Plant Stress Encourages Slug Problems
While both slugs and snails are attracted to well-mulched areas with moist, acidic soil, close observation suggests that they actually most attracted to plants in those areas that are suffering stress for some reason. In most parts of the country, plants that are very healthy and live where there is a balanced population of slug predators are less vulnerable to slugs and snails. So treat the immediate snail or slug problem, then try to figure out what might be stressing affected plants and correct that problem.
Some causes of plant stress include:
Too much or too little light or moisture
Inappropriate plant for the local climate or site conditions
Excessive use of nitrogen-rich fertilizer, which encourages too much leafy plant growth--perfect slug and snail food!
Drastic pruning of trees or shrubs, which encourages growth of succulent suckers (side shoots)
Use of pesticides against other pests which also kills off the slug or snail’s natural predators and parasites.
Shock resulting from transplanting, which makes plants vulnerable to pests for a few days to a week
Other Conditions That Foster Slugs And Snails
Nitrogen deficiency. Slugs prefer to eat soft, slightly rotting plant debris. When plants are deficient in nitrogen, their lower leaves turn yellow and gradually decay. This happens most often in poor soils that have not been fertilized. Nitrogen-deficient plants have a hard time making the enzymes that slugs taste bad to slugs. Plants in a good soil that get a light dose of a slow-acting granular fertilizer each season are more likely to withstand attacks by slugs and snails.
Pesticide Overuse. Slugs and snails normally are controlled by various kinds of birds and beneficial insects such as ground beetles, ants and daddy-long-legs (harvestmen) living in healthy home landscapes that host a diversity of plants and wildlife. However, where there has been frequent use of broad-spectrum insecticides which kill indiscriminately, nature’s first line of defense--the beneficial insects--is eliminated along with the pests. Because pest populations rebound faster than those of their natural enemies, the slugs and snails can reestablish themselves unmolested.