Saturday turned out to be a nice day weatherwise here. The sun shone brightly and the greenhouse suddenly warmed up, so, looking forward to spring, I decided to get rid of any pests and diseases which may have overwintered in the greenhouse, by burning a sulpher candle.
This is not very organic, but I don’t profess to garden totally chemical free. I just try to use as few chemicals as possible and look for alternatives if possible. I always look carefully before smoking the greenhouse to see if there are any beneficial insects which I do not want to kill. Plants which have been stored in the greenhouse do not seem to suffer from the treatment.
There are a number of pests and diseases which can populate your greenhouse without you being aware of them until they become a problem in spring and summer. Some overwinter in the greenhouse, so it is worth treating the greenhouse to rid yourself of the worst of them before you start a new year. Remember though, this treatment is indiscriminate and will kill beneficial insects as well as harmful ones.
Pests and diseases in the greenhouse can build up rapidly because of the warmth and humidity. It is always best to keep a careful watch for them and try to prevent them building up. Always maintain scrupulous cleanliness and remove any damaged parts of the plant as soon as you spot a problem. Do not compost that plant material – burn it.
There are a number of fungal diseases which affect your greenhouse plants and one of the worse, in my opinion , is damping off. This shows as a blackened area at the base of the stem and in very short order the affected plant will topple over and die. There’s nothing worse than sowing and nurturing a plant only for it to suddenly die. There are a number of things you can do to prevent it (there is no cure). First, sow your seeds more thinly, water less and increase the temperature in the greenhouse. Sometimes, the disease is carried in the soil and if this is the case you will need to sterilize it by heating it to kill it. Watering other plants with copper fungicide will help prevent itspreading.
Red Spider mite are almost invisible to the naked eye and you don’t see them until there are loads of them. They are green as well as red and they cover the plants with webs and cause fine mottling on the leaves. They are only a problem in a dry atmosphere so increase the humidity to safeguard. There is a parasitic mite which will control it, but if you have a small infestation you can spray with derris
Whiteflies are another serious and persistent greenhouse pest. They are small white flies (as the name suggests) which weaken the plants by sucking sap. They are often found on the undersides of leaves. They can be controlled by a parasitic wasp. Alternately hang a grease coated yellow card in the greenhouse. For some reason, many insects are attracted to yellow and they stick to it. If all else fails, spray with derris three times at five day intervals. Do not spray if you have already introduced biological control.