INSECTindex

Phlox Plant Bug

By Carol Allen

Practitioners of integrated pest management understand that control of a disease organism or insect pest on a favored plant often involves a multilayered approach. It often includes understanding a plant’s environmental and cultural needs, proper sighting, choosing resistant varieties, accepting a few blemishes, trying to outwit a pest by knowing its vulnerabilities, or simply not planting the host plant. With that in mind, let’s look at the phlox plant bug. The phlox plant bug (Lopidea davisi) is a true “bug,” belonging to the order Hemiptera and feeding by “sucking.” These insects use a straw-/stiletto-like mouthpart to inject a cell dissolving saliva into the leaves or stems of a plant, then suck out the juice. As phlox plant bugs are gregarious and gather in high numbers, so they can inflict considerable damage to a stand of tall garden phlox, their preferred phlox host. This insect overwinters as eggs laid in phlox stems. Cutting the stems down to the ground and disposing of them is part of a good control strategy. Composting is probably not reliable unless the pile temperatures can get over 130°F and kill the eggs. Probably those stems should go in the trash or be burned. The first-generation eggs hatch in May to June and a second generation hatches in July and feeds until September. There are five instars and the bugs go through an incomplete metamorphosis, each instar looking similar, but getting larger than the previous. The smaller nymphs are bright orange and as they mature, they take on the typical black-and-orange pattern that indicates to birds that this insect does not taste good or is toxic. No control help from them! How do you know you have them? The small insects are distinctive in coloration even though they are slightly less than a quarter of an inch when mature. The sucking damage leaves brown spots, curled leaves, and eventual defoliation of the phlox plant. Start scouting early in May, but what to do for control? If the phlox are in bloom, the use of a pesticide is out of the question because the phlox will be covered in pollinators. Remember that insecticidal soaps, neem oil, or horticultural oil sprays are generalist pesticides and will damage beneficial insect populations as well as pests. If the phlox are not yet in bloom, these sprays would have a relatively low impact on beneficial insects if applied carefully. In gardens with large patches of phlox, this pest can be devastating. It may be necessary to remove all of the tall garden phlox from the garden for several years to break the phlox plant bug life cycle. Sorry. o

Carol Allen describes herself as a committable plant-a-holic. She has more than 25 years’ experience in the horticulture industry, with a special interest in plant pests and diseases; is a Licensed Pesticide Applicator in the state of Maryland; and is an ISACertified Arborist. She can be contacted at carolallen@erols.com.

Photo credits: Missouri Botanical Garden.