Controlling Pests Organically: Aphids, Whiteflies, and Thrips
In this article, we look at aphids, whiteflies and thrips—three of the most common pests of indoor growing areas.
Most gardeners have had to fight off a pest infestation in their garden at one time or another. The good news is that there is a wide range of pest control options that allow you to deal with common plant pests without unleashing harmful chemicals and potentially exposing you, your family and your environment to harm. Mother Nature has already figured out how to deal with many of the pests that are bad for our gardens, we just need to let her be our guide. Read on to learn more about some of the most common plant pests out there and how you can effectively deal with them the natural way.
Controlling Aphids in Indoor Growing
Aphids, which are sometimes referred to as plant lice, damage plants by sucking out the sap from their leaves. Although they are large enough to be seen without magnification, their presence can go undetected until after significant damage has been done. There are many different kinds of aphids, but their modus operandi is generally the same.
Damage from aphids generally appears as a puckered or blister-like appearance on leaves, which can lead to leaf distortion or stunted growth. To add insult to injury, aphid frass (insect excrement), more commonly known as honeydew, attracts ants. Honeydew is a sweet substance made primarily of the sap aphids have consumed. Plants that have been contaminated with honeydew can develop a disease known as sooty mold, which creates a tar-like appearance on plant leaves that inhibits photosynthesis.
Aphids are prolific reproducers. Female aphids are born pregnant and can start laying their own young within a week of their own birth. Due to their rapid population growth, multiple strategies often have to be employed to effectively control them.
Many different beneficial insects will either feed upon or parasitize aphids, or do both. One of the most effective biological controls that can be unleashed upon an aphid army is the common lady beetle, Hippodamia convergens. Lady beetles are carnivores that will seek out aphids and consume plenty of them every day. Lady beetle larvae will consume aphids and other pests in greater numbers than their adult counterparts.
Aphidoletes aphidimyza and Aphidius colemani are two parasitic wasps that seek out aphids in which to inject their eggs. Their eggs develop inside the aphids and feed on them from within. When they emerge as adult insects, they seek out other aphids to continue the cycle. The remaining hollow aphid carcass that these wasps leave in their wake is known as an aphid mummy.
If using beneficial insects makes you a bit queasy or sounds too much like science fiction, you can use a variety of liquid applications that are naturally derived from plants to effectively kill aphids by suffocating them or interfering with their body functions. Pyrethrins, not to be confused with the man-made pyrethroids, is an extract from the chrysanthemum plant. It is a common ingredient in many organic insecticides. It works by confusing the nervous system of the aphids, leading to paralysis and death.
Azadirachta indica, or the neem tree of India, is the source of another bio-pesticide, neem oil. Neem-based products can be applied to infested plants as either a foliar spray or as a soil drench.
Regardless of the method you have selected to control your aphid problem, multiple applications will be required. If you are using bio-controls such as lady beetles or parasitic wasps, it is important to release them on a regular basis to keep their populations sufficient for pest control. If you opt for a spray treatment, plan on applying the product two or three times every seven to 10 days, making sure to get thorough leaf coverage, both on the undersides as well as the tops and stems.
Controlling Whiteflies in Indoor Growing
Whiteflies, as their name implies, are white, flying insects. There are several species of whiteflies out there, all of which are closely related to aphids. Like aphids, whiteflies are visible without magnification. They damage plants by sucking the sap from them, but their damage appears differently than the damage from aphids. Leaves damaged during whitefly feeding will turn yellow or brown and drop off prematurely. They may get a speckled appearance before turning color.
Like aphids, whiteflies also secrete honeydew with the same potential results of attracting ants and fostering the development of black, sooty mold on leaves that may be below where the whiteflies are feeding. These pests are also prolific reproducers and each female whitefly can lay up to 400 eggs in her lifetime. Her nymphs will immediately begin sucking on leaves once they have hatched and can stay fixed in one spot, feeding for up to four weeks as they pupate into adult whiteflies. A heavy infestation of whiteflies will appear as a burst of smoke when disturbed. Care should be taken to not wear light-colored clothing when working around plants with whiteflies as they can easily be transported to other plants unknowingly.
Whiteflies can be controlled with beetles and parasitic wasps, like their aphid cousins, but different beneficial species are better at controlling them. A small, black beetle, known as delphastus pusillus, which is about the same size as the whiteflies themselves, will feed on all stages of whiteflies, but they prefer the eggs and nymphs. They are especially useful in high-infestation areas, as they require consuming up to 200 whitefly eggs per day in order to reproduce.
Whiteflies also can be controlled via the parasitic wasps found within the genus Encarsia. Encarsia formosa is the most prevalent beneficial wasp used to control greenhouse whiteflies. These tiny insects inject their eggs into the bodies of whiteflies in the same manner as the Aphidoletes aphidimyza and Aphidius colemani do with aphids. Whitefly hosts generally die 10 days after being parasitized. The adult Encarsia will emerge from the dead whitefly in about another 10 days.
To get a handle on whitefly infestations using sprays, pyrethrins and neem are two good options - insecticidal soap is another. For whitefly control, use a combination of different controls in successive sprays. It is nearly impossible to get full coverage in one application given the whitefly’s ability to spook easily and fly off. Plan on at least three applications, possibly more.
Controlling Thrips in Indoor Growing
Thrips are similar to aphids and whiteflies in that they cause their damage by sucking as opposed to chewing. These small flying insects can be anywhere from clear, to black, to reddish orange in color. Along with their black deposits of frass, they are often found on the undersides of leaves. Like the other pests described here, there are numerous thrip species out there, each with their preferred host plants.
Damage from thrips appears as a dappled, stippled or speckled leaf surface. Thrips will also feed on many fruits, which ends up causing damage to the entire crop. Thrips usually don’t kill their host plants; they often cause stunted growth or poor performance as a result of the plant’s cellular losses and reduced ability to photosynthesize.
Controlling thrips using beneficial insects depends on the species you’re tackling. There are actually predatory thrip species that can be released to control the pest thrips. A positive identification of the pest species should be made before deciding on a beneficial insect to release. Predators such as the green lacewing (Chrysoperla rufilabris) and the minute pirate bug (Macrotracheliella nigra) will generally feed on multiple species of thrips. However, you cannot expect stellar results if you are releasing beneficial insects to control thrips on outdoor plants. They are much more effective when used to control thrip infestations of indoor crops.
The most effective spray for controlling thrips is spinosad, a naturally occurring fermented bacterium. This is the active ingredient in many insecticides approved for organic gardening. Unlike many non-synthetic pesticides, spinosad penetrates the leaf surface to reach the undersides where the thrips are feeding.
Written by Chris Bond | Certified Permaculture Designer, Nursery Technician, Nursery Professional
Chris Bond’s research interests are with sustainable agriculture, biological pest control, and alternative growing methods. He is a certified permaculture designer and certified nursery technician in Ohio and a certified nursery professional in New York, where he got his start in growing.