Pittosporum is a tough, widely planted shrub, and most of its problems start when it is stressed, wounded or crowded rather than from a disease that strikes a healthy plant out of the blue. Some of the most alarming symptoms, such as blackened leaves, are not a plant disease at all but a sign of insects feeding on the shrub. Treatment is usually less about the right spray and more about fixing the conditions that let the trouble start.
Leaf Spots That Turn Gray in the Middle
Fungal leaf spot on pittosporum starts as small brown spots on the leaves.1Plant Disease. First Report of Leaf Spot Caused by Alternaria tenuissima on Pittosporum tobira in Anqing, China As they grow, the centres turn gray-white, and each spot keeps a brown edge with a yellow ring around it.2Plant Disease. First Report of Leaf Spot Caused by Alternaria tenuissima on Pittosporum tobira in Anqing, China The spots usually measure about 1 to 8 mm, roughly the size of a lentil or smaller.3Plant Disease. First Report of Leaf Spot Caused by Alternaria tenuissima on Pittosporum tobira in Anqing, China The middle and upper leaves are hit hardest, and in bad cases small spots join into large irregular dead patches.4Fujian Journal of Agricultural Sciences. Identification, Biological characteristics, and Fungicides screening of the Pathogen causing Leaf spot disease on Pittosporum tobira A badly affected shrub can lose a quarter to a third of its leaf surface.5Plant Disease. First Report of Leaf Spot Caused by Alternaria tenuissima on Pittosporum tobira in Anqing, China
Another fungus causes yellowish-brown spots with straight, angular edges, because the leaf veins stop them from spreading.6Mycologia. Angular Leaf Spot of Pittosporum Both kinds are treated the same way.
A yellow ring around each spot is one clue that points to a fungus rather than sun scorch. Spots scattered across many leaves suggest infection, while browning only at the tips suggests stress.
Other leaf damage can be mistaken for leaf spot. Spray or fertiliser burn tends to leave scorched patches that follow the leaf edges or tips, while fungal spots are separate and scattered across the leaf blade. Insect feeding leaves pale stippled flecks or ragged holes. Fungal spots are usually most numerous on leaves that stay wet longest, such as those inside a dense, shaded part of the shrub.
Leaf spot is usually not fatal. The fungus damages leaves, not the stems or roots, and a shrub can grow new clean leaves once conditions improve.
Pick off and bin badly spotted leaves, and rake up fallen ones, because the fungus can survive on dead leaves and re-infect new growth. Removing leaves only helps if the shrub is also kept drier and more open, since wet leaves let the fungus spread.
Black Sticky Leaves From Sooty Mould
A black, sooty coating on pittosporum leaves is a sign of insects such as aphids, mealybugs or scale.7Ask Extension. Pittosporum leaves black and sticky These insects drip sticky honeydew, and a black mould grows on it. The real problem to fix is the insects.
To find them, turn leaves over and look along the stems. Small bumps may be scale, and white fluff may be mealybugs. Clusters of aphids gather on soft new shoots. Ants climbing the shrub are one clue that honeydew-producing insects may be there.
The black coating sits on the leaf surface, and you can often rub or wash some of it off, whereas a fungal leaf spot is part of the leaf tissue and cannot be wiped away. The leaves feel tacky while the honeydew is fresh, a clue that insects are active right now. The coating often appears on leaves beneath the infested branches, because the honeydew drips downward, so look above the blackest leaves for the culprits.
Hose or wipe off the insects, or use insecticidal soap or horticultural oil. Once they are gone, the coating weathers off over time, and washing the leaves brings light back to them sooner. Spraying fungicide on sooty mould does nothing, because the mould only lives on the honeydew.
Soft, lush growth after heavy feeding with nitrogen fertiliser attracts aphids, so go easy on feeding if the same shrub is infested each year. Check again a week or two after treating, since eggs and young insects can hatch after the first spray and need a second round.
Cankers and Branch Dieback
Several fungi cause branch dieback on pittosporum. The fungus enters through pruning cuts, wounds, insect damage and small natural pores in the bark.8Purdue Plant Doctor. Common Pittosporum Diseases and How to Treat Them It then grows just under the bark and forms cankers, which are sunken dead patches on the bark.9Purdue Plant Doctor. Common Pittosporum Diseases and How to Treat Them It is an opportunist that causes disease mainly on plants that are already stressed.10Virginia Cooperative Extension. Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape Those stresses include drought, waterlogging, salty soil and humidity the plant is not suited to.11UC Statewide IPM Program. Botryosphaeria Canker / Home and Landscape In cold areas, frost can split pittosporum bark, and infection by gall- and dieback-causing fungi usually enters through that split bark.12Home & Garden Information Center. Pittosporum
To spot a canker, scrape the bark gently. Healthy wood underneath is green, while infected wood is brown. Wilted brown leaves that cling to one branch point to dieback, which often shows up after a hot, dry spell.
Dieback from a canker usually kills one branch or section while the rest of the shrub looks normal, whereas drought or root trouble tends to affect the whole plant more evenly. If a branch has died back from the tip with no sunken patch, look further down the stem, because the fungus may have entered at a wound well below the dead leaves.
Avoiding plant stress is the best way to prevent this disease.13Virginia Cooperative Extension. Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape Cut out dead branches in dry weather, a little below the visible damage, into clean wood. Wipe your blades with alcohol between cuts so you do not spread the fungus, and bag or bin the cuttings rather than composting them.
Do not paint or seal the cuts, as healthy wood heals best when left open to dry in the air. Watch the shrub over the next season, and if dieback keeps returning, look for an underlying stress such as poor drainage or drought.
Galls, Root Problems and Viruses
Crown gall is a bacterial disease that enters through wounds and causes swollen, lumpy growths.14RHS Advice. Crown gall: Causes, Symptoms & Control The galls form mostly at the base of the stem, at or just below the soil line.15UC IPM. Common Pittosporum Diseases and How to Treat Them Avoid wounding the base of the plant with mowers or strimmers.
Crown gall lumps are rough, woody and often pale or brownish, and they can grow to the size of a walnut or bigger. Natural swellings, such as a healthy root flare where the trunk widens, are smooth and symmetrical, while galls look irregular and bumpy. Pull back mulch or soil to check at the soil line, since buried galls are easy to miss.
Crown gall cannot be cured once the galls form. Badly galled plants should be replaced with a different species, because the bacteria stay in the soil.
Root-knot nematodes, microscopic soil worms, have caused steady decline in pittosporum plantings.16Journal of Nematology. Vertical Distribution of Pasteuria penetrans Parasitizing Meloidogyne incognita on Pittosporum tobira in Florida A shrub that is fading for no clear reason may have knotted, swollen roots. Above ground, the signs are general and easy to confuse with drought: stunted growth, pale leaves and wilting on warm days even when the soil is moist.
To check, dig gently at the edge of the root zone and look at a few roots. Nematode knots are part of the root itself and cannot be rubbed off, unlike the tiny white nodules some plants form with helpful bacteria. Because the signs overlap with so many other problems, a lab test of a root and soil sample, such as through a local extension service, is the way to be sure, especially for a valued hedge.
A virus can cause yellowing along the leaf veins and yellow mottling between them.17Plant Disease. First Report of Eggplant mottled dwarf virus in Pittosporum tobira in Spain Similar yellowing can come from nutrient or root problems, so rule those out first. Remove plants that are badly affected, because viruses cannot be cured.
When It Is Not a Disease
Many landscape shrubs show leaf burn that looks like salt injury even when little salt is in the leaves.18Journal of the American Society for Horticultural Science. Salt Tolerance of Ornamental Shrubs and Ground Covers Brown leaf edges often reflect water or root stress rather than infection. Extremes of wet or dry soil stress the plant and also invite canker fungi.19UC Statewide IPM Program. Botryosphaeria Canker / Home and Landscape
Stress browning usually affects leaf tips and edges evenly and moves inward from the margins. A shrub next to a road or path treated with de-icing salt may show damage only on the side facing it, which points to salt splash. Cold wind or winter sun can scorch leaves on the exposed side, so look at which direction the damage faces. Damage that appears suddenly across many leaves after a heatwave or freeze is more likely weather than infection, which usually builds slowly.
To check drainage, dig a hole and fill it with water. If the water is still standing hours later, the roots may be sitting in water and need better drainage.
To fix conditions, water deeply but less often during dry spells, and mulch to keep soil moisture even. Improve drainage where water stands after rain.
Do You Need to Spray
Where leaf spot is severe and keeps returning, a protective fungicide can help control it.20Texas Plant Disease Handbook. Pittosporum tobira Protective sprays shield healthy leaves but do not cure leaves already spotted. Sprays do not fix cankers, galls or viruses.
Spray when new leaves are emerging and rain is expected, because the aim is to coat healthy leaves before spores land. Check the label for a waiting period and for any plants the product should not touch, and avoid spraying in hot sun or wind. Choose a product labelled for ornamental leaf spots, cover both sides of the leaves, and repeat sprays at the label interval during rainy periods.
Skip spraying if only a few leaves are spotted; pick them off instead. Skip it during dry weather, when the fungus spreads little. For a large hedge with repeated heavy spotting, spraying plus raking leaves and thinning can break the cycle, whereas one spotted shrub is better handled by cleanup alone. If a shrub is declining for reasons other than leaf spot, spraying will not help, so confirm the problem first.
Products based on beneficial fungi are sold against leaf spot on other plants such as tomatoes.21Novobac. Managing Septoria Leaf Spot Tomato Naturally Their value on pittosporum has not been shown.
Keeping Pittosporum Healthy
Thinning the shrub and the plants around it improves air circulation.22Garden Ninja: Lee Burkhill Garden Design. Is my pittosporum diseased? Removing dead areas stops fungus spreading.23Garden Ninja: Lee Burkhill Garden Design. Is my pittosporum diseased?
Water at the base of the shrub with a hose or drip line. If you must use a sprinkler, run it early in the morning so the leaves dry quickly in the sun. Deep, infrequent watering builds a stronger root system than a light daily splash.
When choosing a spot, pick well-drained soil and give the shrub space for air to move. Where winters are harsh, choose a sheltered site. Check under the leaves each spring for insects, and protect young plants from hard frost in cold areas.
Start with healthy, disease-free plants or cuttings, because plants of unknown origin can bring in disease and insects.24Oklahoma State University Extension. Propagation of Ornamental Plants for Oklahoma Before buying, check leaves for spots, sticky residue or tiny bumps on the stems, and look at the root ball for swellings. Keep a new plant for a couple of weeks away from your other shrubs, so any hidden insects or disease show up before they spread. Buy from a reputable nursery that can tell you where the plants came from.