Scaly bugs in my planter boxes

(Question)

Please help! For the past ten years, I’ve been growing herbs in planter boxes built into my deck. The boxes are metal, about 8 inches deep, and set into a wood frame on the deck. For a decade I’ve grown beautiful herbs every year. Last summer these scaly bugs appeared- about 1/2 cm long, silvery, fast moving. They killed most of the herbs, ate the basil from the base, etc. I replanted – and they ate destroyed the herbs again. This year – I emptied out the planters, put in fresh new soil, and they’ve reappeared in smaller numbers. Perhaps there is rotting wood under my deck, but none that I can see. Please help. What can I do to get rid of these and save my herbs

(Answer)

Dear herb gardener,

Your problem has been causing a wee bit of head-scratching, especially related to the photo evidence you’ve kindly attached. Your un-invited beasts resemble the woodlouse, commonly referred to as the “sow bug”, “potato bug”, or “pill bug” (so-named because they can defensively roll into round pill-like balls). Woodlice are actually crustaceans, like lobsters or crabs, and are in the genus Armadillidium. And the love of their life is nice, damp, woodsy spaces.

But the “silvery” colour you mention is a little bit puzzling, as the woodlouse has a layered, shell-like exoskeleton that varies in colour from dark to light brown. But let’s assume, for now, that you’ve photographed some immature, light-coloured, offspring, perhaps recently hatched from eggs.

Next, you say they “killed most of the herbs, ate the basil from the base, etc.”, and I’m wondering if you mean to say that they ate the roots under the base of the plant stalk?  Or the actual stalk of the basil? Woodlice are not generally considered to be a direct pest on plants: that is, they do not thrive on the juices of plant leaves and stems, as do aphids, or scale. In fact, woodlice and earthworms are generally considered to be entirely beneficial to ornamental and vegetable gardens, as they move about, producing compost and overturning the soil. However, in large numbers, it’s not impossible that they could be feasting on tender roots and seedlings of leafy basil, parsley, savory or tarragon.

And speaking of last year : the summer of 2014 was particularly wet, both in quantity, and overall duration, of rainfall. Gardeners had to be particularly vigilant in keeping outdoor planter saucers, and all variety of plant containers, regularly emptied of accumulated rain water. Your metallic planters may have been holding water after the wood was saturated. Also, your 10-year-old planter wood will be aging, and becoming more porous over the years, and hence more inviting to these creatures. If camps of woodlice became established, it may take a while to eliminate them completely, although from what you say they are diminishing. In the meantime, keep your planters high and dry — and pray for a long, sunny summer !

You may find it helpful to peruse our TMG Guide on controlling pests:

http://www.torontomastergardeners.ca/wp-content/uploads/2012/08/Organic-Pest-Control-Products.pdf