A new growing season is barely under way and I’ve already had to deal with a plant pest that, if not deadly, is arguably the most prevalent – greenfly.
It first appeared on scented geraniums in January, part of a collection that enjoy the modest warmth of a conservatory. February revealed the beginnings of a colony on strawberry plants, brought into the cold greenhouse from the garden and potted-up for early fruiting.
But this is just the beginning. The green menace will appear on the roses, shrubs, certain herbaceous perennials and annuals as the season unfolds.
Black aphids will try to occupy the tips of our broad beans and, given half a chance, the grey type will invade the cabbages.
Should you see a substance that looks like a small bundle of sheep wool high on an apple tree, it has not been carried on the breeze, but produced by the woolly-aphid, which it protects.
Aphids, along with other sap-sucking and leaf-nibbling pests, represent a negative aspect of plant growing that can be largely avoided through good cultivation and vigilance.
The invasion starts with a small group in the soft growth at the apex of a plant, on the stem and underside of leaves.
As their size increases, they cast their skins, which appear as white specs on lower leaves. These become sticky to touch, a result of the honeydew they excrete. Left untreated, this attracts a dark, sooty mould.
In summer, winged females take to the air, travelling between plants and producing living young. They carry and transmit disease as they go.
Traditionally, greenfly have been controlled by spraying the affected plant with an insecticide, which zapped them on contact. The alternative chemical solution was a systemic type, which entered the sap stream on which aphids fed. The contact type is widely available, but this fellow much prefers playing safe and giving them a regular shower with a soft soap solution.
It’s so disappointing to find your carrots riddled with larvae, more so if they’re grown for show. Therefore, don’t sow the seed thickly in a drill and avoid thinning-out of seedlings, which attracts the carrot fly. Covering them with Enviromesh from sowing to harvesting will also prevent fly damage.
There’s a mistaken belief that this pest is a low flyer and that a surrounding screen 60cm high will prevent access to the crop. However, friend Jim, who grows them in tall, 45-gallon drums, expected the pests to crash into the drums, but they flew high and ruined some of the carrots.