Rhododendron (Garden Hybrid)

Deer are the largest garden problem across much of the country, and where pressure is high they set the limit on what you can grow at all. They browse at night and around dawn and dusk, taking tender shoots, leaves, buds, flowers, and fruit within about five feet of the ground, and they come back night after night to anything they have found and liked. Because they have no upper incisors they tear rather than cut, leaving ragged stem ends - that is how you tell deer damage from a rabbit's clean angled cut. In fall, bucks rub their antlers on young trunks and can strip the bark right around a stem, which kills a young tree outright. Palatability varies enormously between plants and between seasons: a herd short of food in late winter eats things it ignores in June, and no plant is truly deer-proof.

Watch for: Growth cleanly missing overnight, with the plant browsed back to a level line about as high as a deer can comfortably reach. Ragged, torn stem ends rather than the clean angled cut a rabbit leaves - the single most reliable identifier. Buds and flowers gone while the foliage below is untouched, since deer often take the best part first. Hoof prints and droppings in soft ground near the damage. Repeat visits, with fresh damage each morning once a planting has been found. On young trees, shredded and stripped bark and broken low branches in autumn - that is antler rubbing rather than feeding.

Prevent: Fencing is the only thing that reliably works. Eight feet is the standard for excluding deer, or two parallel four-foot fences a few feet apart, which they will not jump because they cannot judge the landing. Short of that, cage individual plants: a sturdy wire cage or trunk guard around every young tree, left on until the trunk is thick and the canopy is above browse height, prevents both browsing and antler rubbing and is the single highest-value thing you can do for a young tree. Repellent sprays do help at moderate pressure, but they wash off and deer habituate, so reapply after rain and rotate between different types through the season. Motion-activated sprinklers, scent deterrents, and noise devices work for a while and then stop. Siting matters too: plants close to the house, in daily traffic, and screened behind other planting get browsed less than the same plant out at the boundary.

Treat: There is no chemical fix, only exclusion and recovery. Get physical protection up immediately after the first damage, because deer return to a known meal, and reinforce or rotate whatever you were relying on before. Most plants regrow from browsing if the crown and roots are intact - feed and water a grazed plant and protect the regrowth while it comes back. What does not recover in the same season is anything whose buds or flowers have been taken, and a young tree whose bark has been rubbed right around the trunk is usually lost. Where deer pressure is genuinely heavy, the honest answer is to fence properly or to grow the plants deer leave alone, rather than to keep replacing losses.

The grayanotoxins do not protect it. Evergreen rhododendrons are prime late-winter browse precisely because they are the only green leaves left, and a herd can strip a mature shrub to bare stems in a night. Protect from autumn onward, not in spring once the flower buds are already gone.

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.

Watch for: 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.

Prevent: 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.

Treat: 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.

Phytophthora is the number-one killer of garden rhododendrons, whose fine surface roots suffocate quickly in saturated ground. Almost every case traces to planting too deep or into unimproved clay: set the root ball an inch or two above grade, build a raised bed of composted pine bark, and never use a low spot.

Not an infection but a nutrient lockout caused by soil chemistry. Iron is abundant in almost every soil, but as pH rises it converts to forms roots cannot take up, so a plant that needs acid ground slowly starves for iron while standing in soil full of it. The symptom is unmistakable: new leaves go pale yellow or cream while the veins stay green, giving a fine green net over a yellow leaf. It shows first and worst on the newest growth, because iron does not move around inside a plant to be recycled. It does not spread between plants, does not respond to fungicides, and does not resolve on its own - left uncorrected the plant grows less each year, leaves get smaller and paler, shoot tips die back, crops fall away, and it eventually dies. Worst near concrete, mortar, paths and limed ground, and in cold, wet, compacted soil.

Watch for: Yellow leaves with a distinct network of green veins, worst on the NEWEST growth at the shoot tips - that vein pattern is what separates it from a nitrogen shortage, which yellows the oldest leaves uniformly. Whole plants going progressively paler over a season rather than suddenly. Brown scorched leaf margins and shoot-tip dieback in advanced cases. Symptoms concentrated on the side of a plant nearest a foundation, wall, path, driveway, or a stretch of limed lawn. One plant affected while a neighbor that does not need acid soil looks perfect.

Prevent: Test the soil pH before you plant, not after, and match the plant to the ground - an acid-loving plant in limy soil will never be truly healthy however it is fed. Where the pH is too high, acidify with elemental sulfur worked in the season BEFORE planting, since sulfur takes months of soil biology to work and cannot be rushed, and retest before you commit plants. On genuinely alkaline ground the honest answer is often a raised bed of acidic mix, or a container, rather than fighting the native soil forever. Keep an acidic organic mulch topped up - pine bark, pine straw, sawdust - and site acid-lovers away from concrete foundations and mortared walls, which leach lime for decades. Never apply lime, wood ash or mushroom compost where the roots reach, use acid-forming fertilizers such as ammonium sulfate, and improve drainage, because cold waterlogged soil hurts uptake even at the right pH.

Treat: Correct the soil, and use iron only to buy time. Chelated iron sprayed on the leaves or drenched into the root zone greens a plant up within a week or two, but it wears off in a season and has to be repeated indefinitely - it fixes nothing. The real fix is lowering pH with elemental sulfur applied to the surface and watered in, retesting each season until you are in range, then holding it there with acidic mulch and acid fertilizer. Expect one to two years; there is no fast route. Note that other shortages look identical - manganese deficiency produces the same yellow-with-green-veins pattern on some plants - so a plant that does not green up from iron should be tested rather than dosed again. Where the pH is high because of nearby concrete or genuinely calcareous subsoil, the plant is in the wrong place, and moving it into a properly built acidic bed or container will succeed where years of amendment will not.

Rhododendrons need a pH around 4.5-6.0 and go chlorotic fast above it, which is why they fail so consistently in alkaline-soil regions and in beds tucked against a concrete foundation. Test before planting; on limy ground a raised bed of composted pine bark beats years of chelated iron.

Leaf scorch is not a disease and there is nothing to spray for it. It is what happens when a leaf loses water faster than the roots can replace it: the tissue farthest from the veins - the margins and the tips - dries out first and turns brown and papery, and the browning works inward while the rest of the leaf stays green. Hot sun, dry soil, drying wind, heat reflected off paving or a wall, a small or damaged root system, and a plant sited somewhere sunnier or drier than it wants are the usual causes, singly or together. It also happens in winter on evergreens, when bright sun and wind pull water out of the leaves while the ground is frozen and the roots cannot resupply. Shade and woodland plants, shallow-rooted plants, and anything recently planted scorch most easily.

Watch for: Browning that starts at the leaf edges and tips and spreads inward, with a fairly sharp line between the crisp brown tissue and the green that is still healthy. Leaves and fronds going dry, papery, and crisp rather than soft, yellow, or spotted - that is what separates this from a fungal problem. Damage worst on the side of the plant facing the sun or the prevailing wind and on the most exposed upper leaves, while the shaded interior stays fine. Symptoms appearing sharply after a heat wave, a dry spell, or a bright windy week in winter. Whole leaves or fronds shed early as the plant cuts its losses.

Prevent: Site the plant where it actually wants to be. This is a placement problem far more often than a watering problem, and a shade plant in hot afternoon sun will scorch every summer however much you water it. Give shade and woodland plants part-to-full shade and shelter from hot afternoon sun and drying wind. Keep the root zone consistently moist and mulch it well with leaf litter or another organic mulch, which holds water and keeps the roots cool - the single most useful routine step. Water deeply and thoroughly during dry spells rather than little and often, so moisture reaches the whole root zone. Pay particular attention through the first year after planting, when the root system is small and cannot keep up with the leaves. On evergreens in cold regions, make sure the plant goes into winter well watered, and keep it out of bright, windy, exposed positions.

Treat: Water deeply, mulch, and improve the shade - that is the whole treatment, because there is nothing here to kill. Leaves that are already scorched will not recover, so trim off badly browned foliage or fronds for appearance if you want to; the crown and roots are usually unharmed and push out fresh growth once conditions improve. On a plant that scorches badly every year the answer is to move it rather than to keep watering harder, because the siting is what is wrong. Some plants respond well to being cut back hard, which brings a clean flush of new foliage. And on plants that naturally die back or brown off late in the season, scorching at the end of a dry summer is normal and needs nothing at all.

On rhododendrons this shows up mostly as WINTER burn: brown crisp leaf margins appearing in February on plants that went into winter with dry roots and stand in open sun and wind. A deep late-autumn soak, a thick mulch, and a burlap screen on the windward side prevent nearly all of it.

Root weevils - black vine weevil and its relatives - do their obvious damage as adults and their serious damage underground. The adults are flightless, dull black or grey, about a quarter to a third of an inch long with a short snout; they feed only at night and hide in mulch and leaf litter by day, so most gardeners see notched leaves for weeks before ever seeing the insect. The larvae are small white legless grubs with tan heads that live in the soil, eat fine roots, and then strip the bark from the root crown itself, which is what actually kills plants. Males barely matter - the females reproduce without them, so one insect can start an infestation. Container plants and newly set shrubs suffer most, because a small root system has nothing to spare.

Watch for: Neat crescent-shaped notches chewed into leaf margins, appearing overnight and building up through summer - unmistakable once you have seen it. Damage with no insect in sight during daylight; go out after dark with a flashlight and you will find the adults feeding. Wilting, dull foliage, or an unexplained slow decline in a plant whose leaves are also notched, which is the combination that points at larvae on the roots. Container plants that loosen in their mix or lift out with almost no fine roots left. Chewed, girdled bark at the root crown just below soil level on a young shrub that has collapsed.

Prevent: Check new plants before you buy, since weevils travel in nursery containers and that is how most gardens acquire them. Keep deep loose mulch and leaf litter pulled back from the base of vulnerable shrubs, because that is where the adults shelter through the day. Keep plants vigorous and steadily watered so root feeding is easier to shrug off. A sticky barrier band around the base of a container, or a smooth-sided pot, stops the flightless adults climbing back up. Encourage ground beetles, birds, and shrews by leaving some rough ground, and avoid broad-spectrum insecticides, which do nothing about the larvae underground and remove the predators that eat the adults.

Treat: The notching itself is cosmetic and needs no treatment on an established plant, and spraying for the adults is largely wasted effort since they feed at night and hide by day. The larvae are the target. Drench beneficial nematodes into moist soil in late summer or early autumn while the grubs are small and the soil is still warm - that is the single most effective home control and it works especially well in containers. Repeat the following year if damage continues. Hand-collect adults after dark from small collections of plants. Repot badly affected container plants into fresh mix, washing the roots and removing every grub you find, and cut your losses on a shrub whose root crown has already been girdled.

The classic rhododendron pest, and the notched leaves are the early warning rather than the injury: black vine weevil larvae girdling the root crown are what kill young and container-grown plants. Nematodes drenched into moist soil in late summer are the practical home control.

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.

Watch for: 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.

Prevent: 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.

Treat: 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.

Rhododendron lace bug is a sun-and-drought diagnosis on this shrub: plants in high shade with steady moisture rarely carry enough to matter, while the same cultivar out in open afternoon sun goes grey by August. Check leaf undersides in late May, before the damage shows.