Purple cone witch hazel aphids
Hello, We have one witch hazel shrub badly infested with purple cone aphids. It is the only one of about 8-10 witch hazels on the edges of two retention ponds in the vicinity. Is one shrub acting as a “sink”, or is the infestation likely to spread more widely this summer or next? What solution would you recommend. Are lady beetles enough? Removal of the shrub? We prefer not to use pesticides near the stormwater ponds. The location is Towson University, Towson, MD Thank you.
Baltimore County Maryland
If the witchhazel grouping consists of different species/varieties, there may be variation in susceptibility, though we have not seen lists ranking varieties for this resistance. We agree that pesticide use in general is not warranted, though you could try using a dormant oil treatment of the witchhazel in winter to smother overwintering eggs. If only a handful of leaves are affected, clipping them off individually may help break their life cycle, though populations coming from area birches during other seasons could recolonize the plant. The aphids are well protected in the gall, so predators such as lady beetle may not be very effective.