This is the third spring that the delphiniums in my garden in northeastern British Columbia have suffered some sort of bug or blight. Now it is spreading to the monkshoods as well. Some of the foliage curls up, and inside are black specks. The plant doesn't die, but keeps coming back in the spring; in fact, the bigger plants even bloom in spite of the infestation. I have tried Schultz Insecticide, without lasting results. Someone suggested spreading poplar ashes in the garden to ward off bugs, but that didn't help, either. Some of the plants have sentimental value, and I don't want to destroy them if I can avoid it. I would appreciate help identifying the problem and coming to a solution.
This is from an insect. They can bring diseases of other types with them, but the puckered up leaves are forming a nest or cocoon for what is likely a caterpillar of some sort. Other types of insects and arachnids can do this, too. The frass, the beige and black specks inside and around of excrement and detritus, indicate it's somebody's home for now. If you dissect one of the clusters, you may find your culprit and can then target your counteroffensive. I'd suggest pinching any of these off and destroying immediately.
Thank you for your help. Because the insect comes back every year, is it possible that it winters over in the dormant root?
Certainly possible, and even likely. But if you are vigilant and each year pinch out or remove them before they mature you have an excellent chance of winning the war.
