Bring Houseplants Indoors – But Not Bugs

Summer means vacations—for houseplants as well as people. If your plants have sojourned on a sunny deck or porch, autumn’s chilly nights signal that it’s time to bring your houseplants back indoors.

Photo credit: earl53 | morgueFile.com

Cold air can damage tender tropical leaves and cause flower buds to drop, so you need to take action before cold nights settle in. For most houseplants, when night temperatures dip below 45-48 degrees F, you’re flirting with danger and should start bringing plants inside.

Before shifting plants from the Great Outdoors, check for hitchhiking pests that may have established a home on plants during summer months. You’re basically searching for two types of pests: leaf-dwellers and soil-dwellers.

Leaf-Dwelling Pests

Leaf dwellers that attack plants include aphids, spider mites, scale and mealy bugs. Other hitchhikers might be spiders, gnats or lacewings. Carefully examine leaves and stems. Inspect leaf undersides in particular; insects like to hang out under leaf surfaces. You might also spot insects at the intersections of leaves and stems.

An easy way to remove insects is to hose down plants. It’s best to use a hose with a nozzle so you can direct water underneath foliage. Apply a gentle spray; too hard a jet will not only dislodge insects, but will likely tear leaves from stems. You can also use a pressurized sprayer to apply water to leaf surfaces.

Aphid (Photo credit: vintagelolkats | morgueFile.com)

For small specimens, consider dunking the entire plant into a 5-gallon bucket of water for 15 minutes. This will cause insects on leaves or in soil to flee. Add a few drops of liquid dish or hand soap to the water as a further deterrent to insects. The only plants you shouldn’t dunk are ones that demand dry soil, such as succulents, cactus or plants that go dormant for the winter.

If you spot inspects living on plants after washing leaves and allowing them to dry, apply an insecticide to the plant. When you move the plant indoors, isolate it from other plants to avoid allowing pests to spread. Keep the plant in isolation for about six weeks; make visual inspections to ensure pests are gone.

Soil-Dwelling Pests

Insects can also set up housekeeping in the soil of plants set outside for the summer. These pests include slugs, sow bugs, earwigs, fungus gnats and ants. For plants in small containers, gently slip the plant from the pot and examine the soil. Typically, slugs, sow bugs and ants will be visible on the outer layer of soil near the drainage holes. Flick them off with a finger or stick.

Ants (Photo credit: rollingroscoe |morguefile.com)

Pests like fungus gnats and earwigs typically dwell in the upper regions of soil. Remove any dead foliage or flowers from the soil surface, and dunk the soil into water as described above.

For houseplants in large containers, where slipping the plant from the pot or dunking the entire pot is impractical, apply an insecticide to the soil surface and also to soil inside drainage holes. Apply enough insecticide to soak the soil, and you will kill pests or cause them to exit. If pests were present in soil by climbing through pot drainage holes, consider repotting the plants next spring and placing wire mesh or hardware cloth inside the base of the pot to exclude insects.

Impatiens Tale of 2013

If you depend upon impatiens for all-season color in your containers or garden, you may be disappointed this summer. If your impatiens die quickly, it probably isn’t the fault of the grower, the garden center or your own failing. The problem is a virulent strain of a water mold called downy mildew that has destroyed impatiens production in Europe and South Africa – and has now been confirmed in twenty states in America. Homeowners and businesses that expect masses of flowers, instead will see masses of dying, ugly plants.

(Left) Downy mildew-infected impatiens showing leaf abscission. (Right) Landscape planting of impatiens following an epidemic of downy mildew. Photo credits: Mary Hausbeck, MSU

Not all impatiens are alike, and this disease only infects some of them – Impatiens walleriana is the victim, known to many people as the old-fashioned impatiens they buy in flats or as balsam or jewelweed. Newer cultivars such as double impatiens, Fusion and Spellwood are also susceptible. Fortunately, all the New Guinea type impatiens are not affected, including the Sonic and Supersonic series, Sunpatiens and the Divine series. 2013 may be the year of the New Guinea impatiens.

The Disease Story

Oval spores produced on stalks that extend from the underside of the leaf. Photo credit: Mary Hausbeck, MSU

All diseases require three elements to succeed: 1) the pathogen, 2) the environment it requires, and 3) susceptible organisms. In the case of downy mildew, the organism is the impatiens crop. The pathogen consists of aerial spores that settle on plants. The environment for the spores to germinate is cool, moist conditions (temperatures from 59º to 73º Fahrenheit and either rain or overhead watering, especially late in the day). Here in Michigan, the rainy, cool spring was the perfect breeding ground for the downy mildew. Impatiens downy mildew also produces oospores that can survive through winter on plant debris above or below ground. So any soil where infected impatiens has grown is probably unsuitable for this crop for many years.

What You Saw

In greenhouses and garden centers, most impatiens looked healthy well into late spring. In those controlled situations, growers have products that manage disease outbreaks in early stages, and wind-blown spores aren’t likely to land on plants. When you bought and planted the impatiens flats or 4 inch pots at home – that’s when they were at risk. In two or three weeks, the plants showed pale green or yellowing leaves, some mottled foliage and eventually wilting, stunted growth, distorted leaves, severe leaf drop and total plant collapse. Light grey or white fuzz under some leaves is the definitive sign.

MSU greenhouse trial results. (Top left) Untreated control. (Top right) Adorn SC 2 fl oz drench. (Bottom left) Subdue MAXX EC 1 fl oz drench. (Bottom right) Heritage WG 4 oz + Capsil 4 fl oz spray. Photo credits: Mary Hausbeck, MSU

Prevent and Limit Diseases

For home gardeners or landscapers, some general principals can minimize the effect of this or another disease:

• Avoid mass planting of anything. Mono-cultures incur the risk of a single species problem; diversity is good.
• Water at the base of plants, if possible, rather than sprinkle all the foliage.
• Water early in the day, if possible, so the garden can dry out before nightfall.
• Thin out crowded plantings; lack of air circulation favors some diseases.
• Do not compost diseased plants, but discard in garbage bags or bury them in a deep hole.

In the impatiens case, plants in brighter areas fared better than plants in deep shade.

Red Begonia Background | Photo credit: Andrew Schmidt | publicdomainpictures.net

Greenhouse growers are not writing off impatiens completely. They suggest planting impatiens in containers instead of in the ground. Some growers will suggest planting New Guinea impatiens as mentioned earlier; others will suggest shade garden alternatives such as begonias.

As consumers, we should respect the risk that plant growers and farmers must take – weather, disease, insects, animals and an ever-changing marketplace.

How To Keep Wasps Away From Your Home

Wasps can be a nuisance to humans, but they do benefit the yard and garden because they prey on other insects that can destroy landscaping. However, if you are allergic to their venom, or if they get too close for comfort, wasps can become a problem. While there are no surefire techniques to prevent wasps from building a nest, you can take steps to discourage nest building near your home this spring:

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  Photo credit: Mem666 | morgueFile.com

  Search your home for open entry points. Check for cracks in door frames and window frames, unsealed vents and torn screens. Paper wasps can build nests inside your walls, so use a sealant to close off all possible means of access.

• Buy a garbage can with an airtight lid. Wasps will forage for food anywhere, and if discarded food is easy for them to find, they are likely to build nests nearby.
• Wipe any spills and clean up any crumbs after eating outdoors. If wasps find anything worth eating on your patio, they will come back. In late summer and early fall, the food preference for wasps turns to the sweet. Their behavior is also more aggressive. Open cans of pop, fruit juice, fallen apples beneath fruit trees and other sweet food sources will attract wasps. Remove any fallen fruit rotting on the ground.
• Place decoy wasp nests around your home. You can buy them at a gardening supply store or online. Wasps tend to avoid other wasp nests, so the fake ones will trick them into staying away. Decoy nests are a safe and environmentally friendly alternative to using pesticides.
• Hang clothes dryer sheets around your home. Dryer sheets seem to repel wasps.

Photo credit: DuBoix | morgueFile.com

If you feel you must spray store-bought chemical pesticides around your home, keep pets and small children away from the areas you spray. Protect your eyes, mouth and skin from the chemicals with goggles, mask and gloves.

If you are stung, the wound should be washed with water which helps remove some of the venom, and treated with an anti-sting product or antihistamine cream which can reduce the pain and spread of the venom.

If the sting is in the throat or mouth, or if an allergic reaction occurs, seek medical treatment immediately. Anyone with a history of hypersensitive reactions should have a sting emergency kit available. High-risk persons should wear a medical alert bracelet.