees and can distort the growth of fruit.
Thrips (More images)
Thrips (More images)
Thrips (More images)
Damage to Apricot leaves, distorted growth and brown edges.
Thrips (More images)
Thrips (More images)
Thrips (More images)
Thrips on Snapdragon, you can see small brown spots where they've caused damage.
Insect Damage
Borers
Sap oozing out of the bark, and tin pen tipped sized holes.
Borers are always in the environment, but they are more likely to attack plants that are stressed from lack of water.
Chemical Treatment: If the plant is ornamental and you won't be eating from it then you can use a systemic drench insecticide.
If the plant is going to be producing food then you will need to wait a season.
Topical sprays won't be able to kill the insects under the bark.
Phosphorus Deficiency
On Ligustrum (Privet)
Phosphorus deficiency can often look like a disease, with slow growth rates and yellowing leaves that are usually accompanied by brownish/purple splotches.
This plant also has some environmental damage, leaves are torn up from a storm that kicked up sand and small rocks damaging the leaves.
In this picture, the watering schedule may also not be sufficient.
For this mature plant we reccoment a deep watering once a week during the growing season.
Other examples of nutrient deficiency that may look like "disease" https://fruitsandnuts.ucdavis.edu/peach-nectarine-deficiencies
Chemical Treatment: A balanced fertilizer a couple of times a year.
Iron Deficiency
On Viburnum
Iron deficiency usually looks like yellow leaves with green "veins". It's very common in our climate because we have high pH soil (around 8.2).
Iron gets bound up and becomes inaccessible to plants when the pH is high like this.
Other examples of iron deficiency
https://pubs.nmsu.edu/_h/H171/index.html
Chemical Treatment: Chelated Iron fertilizer.
Bacterial Damage: Fire Blight
How does the infection happen?
Erwinia amylovora is the bacterium responsible for Fire Blight. This is a naturally occurring bacteria that is always in the environment.
Infection can happen through injury, but the most common infection site is through the flowers.
When we get rain while the trees are blooming, there is a chance for infection. Luckily we do not normally get precipitation during he flowering cycle in Arizona.
However, in 2025 we got rain in April and May and we had many cases of fire blight.
Pears, Apples, Pyracantha, and Photinia are the most affected by this in our climate.
More resources:
What does the infection Look Like?
The leaves will turn brown and Individual branches will start shriveling and turning black. This is often accompanied by the branch taking on the shape of a Shepard's Hook.
If the tree has set fruit, the small fruits may also shrivel and turn black.
More symptoms
More symptoms
Tan colored ooze that turns dark as it dries is another symptom.
Treatment: Unfortunately, there isn't much you can do if you have severe symptoms, the tree will probably have to be removed.
If there are only a few afflicted branches you can cut them off 6-8 inches below the infections site.
Chemical Damage
Herbicide Damage
Herbicide Damage
Herbicide Damage
Arizona Cypress
Normal growth on the left. "Fasciation" contorted growth on the right.
Herbicide Damage
Herbicide Damage
Herbicide Damage
Boxleaf Euonymus
Normal growth on the left. "Fasciation" contorted growth on the right.
While this can occur naturally it is often the result of herbicide build up in the soil.
You may find this growth plagued by other pest and disease problems since the immune system of the plant has been compromised.
Treatment: Water, water, water! Flush the soil with a deep soaking to try to move the toxins out of the rootzone. If you're applying herbicide for weeds, be more careful about how much is applied, or change your tactic and physically remove weeds instead of spraying.
If you aren't spraying you can still have herbicide build up from your neighbors or city clean up crews that apply herbicide. Flush with water, do not fertilize.
Environmental: Wind/Debris Damage
Holes, scratches, ripped edges
This is a common symptom of wind and debris damage.
We can get very windy in the spring when new leaves are emerging and the dust and debris can damage the leaves.
Treatment: None! There is nothing wrong with these leaves, even if they do look a little rough.
Environmental: Sunburn Sunscald
Blue Glow Agave with Sun Damage
Blue Glow Agave with Sun Damage
Blue Glow Agave with Sun Damage
Even desert plants like Agave can be damaged by the sun.
Blue Glow is especially susceptible because it doesn't have the same leaf thickness or color as our native Agaves.
Artichoke Agave with Sun Damage
Blue Glow Agave with Sun Damage
Blue Glow Agave with Sun Damage
Extreme temperatures and sun exposure burned this agave during July.
Plants grown in a nursery are used to a little more protection and may burn in extreme weather.
Over time they will adapt, and the new growth from the center of the plant will not burn like this.
Avoid buying and planting when going into the heat of summer.
Or introduce the plant to part sun for a few hours a day for a week or two before planting in full sun.
Privet With Sun Damage
Blue Glow Agave with Sun Damage
Privet With Sun Damage
Yellowing of the leaves followed by dead brown patches.
On Glossy Leaf Privet.
Privet With Sun Damage
Fruit Tree Branches with Sun Damage
Privet With Sun Damage
More intense example of burn on Wax Leaf Privet.
Fruit Tree Trunk with Sun Damage
Fruit Tree Branches with Sun Damage
Fruit Tree Branches with Sun Damage
South or west side of the trunk darkens and cracks, killing the bark layer and exposing the wood.
Fruit Tree Branches with Sun Damage
Fruit Tree Branches with Sun Damage
Fruit Tree Branches with Sun Damage
Branches without canopy or leaf coverage can burn on the top.
Environmental: Heat/Sun + Inadequate Watering
Inner leaves turning yellow
Inner leaves turning yellow
Inner leaves turning yellow
This is a common symptom of drought Stress.
When the inner leaves turn yellow, but the outer leaves are still green, this means this plant got too dry at least one time.
It can take a couple of days for this damage to show up, so even if the ground looks wet when you notice this symptom, it could have been too dry a couple of days before.
Treatment: Water, water, water! Make sure your irrigation system is operational and that driplines aren't clogged. If it's really hot you may need to increase the volume or water or the number of times you water.
Do not fertilize. This plant is already stressed and fertilizer will not help.
Example in a Tree Canopy
Inner leaves turning yellow
Inner leaves turning yellow
This variety of tree (Robinia pseudoacacia 'Purple Robe') is especially dramatic and will let you know when its stressed out.
This happened during one day when the irrigation emitter was clogged.
After a few days these yellow leaves will begin to fall and the plant will continue growing from the ends of the branches.
Recovery is 100% possible in this situation with corrective watering.
Example on Kiwi Vine
Inner leaves turning yellow
Example on Kiwi Vine
You can see the viable growth node at the bottom left of the photo.
Recovery is 100% possible.
Example on Maple
Example on Japanese Maple
Example on Kiwi Vine
You can see the new growth coming out along the stem.
Maples are recommended for elevations above 5000ft (Prescott and Flagstaff).
Recovery is 100% possible.
Example on Japanese Maple
Example on Japanese Maple
Example on Japanese Maple
These trees aren't recommended for areas that get hotter than 95 degrees.
Keep out of harsh sun and protect from the dry wind.
Damage like this can occur in just one day of drought stress
Drought Stress in the most common issue for new plants in Arizona.
If your plant is showing symptoms similar to any in the above image, increase the amount of water.
Within 10-14 days of better watering practices, most plants will push out new growth.
Example of Recovery
Plants recover quickly when watered
Many plants can be saved if they are watered in time.
This lantana would have died if it had gone 1 more day without water.