Ohio State University Extension Fact Sheet

Ohio State University Extension Fact Sheet

Entomology

1991 Kenny Rd, Columbus, Ohio 43210-1090


Common Insects and Associated Pests

Attacking Bedding Plants and Perennials

HYG-2151-91

David J. Shetlar

Bedding plants and perennials provide the home owner and landscaper with a multitude of colors and textures. Unfortunately, numerous insects, mites and other invertebrates (ie. slugs, sowbugs and millipedes) consider these same plants as food!

In order for you to manage the activity and damage caused by these pests, you must understand "pest management" and learn how to identify each pest. There are numerous "bugs" in a healthy garden and most do no damage. A common mistake is to spray anything that moves.

Each plant has a number of pests that may attack the flowers, foliage, stems or roots. Some of these pests will only attack a certain kind of plant. Other pests are generalists and can feed on a variety of plants. This fact sheet will attempt to help you identify the common "generalists" and suggest methods of keeping them under control.

Pest Management

We now use the term "Pest Management" because we know from experience that there is no way to totally rid the garden of unwanted pests. We can merely attempt to keep pest numbers low to minimize their damage - this is management.

When we use pest management there are two important principles to remember: 1. The mere presence of a pest is no reason to attempt control. 2. Reliance on a single control technique will eventually fail.

Perhaps the old farmer's saying of "plant five seeds - one for the weather, one for the crow, one for bug, and two to grow!" should be considered in our gardens today. Pests will always cause some damage to our flowers but is the amount of damage unacceptable?

We know that complete reliance on pesticides will eventually fail. In order to manage pests and their damage, we need to use cultural (and mechanical) control (ie. resistant plants, traps, crushing and sanitation) and biological control (ie. predators, parasites and diseases) with chemical control.

Diagnosis of a Problem

In order to manage pests, you must become a pest detective. To do this, you must learn some of the terms used to describe pest damage to plants. Generally, pests have either chewing or sucking mouthparts.

Pests with chewing mouthparts eat portions of the plant. They may defoliate the plant by eating all the leaves. They may only eat portions of leaves, resulting in skeletonized foliage (the leaf tissues between the veins are eaten), notched foliage (only the edge of the leaf is eaten), shot holed foliage (tiny holes in the leaves), or shredded foliage (most of the leaf eaten except for the major veins). Other chewing pests feed inside leaves (leaf miners), or bore into stems and roots (borers).

Pests with sucking mouthparts usually cause the plant to discolor or twist and curl. The plant may discolor from tiny yellow speckles (spider mites), larger darkened spots (plant bugs), or coatings of black sooty mold growing on honeydew deposits (from aphids and whiteflies). Many plants react to the saliva and damage of sucking pests by causing the foliage to curl or the young stems to twist.

Locating an actual specimen of the pest makes diagnosis easier. Many pests stay on the plant at all times and a close inspection is all that is necessary. Others run or fly when disturbed and you may need to sneak up on the plant to avoid scaring the pests. Carefully approach the plant low to the ground and try to observe the plant's upper and lower leaf surfaces without casting a shadow. Many pests come out at night and you will have to look for these with a flashlight.

If you have located a suspected pest and you cannot identify it from the illustrations included here, try to capture a specimen and take it to your county's Extension office. Most pests can be placed in a dry jar or plastic bag. A dry tissue or paper towel placed inside the jar or bag will keep the specimen dry. Be sure to keep this container out of direct sunlight and get to the office as soon as possible.

Snails and Slugs

Snails and their "shell-less" cousins, the slugs, are common residents in the garden. Most of these feed on decaying organic matter but many can chew the foliage of living plants. Snails and slugs prefer the dark and usually do their damage at night, leaving ragged leaves. Use a flashlight at night to detect these pests or look for the slime trails on damaged plant foliage in the early morning.

These pests require high humidity or moisture and usually reach pest status during wet years or during the rainy periods of the spring and fall. Control is best achieved by making the garden less suitable for snails and slugs. Remove excess mulch in order to allow the soil to dry slightly, clean up any fresh plant debris and open the plant canopy so that sunlight can reach the ground.

Snails and slugs are attracted to the yeasty odor of beer and several traps are available that use this odor. The larvae of fireflies, ground beetles and parasitic flies feed on snails and slugs.

If habitat modification, traps or natural predators do not reduce snails and slugs, pesticide-laced slug and snail baits can be use.

Sowbugs and Pillbugs (Isopods)

Isopods (commonly called pillbugs) are not insects but relatives of the crab and shrimp. They have a head with obvious antennae and a trunk region with 11 pairs of legs. They tend to hide during the day and emerge at night to eat irregular holes in leaves of young plants. These pests are easily detected at night with a flashlight or by pulling back mulch around the plants.

Under normal conditions, these general feeders rarely cause much damage to living plants since they prefer to feed on decaying organic matter. During rainy weather or where gardens are mulched too heavily and watered constantly, isopods can build up large populations and cause visible damage.

The best control for isopods is to remove excess mulch, use irrigation sparingly, and remove any old leaves or dead plants immediately. This will reduce habitat and food necessary for large populations. Some of the general insecticides also have sowbugs or pillbugs on the labels and these can be used during wet seasons when cultural controls are not effective.

Millipedes

Millipedes are often confused with their fast running, predatory cousins, the centipedes. Millipedes have heads with antennae and elongate trunks with 20 or more segments and two pairs of legs per visible segment. These slow moving animals are usually scavengers but occasionally feed on living plants, causing damage similar to isopods. Centipedes have only one pair of legs per body segment, run rapidly and are beneficial predators.

Control millipedes with the same techniques used against isopods.

Spider Mites

The most common spider mite attacking bedding plants and perennials is the two-spotted spider mite. This is a common pest in greenhouses and is often transplanted into the garden with bedding plants. This mite, however, can overwinter as an adult female hiding in protected areas.

The tiny mites are about 1/50 inch long and usually feed on the undersides of leaves. You will need a 10x hand lens to see these pests. They make tiny cuts into plant cells and suck out the contents. This results in tiny yellow or white speckles on the upper leaf surface. Spider mites also produce fine webbing which may coat the plant when populations are extremely high. This is often easy to observe in the morning dew.

The twospotted spider mite is a sun and heat loving pest that can complete a cycle from egg to adult in less than two weeks. Therefore, populations tend to be a real problem in the heat of summer.

Since spider mites are not insects, most insecticides are not effective for control. Beware of standard insecticides that claim "mite suppression" on the label. Look for true miticides or pesticides which claim "mite control".

Spider mites are best managed by selecting bedding plants or new perennials which are not infested. Since the mites are very tiny and prefer dry, sunny weather, attempt to grow mite susceptible plants in the shade. A regular washing with a firm jet of water (syringing) can help keep populations down.

Several of the insecticidal soaps are also registered for mite control and can be effective if thoroughly applied to the upper and lower leaf surfaces.

Most soap and miticide applications will have to be repeated two to three times in order to kill resistant eggs and resting stages of this pest.

Earwigs

The European Earwig is a common inhabitant of home gardens. The adults and nymphs have elongate bodies ending in a pair of forceps like pinchers. Though these insects look dangerous, they are harmless and can be considered beneficial when they prey on other insects. Some of the larger males may be able to pinch soft skin when picked up but most protect themselves by releasing a foul odor.

Unfortunately, European Earwigs are omnivores that eat both plant and animal matter. When populations are low, most people would never notice the occasional notch or hole in plant foliage and flowers. When mild winters are combined with above normal rainfall, Earwig populations explode and the adults and nymphs can be packed by the hundreds in flowers and every other crack and crevice of the garden. In most years, earwigs should be ignored or appreciated for their predatory behavior.

When Earwigs reach intolerable populations, they can be fairly easily controlled with standard insecticides. Non-chemical control can also include the construction of trap boards. These are two flat boards with 1/4 inch grooves tied together so that the spaces are enclosed. The Earwigs like to hide in these spaces and the boards can be collected regularly and dunked in soapy water to kill the pests. Other cultural controls use the same types of habitat modifications (ie. reducing mulch and sanitation) listed under isopods.

Plant Bugs

The tarnished plant bug and fourlined plant bug are common sucking pests that attack a variety of bedding and perennial plants. The daisy and mint families are especially susceptible to attack. Both bugs are quick to fly and the nymphs quickly run to the under surface of leaves when approached. They damage plants by causing small (1/16 inch), round, sunken spots on the leaves. These spots occur when the leaf bugs kill the leaf tissues during feeding. When these spots are numerous, the entire leaf may curl and wither.

The tarnished plant bug has a light-green nymph and the adult has mottled brown colors. The fourlined plant bug has a bright red-orange nymph and the adults are lime green with four black stripes.

Damage to plants usually occurs in the late-spring and early-summer when the nymphs are active. If this activity is several weeks before flower bud initiation, no damage will be evident at the time of flowering. However, early flowering plants can be severely damaged. These are the plants that need protection.

Since the plant bug nymphs cause most of the damage, control of this stage is suggested. Inspect plants early and try to detect the first signs of the sucking damage. Small numbers of nymphs can be dislodged from the plants into a container of soapy water. Higher populations are best controlled with a registered pesticide or insecticidal soap. Check the plants again in two weeks to catch any late emerging nymphs.

Aphids

Every plant seems to have some type of aphid which may feed on it. These pear-shaped, soft-bodied insects with long legs and antennae may cause young, soft leaves and stems to twist and curl. Aphids also produce considerable honeydew, a sugary excrement, which is attractive to ants and may allow for the growth of black sooty mold. Aphids may be any color with winged and nonwinged forms present in a colony. Most of the reproduction is asexual, with females giving live birth to the nymphs. Populations can therefore explode in a short period of time.

Fortunately, there are numerous predators and parasites which attack aphids. Lady beetles, lacewings and aphid wasps are good examples. Learn how to identify these beneficials and do not apply pesticides when they are active. Often, the beneficials arrive after an aphid population has built up to alarming numbers. In order to reduce these populations, the aphids can be washed off the plants with a strong jet of water (syringing) or insecticidal soaps can be used.

Whiteflies

Whiteflies are not true flies but relatives of aphids and scales. These 1/16 inch long pests are usually first detected when the plant is touched and the small white insects take flight. They damage plants by discoloring the leaves and depositing honeydew.

Most of its life cycle is spent as a sessile nymph and pupa attached to a leaf. Female whiteflies attach eggs on leaf surfaces and the nymphs (called crawlers) move to find a suitable spot to insert their sucking mouthparts and begin feeding as a sessile nymph. The nymphs feed for about two weeks and excrete honeydew. They then form a pupal stage from which the adult emerges.

Whiteflies are very difficult to control because only the adults and crawlers are susceptible to normal pesticides. However, insecticidal soaps seem to control some of the recently settled nymphs.

It is best to avoid whiteflies. The greenhouse whitefly normally gets started in the garden after being brought in on bedding plants. Check new plants carefully for signs of whiteflies.

Japanese Beetle

Japanese beetles are bright, metallic-green and eat the flowers or skeletonize the foliage of ornamental plants. These pests begin to emerge in late-June and continue their activity until early-fall. It is best to use plants that are not attractive to adults. Control is a difficult process and several applications of an appropriate pesticide are usually needed to protect susceptible plants. Refer to, HYG-Fact Sheet - 2002, Control of Japanese Beetle Adults and Grubs in Home Lawns.

Cutworms and Caterpillars

There are numerous caterpillars that may be found attacking bedding plants and perennials. However, the most damaging group are the cutworms that may kill newly-transplanted seedlings. These thick bodied caterpillars live in the soil during the day and emerge at night to find seedling plants. When a seedling is found, the cutworm chews into the plant's stem at ground level and fells it like a miniature lumberjack. The caterpillar may drag the plant back to its burrow or may crawl under the dead plant to feed. When seedling stems get too hard to cut off, the cutworms may crawl up to the leaves and dine until daybreak. They then return to the soil to hide.

Examining the soil near recently felled plants often exposes the culprit and allows one to eliminate it by crushing or drowning in soapy water.

Cutworms can be controlled by placing a plastic or cardboard collar around newly transplanted seedlings. This ring should extend one to two inches into the soil and be three to four inches tall. Several pesticides are registered for control of these pests and the dusts applied to the soil seem to be most effective.


This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.


All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-6181



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