Time To Spray: Before Trouble Begins

Press, Volume CX, Issue 32381, 21 August 1970, Page 8

Time To Spray: Before Trouble Begins

The use of chemicals to combat insect pests or to control disease is unfortunately often unavoidable if it is desired to grow healthy plants. What is not generally appreciated however is that the main purpose behind an application of a fungicide or an insecticide is to provide protection or give control. Once a disease has entered a plant it will have caused some harm, which it may not subsequently be able to overcome even though it has been possible to control the pathogen. Sometimes, of course, there is no available control and an infected plant must be destroyed to avoid further spread. In a similar way the damage caused by a severe infestation of insects may not ever be remedied in some cases such as virus transmission, or it may take a considerable time before the plant has fully recovered. Such debility in short-term plants such as vegetables or annuals, which may only be ' grown for as little as two months, cannot be tolerated 1 and still give the required ■ results.

The primary objective, then, is to spray before the onset of trouble. This may sound as though it is necessary to set up perpetual vigilance and sit in the garden armed with a loaded spray gun. But this is not the case,

for the simple reason that research long ago , revealed that both diseases' and in. sects' have life cycles, dur-»s ing which they have .periods > when they are mose active and damaging to plant than ■ at other times. ] Spring through to midautumn is, the time when there is the greatest danger < from. both. For this reason s spray schedules have been devised for certain crops and plants. Examination of one of these will reveal not. only when to spray but also what to use and what quantity is ] needed for a given dilution. 3 To be effective the correct ( material must be selected for , a particular problem and ' it is rib use expecting an , insecticide such as malathion ( to control a fungus disease , on your roses. In a similar ’ fashion it is often thought that one timely application : of something or other will give immunity for the rest of the season: again a false hope. The effectiveness of most materials available to the home gardener generally lasts for up to two weeks. A very few exceed this period, while some have a residual life of little more than a day or two. Seasonal conditions and growth factors greatly influence the persistence or effectiveness of a chemical. ■ For instance most plants, par- . ticularly annuals, vegetables and deciduous subjects make much growth in a short time over the usually favourable spring to early summer months, a time when there is also a greater risk of disease and/or pest attack. Because of the rapidity of growth a covei' spray applied at the beginning of the week may be considerably weakened by the end of it if it is of systemic nature. In the case of a contact spray there will be many new leaves by the end of this time which will not have had a protective cover. The weather can also restrict the effectiveness of a particular material, particularly if there is heavy rain shortly after the spray has been applied. The points mentioned may provide the answer just why your spraying seemed ineffective at the itime it was done.