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5 Plant Pest Problems That Will Give You Headaches

Maryland gardens are faced with many plant pest problems. While it is practically impossible to recognize and know all of them, one can learn the ones that will inflict the most damage.

Every plant gets some diseases and has some insects that are going to do damage to it. That is nature. Be that as it may, most plants have that one pest that stands above all the others as a threat. The rest of the diseases and insects may be a threat, but probably not quite as severe as the one’s we are calling the Achilles Heel.

Instead of learning all of the potential threats to a plant variety, focus in on the one that will do the most harm and put the plant variety at most risk. By focusing on managing these plant pest problems, you will have taken great steps in the overall health of your landscape.

Burning Bush – Spider Mites


Plant Pest ProblemsSpider Mites are tiny (smaller than a pin head) relatives of spiders. In mid-summer, the damage they are causing to Burning Bushes will reveal itself by the planting turning tan color with a stippling pattern on the upper leaf surface. The spider mites are literally sucking the life out of the plant.

Controls Red Spider Mites

  • Apply dormant oil in later winter to cover overwintering adults and eggs.
  • Spray horticultural oil and insecticidal soaps during the summer.





Powdery Mildew – Lilacs


Plant Pest ProblemsPowdery Mildew is a common disease that appears during the late spring and summer when weather conditions are right for it. It is easily diagnosed as a white, powdery coating on leaves and possibly some stems. It rarely causes serious damage but it can cause defoliation and weakening of plants, creating an opportunity for other pests to invade.

Controls for Powdery Mildew

  • Select resistant plant varieties.
  • Improve air flow through thinning.
  • Horticultural oils and neem oils can help prevent Powdery Mildew when applied prior to infection.


Manhattan Euonymus – Scale


Plant Pest Problems

Credit: John Davidson, UMD

Euonymus Scale is a very common and once you see it, an obvious pest. Tiny white fleck will appear on leaves and stems of the infected plants. In time, it will absolutely cover the entire plant which will decline rapidly.




Controls for Euonymus Scale

  • Apply dormant oil in later winter to cover overwintering adults and eggs.
  • Spray horticultural oil in May through June to suffocate crawlers (young scales).
  • An imported specie of lady beetle, Chilocorus kuwanae, has also proven effective.



Azaleas – Lace Bug


Plant Pest Problems

Credit: UGA Extension

Lace Bugs are piercing/sucking insects meaning their mouth parts are shaped like hypodermic needles which are used to pierce into the plant tissue and suck out the juices. Azalea Lace Bug damage is most prevalent on plants that are planted in full sun. Being a shade loving plant, Azaleas planted in full sun tend to be more stressed out, making them more susceptible to pest problems. The easiest way to prevent Azalea Lace Bugs is to plant Azaleas in their culturally correct environment; shade to partial shade.

The damage appears on he leaves as a chlorotic bleached out coloring with stippling of darker tiny spots. The insect and its eggs are actually on the underside of the plant. Turn an affected leaf over and you will see them.

Controls for Azalea Lace Bug

  • Dormant oil, horticultural oil, insecticidal soaps all work well. There are several pesticides that will work also. Make sure to spray the underside of leaves.



Roses – Japanese Beetle


Japanese Beetles begin to appear in early June and begin eating voraciously right away. They are chewing insects and the damage skeletonizes leaves, leaving only the veins. Japanese Beetles are about ¼” long with shiny copper colored bodies.

Controls For Japanese Beetles

There are several effective strategies available to control Japanese Beetles:

  • Before Japanese Beetles emerge, they are grubs that live under your lawn and in your garden beds. Controlling the grubs will help prevent the beetles.
  • Hand picking the beetles from the plants and putting them in a bucket of soapy water is effective.
  • Traps are available that attract the adult beetles with a pheromone bait works well. There are also several
  • Apply Neem Oil as soon as beetles appear.
  • There are several pesticides in the pyrethrin class available.



Arborvitae – Bagworm


You will probably not ever see the bagworms themselves, but you will see the home they make. The bags are brown, 2” long, and constructed of dead leaves. Inside, the adults lays over 1,000 eggs which hatch in late spring and the larvae soon emerge to start the cycle over.

Bagworm caterpillars are chewing insects and can defoliate large areas of host plants. The adult is a moth.

Controls for Bagworms

  • Hand picking off the bags and disposing of them.
  • Horticultural oils and insecticidal soaps are effective in late May to early June when the young caterpillars are crawling around as are insecticides in the pyrethroid class.

Common Plant Pest Problems


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