Post category: Spraying
Is it necessary to spray?
The aim of spraying is to water as a carrier to apply a chemical substance accurately and safely. The chemical might be a weed-killer, insecticide, fungicide, or foliar feed. Some of these can be harmful to plants, animals and the environment, and the user, when not properly used.
Chemical sprays should only be used when necessary, and there are very few situations in the garden where a routine spray is justified.
In terms of disease control, blackspot of roses, pear and apple scab and potato blight are four diseases that can be depended upon to appear under Irish conditions, and that need to be routinely sprayed against. If resistant varieties are grown, even this limited use of sprays may no be necessary.
As regards pests, much depends on the particular pest involved, the amount of damage it may cause, and the numbers of the pest present. Greenflies, slugs and caterpillars can cause problems on fruit and vegetable crops and may need to be controlled. Codling moth can be troublesome on apple trees. Red spider mite and whitefly can be a problem in the greenhouse.
Special caution should be exercised when using insecticides because many of them are poisons. Ways of dealing with a problem, other than spraying, should be considered first. These include cultural practices, barrier methods, growing resistant varieties and growing some else entirely. The section on Pests and Diseases has more on this.
As regards weeds, there is no weed problem that cannot be controlled by non-chemical means, but weedkillers can be very convenient and effective. If they are used properly, the weedkillers available to home gardeners pose relatively little risk to the user, to plants, or to the environment.
If you decide to use a spray, make sure to apply it correctly according to the packet instructions.
First, make sure that the chemical is capable of doing the job required. Next, ensure that both the crop and the pest, disease or weed are at the right stage for it to work. Too early, or too late, can be a waste of time.
Make sure the weather conditions are right. Do not spray on windy days, because the chemical can get on to the wrong plants. Do not spray on hot, sunny days, for fear of scorching the plant foliage. Do not spray while foliage is wet, or when rain threatens, unless the chemical is rain-fast.
The cool, calm conditions of evening are often a good time for spraying. Mix the correct amount of material in the appropriate quantity of water, and make sure it is thoroughly dissolved. Do not use extra spray chemical “for good measure”. Not only is this wasteful and potentially dangerous, but might even give a poorer result than the correct amount.
Apply sprays under fairly high pressure, and thoroughly wet all foliage, top and undersides of leaves, and the centre of the plant. Apply enough liquid to give ‘run-off’, when the first drops drip from the leaves. A single correct application will be more effective than repeated bad spraying, causing less damage to the environment.
General safety precautions include the following: reading the label on the bottle or packet and any other supplied leaflets; keeping the chemical, in its original pack along with the instructions, in a safe place; staying out of the spray mist and wearing rubber gloves and protective gear, if advised in the literature.
Caution when using chemicals
Chemicals may not be poisonous, but they can cause severe skin irritations and allergic reactions. In some cases, these are caused by solvents and adjuvants in the spray product, not be the active ingredient itself. Dispose of empty bottles and packets by placing them in the rubbish bin – do not burn them or wash them out.
Rinse the sprayer, at least twice, immediately after spraying, using washing up liquid ideally, and pour the rinse water onto soil in a little-used corner – not down the drain.