Greenhouse Pests: The Top 4 Most Common Culprits

When it comes to greenhouse pests, the list goes on and on.

From our own experience in our own greenhouse and in helping hundreds of other growers, there are 4 that top the list.

Here they are...

1) Aphids

Everybody know aphids- those lightly colored, soft-bodied pests that line the leaves of your sweet (and expensive) greens.

Every gardener, aquaponics or conventional, has their own greeting for that bothersome bug- most of which I can't repeat here.

Aphids are hemiptera: they have piercing-sucking mouth parts. Unfortunately, this means that they love to pierce and suck the juices from your crops. If you have aphids, you'll notice a yellowing of leaves where aphids have interrupted xylem flow. Before you chalk up this yellowing as a deficiency symptom, take a look at the underside of the leaves, which is where aphids prefer to congregate (i.e. "wreak havoc").

Yellowing isn't the only result of our least favorite pest. The feeding of aphids may also cause stunting, and aphids are a common vector (carrier) of plant diseases. When you control aphids, you are not only managing the damage that the directly inflict on your crops, but you are taking a preventative measure against pathogens.

Controlling Aphids

In addition to selective pruning, coverings, and best practices such as cleanliness, there are several biological and chemical controls that are effective with aphids.

Biological controls include Ladybird Beetles ($12.95 for 1500) and Lacewings (~$8 for 1000). Both predators of aphids.

Other biological controls are the parasitizing aphidius wasps and beauveria bassiana, the fungal spore of which is present in Mycotrol.

If growing with aquaponics, take great care when applying chemical controls.

Fish are extremely sensitive and pesticides must be measured carefully to avoid harming fish. PyGanic (OMRI listed) is a favorite with other commercial farmers. Neem oil and AzaMax are both semi-effective and best used as background controls.

 2) Thrips

Like aphids, these slender, segmented insects feed on plant sap.

Thrips leave behind damage ranging from mild to severe. You may notice light colored markings, a papery texture, or distortions, especially on young growth and buds.

Thanks to gbohne for the image.

Controlling Thrips

Specific thrips traps can be effective, as well as lacewings, minute pirate bugs, and Botaniguard as biological controls.

Thrips are subject to the same chemical controls as aphids. Bonide and Safer Soap are also effective.

 3) Whiteflies

Whiteflies are just what they sound like: tiny white flies, about the size of gnats (1/16 inch). Like aphids and thrips, whiteflies have made our list of "the most hated greenhouse pests of the 21st century." White flies are extremely difficult to completely eradicate. After you've had a white fly out break once, there is usually a "pilot population" that sticks behind and attempts to make a come back as soon as your attention is diverted.

Controlling Whiteflies

Lacewings will prey upon whiteflies, as will the predatory mite Amblyseius swirskii.

Amblyseius swirskii also feeds on spider mites, which allow the population of Amblyseius to be sustained longer.

A third control is the parasitic wasp, Encarsia formosa.

 4) Snails and Slugs 

If you've noticed that unmistakable trail of slime on your lettuce lately, you are no stranger to our friend the slug. While the actual damage to your crops may be relatively unimportant, the look of disgust on a customer's face when they discover a slug on their produce is not.

 

Thanks to Andrew E. Larsen for the photo.

Controlling Snails and Slugs

When it comes to snails and slugs, natural enemies include snakes, beetles, and birds. Have a resident garter snake? Consider letting him hang out in your greenhouse. Traps such as beer and yeast traps have commonly been used as home-remedies.

Sprinkle diatomaceous earth on plants and around the ground near your crops. (You can get 10 Lbs for less than $20)

Precautions

Lowering the pH of your system to about 6.0 for a week or two is a wise measure to take in the face of a snail problem, as snails use calcium carbonate when forming their shells.

Since snails feed on algae, having proper algae controls in place (such as shade cloth) could help prevent and control a snail population.

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