Common Plant Diseases 

Use the following list to help determine what your plant(s) may be infected with. Look at the damage on the plant(s) and try to match it up to the list. If you are still unsure of what it may be, come down to Lacoste Garden Centre with a sample (in a closed bag or container!) to check with one of our experts.


Aster Yellows

 Yellowing, stunted growth, flower sterility

Destroy infected plants. Avoid planting susceptible plants in same spot for several years

Downy Mildew

Soft and fuzzy gray, brown, or purple growth under leaves. Yellowing and leaf drop Adequate spacing in garden to allow for air movement. Remove and destroy infected leaves

Gray Mold (borytis blight)

Gray, powdery growth, wilting shoots, blackened and rotten stems Cut back infected parts

Leaf Spots

 Small brown/purple spots. Possible yellowing and leaf drop  Remove infected leaves. Spray with sulfur-based spray

Powdery Mildew

 White powdery growth on leaf. May blacken and die  Allow for adequate air movement by spacing. Year-after-year disease so planting resistant cultivars is the best control


 Yellow spot on top of leaf, orange spores under leaf  Watering plants below foliage to prevent leaves from getting wet

Stem Rot/Wilt

 Wilting in moist soil. Discolouration inside stem  Cut away damaged parts with sterile cutting tool (dipped in bleach/water solution)


 Mottled appearance, stunted growth, and/or lack of vigour.  Controlling virus-carrying insects is the best control. Infected plants should be dug up and destroyed