DAMAGE TO CROPS BY SLUGS

Southland Times, Issue 23437, 18 February 1938, Page 2

DAMAGE TO CROPS BY SLUGS

SERIOUS PEST ON FARMS METHODS FOR ERADICATION Slugs belong to the same, division of the animal kingdom as snails, clams and oysters. They are typically. nocturnal in habit, and by far the greater portion of the damage caused by them is carried on at night, in dark, moist, cloudy weather, states Mr. J. Muggeridge, Government , Entomologist. However, slugs remain active throughout the day, he points out. The food habits of the garden slug are surprisingly variable; it is almost an omnivorous feeder with a preference for a vegetable diet Feeding takes place above, at the surface or below the surface of the soil. Among vegetables, lettuce, cabbage and cauliflower seem particularly favoured by the slug, but it likes radishes and turnips to nearly the same extent. Peas, beans, tomatoes, potatoes and beet are seriously attacked. Among field crops probably peas and beans are more generally injured, though rape, clover, wheat, oats and many other crops suffer. Data concerning life-history studies is meagre. The eggs occur at all seasons of the year, but are more common in the spring and early summer. They are placed under stones, boards, and rubbish, under accumulations of grass and weeds, about fence rows and in other moist, shady places. Where natural protection is not available the slugs burrow out a small shallow pit in the surface of the soil with smooth rounded sides and a surface opening. The eggs are laid in clusters of from two or three to fifty or sixty and more. The period from egg to maturity will vary with the season and abundance of food, but is probably from ninety days to nearly a whole year. No data is available concerning average longevity of the slug, though one writer states that the average span is probably from eighteen months to two years. ■ CONTROL FOR SLUGS Adverse climatic conditions, such as dry, hot weather, drives the. slugs into seclusion and tends to minimize injury. Under conditions where plant foliage is luxuriant, however, slugs may find conditions suitable for their depredations—for example, during summer months it is common to find slugs in leafy cabbages or cauliflowers. Excessive rain drives slugs from their seclusion, and frequently they will drown in small pools of water. During cold weather they are likely to remain dormant, but probably cold does not kill them. Poultry, particularly ducks and geese, .seem especially fond of slugs, and several birds, such as the thrush and blackbird, occasionally feed on them. They are attacked by some species of insects, but comparatively little has been done on this aspect of the problem. Because of the habits of the slug in seeking shelter among debris, in long grass, under boards, and so on, it will be clear that, following a thorough clean-ing-up of all such'places, a considerable reduction of the slug population should result. Remove and bum all trash and rubbish when possible. Autumn ploughing should be adopted where practicable and the ground kept clean from weeds.

The use of quicklime is, of course, an old remedy and quite effective under some conditions. A more recent remedy which has been recommended by some writer consists of dehydrated copper sulphate (bluestone) plus hydrated lime in the proportions of one part of the former to ten parts of the latter. This mixture must be kept in closed cans to avoid dampness.' No experimental work has been conducted in New Zealand to determine the relative value of this compound as compared with other “slugicides,” but it has been found useful in checking an outbreak of slugs found to be infesting field cabbages. The mixture should be applied with a dusting machine at the rate of 301 b to 501 b .an acre. The best time, to apply it is on a warm evening after a drizzling rain or, perhaps better still, in the early morning following moist conditions and at a time approximately when the day is breaking. The effect of the dust on the slugs is to cause profuse salivation, and death within a few minutes.