Answer: Generally speaking hostas are very healthy plants with very few problems -- with two common exceptions: slugs and deer. While you may have seen red spiders on or near them, spiders are not usually harmful to plants so in all honesty I would suspect the culprit to be slugs instead. Gardeners may not see the slugs because they work at night, and they can really decimate a planting. Slugs can be controlled by hand picking at night as well as by traps and by using commercial baits (be careful with these and follow the directions). Another possible culprit is deer -- in my experience they can devour plants overnight, too. These can be deterred in some instances by repellant sprays (either commercial or homemade and applied and reapplied often) or more reliably by a fence.
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