Dragon Fruit

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.

The most common way a dragon fruit dies, and it usually happens in winter rather than summer: cold soil plus water rots the base and the buried end of a cutting. Cut water right back in cool weather, plant shallow rather than deep, and never plant a cutting whose cut end has not calloused for a week to ten days. A rotted plant can often be saved as a cutting taken from firm green tissue well above the damage.

The main disease of dragon fruit worldwide, caused chiefly by the fungus Neoscytalidium dimidiatum, with Colletotrichum anthracnose behaving much the same way. It infects stems and fruit through wounds and spreads in warm, wet, humid weather, so it is far worse in a Florida or Gulf Coast summer than in a dry California one. Small orange-yellow spots become sunken, bleached, or rotted lesions dotted with black fruiting bodies, and on a badly infected plant whole branch sections turn soft and collapse. Infected fruit is marked and unsaleable but the plant itself is what is at stake: repeated infection weakens a crown over several seasons.

Watch for: Small round yellow-to-orange spots on green stems that turn into sunken, bleached, tan or rust-colored lesions, often with tiny black specks in the center. Soft, rotting sections of branch, particularly where growth crowds together, rests on the ground, or was damaged by wind or handling. Orange or brown blotches on ripening fruit. The pattern is worst after long warm rainy spells and on the shaded, poorly ventilated inside of a dense crown.

Prevent: Keep the crown open and off the ground: prune to a manageable number of hanging branches, remove anything trailing on soil, and space posts so air moves through. Water at the base rather than over the plant, and avoid working in the crown while it is wet. Handle stems carefully - most infections start in a wound, including the ties and cuts you make yourself. Start with clean cutting material; the fungus travels in infected stems, which is the most common way it arrives in a new garden. Remove and bin infected material rather than composting it.

Treat: Cut affected sections well back into clean, firm green tissue, sterilizing the blade between every cut, and bin the removed material. Let the cut surfaces dry rather than sealing them. Copper-based fungicides labeled for the crop give some protection on new growth in a wet season, but they do not cure existing lesions - sanitation, pruning, and airflow are the real controls. Badly infected, repeatedly cut-back plants are usually best replaced with clean cuttings taken from a healthy plant.

The single most likely thing to go wrong with dragon fruit in a humid climate, and the reason growers in Florida and the Gulf keep crowns open and off the soil. Dry-climate growers in California and Arizona see far less of it.

The commonest disappointment in home dragon fruit growing: a healthy plant flowers spectacularly and sets almost nothing. There are two causes and they compound. First, the flower opens for a single night and closes by mid-morning, and in most US gardens the moths and bats that pollinate it in its native range are simply absent, so nothing visits it. Second, many red- and magenta-fleshed selections and most Selenicereus costaricensis hybrids are self-incompatible - their own pollen will not set fruit at all, no matter how many insects visit. Unpollinated flowers wither and drop within a day or two.

Watch for: Large flowers opening after dark and closing by late morning with no fruit forming behind them. Small green ovaries that yellow, shrivel, and drop three to seven days after flowering. A plant that flowers heavily year after year and produces only a handful of fruit, or none. Fruit that does form being small and lopsided, which points to partial pollination rather than none.

Prevent: Hand-pollinate as routine rather than as a rescue. Brush pollen from the anthers onto the star-shaped stigma once the flower is fully open in the evening, or at first light before it shuts. If you cannot be there at night, snip a few anthers into a closed container in the evening, refrigerate them, and pollinate at dawn. Plant at least two different varieties that flower in the same season so cross-pollen is available, and ask the nursery whether a variety is self-fertile before buying a single plant. Refrigerated pollen keeps for several days and can be frozen for longer if two varieties bloom out of step.

Treat: Nothing can be done for a flower that has closed unpollinated - it will not reopen. The fix is entirely for the next flush: get a brush into the crown at night, and get a second variety planted. Where fruit sets but is small and misshapen, more thorough pollination across the whole stigma usually corrects it. Bud drop before flowering is a different problem - that one is heat or water stress.

This is the single most useful thing to know before buying a dragon fruit plant, and it is the reason so many well-grown plants never fruit. Ask about self-fertility at the nursery, and plan on two varieties.

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.

Netting a spiny crown is unpleasant, so individual mesh or organza bags over ripening fruit are the practical answer on dragon fruit. Rats and ants take fruit on the same schedule, and a fruit that has already split is what draws all three.

A physical injury rather than a disease: intense sun on unhardened or newly exposed stem tissue kills the surface, leaving papery white, tan, or bleached patches on the sun-facing side. It is common on young plants, on cuttings moved straight from a shaded nursery into full sun, and on stems suddenly exposed by pruning, and it is worst in the low desert of Arizona, inland southern California, and south Texas where summer temperatures run well above 100 degrees F. Damaged tissue never recovers, and badly scarred sections are an entry point for stem canker.

Watch for: Papery white, cream, or tan patches on the side of the stem that faces the afternoon sun, usually with a sharp boundary. Yellowing or reddening of stems as a first warning before tissue actually dies. Damage concentrated on newly planted cuttings, on the outer face of the crown, and on growth that was shaded until a recent pruning.

Prevent: Harden new plants gradually rather than moving them straight into full sun, and give young plants and fresh cuttings 30-50 percent shade cloth or a morning-sun position through their first summer in a hot-summer climate. Keep water steady in heat, since a water-stressed plant burns far more readily. Prune in stages in the desert, so you do not suddenly expose interior stems that have never seen direct sun. Established, well-watered plants in coastal and humid climates need no shading at all.

Treat: There is no repair for burned tissue - the patches are permanent scars. Leave them unless they are large or start to rot, in which case cut back into clean green tissue. Shade the plant, correct any drought stress, and let new growth cover the damage. Watch scarred areas for the sunken lesions of stem canker, which often colonises them.

Almost universal on first-summer plants in the desert Southwest and almost unknown in humid Florida shade. Cosmetic on its own, but it opens the door to stem canker, which is not.

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.

On dragon fruit, scale and mealybugs shelter in the crowded shade of the crown, under ties, and in the grooves along the stem ribs, usually with ants farming them. Opening the crown up and controlling ants does most of the work; oil sprays reach into the grooves better than soaps do.