Q&A With Eli Snyder
This spring and late winter have brought us mixed weather, as well as mixed questions to the Cooperative Extension Center. Today I am sharing a couple of relevant questions that have come in lately, as they are concerns for homeowners and gardeners alike.
Question: What is on my houseplant and what can I do to control it?
Answer: The damage and defoliation you are seeing is caused by a pest called the mealybug. Mealybugs are small soft-bodied insects that feed on plant sugars by inserting a feeding tube into the plant.
They are a common pest of houseplants and are often found on the underside of leaves, in crevices or flowers. They can also be found at the junction between leaf and petiole, the stem-like section between the base of the leaf and stem or branch, as seen in the photos. There are several species of mealybugs. Female mealybugs are soft, oval-shaped insects up to 3 mm long. They develop a wax coating with a cottony appearance, and though the eggs are very small, egg masses will contain 200-600 eggs and are also covered in a fluffy, white wax. Males are small gnat-like winged insects with a waxy coating on their tails.
Through their feeding, mealybugs can cause leaves to turn yellow and fall prematurely. The citrus mealybug, which will infest plants other than citrus as well, secrete a toxin that causes plants to drop their leaves and buds. Mealybugs may excrete a sugary substance onto plant leaves, leaving a substrate upon which black ‘sooty mold’ or black fungal growth occurs.
Mealybugs are relatively difficult to control and can cause serious damage. For smaller infestations on indoor plants, apply rubbing alcohol to the mealybug bodies using a cotton swab.
Avoid contacting the plant with alcohol as this can damage leaves. Then, follow up with several applications of insecticidal soap labeled for use indoors. This will control nymphs that hatch from eggs invisible to the human eye. There are fewer options for indoor control of mealybugs than there are for outdoor plants. Consult the NC Cooperative Extension –Caldwell County Center for specific recommendations, and only use pesticides in a manner in accordance with the label.
Mealybugs may appear indoors on houseplants as a result of mealybugs traveling with plants coming in from outside. These plants may be indoor plants that have spent some time outside or newly acquired plants. Mealybugs are not as common of a problem on plants growing outdoors as predators help control populations outside. One predator is the Mealybug Destroyer (Cryptolaemus montrouzieri). The Mealybug Destroyer is a member of the ladybeetle family (Order: Coleoptora), and its larval stage has white woolly appendages that make it resemble a mealybug. Female Mealybug Destroyers prefer laying eggs in and feeding on mealybugs but will also parasitize aphids when mealybug populations are low.
They will also parasitize cockroach eggs. Mealybug Destroyers may need to be reintroduced in an area following cold winters, and will not stay around without a healthy population of prey to parasitize.
Question: I am hardening my seedlings so that I can plant them outside soon. I put them outside in the afternoon and they developed bleached spots on the leaves. What happened?
Answer: The damage on these leaves is a condition called sunscald. This is essentially a sunburn on plants. It occurs when young, tender tissue in the transplants is exposed to strong sun. The sun exposure heats up the tissue and burns it. While damaging, it is not usually fatal to the plant.
Many gardeners start seedlings inside, and then transplant the seedlings outside to obtain earlier produce, to outcompete weeds, or to reduce the time that each crop occupies a garden bed. Seedlings started indoors under grow lights or in protected areas such as greenhouses often experience lower light conditions and more humid conditions than when they are outside. Their leaf tissue is sensitive to direct sunlight. Heat created with direct sun and dry conditions caused by wind can lead to scald, or burning.
Therefore, it is a good practice to “harden” plants to outdoor conditions for a few weeks prior to transplanting them outside from an indoor climate. Start the hardening process by placing young non-hardened plants outside for an hour or two outside in an area protected from wind and direct sun each day. At first, place them outside in morning or late evening when sun is less strong. Seedlings can be exposed to more light and wind each day. The time spent outside should increase by a couple of hours per day. Bring plants inside if extreme temperatures, high winds, or storms are predicted. The hardening process typically takes 2-4 weeks, after which the plants should be ready for transplanting to outdoor beds.
Houseplants that spend winter inside but prefer to be outside for the summer should also be hardened before they are moved outside for long periods of time. New growth produced through the winter months is sensitive to light and wind. To avoid damage to this new growth, follow the hardening procedure described above.
With more gardening questions, please contact the North Carolina Cooperative Extension – Caldwell County Center at 828-757-1290 or stop by the office between 8 a.m. and 5 p.m., Monday-Friday. We wish you a safe and fruitful gardening season in 2018!