Powdery Mildew


It appears as though many of the flowering plants in my garden have powdery mildew. There’s a grey substance that covered the leaves; some of the flowers died, others did not bloom. There also seems to be bugs: small orange eggs and small black eggs. All flowers were stripped from my Lupins, for example. What can I do this fall and next spring in order to bring the flowers back to health?


To combat the fungus this season try using a biofungicide containing Bacillus subtilis. You can also use fungicidal soap, sulfur or lime-sulfur sprays but check the instructions on the container carefully to make sure these products can be applied to the affected plants.

Next year look for and plant cultivars that are resistant to this fungus. Good garden practices can also help to prevent the spread of this disease. During hot weather, powdery mildew attacks many herbaceous plants especially plants that are stressed due to drought. To help control it give your plants good air circulation and water well during hot spells.  A good layer of mulch can help to keep plants from drying out.  Remove and dispose of any diseased leaves in the garbage. Do not compost them as the spores will remain viable. A good source for the description of various plant diseases and pest and how to control them is:

The Organic Gardener’s Handbook of Natural Pest and Disease Control . Fern M. Bradley, Barbara W. Ellis, and Deborah L. Martin; Rodale, 2010.

Take a look at the following link to the answer for a similar question that appears on our web site.


Although, Lupins are frequently attacked by aphids, there are a host of other pests that could be attacking them. Puckered and twisted leaves with a sticky residue is a symptom of aphids and mites  for example.  Defoliated plants could be caused by Asiatic beetles, leaf beetles, Japanese Beetles, slugs, snails and cutworms etc. In addition, the eggs you describe may not be the eggs of the pest eating your plants. Lady Beetles, for example lay their orange coloured eggs on leaves where their prey, aphids, are located. Many of the pests that could be eating the plants lay their eggs in the soil.  You will have to do a bit of detective work to nab the culprits and properly identify them before finding out how to control them. Here are some steps that can help identification:

  1. Check to see if other plants besides the lupins are affected. Some pests target specific plants while others are generalists.
  2. Note what the damage looks like ie nibbled edges of leaves, skeletonized leaves, small round holes in leaves, partially or completely defoliated plants, flowers only attacked. This can help to identify how the pest attacks the plant.
  3. Check the plants at night as the pest may be a night feeder. Examine the plants with a flashlight. Slugs, snails and weevils for example are most active at night. You can also often find slugs and snails in the early morning or after a rain. During the day slugs may  crawl under the cover of garden debris. You can monitor their presence by placing a flat piece of wood on the soil near the plants. Turn it over in the morning to see if there any slugs or snails on the underside. If you find insects etc on your plants, take a sample so you can accurately describe its appearance when seeking identification.
  4. The insects may be well hidden among the plant foliage. Place a white cloth beneath the plant and shake it to knock the insects off onto the cloth where you can see them.
  5. Dig carefully in the loose soil around the base of the plants. Cutworms burrow into the ground during the day.