An investigation into methods currently employed to control damping-off in seedlings : Presented to the Royal New Zealand Institute of Horticulture in fulfilment of the requirements for the National Diploma in Horticulture (Nursery Management)

Abstract

Damping-off diseases of seedlings are a problem of considerable magnitude in nurseries throughout the world. Often losses can be one hundred per cent and the consequent economic losses are considerable. Even the most successful of nurserymen are not spared the scourges of these diseases. In nurseries where I have worked, and seen damping-off epidemics, I have wondered at the losses suffered at the hands of the diseases and very often I have felt that the losses could have been avoided or reduced. Sometimes, the causes, or at least the contributing factors were obvious. At other times the causes, when investigated, appeared to be more subtle or were uncertain. An observation of these factors has enthused me to investigate this major nursery problem in order to evaluate common cultural methods employed in New Zealand nurseries and to attempt to formulate a standard procedure, which, if followed, could eliminate or reduce the incidence of the damping-off diseases. At first it is very obvious that there are many contributing factors and conditions. It is obvious too, there are many areas where infection or reinfection of the growing medium, or of the plant material, can occur. This becomes clear when we follow the complete process of the nursery production from procuring the constituents of the growing medium to the establishment of a pricked out seedling. From my own observations and from reading various texts relating to investigations into this subject,( there appears to be a stage that seedlings reach when they become immune to the causal organisms of damping-off diseases.) The aetiology of these diseases then, should include investigations into every aspect of seedling production up to this stage of seedling growth. Any material, working surface, or tool that comes directly or indirectly into contact with the growing medium of the plant material, must be suspect. Once we grasp the scope of this statement we begin, I believe, to come to grips with these insidious diseases. To investigate this problem fully, the possible sources of infection, as mentioned above, must be investigated along with optimum conditions for infection of the host and development of the innoculum potential of causal fungi. These two often go hand in hand. The ecology of the soil microflora is significant in its effect on the innoculum potential. This will be discussed further, later in the thesis.