Major Insects & Mites That Attack Ohio Landscape Perennials

Dr. David Shetlar (the BugDoc) The Ohio State University OARDC/OSU Extension Columbus, OH

© D.J. Shetlar, 2006, all rights reserved

Major Insects & Mites That Attack Ohio Landscape Perennials

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Plant bugs, Aphids & Psyllids Sawflies & Caterpillars Twospotted spider mite Leafminers Slugs (not arthropods!)

Notes:

Each perennial plant has its own set of insect and mite pests, but many of these pests are very similar in their life cycles and/or feeding habits (e.g., aphids, plant bugs, caterpillars, sawflies, borers, spider mites, etc.). This presentation will cover some examples of generalist pests (ones that attack a wide variety of perennials), and pests that can serve as examples of their group type. These are herein considered to be “major” pests.

The presentation will also cover some non-arthropod pests – such as snails and slugs.

“Bugs” & Aphids On Perennials

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Fourlined plant bug - one generation.

• Most damage in May & early June.

• Prefers mint family.

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Aphids – many species, several generations per season.

• Look for predators – be patient!

• Syringe (hose off with water).

Notes:

Most people think that all “bugs” suck, but actually only certain kinds of insects have sucking mouthparts. The “bug” group (Order Hemiptera) contains plant and leaf bugs, seed bugs, stink bugs, aphids, scales, spittlebugs, whiteflies, and plant hoppers. All have gradual life cycles with egg, nymph and adult stages though this type of life cycle can be highly modified (e.g., scales and whiteflies) or complicated by different forms that move from plant to plant over the season (e.g., aphids).

Fourlined plant bug (damage above), late instar nymph (above right), and adult (right).

Notes:

While the fourlined plant bug prefers perennials in the mint family, it is known to attack several hundred perennials, annuals and small woody shrubs. There is only one generation per year with the small red and black nymphs causing noticeable twisting and distortion of expanding leaves and shoots as well as making distinctive black or purple sunken areas in the leaves. These are spots where the bugs have inserted their sucking mouthparts, injected saliva to liquefy the plant tissues and removed this predigested material. In young tissues, the scars that remain cause the plant distortion.

Since this bug overwinters as eggs inserted into remaining plant stems, cutting and removal of these parts in the fall can help control the pest.

Tarnished plant bug nymph (above), and adult (right).

Tarnished plant bugs also damage various perennials as well as several shrubs.

Notes:

The tarnished plant bug is another generalist feeder in landscapes and while the green and brown nymphs can cause damage to expanding foliage that is similar to the fourlined plant bug, the major damage caused by the tarnished plant bug is to flower ovaries. Larger nymphs and adults feed at the bases of flowers, thereby killing developing seeds. This is usually only important where seeds are being collected from the plants. This pest can have several generations over the summer and adults commonly overwinter in litter.

Chrysanthemum lace bugs are unique in that they prefer leaf upper surfaces!

Other Miscellaneous Bugs

Many stink bug species feed on seeds and flowers.

Notes:

There are dozens of small species of stink bugs that tend to feed on the flowers of perennials. This often causes the flowers to wilt earlier than normal and causes a lack of seed set or development. Most stink bugs are mere nuisances.

The chrysanthemum lace bug is unique in that the adults and nymphs are often located on the upper leaf surfaces of perennials in the mum and goldenrod families. They can cause blanching of the foliage and poor overall growth.

Other sucking insects that attack perennials include tree hoppers (left) and leafhoppers (below). The painted sharpshooters (a kind of leafhopper) cause puckering of leaves. The nymphs (below) run sideways.

Notes:

There are several species of treehoppers, planthoppers and leafhoppers that may be found infesting perennials. Some are very host specific and others feed on a variety of plants.

The treehoppers and planthoppers rarely cause any noticeable damage, but the insects jumping around when disturbed can annoy gardeners.

Leafhoppers are wedge-shaped insects that run sideways and readily jump and fly when disturbed. These insect often distort the growth of expanding leaves or stems and some transmit diseases that can slow the growth of infested plants.

The psyllid nymphs and pupae look like scales.

Rudbeckia psyllids cause disease like purple blotches on the leaves of host plants.

Notes:

Psyllids (jumping plant lice) are fairly common pests of landscape plants, but many go unnoticed. Recently, the brown-eyed Susan psyllid was discovered in Ohio because the nymphs make distinctive purple blotches on the leaves. This blotch was thought to be a disease until the nymphs were discovered on the undersides of the affected leaves.

Since its discovery, this psyllid is now found across Ohio and most of North America. Not much is known about this pest, but is appears that adults overwinter in leaf litter, so cleaning out perennial beds may help in reducing the survival of these adult psyllids.

The goldenrod aphid (above) feeds on a variety of daisy and composite flowers. The milkweed aphid (right) feeds exclusively on plants in the milkweed family.

Most perennials have one or two species of aphids that may feed on them.

Generalized diagram of an aphid life cycle showing a species that alternates asexual and sexual forms along with alternation of hosts.

Notes: There are hundreds of species of aphids! Almost every perennial has its own species, but there are also some generalist species that can infest several different perennials. Aphids often have complicated annual life cycles in which the alternate from asexual to sexual reproduction and they may use two alternate host plants during the season. Most aphids overwinter as eggs attached to a woody perennial plant. These eggs hatch into “stem mothers” that give live birth only to females. These females also give live birth (ovoviviparous) without mating (parthenogenic) and development can be completed in five to 10 days. In June and July, these aphids often develop wings and fly to alternate, summer hosts where they continue their asexual reproduction, but their forms can change! In September and October, these aphids give birth to sexual forms (males and females) that mate, fly back to the spring host plant, lay eggs and die!

These alternations of hosts and reproduction types probably inhibit predators and parasites, and also help explain the sudden appearance and disappearance of aphids during the season.

Plant Bug & Aphid Control

(for homeowners) Traditional

• Sevin • Orthene • DiSyston (Bayer Advanced 2-in-1 Rose Systemic Granules)

Still/Now Available

• Pyrethroids (permethrin, resmethrin, esfenvalerate, bifenthrin, cyfluthrin) • Soaps & Oils • Sevin, Malathion • Imidalcoprid (Bayer Advanced Tree & Shrub Concentrate)

Sawflies & Caterpillars On Perennials

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Columbine sawfly – one generation (May to June).

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Hollyhock sawfly – 3-4 generations.

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“Generalist” caterpillars – cabbage looper, European corn borer, green fruitworm.

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Stalk Borer & Iris Borer – not much you can do other than remove!

Notes:

While sawflies and caterpillars may look alike, they are the larvae of completely different types of insects – wasp-like insects and butterflies or moths. In the past, this wasn’t too important as insecticides usually killed either one. However, newer insecticides may kill sawflies, but have little action against caterpillars! Both larva have fleshy leg-like structures on the abdomen, called prolegs. Sawflies have seven to nine pairs of prolegs while caterpillars will have five pairs of prolegs or fewer. Caterpillars with only two or three pairs of prolegs are usually called inchworms or loopers.

Most sawflies are very host specific, but several caterpillars are generalists, feeding on a wide variety of hosts.

Columbine sawflies hide on the undersides of host leaves during the day. Though the larvae look like caterpillars, they have more than 5 pairs of prolegs on the abdomen – a sawfly characteristic.

Columbine sawflies can completely defoliate plants by the time they are ready to flower.

Hollyhock sawfly larvae skeletonize leaves and the damage is often mistaken for Japanese beetle damage.

Larva (below) Adults look like small wasps or flies.

The violet sawfly produces damage that often looks like slug damage – look on leaf undersurfaces to determine if the sawfly larvae are hiding there.

Lysimachia sawfly larvae are covered with a white powdery material.

Fruitworms usually attack fruit tree foliage, but they may be found on roses and perennials.

The cabbage looper may be found on a variety of annual or perennial flowers as well as vegetable crops.

American painted lady caterpillar feeding on perennial.

The milkweed tiger moth has a striking caterpillar that feed on all plants in the milkweed family.

Sawfly Insecticides

(for homeowners) Traditional

• Sevin • Orthene

Still/Now Available

• Pyrethroids (permethrin, resmethrin, esfenvalerate, bifenthrin, cyfluthrin) • Merit • Sevin & Orthene • Soaps or Oils

Caterpillar Insecticides

(for homeowners) Traditional

• Sevin • Orthene

Still/Now Available

• Sevin & Orthene • Pyrethroids (permethrin, resmethrin, esfenvalerate, bifenthrin, cyfluthrin) • Merit (imidachloprid – not recommended) • Bt • Soaps or Oils

The iris borer overwinters in the egg stage attached to old leaves. The eggs hatch in spring and the larvae burrow down the leaves to the rhizomes. They continue feeding all summer, nearly eating all the rhizome internal tissues. The larvae drop out in August, pupate in the soil and the adult moths emerge in October into November.

Notes:

The iris borer is actually a caterpillar of a moth that is in the same family as cutworms. However, this larva burrows into the stems and rhizomes of iris, feeding inside them. By late July and August, the mature larvae can have completely hollowed out the rhizomes and killed the iris plants. While this pest prefers bearded iris, it will attack almost all species, except for the bulb-type iris.

Iris Borer Insecticides

(for homeowners) Traditional

• Cygon (dimethoate)

Still/Now Available

• Cygon (dimethoate, Bayer Advanced 2-in-1 Rose Systemic Granules) • ???

Twospotted Spider Mite On Perennials

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Prefer hot-dry conditions.

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Females overwinter in mulch & protected areas OFF THE PLANT.

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Often “reinstalled” on new bedding plants.

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Often resistant to common miticides.

Twospotted spider mite eggs, nymphs and adults generally reside on leaf undersurfaces unless they have completely covered their host foliage.

Twospotted spider mites can completely web over the foliage of their hosts.

Traditional

Miticides

(for homeowners) Still/Now Available

• Soaps & Oils • Soaps or Oils • DiSyston (Rose Systemic Granules) ?

• Conserve (=Naturalite) ??

Notes:

At present, we have lost all true miticides that used to be available in the over-the-counter market! While some of the pyrethroids and Orthene claim spider mite control on their labels, these tend to make spider mite infestations worse, not better! Insecticidal/miticidal soaps and horticultural oils work well, but these can damage flowers when plants are in full bloom. Products containing Spinosad are available on the Internet and these can provide some suppression of spider mites.

Coneflower flowergall mites are eriophyids. Eriophyids are often not susceptible to regular miticides.

Notes: There are few eriophyid mites (gall and rust mites) that seem to cause much damage in perennials. This coneflower flowergall mite is commonly found in Ohio plantings, but the damage can be mistaken for disease or herbicide damage. There are no insecticide or miticides available to control this mite, but thorough cleaning of the flower bed in the fall can help reduce the infestation for the next season.

Leafminers on Perennials

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Columbine leafminer(s) – several species with multiple generations per year - dipterous.

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Serpentine leafminers – several species that attack Phlox, hollyhocks and others - dipterous.

Notes:

Leafminers are insects that have small, flat larvae that can live between the epidermal layers of leaves. These flat larvae “mine” the spongy tissues, leaving behind a characteristic trail or blotch that is visible on the leaf surface.

There are leafminers that are sawflies (hymenopterous), flies (dipterous), beetles (coleopterous), or moths (lepidopterous). Most of the leafminers that attack perennials are dipterous leafminers.

Columbine leafminer adults (above left) feed by making “pinholes” in leaves (left). Eggs are inserted into leaves and the larval maggots make winding mines which may end in a large blotch.

Leafminer Insecticides

(for homeowners) Traditional

(dimethoate) • DiSyston • Orthene • Neem (azadirachtin)

Still/Now Available

• Pyrethroids (permethrin, resmethrin, esfenvalerate, bifenthrin, cyfluthrin) • Merit ?

• Neem ?

• Conserve ?

• DiSyston & Orthene ?

Notes:

Since most leafminer larvae are not discovered until they have started feeding within their host’s leaves, systemic insecticides are needed in order to reach them. Surface applications of pyrethroids are used to knock out the adults that are laying eggs into the leaves, but these types of applications are difficult to time and several applications may be needed in order to cover the time that the adults are active.

Garden snails are not common in Ohio, but they occasionally become established through recent plantings of new plants. Most can’t survive Ohio winters.

A half dozen species of slugs can be found in Ohio landscapes and most will feed on the leaves of plants while others specialize on feeding on fungi.

Notes:

There are about a half dozen species of slugs in Ohio and these are the most common mollusk pests of perennials. Snails can be damaging, but these are rarely found in Ohio landscapes. Since slugs and snails are not arthropods, special pesticides are usually needed for their control.

Over mulching and over watering commonly contribute to slug buildup in landscapes. For every slug you see on the surface, there are probably five to 10 in the mulch and soil profile! Therefore, several applications of a slug bait may be needed in order to greatly reduce this pest. Most baits also loose their attractiveness if wetted by rain or irrigation.

Molluscicides

(for homeowners) Traditional

• Metaldehyde

Still/Now Available

• Iron Phosphate (Sluggo) • Metaldehyde (Deadline)

Black Vine Weevil On Perennials

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Not a common landscape pest of perennials, mainly in container production areas.

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One generation per year, females lay eggs over long period of June & July.

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Larvae overwinter in soil or pots.

Black vine weevil larvae look like scarab white grubs, but weevil larvae have no obvious legs (right).

Black vine weevils are commonly called the Taxus Weevil because this is one of their favorite hosts.

Black Vine Weevil

Traditional

(adults only)

(for homeowners) Still/Now Available

(professionals only) • Pyrethroids (cyfluthrin, resmethrin, bifenthrin)???

• Cygon & DiSyston?

Simple Black Vine Weevil Management Merit!

(home owner product available, Bayer Advanced Tree & Shrub Concentrate) apply to soil for larval control, NOT mulch, not for adults!)