There is a heavy infestation of leafminers this spring, see photo above showing the yellow mosquito-like critters (now in their adult stage) on our boxwoods. When I stopped at Bowood Farms Wednesday to talk to horticultural expert Ellen Barredo, a neighbor happened to walk in with leafminers trapped on sticky tape with questions of her own—the bugs had infested her clematis.
According to Ellen, this is an insect problem that occurs when Weigelia bloom, see below, around the first of May. Because of the late spring we've experienced, the critters are showing up a little later, though the larvae were visible last month.
Ellen suggests "using a Neem, such as Safer BioNEEM left, ($17.50 at Bowood Farms) for best effective organic
control. Start now and spray for three consecutive weeks.
Neem provides a barrier that may repel the adults from laying
eggs, it reduces life span and egg-laying ability, and it also affects
the life cycle of the larvae. It is considered an IGR (insect growth
regulator) for those pests that feed on Neem treated plant tissues.
An organic product such as Neem still
needs to be used with care. When used properly and according to label
directions, it is safe and highly effective for the control of a wide
variety of plant feeding pests…without providing a significant problem
for beneficial bugs. It also has some excellent disease fighting qualities,
too.Other organic controls are Safer Soap/Concern or horticulture oil."
Ellen also stressed the importance of cleaning up clippings after trimming boxwoods, and clearing away debris to prevent leafminers from attacking in the future. Keep the plants stress-free by following a regular watering schedule year 'round.
Bowood Farms, 4605 Olive, (314) 454-6868.