In the Garden:
Northern & Central Midwest
Check out the mildew on my currants!
I had to make a hard decision this week. I've grown currants for many years and always harvested a great crop from my five currant plants.
However, last spring's long cool stretch caused my currants to contract powdery mildew. This is a white powdery fungus that coats leaves, and in this case, the developing fruits also. I lost the entire crop because mildew does not wash off and taints the flavor. I cut the shrubs back at the end of the season and assumed the problem was just a function of the weather that spring.
Watch for Powdery Mildew
This year, even before the fruits were one-eighth inch across, the mildew started again. We haven't had the same conditions as last spring, but the fungus overwintered on the remaining stems or perhaps on leaves that I didn't get picked up in fall. My hard decision was to take out the plants. I have removed them and am making plans to purchase new currants next year for an entirely different spot in the yard.
Steps in an IPM System
This type of decision was the result of methodically working through the steps in an integrated pest management system (IPM). IPM is an ecological approach to pest control that works with the ecosystem and its natural balance. IPM minimizes the use of chemicals by focusing on preventing pests.
In the case of powdery mildew on lilacs, we tend to tolerate it because it doesn't do any real damage to the shrub. The same disease on bee balm makes it unattractive, so some people choose to use a fungicide to prevent it.
In my case, my currants are edible and I don't want to spray a fungicide on something I will eat. Besides, by the time the mildew had appeared, it had already infected the fruit and fungicides only work as preventives.
Decision to Discard Plants
So I made the decision to discard the plants. When I replant not only will I move the planting site, but I will also purchase certified disease-free plants and will plant them further apart to encourage plenty of air movement between bushes. These cultural corrections should help me have healthy currants next year.
Correctly Identify the Pest
The first step of an ecologically sound pest management system is correctly identifying the pest or disease. Treating for the wrong thing is costly, a waste of time, and at the worst can be damaging.
Determine Damage Threshold
Next, you need to determine your damage threshold for an insect population or disease. Sometimes, as with the lilac, treatment is not necessary if an insect or disease causes only minor damage. If your roses have a few aphids, you may only need to get out the hose and spray them off. However, if the aphids begin to distort the foliage and destroy the flowers, you need to take action.
Least Toxic Solution
IPM does includes pesticide use as a last resort when there is no other alternative, but it stresses using the least toxic, most environmentally friendly pesticides available. Insecticidal soaps and horticultural oils are two of the most commonly applied.
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