After the late summer’s warm and dry weather, the first showers of autumn has seen a flurry of aphids on the roses. Some roses appear to be very attractive to aphids, others less so. I don’t know what variety of roses are in the garden as yet – there were no tags and I’m a very long way from being able to identify a variety from the shape and leaves at this point.
My usual approach to aphids is to ignore them because hover flies (syrphids?) would be around before too long – but as this is a new garden my usual ‘parsley in flower’ hover fly attraction devices are still in seed form. I hope the hover flies are next door at my neighbor’s garden, and that they’ll zip over the fence, lay their eggs, and launch their young on the aphids. A nice steady supply of ladybirds would be useful, and then there are the tiny parasitic wasps.
It’s probable that the herbivores (aphids) are feeding a good population of carnivores, up to and including sparrows and other insectivorous birds, so my spray gear (bought specifically for fertiliser and insecticides and yet to be discovered after we moved into the house) will remain unused. If I could find it, I’d like to try a safe aphid spray I came across – 1 tablespoon Epsom salts, 1 teaspoon Condy’s crystals (Potassium permanganate) in a bucket (5 litres) of water, applied every two weeks as a test to see how effective it is. Previously I’ve used soapy water, or hosed the aphids off; but mostly I’ve simply ignored them. With all the carnivores with families to raise that seems like a good option.
Michael J. Raupp has written in splendid detail about aphid predators in ‘Murder and mayhem in aphid land – Ladybugs, Coccinellidae; Flower flies, Syrphidae; and parasitic wasps, Chalcidoidea and Brachonidae‘.
From the USA National Wildlife Federation’s Gardener’s Guide to Global Warming (.pdf, 40pp, 1.55mb),
According to one study, a 5.5-degree Fahrenheit increase in temperature could mean the difference between aphids that produce 300,000 offspring versus those that produce more than 1 million offspring over a 2-month period. (M. R. Frazier, R. B. Huey, and D. Berrigan, “Thermodynamics Constrains the Evolution of Insect Population Growth Rates: ‘Warmer is Better,’” American Naturalist, 168 (2006): 512–20.)