Cucumber mosaic virus

What you see

Mottled yellow-and-green leaves, often puckered and reduced to narrow strap-like blades. Fruit is warty, mottled, misshapen and bitter. Plants are dwarfed and set little.

Conditions

Carried by aphids in seconds - the aphid does not need to settle and feed, it merely probes. Has an enormous host range including many weeds, which act as the reservoir over winter.

Treatment

There is no cure. Remove infected plants promptly so they stop being a source. Everything else is aphid management and weed control around the plot.

Prevention

Control perennial weeds along bed edges. Use reflective mulch and insect mesh over young plants. Encourage ladybirds, hoverflies and lacewings. Grow resistant varieties.

Months: May, June, July, August, September

Plants

Cucumber, Marrow / Courgette, Melon, Tomato, Sweet pepper, Butternut squash, Lettuce

Remedies

Insect mesh and fleece barrier, Encourage predators, Insecticidal soap spray, Yellow sticky traps

The thing people get wrong

Killing the aphids after you see mosaic achieves nothing - transmission takes a few seconds of probing, long before a colony builds. The useful control is upstream: cut the weedy edge of the plot, which is where the virus sits all winter, and keep young plants under mesh for their first month, when infection does the most damage.