Wednesday, November 29, 2023

How to Eliminate Pests in a Fall Greenhouse

It’s November, which means that the last dregs of fall are fading fast. US growers in zones three and four have likely already experienced some freezing temperatures overnight. Wherever you are, temperatures are dropping, which means that garden pests are looking for a place to take shelter and get away from the cold. 

Unfortunately for you, your greenhouse is the perfect place for pests to shack up for the winter!

Regardless of what you do, a greenhouse will inevitably attract pests during the colder months. By definition, a greenhouse is warm, climate-controlled, and usually has a high humidity level relative to the outdoor environment. Don’t fret! There are ways to minimize pest attraction and manage existing infestations.

Get Rid of Dead Plant Matter
Truthfully, the best time to clean a greenhouse for winter is in September or October, but November is a good case of better late than never. Look at your forecast and select the warmest, sunniest day possible (even if those are in increasingly short supply in the northern US) for cleaning. Before you clear out your greenhouse, check any plants that will be overwintered in the greenhouse. Are they looking healthy? 
If you need to prune away unhealthy or dead branches/stems, now is the time to do it.

Once your plants are pruned, move everything outside. You’ll inevitably have some dead plant matter on the ground, and you’ll likely have bits of mold tucked into the dark corners of your greenhouse. Grab a hose and spray it down! After power washing away the obvious plant matter, apply a cleaner to the structure of the greenhouse. Make sure to pay attention to corners and recesses that offer shade - these areas are hotspots for pest breeding and fungus. Windowsills are another area to focus on.

Tip: Check out SaniDate® All Purpose Disinfectant for a reliable all-purpose cleaner. 

After you’ve applied the cleaner, make sure to wait at least 15 minutes to air the greenhouse out before bringing plants back in.

Seal and Secure

During the cleaning process, keep an eye out for noticeable gaps in your greenhouse structure. Simple repairs on a plastic frame can be done with greenhouse repair tape, which will also be labeled as a polyethylene tape. Make sure the tape is UV resistant. 

If the damage is too severe, we recommend talking with professionals to determine your next step. Some greenhouses you can simply replace one wall, while others might require a complete refitting. As common sense implies, sealing up your greenhouse limits the amount of entry points for pests.

Keep Plants Apart
It can be tempting to fill your greenhouse to the brim during the winter months. After all, where else are you going to grow? However, putting too many plants in your greenhouse can lead to more harm than good. Pests can easily move from plant to plant when leaves from two plants overlap. A single pest can multiply rapidly in an overcrowded greenhouse.

Fight Back!
Keeping your greenhouse free of plant matter and sealed up tight does a great job at preventing most winter infestations, but insects are called pests for a reason. They have a nasty habit of showing up exactly where you don’t want them. When pests do breach your first line of defense, make sure you’re equipped to fight back. Aphids are a pest no matter what time of the year, and they’re more than happy to invade your warm greenhouse.

Sticky Traps are a greenhouse essential when it comes to monitoring pest populations. However, to keep pests like aphids under control, check out biological pest control, such as the green lacewing. Keep in mind that green lacewings are most effective in a setting with temperatures between 67-90 degrees F and relative humidity of at least 30%. Check out this article for more information about maintaining a green lacewing population and using them as a means of pest control.

From Robin @ARBICO Organics

Wednesday, November 8, 2023

How to Eliminate Fungus Gnats

Gardeners across America are gearing up for the winter growing season in their greenhouses or scrambling to bring their potted plants indoors before the first frost hits. 

Unfortunately for these gardeners, the winter season also means that fungus gnats are ready to throw a baby shower. They’re using your plants as the venue, and they’re not going to stop with just one baby shower. Like most pests, fungus gnats breed quickly and can devastate your garden if left unchecked. 

So how do you deal with fungus gnats?

KNOW SOME FACTS: Fungus gnats have a reputation as winter pests, but they don’t exclusively operate in the winter. They’re active year-round, but fungus gnats have unusually high tolerance to cold for an insect. Some species even have antifreeze proteins, which allows the bug to stay alive and somewhat active throughout the winter, instead of remaining in an egg like other insect pests.

Thankfully, despite the fungus gnat’s high cold tolerance, fully mature members are not all that threatening. In fact, they’re largely passive. Adult fungus gnats are poor fliers. What limited flight they have is more analogous to extended, meandering hopping rather than the precise flight exhibited by a housefly. The adults cannot eat any part of your plant. In fact, adult fungus gnats cannot eat any solid food. They live out their 10-day lifespans on a liquid-only diet of water and plant nectar (if they can easily access it.)

However, adult female fungus gnats can lay over 300 eggs during their brief lifespan. And while the adults are nuisances, the larvae are actual pests to your plants. Fungus gnat larvae will eat through plant roots and leave plants highly susceptible to root rot. With their rapid breeding cycles, fungus gnats can quickly overrun a greenhouse if you aren’t paying attention.



Soggy, overwatered soil is a fungus gnat’s favorite place to start a family. Eggs and larvae like to hang out in the first couple of inches of soil, so make sure that your topsoil stays dry between watering. To keep topsoil dry, try watering at the root of the plants. While you can go all out and use a drip irrigation system if you have a large grow operation, there are ways to water generic potted plants at the root. Check your pot. Does it have any holes in it along the bottom? If it does, place the pot in a large container. Water the container itself and watch as the water is sucked up through the holes in the bottom of your pot.


You don’t want to search for eggs and larvae manually. These things are tiny and often buried under an inch of topsoil. Instead, track your pest control efforts by monitoring the adult population (more on this in the next section). Of course, it’s not unusual to see a fungus gnat eggs and larvae, though both are near microscopic. Eggs are tiny white dots while larvae have black heads, white-to-translucent bodies, and are about ¼ inch long when fully grown. If you see one, just know that many more are likely just below the initial topsoil layer.

To control egg and larvae populations, use a spray, such as the BONIDE® Captain Jack's™ Neem Max or maintain a population of fungus gnat predators in your soil, such as beneficial nematodes.


Since adult fungus gnats aren’t a threat beyond their egg laying capabilities, using normal fly/sticky paper is sufficient to control populations. Fungus gnats are very weak fliers, so making minimal contact with the adhesive is enough to immobilize the adult. Make sure you get yellow sticky paper—this color attracts the most fungus gnats. A bonus of using fly paper is that you can monitor adult population levels over time. 

Once new adults stop getting stuck to the fly paper, you’re on the path towards wiping out your unwanted winter gardening guests.

By: Robin @ ARBICO Organics 

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