Rob Browder, pruning expert, was in my garden last week while I was in someone else's landscape designing. While pruning he called me. After discussing pruning he politely mentioned my boxwoods.
"Have you noticed your boxwoods are full of leafminers?"
Ugh. It was obvious the phone call was more about boxwoods than pruning.
Until he said something about the leafminers I was in denial there was a problem. Of course I saw damage to the leaves but only in a walking-by visual la-ti-da this-isn't-really-happening manner. He put into words what my eyes hid from the brain.
I knew the easiest solutions were toxic chemicals. Galvanized by his input an organic solution had to be found.
Leafminers prefer boxwoods, especially American boxwood. English boxwood get them too with some varieties labeled leafminer resistant. Googling boxwood problems brought up a range of toxic solutions - not an option.
Knowing horticultural oils kill organically I Googled again. Neem oil is derived from a plant. The label lists myriad insects controlled. Leafminers were listed but not leafminer larvae. If a bug or larvae is not listed on a product label; do not expect it to work against those bugs.
A leafminer lays its eggs inside a leaf, typically in April. Those larvae grow for months within the leaves, damaging them, before hatching. Not finding a solution I moved on to other horticultural oils. Dormant oil is the historical choice and its name implies when it should be used: During winter when most plants are dormant. Waiting till winter to use dormant oil against leafminer larvae guarantees unsightly foliage.
The new generation of horticultural oils are much lighter than dormant oil. And they can be used throughout the year. Ultra-Fine horticultural oil is labeled for leafminer larvae. Fabulous, an organic solution. Yes, damage has already occurred to my boxwood foliage but treating it now will prevent further damage.
Days are still sunny and hot. Use precautions against possible leaf scald by spraying in the evening. Be sure to spray the top and bottom of the foliage. Spray only the afflicted plants. You don't want to kill beneficial insects.
I'll spray the foliage again in April to ensure against leafminer problems next year. Pleasingly, there are other attributes for Ultra-Fine oil. It can be used for mites and fungus. Thank you Rob for exquisite pruning and holding me accountable for the boxwood bugs.
Stone Mountain resident Tara Dillard designs, installs and writes about gardens. Her most recent books include "Garden Paths and Stepping Stones" and "Perennials for Georgia." E-mail her at email@example.com or visit www.agardenview.biz.