"Managing Leaf Diseases," by the Whistling Gardener

The daylilies are popping up in my yard. Photo courtesy of Sunnyside Nursery.
The daylilies are popping up in my yard. Photo courtesy of Sunnyside Nursery.

This weekly column is being reproduced with the permission of Steve Smith, The Whistling Gardener, and owner of Sunnyside Nursery in Marysville.

One drawback to living in a maritime climate like the northwest is that all the extra moisture in the air encourages fungus and bacterial issues with our plants.

Specifically, the foliage becomes susceptible to infections such as black spot on roses, mildew on lupine, rust on hollyhocks, Alternaria leaf spot on Photinia, blossom and twig blight on cherries and currently all around town a fungus called Sirococcus conigenus on blue Atlas Cedars.

What on earth is a gardener to do when this happens in their garden?

Controlling fungus (and bacterial) diseases is a huge challenge for most of us because by the time we realize there is a problem it is too late to stop it.

Take for example the Atlas Cedars that are just hammered right now with Sirococcus which causes the needles on the new growth to turn a tan color and eventually fall off.

The time to control this disease would have been when the new growth was just emerging about a month ago, before we saw any signs of trouble.

The same is true with blossom and twig blight on cherries. The time to apply a fungicide would have been before, during and immediately after the tree bloomed (it takes three applications of copper to manage this problem in most years).

Timing is everything when it comes to managing diseases and prevention is the key to success. Keeping a garden journal can help us remember to plan ahead for the next season.

Here are several things we can do to minimize foliar diseases in our gardens.

  • First and foremost is to plant resistant varieties.
  • Second is to not crowd plants so that there is good air circulation in and around the foliage (pruning will help here as well).
  • Third is to plant the right plant in the right place (putting a sun loving plant in too much shade is a recipe for disaster).
  • Fourth is to practice good hygiene. Get rid of infected leaves by stripping them off and raking them up underneath plants. Applying a fresh layer of compost over the soils every year will do wonders to minimizing diseases.
  • Fifth is to treat the infected plants with a fungicide, either natural or synthetic depending on your preferences. Synthetics tend to last longer and are often systemic which means that they are absorbed into the plant’s vascular systems and provide more thorough protection. Most natural products are only contact and need to be reapplied weekly to be effective. Again, the key to applying fungicides is to get them on before you see problems.
  • Sixth is to not expect perfection. Some degree of foliar damage is normal and perfectly acceptable. Often, as the weather improves, a plant will grow out of the condition and the new growth will be just fine.
  • Seventh is to be willing to do some serious pruning. I have taken roses that were smothered with mildew, stripped off all the leaves and pruned them half way back to the ground, fertilized and mulched them and in 6 weeks they were in full bloom and gorgeous.

Pruning can work miracles, which is my cue to remind you that this coming Saturday, June 25th, at 10:00 am at the nursery we are having our Summer Pruning class which you won’t want to miss.

This is your chance to fix all the screw-ups from the last time you tried to prune the garden and to address the problems that Mother Nature heaped on us from this lousy wet spring.

Summer pruning is critical to a healthy garden and you can learn all about it this Saturday. Hope to see you here.

Steve Smith is owner of Sunnyside Nursery in Marysville and you can send your questions

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