The greatest stumbling block to successful plant propagation is the loss of cuttings and seedlings from the action of various pests and diseases. In many cases this occurs because the gardener has failed to maintain good hygienic standards.
A system for successful propagation must be based on regular prevention and control of all possible pathogens. It is not just a question of keeping the cuttings or seedlings free of such agencies; it is also necessary to practise good standards of hygiene in the potting and propagation environment, the containers and tools used for propagation, the composts, the propagating material itself and the subsequent husbandry practised.
Always keep a scrupulously clean and tidy work bench in the potting shed. Before leaving plants to propagate in a greenhouse, scrub out all of the nooks and crannies with a solution of disinfectant so all residual infection is eliminated. It is considerably easier to do this job effectively in a modern metal-structured greenhouse than in a traditional
wooden-structured greenhouse, so take extra trouble when cleaning the latter. The best time to do this is in the early winter, when the gardener's other activities in terms of propagation are at their lowest ebb. Once clean, any remaining problems can be controlled by the routine use of various fungicide and pesticide smoke canisters, which will permeate throughout the greenhouse. At this stage, especial attention, by the use of the requisite chemical, should be paid to the control of such agents as red spider mite, whitefly, sciarid flies, mildews and damping-off fungi.
In order to avoid cross-infection in a propagating area, at the earliest opportunity always remove containers and spent compost that are not in use. Spent compost will provide a splendid home for the multiplication of both damping-off fungi and sciarid flies.
Perhaps the chief cause of infection of compost-borne rots is in the use of dirty containers for propagation. It is of paramount importance to ensure that the containers are clean, not only of fungal spores but especially of weed seeds such as chickweed, bittercress and annual meadow grass. Their source of infection usually occurs in the "crusty" layer of soil and chemicals that occurs as a tidemark on pots and seed trays. Hence the containers should be scrubbed and washed with soap solution so that they are completely clean. Clay pots will also need soaking to ensure their cleanliness. It is important to wipe all tools absolutely clean after use to ensure they do not become a potential source of infection.
The compost used for propagation must be sterile. Usually this is achieved by making up the compost from sterile ingredients. Peat, by its nature, is highly acidic and consequently to all intents and purposes is sterile. Sand should already be sterile, as will be the chemical additives. The only component that may require to be sterilized is the loam and this can be done in an oven at 82°C/180°F in a broad, flat container covered with foil so that the steam generated encourages the sterilizing process.
It is important however to remember that while all these components are sterile when fresh, if they are left lying about open to the elements they can no longer be considered to be sterile. All composts and their components should be kept bagged and covered to maintain their reliability. Incidentally, do not attempt to reuse spent compost, even if sterilized, as the chemical balances will be out of proportion.
The plant material itself must also be free of infection—do not use diseased cuttings or grafting scions for propagation. As a precaution against disease, dip leafy cuttings in a dilute solution of fungicide such as Captan or Benlate. After they have been planted, it is a good precaution to water with another dilute solution of fungicide. Similarly, germinating seeds should be sprayed with Captan or a copper fungicide in an attempt to reduce damping-off diseases to a minimum.
As cuttings and seedlings develop, regularly use aerosol sprays or smoke canisters of fungicides and pesticides as a routine precaution against possibleinfections of damping-off diseases and mildews, and infestations of red spider mite, whitefly and sciarid flies.
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