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Pest Identification & Troubleshooting

Identifying and Treating Pests/Trouble-shooting Problems

By Katie Whitehouse

Identifying pests and learning to troubleshoot potential problems in your plants is essential for healthy plant care.  Becoming familiar with the common pests and using observation to identify problems early on can make the difference as to whether or not your plant can be saved when something does go wrong. Get in the habit of inspecting your plants every time you water!  Note any subtle changes in appearance…being a good observer is really key to being a successful plant parent! Here are some common issues (and their causes and solutions) to help you nip any problems in the bud before they lead to the death of your green babies.

PESTS

Mealybugs 

Symptoms: lack of growth, deformed new growth 

Identify: Cottony white blobs, common in “crotches” and on new growth

Treat: Q-tip dipped in alcohol/hydrogen peroxide (recheck weekly to break cycle)

Natural predators: Green lacewing, Crypt (black ladybugs)

Spider Mites 

Symptom: Webbing between leaves, dying leaves (dry conditions)

Identify: tiny red dots that move 

Treat: Sharp spray of water to remove, spritz with dawn solution

Prevent: Keep humidity up by misting/using humidifier

Scale Insect 

Symptoms: Sticky honeydew resin on leaves, leaves dying/yellowing

Identify: adults are brown, rounded dome shaped and usually found on stems and the undersides of leaves at a vein. 

Treat: Spray down completely, including soil, with dawn solution. Repeat weekly to break cycle.  Insects can also be scraped off with a fingernail or other implement.

Aphids

Symptoms: misshapen, curling, stunted, or yellowing leaves, also presence of ants or parasitic wasps indicate infestation, powdery mildew

Identify: Often in clusters, usually found on stems and the undersides of leaves at a vein. They also leave a sticky honeydew behind that attracts ants (may be white, black or red...usually winged)

Treat: Sharp spray of water to remove bulk.od infestation, spritz leaves and soil with dawn solution. Retreat every 2-3 days for 2 weeks to break cycle

Natural predators: ladybugs, lacewings, praying mantis, parasitic wasps

Fungus Gnats 

Conditions: soggy soil, visible flying pests

Identify: tiny, dark winged, hovering in/around plants with damp soil

Treat: (annoying, but not harmful to plants) mosquito bits pellets sprinkled on soil, yellow sticky pest sheets, dry out soil, water with dawn or peroxide solution to kill larvae, and use a soil with less organic and more amendment material, such as perlite, pumice or crushed lava rock, so the soil drains faster and doesn't stay wet for so long.

Not seeing your insect here? 

Here’s a link to an insect identifier

https://www.insectidentification.org/insects-by-state.php?thisState=Michigan

OTHER ISSUES:

Fungal infection

Conditions: Wet conditions, lack of air flow

Identify: powdery white/grey substance on leaves

Treat: anti-fungal spray, decrease humidity, increase airflow, remove affected leaves and dead tissue

Root and stem rot

Condition: overly wet soil, or damage to the plant from cold or sunburn that results in rot

Identify: Plants wilt, brown to black soft root or stem, Girdled soft stems with a brown or black ring near the soil line

Prevent: Avoid overwatering, acclimate plants slowly to sun, protect tender growth from cold, make sure pots have adequate drainage and that the soil is well-draining

Treat: Remove affected portions of plants.  Cut out affected roots, then repot the plant using sterile potting mix and a clean pot. (Some plants can be re-rooted if tops are not yet affected)

Using observation to assess a problem

COMMON PROBLEMS/CAUSES:

Spindly plants (etiolation): Not enough light or poor lighting conditions

Few flowers: Poor lighting conditions

Yellowing leaves: Overwatering, Not enough light. Soil drains poorly and remains wet for too long. Injury by low temperatures resulting from a draft caused by an open door, window, or air conditioner.Leaves scorched: Too much direct sun 

Brown leaf tips: Chemical burn from overapplication of pesticides or fertilizer, or not enough humidity in the air. Using tap water to water. Soil remains dry for extended periods of time (inconsistencies in watering). Temperature is too low.

Small leaves: Soil remains either too wet or too dry

Weak growth: Incorrect lighting. Root system is damaged from being kept too wet.

Wilting plant: Soil remains either too wet or too dry 

General defoliation: Overwatering, Poor lighting conditions, Injury from low temperatures


Overwatering 

Note the limp, yellowing leaves, and the loss pattern that starts from the bottom of the plant.  Check that the pot has adequate drainage holes and that the soil is well-draining.  Rootbound plants can start to "smother" if roots fill up the pot…check the drainage hole for the presence of roots to see if the plant is rootbound and needs a larger pot.

Underwatering 

Note how the soil has contracted, and has pulled away from the edge of the pot…the compaction of the soil is preventing the plants roots from being able to extract water from the soil. (Note that the dead leaves are “crispy” versus limp.) Once the soil has been compacted in this manner, it must be removed.  Soak the plant to loosen the soil.  Break up the soil medium and massage the roots to remove the old soil. Remove the dead leaves and repot the plant in a well-draining mix.  Adding some amendment materials such as pumice, perlite and crushed lava rock can help keep the organic material from compacting in future.

Note the shriveled appearance of the leaves, and the “crispy” appearance of the dead leaves.

What could be causing the problem: 

Infrequent watering, or not giving a proper soak when watering.  Make sure to water THOROUGHLY when you do water, allowing the soil to dry between watering rather than giving tiny "sips" of water at a time.  Watering thoroughly encourages growth of a robust root system, which makes it easier for the plant to take in the water once it does come, versus watering in one small spot, or very little at a time, which can cause roots to shrivel. Pot and soil combination are draining water too quickly.  If you are using both a gritty mix AND a terracotta pot, the combination of both may be too much.  Consider switching to a plastic pot, OR adding more organic matter to the soil mix…both of these solutions will allow the soil to retain water for longer, allowing the roots to get an adequate drink.

Etiolation

The plant is stretching for light.  Many cactus and succulents grow best when given a period of time outdoors for the summer, soaking up natural sunlight.  Remove the sickly growth and gradually acclimate the plant to full sun.  In winter, be sure to allow your plants a period of dormancy, which most cacti and succulents need (be sure to identify your plants and know when their dormancy occurs.)  

Fertilizing and watering too frequently during the darker months when plants are not able to process these things without adequate light can cause spindly and unhealthy growth.  Give them a cool place to rest, and water only when they exhibit signs of underwatering or to keep the flesh turgid.

Sunburn damage

The brown areas are necrotic tissue that is the result of scarring from sunburn. Move the plant to a shady spot and allow it to recover before reintroducing to more sun.

Scarification

The plant was likely damaged by a pest or sunburn, leaving behind some scarred tissue. If the scarring occurs on a succulent with leaves, the affected areas can be removed, but for cacti, the scarring will likely always remain.  If you catch the damage right after it happens, treating it with an antifungal can help prevent a secondary infection from settling in, and can lessen the scarring.