Practical Pest Control for Houseplants
This guide describes how to identify and eliminate common houseplant pests.
Prevention is always better than cure, so make sure to inspect plants regularly for any of the following symptoms.
Katja Schulz https://commons.wikimedia.org/wiki/File:Mealybug_-_Flickr_-_treegrow.jpg
Mealybugs deposit a white cotton candy material onto stems and leaves. These fluffy deposits are the nests of the mealybug. Adult females can lay 300-600 eggs within two weeks.
The bugs themselves are ¼ inch long and oval shaped. They feed on and kill the plant by sucking its juices from leaves and stems.
To treat mealybug, isolate infested plants so the pests do not spread. Prune off parts with light infestation. Mix 1 oz of neem oil per gallon of water and spray this solution onto the whole plant every 7 days. Neem oil disrupts the growth of mealybugs but non-toxic to many other insects. Alternatively, you can spray your plant with a solution of 9 parts water to 1 part rubbing oil.
For severe infections, mix equal parts water and methylated spirit and spray on the plant.
Ron Hammond, bulletin.ipm.illinois.edu/print.php?id=1309v
Root mealy bugs look like grains of rice. They are the same as mealy bugs but attack the root just below the soil surface. Symptoms of root mealybug are yellowing, wilting, and stunted growth. The bugs transmit easily to neighbouring plants.
Remove all soil from the roots and dip them in 120 degrees Fahrenheit hot water. Higher temperatures will damage the root. If the entire root system is infected however, you should discard the entire plant.
Gilles San Martin https://commons.wikimedia.org/wiki/File:Scale_insects_(7244837120).jpg
Scale insects can target either stems or leaves or both. Like the mealybug, they suck the plant's juices and stut plant growth. Ficus are particularly susceptible to this pest.
Scale insects cover a range of species that look very different from each other. All have a shell covering their body and are between 1/16 inch to 1/8 inches in diameter. They range in shape (oval or spheres) and color (white to black). Young scale insects crawl but adults lose their legs and antennae and develop a shell.
The best cure is to simply throw out the plant but if the scale insects have infested your favourite plant, it may be salvageable. Prune heavily infested areas and manually remove all the adults from the plant with a toothbrush and soapy water. Make sure the soapy water comes into contact with the adults. Rinse the plant and dry. You must repeat the process over a period of several weeks until no more adults appear.
Red spider mites
Gilles San Martin https://commons.wikimedia.org/wiki/File:Tetranychus_urticae_with_silk_threads.jpg
The Begonia vine is particularly susceptible to red spider mites. It causes stunted growth, yellowing leaves, and leaf distortion. It can also deposit a dusty film on waxy leaves. In summer, the mites are yellow-green and blends easily into the foliage.
One way of detecting these creatures is to tap the leaves over a blank sheet of white paper. Watch out for any moving green, yellow, or red specks that fall onto the paper. Begin your treatment immediately once you spot them.
You can remove some mites manually using a shower head or hose to wash the entire plant. Then, spray foliage with insecticide to remove remaining mites. Repeat every ten days until there are no mites left. Do this for several weeks to ensure that recently hatched mites are removed.
This pest thrives in warm, dry conditions. Raising humidity around your plant can help prevent them.
United States Department of Agriculture. https://commons.wikimedia.org/wiki/File:Acarapis.jpg
Tarsonemid mites are among the most difficult pests to eliminate. They cause large financial losses for nurseries and other large-scale cultivators.
These tiny mites suck the sap of indoor and greenhouse plants. They are only 1/30 inch so you’ll have to detect them by looking for stunted growth, leaf distortion, brown or white specks on petals, and brown stem marks. Shoots may stop growing if the infection gets severe.
Tarsonemids require a humidity of more than 70% to reproduce. If possible, move your plant to a low humidity environment to kill the infestation.
A biological method for removing tarsonemids is to apply Amblyseius swirski, a predatory mite species, to your plants. You can buy this species for pest control online.
John (iNaturalist user: zabdiel) https://commons.wikimedia.org/wiki/File:Phytomyza_scolopendri.jpg
These are the larvae of tiny flies. Their maggots tunnel through leaves to create squiggly pale trails across leaves. There may also be white dots on the leaves.
Squash the larvae within the leaves or pick off leaves that are infested, then spray foliage with an insecticide.
Martin Cooper https://commons.wikimedia.org/wiki/File:Vine_Weevil_(Otiorhynchus_sulcatus).jpg
Vine weevil grubs are white and C-shaped. They infest the soil or potting medium and eat roots, bulbs, and tubers, leading to sudden wilt. The larvae can get into your houseplants if placed outside, so always check the soil before bringing any plants into the house.
The grubs cause more damage than the adults, which are ½ inch long black beetles. Small infestations of adult vine weevils can be removed manually.
You can remove vine weevil grubs from the soil manually by hosing down the roots, then repotting in new soil. If there are still healthy roots to salvage, drench the root system in insecticide in late summer to early autumn.
A biological method for killing vine weevil grubs is to apply Steinernema kraussei to the soil in autumn. These are tiny eel worms that eat the weevil grubs. You can buy live Steinernema krausseionline online.