Mites on cucumbers

Dear Julian

Having returned from holiday to find our (new this year) greenhouse a disaster zone, we desperately need some help. Should add, we are complete novices to Greenhouse gardening.

When we left for holiday we knew there was a problem, the bottom cucumber leaves had taken on a mottled look and there were signs of what appeared to be webs being formed near the heel of the leaves. 

Whilst we had numerous cucumbers from the plants prior to the holiday it would appear that whatever it is that has attacked the plants has gained total control and although we obviously need to get rid of all of the plants we would desperately like to destroy the problem first.

From a visual point of view there appears to be several very small (light brown) mites moving around in the webs (see image attached). Could you recommend a course of action?

Kind regards


Dear Dennis

This sounds like spider mite. They create webs on the plant and very quickly take over in warm conditions. They reproduce very fast in greenhouses. If you have webbing, it is a bit late for predators as the numbers of spider mite will be too high. If left the spider mites will turn the plants completely yellow and kill them. If the plants are completely covered in webbing, you might be better to remove the plants. If there is only some, then I suggest you purchase some Savona Fatty Acid concentrate from Harrod. This kills the mites on contact but it is important to spray under and over the leaves to get good coverage and spray every 7 days until the problem is solved. Also make sure old plants are removed before October. This will help reduce the spider mite overwintering. They do tend to leave the plants in the autumn and overwinter in the structure of the greenhouse, so it is good to get rid of them before this. Hope this helps.