Mountain Laurel

Pale stippling or fine white speckling across the upper leaf surface, worst on the leaves most exposed to sun. Hard shiny black specks and rusty cast skins on the leaf undersides - the confirming sign, and what separates lace bugs from spider mites, which leave fine webbing instead. Small flat insects with lacy transparent wings on the undersides when you turn a leaf over. Whole plants looking bleached, grey-green, and tired by midsummer, with the worst of it on the sunny, dry side. Early leaf drop and thin, weak growth on plants attacked hard several years running.

Treat early, and treat from below. Insecticidal soap or horticultural oil kills lace bugs on contact but only where it lands, so the spray has to reach the leaf undersides; go after the first generation in late spring rather than the bleached plant in August, and repeat after seven to ten days. A strong jet of water on the undersides knocks nymphs off and helps. Foliage that is already stippled will not recover its colour - it stays that way until it drops, so judge success on the new growth, not the old. Anything you spray must be labeled for the plant you are treating. Where a shrub is hit badly every single year, the honest fix is more shade and more water, or a different plant in that spot.

Siting does most of the work. Plants grown in cool part shade with steady moisture and a good mulch carry a fraction of the lace bugs that the same plants carry in hot afternoon sun and dry soil, so move a chronically infested shrub rather than spraying it every year. Keep the root zone mulched and evenly watered right through summer. Avoid broad-spectrum insecticides, which remove the lacewings, predatory bugs, and spiders that hold lace bug numbers down. And turn a few leaves over in late spring, when the first generation is small and easy to deal with, rather than waiting until the plant has gone pale.

Lace bugs are small flat sap-suckers with clear, intricately veined wings that sit on the undersides of leaves and drain them one cell at a time. You almost never notice the insect first - what you see is the leaf going pale and stippled from above, as though the colour had been lifted out of it in fine dots, while the underside carries scattered hard black specks of varnish-like excrement along with the shed skins of the nymphs. Several generations run through a single season, so damage accumulates from late spring onward and a badly attacked plant looks bleached and exhausted by August. Damaged leaves never re-green. Above all this is a pest of plants growing in more sun, heat, and drought than they want: the same shrub in cool part shade with steady moisture often carries almost none.

Phytophthora is the specific culprit here, and it follows heavy or waterlogged soil. Plant in acidic, humusy, well-drained ground, never too deep, and use raised or bermed beds on heavy soil.

Wilting in the middle of the day on a plant whose soil is damp - the classic tell, and the reason people water a rotting plant and finish it off. Leaves yellowing from the bottom up, dull off-color foliage, and growth that stalls for no visible reason. Whole shoots, or one side of the plant, collapsing while the rest still looks fine. Soft, dark, or mushy tissue at the base of the stem or at the crown, sometimes with a sour smell. Lift a failing plant and look at the roots: healthy ones are firm and pale, rotted ones are brown or black and slimy, and the outer layer slips off between your fingers leaving a thread of core behind. Seedlings that topple over at soil level are the same problem, called damping-off.

There is no cure for tissue that has already rotted, so act on the conditions rather than looking for a spray. Stop watering at once and fix the drainage - open up compacted soil, or move the plant to a raised, sharply drained position or a container. Lift a badly affected plant, cut away every soft dark root and rotted section with a clean blade back to firm pale tissue, and replant only the healthy parts into fresh free-draining soil or mix. Often the better move is to give up on the plant and save its offspring instead: cuttings, offsets, or divisions taken from firm healthy growth root readily and give you a clean start. Bin the rotted material rather than composting it, and correct the drainage before you replant, because the rot comes straight back in the same wet spot.

Drainage is the whole defense. Match the plant to the site first - something that wants sharp drainage will not survive heavy clay or a low, water-collecting spot however well you tend it. Where the ground is heavy, plant on a raised bed, berm, or slope, or grow in a container. Set plants at the depth they were already growing, since burying the crown or the root flare is a common cause of rot, and keep mulch pulled back a few inches from the stem base instead of piled against it. Water the soil rather than the calendar: check that the top inch or two is dry before watering again, cut back hard in cool weather and winter dormancy, and never leave a pot standing in a full saucer. Do not plant or dig in soggy ground, and go easy on rich amendments for plants that want it lean. Rotate annual crops, and start with clean healthy plants and fresh mix.

Root rot is not one organism but a group of soil fungi and water molds - Pythium, Phytophthora, Fusarium, Rhizoctonia and others - that sit harmlessly in most soils and only turn destructive when the ground stays saturated. Waterlogged soil drives the air out, the roots suffocate, and the weakened tissue is invaded and goes soft, brown, and stringy. Because the damage is underground you usually see it first as something that looks like drought: wilting, yellowing, stunting, a plant that does not respond to being watered. Overwatering, heavy compacted ground, a low spot that collects runoff, a pot with no drainage or a saucer left standing full, and cold wet soil in winter are the usual causes. Once roots have actually rotted there is no cure - this is a problem you prevent rather than treat.