Hawthorn

A fast, destructive bacterial disease (Erwinia amylovora) of the rose family. It enters through open blossoms and soft shoot tips in warm, humid weather, then runs back down the shoot, blackening leaves and wood as though scorched and bending the tip into a telltale 'shepherd's crook'. From there it moves into limbs as dark sunken cankers, and it can kill a young tree in a single season. Apple, pear, quince, loquat, hawthorn, serviceberry and toyon are all hosts, and susceptibility varies enormously between species and between varieties.

Watch for: Sudden wilting and blackening of blossoms and shoot tips that look burned rather than diseased, shoots bent over into a hook, dark sunken cankers on limbs, and amber bacterial ooze on the bark in warm humid weather.

Prevent: Where a resistant option exists for your crop, variety choice matters more than any spray - check before you buy. Avoid heavy nitrogen and hard pruning, both of which force the soft succulent growth the bacteria enter through, and never prune or work the plant in wet weather. Keep susceptible hosts spaced apart rather than planted hard against each other, and do not prune two of them in the same wet spell.

Treat: Cut strikes out at least 8 to 12 inches below the visible damage, sterilizing the saw or pruners between every single cut, and remove and destroy the prunings rather than leaving them lying. Cut cankers out in dry dormant weather. Copper or biological sprays at bloom help in high-pressure areas - use only a product labeled for the crop you are treating, follow the label exactly, and observe the pre-harvest interval before you pick.

Crataegus is one of the most susceptible genera there is, and a hawthorn hedge is often the reservoir that reinfects nearby apples and pears each spring. Blossom is the usual entry point, so a May-flowering hedge in warm humid weather is at real risk. Trim only in dry weather, sterilize between cuts, and keep nitrogen at zero. On a long hedge you cannot cut 12 inches below every strike - take out what you can reach and accept some loss rather than shearing hard into infected wood in the wet.

A fungal leaf-spot disease of woody rose-family plants, caused by Diplocarpon mespili (the fungus long known in its asexual stage as Entomosporium maculatum). The same pathogen causes the leaf spot that disfigures photinia, and it also attacks pear, quince, loquat, serviceberry and related hosts. Infection needs extended leaf wetness, so it flares in a wet spring and in dense, poorly ventilated plantings, and it works upward from the lowest leaves. It rarely kills an established plant, but repeated summers of early defoliation weaken it and leave a hedge looking bare and brown from midsummer onward. The fungus overwinters in fallen infected leaves and in lesions on twigs, so a planting that drops its own leaf litter around its base reinfects itself every year. Susceptibility varies enormously between species and between cultivars, and variety choice is the single most effective control.

Watch for: Small round spots on the leaves, at first reddish-purple to brown and often with a darker margin or a pale centre, appearing first on the oldest and lowest foliage. As spots multiply they run together into large dead blotches and the leaf yellows and drops. Look for a tiny dark pinhead-sized fruiting body in the centre of an older spot. Heavy leaf fall from midsummer, working up from the bottom of the plant, so that a hedge is bare below and thin above by August. Small dark lesions on green twigs in a bad year. Damage that is markedly worse on the shaded, crowded, slow-drying side of a planting, and worse in a wet spring than a dry one.

Prevent: Choose a resistant species or cultivar before anything else - susceptibility differences are dramatic, and no amount of care rescues a variety that is genuinely prone. Get air moving: space plants properly, thin crowded interior growth, and avoid planting hard against a wall or fence where foliage stays wet. Water at the base rather than overhead, and never in the evening. Rake up and remove fallen leaves in late summer and again in autumn, since the fungus overwinters in that litter and a plant that sits in its own leaf fall reinfects itself every spring. Avoid heavy nitrogen, which produces flushes of the soft new foliage the spores infect most easily.

Treat: There is no cure for a spotted leaf, so treatment means reducing next year's inoculum and helping the plant carry the load. Rake and destroy fallen leaves rather than composting them, and prune out badly affected interior growth in dry weather to open the plant up. Keep an affected plant watered in drought and unstressed otherwise, since defoliation plus drought is what actually causes decline. Where a specimen is valuable and the disease is severe year after year, protectant fungicide programmes exist but must begin at bud break and be repeated through the wet spring, which is rarely practical on a hedge - use only a product labelled for the plant, and follow the label. Replacing a chronically diseased susceptible variety is usually the better answer.

The most common cosmetic complaint about ornamental hawthorns and the reason a hedge can look half-dead by August in a wet summer. Raking the leaf litter out from under the plant is the highest-value thing a home gardener can do. Variety choice matters enormously: 'Paul's Scarlet' is notoriously bad, 'Crimson Cloud' and green hawthorn 'Winter King' are markedly better, and plain seedling hedging hawthorn sits in between and generally shrugs it off.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Watch for: Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Prevent: Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Treat: Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

Hawthorn is the winter host for several aphids that spend summer on crops - rosy apple aphid among them - so a hedge next to an orchard is a launching pad each spring. On the hawthorn itself the damage is cosmetic curling of shoot tips. The reason to knock them back is fire blight: aphid feeding wounds and the soft growth they favour are exactly where the bacteria get in. Keep nitrogen at nothing and leave the ladybirds and hoverflies to it.

Japanese beetles are metallic green-and-copper beetles about half an inch long that emerge in early summer and feed for six to eight weeks. They feed in aggregating masses - one beetle's feeding releases a scent that draws in more - so a plant goes from untouched to covered in a couple of days. They chew the soft tissue between the leaf veins and leave the veins standing, so the leaf ends up as a brown lace skeleton, and they shred open flowers and sometimes ripening fruit as well. They work the sunniest upper parts of a plant on warm afternoons. The white C-shaped grubs spend the rest of the year in turf and pasture soil eating grass roots, and the adults then fly in from wherever they hatched, which can be some distance away.

Watch for: Clusters of shiny metallic beetles massed together on the upper, sunniest foliage and down inside open blooms, heaviest on warm sunny afternoons from around late June. Leaves reduced to lace, with the veins left intact and the tissue between them gone - unmistakable, and quite different from the ragged chewing of a caterpillar. Ragged, chewed petals and blooms that never open properly. Beetles that let go and drop straight to the ground when you disturb the plant. Feeding damage on ripening fruit, on the plants they also take fruit from. Whole branches going brown and lacy at the top of a plant while the shaded lower growth stays untouched.

Prevent: Hand-picking is genuinely the main defense in a home garden. Go out in the cool of the morning while the beetles are sluggish, hold a tub of soapy water underneath, and knock them in - they drop when disturbed, so most fall straight into it. Do it daily through the flight: because the beetles call each other in, taking them off early stops a plant becoming a beacon. Do not put pheromone or lure traps anywhere near the garden - they demonstrably pull in far more beetles than they catch. And do not count on lawn grub control: milky spore has performed poorly and inconsistently in field trials across most of the US, and treating your own turf does not reduce the adults feeding on your plants, because they fly in from surrounding properties. Where it is practical, row cover or netting through the peak flight excludes them outright. Otherwise riding out the six-to-eight-week wave is a legitimate strategy, since most established plants absorb the damage.

Treat: Persistent morning hand-picking into soapy water is the most effective home control there is, and on a vigorous established plant the damage is usually cosmetic and needs nothing else. Neem deters feeding rather than killing, and has to be reapplied. For heavy pressure, spinosad or a targeted insecticide labeled for the plant will work - but time any spray away from bloom and apply it at dusk to protect bees, and observe the pre-harvest interval on anything you eat. On flowering plants, some gardeners simply shear the blooms off for a couple of weeks and let the plant rebloom once the wave has passed, which removes the lure as well as the damage. Young plants and young trees are the ones worth defending: a mature tree or an established vine tolerates several weeks of leaf loss without lasting harm.

Crataegus sits high on the Japanese beetle preference list, and where the beetle is established a hedge can be lace-curtained across the top in a fortnight in July. A mature plant tolerates it and releafs; a young one takes a real setback. Hand-pick into soapy water in the cool of the morning, and do not hang a pheromone trap anywhere near the plant - it draws in far more beetles than it catches.

Birds find ripening fruit and seed before you do. Robins, waxwings, starlings, catbirds, jays, sparrows, finches, blackbirds, and doves all work a garden, and the pressure arrives in a narrow window - the last days before harvest, when sugar rises, color changes, and the crop softens or the grain hardens. A flock can strip a small planting in a day or two, and birds that only peck rather than take whole fruit still leave wounds that rot or draw wasps. Squirrels, chipmunks, and other wildlife usually turn up on the same crop at the same time. This is competition rather than disease: the birds are not harming the plant, and a big tree or a heavy-cropping bush often has enough for everyone - but on a small planting it can be the difference between a harvest and none.

Watch for: Fruit disappearing from the outermost, most exposed parts of the plant first, and from the top of a tree where you cannot reach anyway. Single neat pecks and gouges in ripening fruit, with several fruits sampled rather than one eaten through - the classic sign that it was birds rather than an animal. Heads of grain or seed going visibly lighter and emptier as they ripen, with hulls and chaff scattered underneath. Freshly sown seed vanishing off the surface of a bed before it germinates. Bird traffic in and out of the plant picking up as the crop colors, and birds waiting on nearby wires and branches. Wasps arriving at the pecked and split fruit shortly afterward.

Prevent: Net, and net early. Bird netting draped over a frame or hoops so it stands off the fruit, with the edges closed at ground level, is the only thing that reliably works at harvest scale - and it has to go on before the crop starts to color, because once birds have found the food they are far harder to displace. Keep fruit trees small enough that netting them is actually feasible; that decision gets made years earlier, at planting. Bags of mesh, organza, or paper slipped over individual heads, clusters, or prize fruit protect a small crop without netting the whole plant. Then shorten the exposure: pick promptly and completely rather than leaving ripe fruit hanging as a lure, clear split and dropped fruit that draws birds and wasps alike, and where a crop can finish off the plant, harvest a little early and ripen or dry it under cover. Rake in or cover broadcast seed so it is not lying in plain view.

Treat: There is no treatment once a crop is being taken - only protection and timing, so the answer is to get netting on and to pick what is ready. Reflective tape, flash ribbon, spinners, and decoy predators do work, but only for a few days at a time: birds habituate fast, so move and rotate them and never rely on them as the main defense for a crop you care about. Cut and gather grain or seed heads a little early, at firm dough, and finish drying them under cover instead of leaving them standing for the flocks. Plant a little extra, or a decoy crop the birds prefer, and accept sharing anything that crops heavily. On a wild or foraged patch, fruit going to birds and small mammals is the point of the plant rather than a problem to solve.

Thrushes, robins and waxwings can strip a loaded hawthorn in under a week, so pick for jelly as soon as the haws colour rather than waiting. This is not really a pest problem - feeding birds is half the point of the tree - but it is the invasion mechanism: the seed passes through the gut intact and germinates far from the parent, which is exactly how C. monogyna escapes into woodland and pasture in the Pacific Northwest.

Cedar-apple rust (Gymnosporangium juniperi-virginianae) cannot complete its life cycle on one host. It needs a juniper - almost always eastern red cedar - and a rose-family host, and it alternates between them every year. On the juniper it forms hard brown galls up to golf-ball size on the twigs; after warm spring rain each gall pushes out bright orange gelatinous horns that release spores. Those spores blow to apples, crabapples and their relatives, where they cause bright orange-yellow leaf spots and, in a bad year, early defoliation and blemished fruit. Spores from the rose-family host then blow back to junipers in late summer to start new galls. Two close relatives work the same way: cedar-hawthorn rust on hawthorn, serviceberry and pear, and cedar-quince rust, which attacks fruit and twigs rather than leaves. None of them spread juniper to juniper or apple to apple - they must have both hosts, which is what makes distance the control.

Watch for: On the juniper: hard, brown, dimpled galls the size of a marble up to a golf ball hanging on the twigs through winter, then swelling in spring rain and erupting into bright orange gelatinous horns like a sea anemone - unmistakable, and the signal that spores are being released right now. On the apple, crabapple, hawthorn or serviceberry nearby: bright yellow-orange spots on the upper leaf surface from late spring, later developing tiny black dots and then fringed tube-like growths on the underside, with heavily spotted leaves yellowing and dropping by midsummer. Blemished, spotted fruit after a wet spring.

Prevent: Distance first, resistant varieties second. The fungus must have both hosts, and infection falls off sharply with separation - a few hundred feet helps and a half mile is close to a cure - so when siting a new tree, put junipers and rose-family fruit as far apart as the property allows. In most of the eastern United States red cedars are so common that removing yours will not clear the air, so anyone wanting apples in rust country should choose resistant varieties rather than counting on removal. Where you own the junipers and the orchard matters more, take them out. Keep canopies open so leaves dry quickly, since infection needs extended spring wetness.

Treat: On the juniper side, cut the woody galls out in late winter, before warm rain makes them push out spore horns - an hour with loppers measurably lowers local pressure. The galls do little harm to the juniper itself, so this is done for the neighborhood's apples rather than for the cedar. On the rose-family host there is no cure for an infected leaf: rake and destroy fallen spotted leaves, and where the disease is severe, protectant fungicide programs timed from pink bud through several weeks after petal fall are used, but they must start before infection and be repeated. On a home tree the honest answer is usually a resistant variety and tolerance rather than a spray schedule.

The hawthorn form of this rust group is properly cedar-hawthorn rust (Gymnosporangium globosum), and the management is identical: it must alternate with juniper or eastern red cedar, so distance from cedars is the whole control. Bright orange leaf spots from late spring, sometimes with small tubes on the underside. Usually cosmetic on an established plant but it can defoliate a young hedge by August. No spray is worth running on a hedge.

Cedar-quince rust (Gymnosporangium clavipes) is one of the Gymnosporangium rusts that alternate between a juniper host and a rose-family host, and it is the most damaging of them because of WHERE it attacks. Where cedar-apple rust mainly spots leaves, cedar-quince rust goes for the fruit, and on hawthorn, quince, and mayhaw it swells, distorts, and hollows out developing fruit, covering it in tufted orange-fungal growth and rendering the crop unusable. It also attacks twigs and thorns, causing swollen cankers that can girdle small wood. The fungus overwinters as a perennial gall or swelling on juniper and eastern red cedar; in wet spring weather those galls produce gelatinous orange horns that release spores, which blow to the rose-family host. It cannot spread host to host - it must have both. Distance from junipers is therefore the whole control, and a few hundred yards makes a large difference.

Watch for: Developing fruit that swells lopsidedly, distorts, and grows tufts or fine tubes of orange fungal tissue - unmistakable once seen and quite different from the flat orange leaf spots of cedar-apple rust. Swollen, cankered areas on young twigs and on thorns, sometimes girdling and killing the shoot beyond. Bright orange gelatinous horns emerging from woody galls on nearby junipers and red cedars during warm wet spells in spring - that is the spore source, and finding it tells you where the problem lives. Fruit dropping early in numbers, or coming off the tarp misshapen and hollow.

Prevent: Site the tree away from junipers and eastern red cedar. That single decision does more than everything else combined, because the fungus cannot complete its life cycle without both hosts, and spore travel drops off sharply with distance - a few hundred yards is a meaningful buffer even though spores can carry further. Where you own the junipers, removing them is the definitive fix; where a neighbor's cedar line is the source, distance and variety choice are what you have. Keep the canopy open so it dries quickly after spring rain, since infection needs extended wetness. Clean up and destroy infected fruit and prunings rather than leaving them under the tree.

Treat: There is no cure for an infected fruit or a cankered twig - remove and destroy them. On the juniper side, cutting out the woody galls in late winter before they produce spore horns reduces local pressure. Where the disease is severe and the cedars cannot be removed, protectant fungicide programs timed to bloom and early fruit development are used commercially, but they must start before infection and be repeated through the wet spring window; on a home tree the honest answer is usually siting and tolerance rather than a spray schedule.

The rust that matters if you want the haws. Unlike the leaf rusts, G. clavipes goes for the fruit and the twigs, swelling and distorting the haws into something inedible and cankering young thorny wood. Same juniper alternate host and the same fix: siting, not spraying. Pick off and destroy distorted fruit rather than leaving it under the plant.

Scale insects are sap-suckers that spend most of their lives immobile, fixed to a stem, twig, or leaf underside beneath a waxy or shell-like cover. They look far more like bumps, blisters, or crusty encrustations than like insects, which is why an infestation is usually well established before anyone notices it. Soft scales excrete large amounts of sticky honeydew that drips onto everything below and grows a black sooty mold - and those blackened leaves are often the first thing a gardener actually sees. Armored scales produce no honeydew but sit under a hard shield that protects them from most sprays. They spread as tiny mobile crawlers in the weeks after hatching, which is the only stage that moves and the only stage that is easy to kill. Populations build on stressed plants, on crowded shaded growth, and above all on plants kept indoors in dry, still air over winter.

Watch for: Rows of small brown, tan, black, white, or waxy bumps along stems, twigs, leaf midribs, and leaf undersides that do not brush off but can be scraped loose with a fingernail. A sticky shine on the leaves - and on the floor, table, or path beneath the plant - that later turns black with sooty mold. Ants running steadily up and down the stems, since they farm and defend scale for that honeydew; often the first sign anything is wrong. Yellowing leaves, weak thin growth, and dieback of individual branches or canes that are heavily encrusted. On fruit crops, scale covers and sooty mold directly on the fruit. Check the leaf undersides and the shaded inner wood, which is where colonies build up unseen.

Prevent: Inspect. Look over leaf undersides and stems regularly - on a crop you pick, every harvest is a scouting chance - and check every new plant thoroughly before you buy it, plant it, or set it beside anything else, because scale almost always arrives on a plant rather than flying in. Quarantine new houseplants for a few weeks. Keep plants unstressed and not over-fertilized, since soft, forced growth is what populations build on. Prune for airflow and light to open up the shaded inner growth where scale hides, and prune out heavily infested wood as routine maintenance - on anything that gets a hard annual pruning, that alone removes most of any buildup. Leave the lady beetles, lacewings, and parasitic wasps alone, since they normally keep scale down to nothing, and keep ants off the plant where you can, because ants protect the colonies from those predators. Indoors, avoid hot, dry, still winter air.

Treat: Horticultural oil is the main control: it works by smothering, so it has to coat the insects thoroughly - stems, twigs, and leaf undersides - and it usually needs repeating, because the waxy covering shields them and no single pass reaches everything. On deciduous woody plants a dormant-season oil smothers the overwintering stage while the leaves are out of the way, and timing a growing-season spray to the crawler stage, when the young are mobile and uncovered, is far more effective than spraying settled adults. On a small plant or a light infestation, scrub or wipe the scales off by hand, or dab them with a cotton swab of rubbing alcohol. Prune out and destroy badly encrusted wood rather than trying to save it. Wash off the sooty mold once the scale is gone - it lives on the honeydew, not on the plant, and stops once the supply does. Anything you spray must be labeled for the plant, and oils can burn delicate foliage, so test first.

European fruit lecanium and San Jose scale both settle on hawthorn twigs, and the first thing you usually notice is sticky honeydew and black sooty mould rather than the insects themselves. Rarely serious on a vigorous plant. A dormant-oil spray in late winter is easy on a hedge you can reach over and deals with most of it.