Posted: 01/08/2016 at 19:17
Once the webs form on the tips of the plants, a red spider mite infestation has reached serious proportions. The cucumber is finished so get rid of it. Remove any webbing from other plants in your greenhouse and spray everything (especially the undersides of all leaves) with SB Plant Invigorator. This sort of glues the mites (which are resistant to nearly all known pesticides) in place and they die. The SB is also a foliar feed which will help plants recover. Repeat two or three times before introducing the spider mite predator. The above is the only way to clear them which I can personally vouch for.
In future years, keep a close eye on the plants as spider mite will over-winter in your greenhouse cracks and crevices. Regularly spraying the inside of the GH with a fine mist of water will help as they don't proliferate so fast in humid conditions.