Perennial pests are best managed within an integrated pest management program (IPM) focusing on preventive strategies. With regular and consistent scouting, early detection of pests helps to ensure proper timing of needed treatments plus more successful use of biorationals. A scouting program consists of random plant inspections using sticky cards and pest-infested indicator plants to evaluate treatment effectiveness.
What to look for
Here’s an overview of some of more common insect and mite pests to be on the lookout for when growing herbaceous perennials.
Aphids
Aphids can be troublesome, especially when growers inadvertently bring aphid-infested herbaceous perennials from overwintering houses into warmer production areas.
Crops: Alcea, Bellis, Dianthus, Heuchera, Hibiscus, Monarda, Papaver, Primula, Salvia, Sedum and Veronica. Many species have a wide host range and can feed upon almost every perennial you grow.
Hiding places: Look on the underside of leaves, buds and on new growth for aphids. As aphids feed, you may see distorted leaves, white shed skins, honeydew and sooty mold.
Controls: Don’t forget to scout for ladybird beetles, parasitic wasps (or evidence of their presence, aphid mummies), flower flies and lacewing larvae, especially when perennials are grown outdoors or in open-roof greenhouses. If natural enemies are present, choose more selective insecticides. Correct aphid identification is important to successfully release the very host-specific parasites.
Fungus gnats
Fungus gnats are especially damaging during propagation, preferring cuttings and young plants that haven’t developed well established root systems. Besides direct feeding damage, fungus gnats also transmit diseases.
Crops: A wide host range. Herbaceous perennials with succulent growth are favored by black-headed larvae.
Hiding places: Place yellow sticky cards close to the growing medium surface to monitor for adults. Place potato plugs on the growing media surface for two days to monitor for larvae.
Controls: Beneficial nematodes (Steinernema feltiae) and insect growth regulators may be used against the damaging larvae.
Thrips
Thrips are small, difficult to find and control.
Crops: Alcea, Asclepias, Campanula, Hemerocallis, Lamium, Leucanthemum, Lupinus, Malva, Monarda, Penstemon, Platycodon, Polemonium, Primula, Phlox and Tanacetum.
Hiding places: As thrips feed, leaves become scarred with white, silvery trails and black fecal spots. Tender new growth may be distorted and flowers are often streaked, mottled or flecked. Besides direct-feeding injury, western flower thrips vector tospoviruses. Use sticky cards to detect winged adults, especially in warmer greenhouses. Outdoors and in cooler houses, focus on foliar inspections. (Don’t confuse springtails with thrips.)
Controls: Thrips have developed resistance to many insecticides, so rotate for an entire generation (often two to three weeks, depending on temperature) before switching to another insecticide with a different mode of action.
Leaf miners
The yellow and black flylike adults puncture leaves to lay their eggs. Eggs develop into larvae that make winding trails or mines within the leaves.
Crops: Alcea, Helenium, Gaillardia, Helenium, Leucanthemum, Polemonium and Veronica.
Hiding places: Inspect incoming plants to exclude leaf miners.
Controls: Spot treat and rotate among chemical classes. Use Hopper Finder yellow sticky tape to mass trap adults. Contact insecticides (such as insecticidal soap tank mixed with an adulticide) can be used against the adults and insecticides with translaminar activity or insect growth regulators can be used against the larvae. Leaf miners have a notorious ability to develop resistance to insecticides.
Two-spotted spider mites
Crops: Alcea, Aquilegia, Buddleia, Campanula, Delphinium, Filipendula, Gaillardia, Hemerocallis, Hydrangea, Iris, Lamium, Lavatera, Monarda, Nepeta, Papaver, Phlox, Potentilla, Primula, Rudbeckia, Scabiosa, Thalictrum, Verbena and Viola.
Hiding places: As spider mites feed, chlorophyll is removed and leaves become flecked or stippled. If the infestation is severe, leaves turn yellow and drop.
A 16x hand lens is often needed to see the small (size of a period) spider mites. Look for round, glossy eggs, white empty egg cases and actively moving mites on the underside of the leaves. Tap foliage over a sheet of paper to see the faster-moving, pear-shaped predatory mites. Because mites can easily be carried on clothing, scout mite-infested areas last.
Controls: With the increased number of miticides available, rotation is easier. Many miticides are specific to certain life stages, so repeat applications may be needed. Different predatory mites are commercially available. Some predatory species are better adapted to greenhouse use and others to outdoor use. Mixes of species are also available.
Tarsonemid mites
Tarsonemid mites (broad or cyclamen mites) are more easily recognized by their damage.
Crops: Aconitum, Clematis, Delphinium, Dahlia, Lysimachia and Stachys.
Hiding places: Infested buds may fail to open. As broad mites feed, leaves turn downward at their edges, with bronzed, distorted foliage and severe stunting.
Broad mites can be distinguished from cyclamen mites by their eggs. With a 16x hand lens, you can see the broad mite eggs are covered by “bumps” that look like a row of diamonds.
Controls: If only a few plants are infested, tossing the most severely infested plants may be best. Not all miticides labeled for spider mites are labeled for cyclamen or broad mites. Repeat applications of translaminar miticides may be needed.
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- Leanne Pundt
Leanne Pundt is extension educator specializing in greenhouse IPM, University of Connecticut, (860) 626-6240; leanne.pundt@uconn.edu.
August 2008