Beautify your Winter Houseplant Pest Problems with Soaps and Oils!

This month’s article is not about spa treatments for your plant but will give you simple pest management strategies and tools to manage houseplant pest problems.

Purchase pest-free plants: Often houseplants are infested with the pest before your buy the plant and bring it home. Use your handy hand-lens to thoroughly inspect plants for pests and damage before you purchase them. You might look weird nit-picking the plant at the store, but this is a sure fire way to avoid serious, inherent pest problems later.

Avoid pests: Often pests infest houseplants during the warmer months when gardeners bring houseplants outside. This is the most common way that fungus gnats and spider mites become problems on houseplants. Keep plants inside or manage the pest problem before re-introducing your houseplant to other plants inside your house.

Squish, pinch, poke and jab pests: Small infestations can be effectively managed by spending some time squishing each pest. Pests are easily killed by physically disturbing them with a pinch. This even works with protected, scaled insects. A good jab can damage mouthparts enough to make them inoperable and the scale will starve.

Euthanize infected plants: Yep, sometimes you have put the poor plant out of its misery. Dispose of the infested plant to avoid infestations of other plants. This is usually a last resort unless you really didn’t like the plant in the first place.

Trap pests: Placing pest-attractive traps can regulate some flying insect pests, like whiteflies and fungus gnats. Yellow sticky traps are attractive to whiteflies and fungus gnats. Blue, yellow and white traps are attractive to thrips.

Hose pests off: Sturdy plants can tolerate a forceful jet of water. Knock off pests by hosing the plant off with water. Be sure that insects are not retreating to the soil for protection. Some insects, like aphids, will just crawl back up the plant. This is a good example of integrating management strategies; in this situation, you want to combine the “hose off” method with the “squish and pinch” method.

Change pest environment: A dry environment will discourage some pests, like fungus gnats. Let the soil dry out completely. Many plants will tolerate dry roots for a little while but fungus gnats won’t.

Insecticidal Soaps and horticulture oils: These products are effective for managing soft-bodied insects like aphids, scales, mealy bugs, thrips and whiteflies. Insecticidal soaps are made from potassium salts of fatty acids, much like hand soaps. Insecticidal soaps degrade the waxy layer of the insect’s outer cuticle and interact with the cellular membranes to cause the insect to desiccate rapidly. Horticultural oils are highly refined petroleum or plant derived oils. They, too, interact with insect’s cuticle and also suffocate insects by blocking breathing orifices. Some oils possess other insecticidal properties and can act as deterrents. Both products are very similar to other household products. However, do not recommend household products for this purpose because many ingredients can burn the plant foliage or be ineffective in controlling the pest. Soaps and oils sold as insecticides are tested and will give the anticipated results, household products won’t. The following are some tips for using these products successfully:

• Both products require full contact with the pest insect to work. Be sure you get good coverage of the plant. Be sure to spray underneath leaves; often insects are on the underside of the leaf. Keep your droplet size that is emitted from the sprayer small and fine.
• Oils and soaps both have the potential to burn the plant’s foliage. Be sure to test the product on a small part of the plant first and wait a few days to see any phytotoxic effects before you treat the whole plant. Also, read the pesticide label carefully and note plants known to have phytotoxic reactions.
• Repeat applications in 4-7 day intervals. Soaps and oils have no residual effect on pests and if contact wasn’t made to all the pests, they will continue to reproduce. Additionally, products may not be effective on all life stages (ie. eggs); multiple applications made over time will ensure that those insects eventually develop into a susceptible stage. Three applications are often used to treat most pest problems.
• If choosing horticultural oil, be sure to use the recommended dilution for houseplants found on the label. Many oils are sold for multiple purposes (such as dormant applications) and may be heavier in concentration. Ultrafine or summer oils are better for actively growing plants.
• Some products react with mineralized water (hard water) and may not be as effective when mixed with hard water.
• Do not apply treatments in extreme heat or cold; room temperatures are best.
• Monitor plants regularly. Pest problems are best remedied before the problem becomes severe.
• Do not apply soaps or oils to drought-stressed plants. Oils and soaps can cause foliar burning to water starved plants.
• Monitor pest life stages regularly. Pests such as scales are best managed when the crawler stage is targeted with a soap or oil application.

Buy good bugs: If you’re like me and you don’t mind bugs on your plants, try using beneficial insects for managing your houseplant pest problems. Predatory mites such as Phytoseiulus persimilis or Hypoaspis miles are great predators for managing spider mite and fungus gnat problems respectively. These can be purchased on-line, mail order or through local garden centers.