Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Biocides; animal or insect repellents or attractants
Reexamination Certificate
2001-07-09
2002-09-10
Levy, Neil S. (Department: 1616)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Biocides; animal or insect repellents or attractants
C424S410000, C424S646000, C424S647000, C424S648000, C424S084000, C514S502000
Reexamination Certificate
active
06447794
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to stomach-action molluscicides, stomach poisons or edible baits containing them and their use in killing, controlling and/or inactivating molluses, in particular, slugs and snails.
BACKGROUND TO THE INVENTION
Slugs and snails are major pests of agriculture in many parts of the world. Their biology tends to favour activity in moist conditions such as habitats which are continually wet and temperate regions, especially during rainy summers and autumns. As a consequence, their potential for damage is considerable.
The ecologies of different types of molluscs, which can be either terrestrial or aquatic, are very different and they usually require different types of treatment. The snail species
Theba pisana, Cemuella virgata, Helix aspersa
and Achatina spp and the slug species,
Arion hortensis, Milax budapestensis, Deroceras reticulatum
and
Limax maximus
are of particular interest as targets. The common garden snail,
Helix aspersa
, and the grey field slug,
Deroceras reticulatum
, are common garden pests throughout temperate Australia. These pests have established themselves in many parts of the world, adapting to a wide range of climatic conditions. They rarely increase in numbers above 20 per square meter but cause damage by feeding, with minor damage due to the mucus on which they move.
Helix aspersa
is, in general, a nocturnal feeder and in the daytime remains hidden on the underside of leaves, under rocks or in cracks in the soil. It flourishes in moist conditions. On the other hand, there are a group of snails which have been introduced into Australia in the twentieth century. The areas in which these are pests (often over 200 per square meter) are still expanding. These are the white Italian snail,
Theba pisana
and the vineyard or Mediterranean snail,
Cernuella virgata
, which can survive long hot summer temperatures by aestivating on weeds and fence posts, retreating into their shells and secreting a hard mucous film to reduce moisture loss and rest. These snails are of some concern to Australian farmers because they also aestivate on the heads of cereal stalks in November and December and during harvest, they clog up the machinery and contaminate the grain, making it either unacceptable or forcing it to be downgraded. There are very significant variations of the pest numbers and in a bad year it is uneconomic to harvest substantial areas of crops. In cold climates,
Theba pisana
hibernates in winter. The slug,
Deroceras reticulatum
, is found throughout temperate areas of the world and it is the major slug variety found in both Australia and the United Kingdom.
Significant crop damage by molluscs also occurs in northern Europe, the Middle East, North and Central America, South East Asia, Japan and New Zealand. In many cases, the rise to pest status of the slug or snail in question is a consequence of change—either in distribution (as in the case of accidental or deliberate introductions) or in agricultural practice, where new crops or systems of cultivation may enable populations to rise to pest levels. For example, approximately two-thirds of the molluscicides in the United Kingdom are used on winter wheat and winter barley. After harvesting, there is a significant amount of stubble left behind. It is present agricultural practice to drill seeds of the next crop directly into the soil, without removing the stubble of the previous crop by, for example, burning. Slugs, which have buried themselves in the soil, move along into these drill holes and eat the inside out of the new seed, thereby potentially destroying the whole planting. Slugs are therefore a major agricultural pest.
Devising methods of controlling these pests presents a formidable task. Control methods involve cultivation practices, chemical and biological methods. Cultivation procedures that remove or make the habitat of the mollusc less attractive, are usually less expensive. Biological control by introduction of natural predators is a preferred method because, in principle, the predator could be snail specific and not harm native snails or non-target organisms. However, very extensive testing is required and, once predators have been introduced, it is very difficult to reverse the process and to remove them. Chemical methods (molluscicides) involve the use of a contact or stomach poison, an irritant or a feeding depressant.
The environment which the mollusc inhabits is generally treated with the molluscicide which is then ingested by the mollusc. Since most snails and slugs thrive in moist conditions, any effective molluscicide should be effective under these conditions. This feature of appropriate water resistance has major implications in broad-acre agriculture, where one treatment is preferred rather than multiple applications throughout the crop season. In this case, it is desirable to have a balance between water resistance and efficacy to prevent the pellets functioning as poisons after the crop has been harvested and livestock has moved into the area to feed. In addition, in areas of very high moisture content there should be effective water-proofing to ensure the poison is maintained in an ingestable form for a sufficient time to permit adequate exposure to the molluscs. Since moisture is essential for slug and snail activity, damage is likely to be more severe on heavy soils due to their greater moisture retention. However, damage is not restricted to heavy soils. Slug and snail activity is encouraged by high levels of organic matter which often provides a moist environment. Green manure crops and old crop residues used in the compost heap often allow populations to build up quickly. Dense leafy plants, such as brassica and curcubitis, provide a moist humid canopy under which snails and slugs thrive. Temperature also affects the level of slug and snail activity. Indeed, this activity peaks around 15-20° C. and decreases markedly below 5° C. and above 30° C. Furthermore, low temperatures significantly delay the hatching of slug eggs. Most slug and snail species are nocturnal feeders. Hence, watering of gardens in the evening often provides an environment which encourages increased feeding activity.
Molluscicides for use against slugs and snails can be divided into three groups. These are contact-action molluscicides, such as aluminium and copper sulfate crystals, which are applied to the area inhabited by the snail or slug and are taken up passively when the snail or slug moves in this area; irritant powder molluscicides, such as silica grains, which act by being taken up in the snail's or slug's locomotion mucus; and stomach-action molluscicides such as metaldehyde and methiocarb pellets, which are ingested by the mollusc.
Contact-action molluscicides are generally applied in the form of sprays and dusts to crops and the mollusc receives a fatal dose of toxin by moving over the crop. Molluscs present problems of delivery of the toxin because their relatively large size means that a large dose of toxin is necessary. They are also relatively inmobile and may remain concealed in comparative safety for long periods. These problems are further complicated by the layer of mucus which invests molluscs. Irritant materials stimulate mucous production and can be sloughed off and left behind in a discarded mucous coat. As the mucus is largely composed of water, the water-solubility of candidate contact poisons is therefore a prerequisite if they are to be able to penetrate the mucous barrier. However, hydrophilic properties in a toxin also increase the rate at which it is diluted by rain and leached into the soil.
Delivery of effective amounts of bait is also a problem. A sufficient amount of poison must be ingested to ensure a lethal dose. In general, most toxic compounds are also repellent and the interaction of toxicity with repellency prevents the ingestion of sufficient poison to kill the mollusc. There are three major effects of molluscs ingesting poison baits. Firstly, there is a possible repellency away from the crop by the
Levy Neil S.
Young Colin Leslie
LandOfFree
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