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Pests and Diseases are common in most areas. Here are 3 Common plant pest and disease problems for the south side of Chicago. Pest and disease issues will vary by location. This article will explain three common pest and disease issues and how to mitigate them.

Pests and Diseases:

Pest: Japanese Beetle

Japanese beetles are an invasive species of beetle originating in Japan, as the name implies. Some of their favorite food sources are shrub roses, birch trees, and linden trees. These pests will defoliate the plants by eating all the leaf material between the veins. Therefore, if the infestation is serious enough it can kill a mature plant.  

Japanese Beetle Life Cycle:

  • Eggs laid underground near surface hatch in 2 weeks forming larvae
  • Larvae feed root systems and grow into grubs
  • Grubs feed on turf grass roots and overwinter in soil
  • Soil temperatures rise and adult beetles emerge


Japanese beetles have a veracious appetite and are capable of defoliating shrubs within a few days. Treatment for defoliation is fairly simple. Firstly, treat the pest infestation by applying granular insecticide at the base of the infested plant. This treatment is a preventative measure that is time released, not fast acting. After that the root system ingests the insecticide and transports it to the rest of the plant. Finally, once the beetle starts to feed the insecticide will be ingested with the plant material and kill the pest.

It is important to note probably the most effective treatment option for Japanese Beetles is prevention. Treating lawn areas for grubs at the begining of the season drastically reduces the number of adult beetles in an area.

Disease: Apple Scab

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What is Apple Scab?

Apple scab is a fungal disease that affects plants in the rose family, usually associated with the Malus family. The leaves become infected and develop dark spots and drop foliage prematurely. As soon as mid-summer the tree can be completely defoliated. New varieties of Malus have been bread to resist the fungus. During wet springs the fungus seems to have more serious outbreaks. For example, this year we had the wettest spring on record and apple scab infections were extensive.

Treatment Options

Reducing the effect apple scab has on your garden is relatively simple:

  • First, remove any leaves that have dropped. Apple Scab can overwinter in discarded foliage and spread to the next growing season.
  • Then, implement annual pruning to increase air flow within the canopy. This pruning will allow for more air to flow, reducing the moisture in the air surrounding the foliage.
  • After that you want to reduce moisture surrounding the tree. Overhead irrigation increases moisture in the air. Increased moisture levels create an environment for apple scab to thrive.
  • Fungicides are a last resort of treatment for apple scab. This fungus rarely kills a host and fungicide treatment involves an extensive and continuous management strategy.

Finally, it seems that the most effective strategy to manage apple scab is to plant resistant varieties. Some apple scab resistant varieties are:

  • Prairie Fire
  • Louisa
  • Tina

Disease: Tar Spot of Maple

Tar spot is a fungal disease that affects maple foliage. This disease is easily identifiable by the black spots that cover the leaf. Generally this fungal disease is not harmful to the health of the plant. However, it may be shocking to see the plant covered in foliage that looks diseased.


  • Light green/yellow spots
  • Signature black spots on foliage
  • Premature defoliation


So how do we eradicate Tar Spot? Above all, the best way to manage this disease is to remove any dropped leaves under the tree. Also, it is a good idea to remove any leaves of maples nearby that could potentially be infected. After all leaves are removed it is important to destroy the infected tissue by burning. It is important to note composting is not an effective mode of disposal as it typically does not get hot enough to kill the spores. Fungal spores thrive in many environments but as long as you recognize the signs and symptoms your plants will stay healthy.


Fungicides are an option for management as well. After managing the disease with the steps above it is important that a fungicide is applied following winter. Spores are released when the temperatures rise. Also, as the trees affected by this fungus drop the infected tissue in the fall, the new foliage has a chance to remain fungus free.

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