SESSION 5: Harmful Pests & Beneficial Insects
There is a rarity of pests in hydroponic gardening. Under certain conditions pests can move in and take over a hydroponic garden. Insects may find their way into your growing space, and depending on what kind of insects move in it can have a major effect on your plants.
The hands down safest way to get rid of unwanted insects, is identify what it is, then find out what other insects eat them. For example if your garden is being attacked by a horde of aphids, find a garden supply center in your area and pick-up some ladybugs. These cute little spotted insects have a voracious appetite for aphids, and will take care of your problem in no time.
Virtually all insects have a predator or enemy and that is what makes biological control?work. There are insectaries (facilities that raise insects) throughout the US and Worldwide ?that breed and sell beneficial insects. Beneficials are shipped as eggs, larvae or adults and are usually sent overnight to the user who quickly distributes them to the problem areas. In the world of beneficial insects, there are predators and parasites.
Predators will actually consume the pest insect. A lacewing is a good example of a predator. Lacewings are welcomed in most gardens because they are know for their voracious appetite and broad diet of various insects.
Some Examples are as follows:
Whitefly are an extreme problem for greenhouse growers, field and orchard crop farmers and home gardeners. The whitefly sucks large quantities of sap from the plant and secretes the sugars as honeydew. This makes the leaves sticky and susceptible to fungal growth and rot. In a serious infestation, the fungus and rot associated with the honeydew can kill an entire crop in a matter of weeks. In addition, whitefly can pose a great threat to plant health because they are able to transmit many plant viruses.
A whitefly looks like a small white moth, 1/8" in length. They rest on plant leaves and will quickly fly away when disturbed. Whitefly lay their eggs on the under side of a leaf. Shiny, sticky leaves are signs of whitefly presence.
Biological Control: Encarcia Formosa
This tiny parasitic wasp lays its eggs in the larvae of the whitefly. Parasitized larvae turn black and are easily recognized. Adult Encarcia Formosa also feed on honeydew and the body fluids of whitefly larvae.
Pest: Spider Mites
Spider mites feed by piercing the leaf surface with stylet-like chelicerae and extracting leaf cells and fluid. This manner of feeding causes tiny holes to be punched into the otherwise protective, waterproof leaf surface. Leaves that have been fed on by spider mites are usually dry and brittle and the usual green color is lost (right). Injured leaves are shed more quickly and eventually the whole plant may die. Even a minor spider mite infestation can have a significant impact on a plant's health.
Spider mites lay eggs when they are threatened with death which is their evolutionary control.
The best naturally occurring active ingredient to kill them is Pyrethrum (Pyrethrin) this active ingredient is extracted from the Chrysanthemum Flower and used in botanical sprays. The spray must contact the mites and be reapplied every three to four days. Check out our entire selection of natural leaf shines and washes.
Aphids inflict serious damage in various crops and their reproductive capacity is enormous. The damage they cause is due to secreted honeydew resulting in contamination of fruit. Aphids are also notorious for carrying vlruses. Aphids are slow moving insects, inhabiting the undersides of leaves. They establish dense colonies of tiny (1/32" -1/8"), soft bodied, pear shaped insects that are light green, pink, yellow, brown or black in color.
Biological Control: Aphidius colemani and Aphidoletes aphidimyza
The parasitic wasp Aphidius colemani is particularly effective against some species of aphids. Parasitised aphids form characteristic white "mummies". Aphidoletes aphidimyza is effective on a wide range of aphid species and lays its eggs in aphid colonies. The orange larvae that hatch from these eggs feed voraciously on aphids.
Pest: Fungus Gnats
Damage first becomes apparent when plants lose their healthy appearance and wilt. Darkwinged fungus gnat adults are usually noticed before injury caused by the maggots is apparent. The larvae begin feeding on the root hairs and roots usually in the upper centimeter of medium, working their way up the plant and into the stem; and they will also feed on any organic matter in the soil.
Biological Control: The parasitic nematode, Steinernema feltiae, has reduced fungus gnats. Also, another nematode, Steinernema carpocapsae, is now on the market for fungus gnat control in greenhouses.
Using bark mixes and avoiding overwatering with clean cultural practices helps prevent infestations of these gnats.
Pest: Flower Thrips
Flower thrips feed on the most tender part of the plant, such as buds, flowers, or leaves. The effect of their numerous but shallow punctures is to give the injured tissue a shrunken appearance, and the damage is described as piercing and sucking fluids from the cells. The thrips feed on the thick fleshy petals, pistils, and stamens of the flower, and then the affected parts turn brownish-yellow, blacken, shrivel up, and drop prematurely
Biological Control: The thrips are vulnerable to contact insecticides. Can also dust bulbs and corms to prevent thrip infestation on the following growing season.
Pest: Greenhouse Thrips
This thrips feeds almost entirely on the foliage, and large populations cause severe damage. Greenhouse thrips usually injure inner leaves and fruit. Damaged leaves appear silvery or bleached and, if the damage is severe enough, turn yellow and drop. Fruit that has been attached is brown, cracked, and has noticeable sunken areas. Dark spots of excrement are often noticeable on the leaves and fruit.
Biological Control: Greenhouse thrips can be controlled through release of biocontrol agents such as predatory mites, lady beetles, and soil-dwelling mites.
Other Beneficial Insects
Three other insects that are always considered beneficial are ladybugs, lacewings and praying mantis. All are predators, known for their voracious appetites and broad diet of insects. Both of these predators will help control almost every pest insect that we have discussed with the exclusion of the beet armyworm.
The ladybug, lacewing and praying mantis actively feed and consume problem pests in the larval stage as well as the adult stage. The praying mantis produces egg cases which contain approximately 200 babies. The babies are also deadly predators.
Ladybugs, lacewings and praying mantis are a welcome addition to any garden, farm or greenhouse.
The earthworm is used to aerate and mix the soil. They tunnel their way through the soil feeding on dead and decaying organic matter and turn it into rich compost.
These microscopic worms seek out and destroy harmful insects in your garden, such as grubs, fleas, gnats, flies, cutworms, billbugs, ants, and Japanese beetles. They control harmful soil-dwelling insects by feeding on their larva – all without harming other beneficial insects.
Trichogramma wasps feed on over 200 types of insects but these tiny insectivores won’t sting people or eat other beneficial insects. This insect gets rid of cabbageworms, tomato hornworms, corn earworms, codling mothes, cutworms, armyworms, webworms, cabbage loopers, corn borers, fruitworms, and cane borers.
Black and Yellow Garden Spider
They feed on all bug juice and are extremely beneficial.
Other Safe Options for Pest Control
Occasionally, additional means of control will be necessary and, fortunately, there are other safe options for pest control.
Insecticidal soap is an environmentally sound method of getting rid of pest insects. It is basically a soap solution that, when sprayed directly on the insect, will smother them. It does not leave a residue and crops sprayed with insecticidal soap can be harvested the same day. As a general rule, insecticidal soap will not harm most beneficial insects.
Insecticidal soap is available as a spray or in a concentrate form to be mixed with water. For best results, use softened or purified water if you are mixing it from the concentrate.
Sticky strips provide a safe method of trapping insects. The insects are attracted to the bright color of the sticky strip and, once they land, they are stuck. When the strips are full, simply discard and replace with a new ones.
Many commercial growers use sticky strips for monitoring what insects are in the greenhouse. By checking the sticky strips on a regular basis, the grower knows what insects are present and whether or not the population is growing. Check out our entire selection of pest control.
Botanical sprays are made from plants that have insecticidal qualities. These products are generally safer than chemical insecticides but, even though the are natural, they are insecticides and should only be used as a last resort. Check out our entire selection of natural leaf shines and washes.
to Session 6: Hydroponics Today