Guava

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.

On guava the birds are not only a harvest problem - they are the dispersal mechanism that makes this tree invasive, carrying seed into pasture and forest well beyond your yard. Bagging fruit and picking at color break protects the crop and cuts the seed birds carry away. Rats, raccoons, and possums work the same fruit at night.

Tephritid fruit flies lay their eggs under the skin of ripening fruit, and the maggots feed inside it, so the first sign is usually a fruit that looks fine and is full of larvae when cut. The Caribbean fruit fly is established across peninsular Florida and the Caribbean; Mediterranean and Oriental fruit flies are established in Hawaii and turn up in California, Texas and Florida as quarantine outbreaks. They prefer fruit that is beginning to soften and color, they build up on any fallen fruit left rotting on the ground, and populations run from late spring through fall. Because several of these species are regulated pests, an infestation is not only a garden problem - moving infested fruit is how quarantines start.

Watch for: Tiny puncture or sting marks on the skin of ripening fruit, sometimes with a weeping drop or a small sunken dimple around them. Fruit that softens, browns, or collapses on one side well before it should. Small white maggots in the flesh when the fruit is cut, and fruit that falls early and rots fast. Adult flies - larger than a housefly, with patterned wings - hovering around ripening fruit and resting on foliage in the morning. Windfalls under the tree squirming with larvae, which is where the next generation comes from.

Prevent: Bag the fruit. A paper, mesh, or organza bag slipped over each fruit once it reaches golf-ball size physically excludes the females and is the only home control that reliably works. Pick fruit at color break and finish ripening it indoors rather than letting it soften on the plant, which removes the window the flies need. Clear every fallen fruit at least weekly and dispose of it by bagging, deep burial, or solarizing in a sealed bag in the sun - never in an open compost heap, which just breeds more. Keep trees pruned small enough that you can actually reach and bag the crop. Hanging traps tell you when flies are active but will not protect a crop on their own.

Treat: There is no cure for fruit already infested - bin it sealed, and never leave it lying. Protein bait sprays are the standard commercial control and are what agriculture departments use in outbreaks; in a home garden, sanitation plus bagging does most of the work. If you find a fruit fly outside its normal range, or receive a quarantine notice, report it to your state agriculture department rather than dealing with it privately: several of these species are regulated, and it is illegal to move host fruit out of a declared quarantine area, including to friends and family in another county or state.

Guava is one of the most preferred hosts of the Caribbean fruit fly in Florida, and unbagged dooryard guava there is routinely close to a total loss. Bagging and weekly windfall collection are not optional for a usable crop; picking firm at color break also helps, since the flies favor softening fruit.

A fungal rust (Austropuccinia psidii, formerly Puccinia psidii) that attacks the young growth of guava and its relatives in the myrtle family - eucalyptus, bottlebrush, allspice, rose apple, and the Hawaiian native ohia. It infects new leaves, shoot tips, flowers, and young fruit, producing brilliant yellow-orange powdery spore masses, then distorting and killing the tissue. It thrives in warm humid weather and spreads on wind, clothing, tools, and nursery plants. It is present in Florida, Hawaii, California, and the Gulf, and in Hawaii it is a serious threat to native forest, which is why moving myrtle-family plant material there is restricted.

Watch for: Vivid yellow to orange powdery pustules on new leaves, shoot tips, flower buds, and young fruit - the color is unmistakable and unlike any other guava problem. Purple-rimmed spots on young leaves before the spores appear. Twisted, stunted, or blackened shoot tips, defoliation of new growth, and repeated dieback that leaves a tree pushing flush after flush and never getting anywhere. Damage is concentrated entirely on young tissue; mature leaves are not attacked.

Prevent: Avoid pushing soft new growth into warm wet weather - time nitrogen feeding so flushes come in drier periods, and prune to open the canopy so foliage dries quickly. Space plants and do not water overhead. Buy clean nursery stock and inspect it, since the rust moves most often on plants. In Hawaii, do not move myrtle-family plants or cuttings between islands or into the state, and follow state quarantine guidance - the rust is a documented threat to native ohia forest there. Some guava selections are less susceptible than others, but no cultivar is immune.

Treat: Prune out infected shoots and buds well below the damage, bag the prunings rather than composting them, and disinfect tools afterward. Protective fungicides labeled for the crop and applied to new flushes give real control in a wet season, but they protect new growth rather than curing infected tissue, and repeat applications are needed while the tree is flushing. Report suspected finds in areas where the rust is regulated, particularly in Hawaii.

The most serious disease of guava in humid US climates, and unusual in that it attacks only the young growth guava needs to produce a crop - repeated infection of every flush is what stops a tree bearing. Its wider significance in Hawaii, where it threatens native ohia, is the reason plant-movement rules exist there.

Meloidogyne enterolobii, commonly called the guava root-knot nematode, is a microscopic soil roundworm that is far more damaging than the common root-knot species and is a regulated pest in parts of the southeastern United States. It invades guava roots and forms large knotted galls that block water and nutrient uptake, and infested trees decline steadily - stunted, yellow, wilting in heat, and eventually dying. It has destroyed guava plantings in Florida and elsewhere, and it also attacks tomato, pepper, sweet potato, and other crops, including varieties bred to resist ordinary root-knot nematodes.

Watch for: A tree that stays stunted and unthrifty despite feeding and watering, with small pale leaves and dieback at the tips. Wilting on hot afternoons in soil that is plainly moist. Poor response to fertilizer. Dig gently at the root zone and look for heavily knotted, swollen, distorted roots - the galls of this species are large and unmistakable. Trouble is concentrated on sandy soils and on ground that has grown susceptible crops before.

Prevent: Buy nursery stock from a reputable source and inspect the roots before planting - this nematode moves in infested plants and soil, which is why it is regulated. Do not plant guava into ground where nematode-stunted plants have already failed, and do not move soil or plants from an infested area. Add heavy organic matter and mulch, which builds the soil life that suppresses nematodes, and interplant French marigolds. Growing in a large container of clean mix avoids the problem completely and is a sensible choice on sandy soil with a known history.

Treat: There is no home cure once a tree is infested. Heavy mulching and organic top-dressing keep pushing new feeder roots and can carry a declining tree for years, but they do not eliminate the nematode. Severely affected trees are best removed and replaced in fresh ground or a large container. Where this species is regulated, report suspected finds to your state agriculture department rather than moving plants or soil off the property.

A distinct and far more aggressive species than the common root-knot nematodes that trouble figs and vegetables, and it is named after this host for good reason - guava is one of its preferred plants. On sandy Florida soil with a bad history, a large container is the realistic answer.

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.

Guava collects several scales and mealybugs, usually with ants farming them and sooty mold blackening the leaves and fruit underneath. The annual after-harvest pruning that a guava needs anyway removes most of a buildup, which is why scale rarely gets serious on a properly managed tree.

Colletotrichum fungi infect guava leaves, shoot tips, and above all the fruit, and they are the main reason a wet summer ruins a crop that otherwise looked fine. Infection often happens on young fruit and stays latent, only appearing as the fruit ripens - which is why guavas can look perfect on the tree and develop sunken dark spots on the counter two days later. It also causes tip dieback on shoots and dark spots on leaves. Warm, humid, rainy weather and dense unpruned canopies are what turn a minor presence into a serious loss.

Watch for: Small dark sunken spots on ripening or ripened fruit that spread into soft, dark, circular lesions, sometimes with pinkish spore masses in the center in humid weather. Fruit that develops rot after picking rather than on the tree. Blackened, dying shoot tips and dark irregular leaf spots. Damage concentrated on the shaded, crowded inside of an unpruned tree and in the wettest part of the season.

Prevent: Prune annually after harvest to open the canopy so foliage and fruit dry quickly - the single most effective measure. Remove and dispose of mummified fruit, fallen fruit, and dead tips, which is where the fungus overwinters. Do not water overhead, and avoid handling or harvesting while the tree is wet. Bagging fruit reduces infection as well as excluding fruit flies. Pick at color break and refrigerate promptly rather than letting fruit soften in warm humid air.

Treat: Copper or other fungicides labeled for the crop, applied protectively through a wet season, reduce infection of developing fruit, but nothing cures fruit that is already infected. Cut out affected shoots into clean wood, bin infected fruit rather than composting it, and rely on pruning, sanitation, and prompt picking as the real controls.

The classic pattern on guava is fruit that looks clean at picking and rots on the counter, because the infection was already there and latent. Annual pruning and clearing windfalls do most of the work; wet-summer climates see far more of it than dry ones.

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.

Aphids ride the spring flush on guava, curling exactly the new shoots that would have carried flowers. Because guava fruits on new growth, that makes them worth knocking off with water early, even though they do no lasting harm to the tree.