Pest ID and Control in Hydroponics
When many of us dream of our ideal hydroponic garden, the thought of plagues and pestilence don’t usually spoil the idyllic image. So, discovering a pest outbreak in carefully reared plants can come as a nasty shock.
While it’s easy to understand how disease outbreaks can inadvertently fire up if fungal spores are brought in through ventilation and can travel undetected in the air, insect pests are another matter, right? After all, how hard can it be to screen out living critters, even if some of them are rather small and camouflaged?
Unfortunately, plant pests are highly developed to travel from crop to crop, even if those crops are protected by an enclosed structure. What can be even more alarming is the fact that once a pest has invaded the comfort of a warm, secure indoor garden, they are usually free to wreak havoc without being pursued or annihilated by any of the natural predators that are present in outdoor environments.
Also, since indoor plants are protected from cold winters, heavy rain, frost and snow, insects can happily exist all year-round with little check on population growth.
Since pests can quickly breed and cause significant damage in an indoor garden, growers need to be highly vigilant—both with prevention of infestations and with regular monitoring. The first step in this process is to know what you are looking for; however, plant pests are highly diverse in appearance, size, the damage they cause and the conditions that favour their population explosion.
Garden Pest Myths
First, let’s unravel some myths about pest attack in hydroponic gardens:
Myth 1: Insect pest will only attack sick, weak plants.
While this might be the case with certain opportunistic diseases, but not with insect pests. In fact, insects love lush, plentiful and healthy growth because it provides them with a nutritious source of plant material or sap to feed on. Healthy plants are also guaranteed to provide food for the next generation of bugs.
Myth 2: Indoor or enclosed gardens never get insect pests as they can’t get into the growing area.
Having procedures and barriers, such as double-door entrances and insect mesh over vents can certainly help prevent many insect invasions, but they do not guarantee an outbreak won’t occur sooner or later. Many insect pests can be transported on clothing, on equipment and materials, on plant material brought in, in growing media and even in water. So exclusion, while helpful, is not always successful.
Myth 3: Pesticides are harmful, toxic chemicals that aren’t used in hydroponics.
While some pesticides are indeed fairly potent chemicals that we want to avoid in our own food production, there are an increasing number of safer options. Technically still pesticides because they kill pests, they belong to less-toxic and non-toxic classes of compounds. Pesticide use with a wide range of chemical classes is common in commercial hydroponics and many crops could simply not be grown economically without them; however, we are free to pick and choose the best options for pest control in our own gardens and to take advantage of new technologies.
Myth 4: Household soap and oil sprays are safe and effective on insect pests.
While careful application of these can smother some insect pests, prolonged and excessive use of soaps in particular has seen the destruction of some plants. Certain plants are more resistant to soap and oil sprays than others; however, sensitive plants can become badly damaged under some circumstances.
Garden Pest Identification
While there is a huge range of pests that infest hydroponic crops, indoor gardens tend to have a few common culprits. These include whiteflies, aphids, mites, thrips, fungus gnat larvae, scales, mealy bugs and caterpillars. Many of the pests that typically infest common house plants are also those that hydroponic growers battle, so bringing a new potted house plant into the indoor garden is a source of many new infestations.
Some pests thrive because of the environment—for example, thrips and mites favor a lower humidity and dry air—while others are not fussy and will take advantage of any succulent plant to make home.
For correct pest identification, growers are advised to use a magnifying glass to see some of the smallest invaders.
Mites are usually too small to be seen without magnification; however, their damage can be severe and is often mistaken for a plant disease or nutrient deficiency since the pests are so hard to detect.
Mites appear as tiny red or brown dots on the undersides of the leaves and they create fine webbing in the leaf axils. They also strip the epidermis of the foliage over time, giving a silvery or bronze appearance.
Thrips are another in the tiny invader class. They are often very difficult to see without magnification, particularly because they move fast and zap undercover when the foliage is inspected.
Thrips are small, black, elongated insects that can be winged or wingless, and they are most common in hot dry conditions. Thrip damage looks like small silvery flecks on the plant surface that can eventually give a bleached appearance. They also cause distortion of new growth, as they inject toxic saliva into plant sap.
Of the slightly larger insects that can be seen on close inspection, aphids and whiteflies are the most common. Aphids are soft-bodied insects that come in a range of colors from green through black. There are a number of different species.
Typically, aphids are found feeding in the top growing points of plant often right in the buds. In peppers, aphid feeding can cause distortion, twisting and deformity of the new leaves, which is caused by the toxins they inject when feeding. This is usually mistaken for a plant virus or disease.
Whiteflies are a notorious and serious pest of hydroponic crops. The adults are small, white flying pests, but it is the juvenile or scale stages of the whitefly life cycle that can suck a crop dry. These juveniles produce masses of sticky honey dew that sticks to all surfaces and grows a black mold (also called sooty mold), which contaminates leaves, fruit and growing surfaces.
While many growers regularly monitor the upper parts of their plants for insects, they often forget that there are some pests that inhabit the root zone. Wet areas and algae attract fungus gnats. Often, growers assume these small black flies are harmless; however, fungus gnats lay eggs in the surface of exposed damp growing media and the resulting larvae attack plant roots, causing damage and allowing the entry of pathogens like pythium into the tissue.
Fungus gnat larvae look like small whitish worms in the growing media or attached to the roots. Root mealy bugs can also infest the root zone. These pests appear as waxy whitish deposits on the roots and in the growing media. Hydroponic crops are also susceptible to nematodes, microscopic eelworms that typically infect crops through water supplies or organic growing mediums. A nematode infestation can be hard to identify, although some species cause obvious root knots to develop on the root system.
Introducing: New, Super-resistant Bugs!
Insect pests common in hydroponics are continuously evolving along with the technologies we use to control them. In fact, there are now super bugs: pests that have developed resistance to many of the spray controls that, in the past, were highly effective. Having a genetically resistant super bug population in a hydroponic garden is a grower’s worst nightmare, particularly if the insects become resistant to more than one product.
The first indication that there is a problem with super bug populations is when a tried and true insect control spray, which is used on a regular basis, become less effective to the point where the insects are no longer controlled at all.
This is due to the fact that the insects who initially had some resistance to the pesticide survived and bred, passing on their resistant genes to the next generation. The entire population then quickly developed resistance to the overused control option due to the pests’ fast breeding rate.
The way to prevent this occurring in pest populations is to use a number of different control options and to rotate the use of different spray classes so that the pests don’t have the opportunity to develop long-term genetic resistance.
New Pest Control Technologies
Some of the most effective technologies for pest control are actually some of nature’s oldest. The botanical compound neem oil, derived from the Indian neem tree, has been used for insect control for centuries; however, only recently have extracts and formulations that dissolve easily into water become available for small growers.
As well as having other modes of action, neem is an insect growth regulator, so it is a longer term approach to breaking the insect life cycle. Although it is safe and non toxic (being essentially a plant extract), hydroponic growers need to be careful with application of some neem products.
Many of them are oil-based (or, emulsifiable concentrates) and should always be tested on a small area over a 48-hour period before spraying all plants. On the other hand, the active ingredient in neem—azadiractin—can also be found in some non oil-based sprays.
Another option is to control insect pests with insect diseases in a process known as biological control. Products containing spores of certain fungal pathogens that target only certain insect pests are available.
A good example is Bacillus thuringiensis, a fungus that targets caterpillars and is widely used in commercial horticulture. Others on the market include Verticillium lecanii, a common soil fungus used to control several different insect species, and Beauveria bassiana for aphid and thrips control. This technology is still evolving, so we are likely to see a larger range of products that work under a wider range of environmental conditions in the future.
One of the control options that has much appeal to indoor gardeners is the use of beneficial insects. These natural predators and parasites can be purchased and released into the garden to control certain pests.
For example, ladybugs (Hippodamia convergens), lacewings (Chrysoperia carnea) and preying mantes (Tenodera aridifolia sinensis) are general predators that eat a range of pests; Encarsia formosa eats greenhouse whiteflies; and Hypoaspis miles controls fungus gnats and spring tails.
While beneficial bugs don’t always establish and survive after release, it is worth trying to develop a diverse ecosystem of these insects in a hydroponic garden, as this could put a serious dent in pest populations.
Controlling insect pests in a hydroponic garden can take multiple approaches, from exclusion, hygiene and careful inspection and monitoring practices to quick and proactive control options. Growers need to experiment and try a range of different products and control methods in order to establish which approach is going to work best for them in the long-term battle against the invaders.
Written by Lynette Morgan | Author, Partner at SUNTEC International Hydroponic Consultants
Dr. Lynette Morgan holds a B. Hort. Tech. degree and a PhD in hydroponic greenhouse production from Massey University, New Zealand. A partner with SUNTEC International Hydroponic Consultants, Lynette is involved in remote and on-site consultancy services for new and existing commercial greenhouse growers worldwide as well as research trials and product development for manufacturers of hydroponic products. Lynette has authored five hydroponic technical books and is working on her sixth.