Pesticides, specifically those used to kill plant pests such as insects and mites, is the group of garden chemicals experiencing the greatest overhaul and change, with more products containing natural or ‘organic’ active ingredients being made available.
Synthetic systemic pesticides
These broad-spectrum, nonnatural substances kill by being absorbed into plant tissues and ingested by the organism.
One of the most controversial in recent years has been the race of broad-spectrum systemic chemicals called neonicotinoids, or ‘neonics’, due to their devastating effects on the health of bees and bee populations, through their paralysing effect on insect central nervous systems. Supported by a sizeable body of scientific analysis, the effects were found to be detrimental to bee and pollinator health, even at low concentrations, through continual ingestion of contaminated plant substances, such as nectar and pollen.
As a consequence, use of neonic chemicals was severely restricted in 2013, mainly affecting agriculture and commercial horticulture, but products containing imidacloprid, primarily to control vine weevil, were withdrawn to gardeners.
In April this year the withdrawal was made permanent, with many of the Provado range of products from Bayer (SBM Life Science) containing the neonic thiacloprid for controlling insects and vine weevil larvae now withdrawn.
Only acetamiprid, which is considered to have lower bee toxicity, now remains, used in products such as Scotts Bug Clear Ultra for sprays, and Bug Clear Ultra Vine Weevil Killer as a compost drench.
Synthetic contact pesticides
These non-natural, broadspectrum substances kill on contact with the insect and are largely derived from chemically altering naturally occurring substances, such as pyrethroids, from the flower pyrethrum.
They have low toxicity to animals, but some can remain active for many weeks, while others break down after a few days. Some can be used on food plants.
● Deltamethrin can be used on ornamentals and a wide range of food crops, and is found in Baby Bio Houseplant Bug Killer, Provado Ultimate Fruit and Vegetable Bug Killer and Sprayday Greenfly Killer, both from SBM Life Science. Westland Horticulture’s Resolva Bug Killer, containing lambdacyhalothrin, can also be used on ornamentals and edibles, as can Py Bug Killer from Vitax, containing cypermethrin.
Organic or natural insecticides
The active ingredients in these products are derived from plant products or other naturally occurring substances. They’re generally safe to use on edible crops, as well as ornamentals, (but check label for timings). They’re not persistent, so multiple applications may be required.
While generally not harmful to mammals and birds, they can harm aquatic organisms, such as fish and amphibians.
Pyrethins, derived from the plant Tanacetum cinerariifolium, will kill a wide range of insects and some beetle pests and are found in Defenders Bug Killer and Bug Clear Gun for Fruit and Veg.
● Products based on plant oils, largely produced from rape and sunflower seed, act by blocking the breathing tubes (spiracles) of insects. Formulations include Origins Bug Control and Bug Clear Fruit and Veg, while Vitax Organic 2 in 1 Pest & Disease Control also contains fish oil, and can treat powdery mildew and black spot on roses.
● Solutions containing fatty acids or insecticidal soaps will help control a wide range of sucking insects, especially aphids, whitefly and red spider mite. Products include Solabiol Bug Free and Doff Greenfly & Blackfly Bug Killer. Seaweed extract is contained in Agralan Whitefly Killer for use in greenhouses.
There are many types of products available to gardeners to control slugs and snails, including biological control using eelworms, and physical barriers and traps. The two main chemical controls are based on ferric phosphate, which is approved by organic growers, and metaldehyde, which isn’t, and usually comes in the form of pelleted bluecoloured bait. Preparations containing ferric phosphate include Growing Success Slug Killer and Neudorff Sluggo Slug & Snail Killer. Those containing metaldehyde include Ultimate Slug & Snail Killer and Eraza Slug and Snail Killer.
Plant oil-based pesticides such as Bug Clear Ultra can be used on fruit and veg
Before using chemicals in the garden, such as slug pellets, find out what effects they have on the environment first
Left, Nemaslug contains eelworms. Right, try a natural insecticide on aphids