Dealing with pesky lilac leaf miner

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Q. This year the foliage on my lilac shrubs developed tan coloured blotches. What caused this and how should I manage the problem?

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A. Lilac leaf miner is the likely cause of the blotches, which are created by tiny caterpillars burrowing into leaves and feeding between the tissue layers.

Small moths lay eggs on the leaves in spring. The eggs hatch into the damaging larvae. A second generation of adults emerges in summer to produce larvae that feed until autumn.

Pick off infested leaves as soon as they are noticed in spring and summer, while the larvae remain within their leafy tunnels (the “mines”). Do not compost them. Freeze them, or bury them deeply. Rake and similarly destroy all fallen leaves during the summer and in the fall.

Q. After enjoying a fine crop of broad beans, I pulled up the plants to make room for a follow-up planting in the same space. As I removed the plants, I noticed tiny white bumps dotting the roots. What are they, and is this a problem?

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A. Small white nodules on the roots of peas and beans are formed by soil bacteria called rhizobia, known as “nitrogen-fixing” bacteria. They work in a symbiotic relationship with pea and bean plants, finding a home and nourishment in the roots. In return, the bacteria absorb nitrogen and pass it along to benefit the plants.

This is a relationship that benefits pea and bean plants, and the soil. Dug into the soil, or composted, the rhizobia-laden roots help to fertilize the soil by enriching it with nitrogen, a major nutrient for plants.

This beneficial relationship is a feature of legumes, a plant family that includes peas and beans, chickpeas, favas (broad beans) and lentils. In dried form they are called pulses.

As Salt Spring Seed’s Dan Jason says in The Power of Pulses, these plants have the ability to “increase the fertility of soil by simply growing in it. They are the epitome of renewable energy.”

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