No one likes to find their flower gardening efforts thwarted by hungry insects intent on making a meal of prize specimens. However, some insect pests do more than just snack on our plants; they can introduce fungi and other diseases that can sound the death knell for our favorite flowers.
01 of 07
Gardeners everywhere curse the presence of tiny aphids on rose, honeysuckle, and other flowering foliage growth tips in the springtime. The sucking action of these insect pests causes stunted growth and deformed leaves and flowers. However, aphids bring more havoc to the flower garden by transmitting plant viruses and fostering the growth of black sooty mold fungus.
Start your aphid battle the natural way:
- Plant sweet alyssum in the flower garden to draw beneficial wasps.
- Include cosmos to attract hungry lacewings, and add penstemon or yarrow to attract ladybugs.
- Insect soap and a strong blast of water will take care of heavy infestations.
- Encourage ladybugs in your garden. A single ladybug can eat as many as 5,000 aphids in its one-year lifespan and larvae eat hundreds before they pupate.
02 of 07
Borers are an insidious pest, destroying your flowering plants from the inside out.
The worst borer in the flower garden is the iris borer, which will tunnel through an entire iris rhizome, leaving bacterial rot in its wake. You should be suspicious if you notice sawdust material around the base of your irises or ragged leaf margins. Pinprick holes in the leaves of iris are the signs of tiny caterpillars that have infiltrated the leaves and are making their way down into the rhizomes.
- Discourage borers by removing iris leaves in the fall, which provide a host for borer moth eggs.
- In the spring, you can apply the systemic pesticide Merit or the nontoxic spray Garden Shield.
- The best non-toxic control is to dig up affected plants after flowering is done, trim out the rotten rhizomes, and replant the good portions.
03 of 07
Only about an eighth of an inch long, leafhopper insects look innocuous enough. The green insects don’t congregate in large numbers on plants and hop away when you approach. However, what you won’t notice is the toxin these hungry pests inject every time they insert their mouthparts into the underside of your flower’s foliage. This allows the damage to travel beyond the chewed part of the leaf, showing up as distorted leaf tips and edges. The insects also spread the aster yellows virus.
- Remove debris from the garden at the end of the season to eliminate overwintering sites.
- Use floating row covers to prevent leafhoppers from reaching your plants.
- Blast leafhopper nymphs from plants with a strong jet of water.
- Spray adults with insect soap, pyrethrin, or Sevin.
- Keep dandelion and thistle weeds away from the flower garden, as they provide cover for leafhoppers.
- Encourage beneficial insects, such as ladybugs, lacewings, and pirate bugs, which all prey on the eggs and larvae of leafhoppers.
04 of 07
Mealybugs don’t draw much attention, as the pests are only 3/16 inch long and move very slowly. The honeydew they excrete supports sooty mold growth. When enough sooty mold accumulates on foliage, it can reduce photosynthesis, weakening the plant and making it even more susceptible to garden pests.
If you notice white fuzzy growths on your plants, you may have mealybugs. Ways to control mealybugs include:
Continue to 5 of 7 below.
- Avoid overwatering and over fertilizing since mealybugs are attracted to new growth and plants with high levels of nitrogen.
- Dip a cotton swab in rubbing alcohol and touch it to the pests to desiccate and kill them instantly.
- You can also spray the pests away with water, or apply Malathion or Orthene pesticide sprays.
- Use insecticidal soap or neem oil as repellants; these products do not harm honeybees and other beneficial insects.
- Encourage beneficial insects, such as ladybugs and lacewings, which are predators of mealybugs.
05 of 07
"Plant bugs" is a term that includes a number of true bugs, members of the Hemiptera order of insects. The most common plant bugs of interest to gardeners are cinch bugs, harlequin bugs, and squash bugs.
Like leafhoppers, plant bugs inject a toxin into your plants’ leaves, buds, and shoots as they feed. The result is a plant mottled with brown or black spots and deformed growth. Dahlias, azaleas, daisies, Liatris, and asters are just a few of the flowering plants these bugs commonly feast upon. Gardeners should be on the lookout for tarnished plant bugs and four-lined plant bugs, growing up to a 1/4 inch long. Plant bugs often have an unpleasant odor.
- Plant bugs are fast moving pests, but you can pluck them off and drop them into a bucket of soapy water if you’re an early riser, as the bugs are sluggish in the morning.
- Spraying young bugs with neem oil or insecticidal soap will offer some control for most plant bugs.
- Protecting edible crops with floating row covers will prevent plant bugs from damaging your vegetables.
- Plant bugs can be killed by spraying your plants with neem, Sevin, or diazinon. Use sparingly, as these chemicals will also kill beneficial insects.
06 of 07
At first glance, scale insects may not even seem alive. The waxy covering that serves as a protective shield on the bugs makes them resemble lichen or other natural growths on their host plants. The scale insect under this waxy covering is very much alive, though, feeding on garden plants throughout the entire growing season and on houseplants throughout the year. Damage appears as stunted growth, leaf drop, yellow spots on leaves, and sooty mold growth that thrives on the scale’s honeydew.
Parasitic wasps love to use scale insects as hosts, and you may see evidence of this as tiny holes piercing the scale’s armor. This same armor makes scale resistant to many pesticides, but dormant oil can suffocate the insects during the winter season.
To control scale:
- Dispose of affected branches and leaves, which harbor the insects.
- Pick off the insects by hand—a viable solution if the numbers are low.
- Dab individual insects with a cotton swab dipped in rubbing alcohol.
- Encourage beneficial insects such as ladybugs and lacewings, which feed on scale insects.
- Use insecticidal soap or oils to coat scale. This will require repeated applications but is very safe for the environment.
- Apply neem oil to affected plants. A concentrated form of neem oil, azadirachtin, is a very effective control.
- If chemicals are needed, those containing acephate or imidacloprid are effective as systemic pesticides.
07 of 07
Upon disturbance, whiteflies flutter about their host plants like an ephemeral cloud, but their damage is formidable. This is another honeydew-secreting pest, encouraging sooty mold while simultaneously leaving plants yellow and stunted after sucking on plant juices. Some whiteflies also carry plant viruses. Whiteflies are the bane of greenhouse growers, who detect their presence with yellow sticky traps. Whiteflies can be controlled in a number of ways:
- Take advantage of the small size and weakness of these insects by using a vacuum to remove them from plants.
- Yellow sticky traps can be used to trap adult whiteflies.
- Encourage natural predators such as ladybugs and lacewings.
- Insecticidal soaps work well on heavy infestations but must be applied regularly.
- Neem oil and other horticultural oils will kill whiteflies; make sure to completely drench plants.
- Where chemical pesticides are needed, use natural insecticides containing pyrethrin.
- Malathion is a more aggressive chemical that can be used sparingly.
Plant Diseases and Insect Pests. National Research Council (US) Committee on Biosciences.
Aphids in Home Yards and Gardens. University of Minnesota Extension
Iris Borers. University of Minnesota Extension.
Aster Leafhopper. University of Nebraska-Lincoln Institute of Agriculture and Natural Resources.
Mealybugs Integrated Pest Management. Washington State University.
Four-Lined Plant Bug Crushing Oregano (and other plants). Ohio State University College of Food, Agriculture and Environmental Sciences.
Scale Insects on Indoor Plants. University of Maryland Extension.
Pests in Gardens and Landscapes: Whiteflies. University of California Agriculture & Natural Resources.