The progress of climate change, increased international transport of grown plants, and the desire to use less toxic pesticides, are combining to create an increasingly problematic situation in large-scale forestry, usually of conifers, as well as in public-amenity parkland with mature specimen trees.

It is unlikely that Riddance™, a natural product, will ever be used on a large scale in forestry. It has a short half-life when sprayed onto plants or trees.

It has, however, two advantages compared to many other pesticides: it has no toxicity towards higher animals including, of course, people, and it acts systemically. It can penetrate leaf lamellae and perhaps more importantly, can be taken up from soil via the roots. It has also been injected successfully into the trunks of mature trees in both Europe and North America, where experiments have shown that this method can control pests such as sawfly.

In the south of UK, a recently-appearing novel threat to both tree and people, is the oak processionally moth, whose larvae can strip the foliage from an oak tree, and which produce a mass of hairs which can cause irritation and allergic reactions in anyone who comes in contact with them. Experiments carried out in Germany have shown that the German version of Riddance™, called NeemAzal™, is very effective against this moth. Unfortunately, the extract is not yet registered in the UK.


Azadirachtin is the only alternative to conventional insecticides currently available for managing most sawfly pests and white pine weevil. This bioinsecticide is safe to mammals and birds. It does not pose a significant risk to most other non-target organisms including bees, fish and aquatic insects at effective dosages, and it degrades readily in the environment.

The short residual life of azadirachtin-based insecticides when applied as a foliar application, although attractive from an environmental perspective, can be a significant limitation for forest management. This limitation may be overcome by applying neem formulations that can persist for a year or more, systemically into trees. For example, systemic applications into large pines for pine false webworm control is a promising approach for selective treatments, including seed orchards, small pockets of infestation, and ornamental trees in urban environments.

The cost of neem insecticide formulations is higher than most conventional insecticides, but their low impact to non-target organisms makes them an attractive alternative. This is even more so with systemic applications, which further reduce any impacts to non-targets, or hazards to handlers.

Source: International Pest Control


Pine weevil (H. abietis)

The large pine weevil (Hylobius abietis) is an important pest of coniferous seedlings throughout Northern Europe, including, of course, the pine and spruce forests of the UK. It attacks seedlings in the replanting of harvested woodland, and frequently kills all the trees. Currently control depends on the pyrethroid α-cypermethrin, but this pesticide will be phased out by 2017. Forestry Research is testing alternative plant protection possibilities. One of these is the use of extracts of the kernels of the neem tree, already widely used throughout the world as biological plant protection products.

The weevil eats the bark of newly replanted seedlings, and depending on the extent of the damage, may kill the young trees. Currently control depends on the pyrethroid α-cypermethrin, but this neurotoxic insecticide has already had a stay of execution, but will be phased out if suitable alternatives become available. Neem extracts have been shown to protect against the weevil in field situations, but for limited periods of time. It is hoped that further experimentation with Riddance™ applied systemically will give longer protection.

Topically applied neem extracts can protect seedlings against the weevil.  Extracts have been shown to act systemically, and to be taken up via the roots. The aim is to develop a formulation of a biological pesticide, which is cost effective and acceptable to the Forestry Commission, and which will reduce losses in commercial forestry, a vitally important resource in Scotland.


Current research project

A study is underway to develop baits based on wood products which are intended to contain a natural insecticide such as Spinosad, and which will attract the pine weevils to baited traps, and kill them.


Resistance to Riddance™

Resistance is a significant issue with neuro-toxin based pesticides, such as organophosphates, pyretheroids, and avermectins.
Neem extracts used as commercial biocides and plant protection products for almost 20 years in the USA and EU, and as yet, there have been no reports of signs of resistance in target organisms.

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