Identifying And Treating Greasy Spot Fungus

Identifying And Treating Greasy Spot Fungus

By: Kathee Mierzejewski

Citrus tree diseases are quite common among orange, lime, and lemon trees. These trees are hardy enough, but they end up with citrus fungus diseases easily if the right conditions allow for it. The reasons you want to prevent fungus from forming on your citrus tree are because they can cause severe leaf drop and eventually kill your tree. The most common form of citrus tree fungus is greasy spot fungus.

Greasy Spot Fungus

The fungus caused by greasy spot is caused by the fungus Mycosphaerella citri. Whether you grow citrus trees for a fresh fruit market or processing plant or just for your own use, you need to be able to control greasy spot fungus. If you allow the fungus to simply live, you will end up with a ruined fruit crop.

Grapefruits, pineapples, and tangelos are most susceptible to greasy spot than other varieties of citrus fruit plants. However, just because you grow lemons and limes doesn’t mean your plants are safe. Citrus tree fungus can run rampant among all your citrus trees.

What happens is greasy spot causes airborne ascospores to be produced in decomposing leaves. These leaves will be on the grove floor or the ground below your tree. They are a primary source for greasy spot to inoculate your trees. The warm dampness on a humid summer night is the perfect atmosphere for these spores to grow.

The spores will germinate under the leaves on the ground. This particular citrus tree fungus will grow on the surface of the ground leaves for a while before they decide to penetrate through the openings on the lower leaf surface. At this point, greasy spot can become a devastating citrus fungus disease.

Symptoms won’t appear for many months, but once they do, black spots will be seen on the leaves of your trees. If it is allowed to fester, you will start noticing the leaves falling off your trees. This is no good for the tree.

Citrus Fungus Treatment

Treatment for greasy spot fungus is easy enough. The best treatment around is to use one of the copper fungicides out there and spray the tree with it. Use the copper fungicide according to directions in order to kill the citrus tree fungus. This treatment does not harm the tree and other than a little leaf drop, you should clear up the greasy spot disease in no time.

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Read more about Citrus Trees

Kaffir Lime Tree Diseases

The Kaffir lime tree (Citrus hystrix) is a citrus tree that yields fruits and leaves used in Asian cuisine. It has a rough, warty green fruit and aromatic, distinctively shaped "double" leaves. At 2 inches wide, the Kaffir lime tree's fruit has a distinctively bumpy exterior. It does not usually have many pest problems, but may become susceptible to mites or scale and also suffer diseases affecting many citrus trees.

Bacterial diseases
Bacterial spot Xanthomonas euvesicatoria pv. citrumelo
Black pit (fruit) Pseudomonas syringae
Blast Pseudomonas syringae
Citrus canker Xanthomonas citri pv. citri
Citrus variegated chlorosis Xylella fastidiosa
Huanglongbing = citrus greening Candidatus Liberibacter asiaticus

Candidatus L. africanus

Nectria haematococca
Fusarium solani [anamorph]
together with other wound-invading agents

Viral diseases
Citrus mosaic Satsuma dwarf-related virus
Bud union crease Virus for some combinations, otherwise genetic or unknown
Citrus leaf rugose genus Ilarvirus, Citrus leaf rugose virus (CLRV)
Citrus yellow mosaic genus Badnavirus
Crinkly leaf Crinkly leaf virus (strain of Citrus variegation virus)
Infectious variegation genus Ilarvirus, Citrus variegation virus (CVV)
Navel infectious mottling Satsuma dwarf-related virus
Psorosis Citrus psorosis virus (CPsV)
Satsuma dwarf Satsuma dwarf virus (SDV)
Tatter leaf = citrange stunt genus Capillovirus, Citrus tatter leaf virus (probably a closely related strain of Apple stem grooving virus rather than a distinct virus
Tristeza = decline and stem pitting, seedling yellows genus Closterovirus, Citrus tristeza virus (CTV)
Citrus Leprosis Virus type I & II
Viroids and graft-transmissible pathogens [GTP]
Algerian navel orange virus GTP
Blight = young tree decline, rough lemon decline GTP
Blind pocket GTP
Cachexia Citrus cachexia viroid (Hostuviroid)
Chlorotic dwarf White-fly transmitted GTP
Citrus dwarfing Various viroids
Citrus yellow mottle GTP
Citrus yellow ringspot GTP
Concave gum GTP
Cristacortis GTP
Exocortis Citrus exocortis viroid (CEVd) Pospiviroidae
Fatal yellows GTP
Gummy bark GTP, possible viroid
Gum pocket and gummy pittings GTP, possible viroid
Impietratura GTP
Indian citrus ringspot GTP
Leaf curl GTP
Leathery leaf GTP
Leprosis GTP associated with Brevipalpus spp. mites
Measles GTP
Milam stem-pitting GTP
Multiple sprouting disease GTP
Nagami kumquat disease GTP
Ringspot diseases Various GTPs
Vein enation = woody gall GTP (possible luteovirus)
Xyloporosis = cachexia Citrus cachexia viroid (Hostuviroid)
Yellow vein GTP
Yellow vein clearing of lemon GTP
Phytoplasmal and spiroplasmal diseases
Australian citrus dieback Unknown procaryote?
Stubborn Spiroplasma citri (spread by leafhoppers)
Witches’ broom of lime Phytoplasma
Miscellaneous diseases and disorders
Algal disease (algal spot) Cephaleuros virescens
Amachamiento Unknown
Blossom-end clearing Physiological
Chilling injury Cold temperatures
Citrus blight Unknown - pathogen suspected
Creasing Nutritional (?)
Crinkle scurf Genetic
Granulation Physiological
Lemon sieve-tube necrosis Unknown, but hereditary
Lime blotch = wood pocket Inherited chimeral agent
Membranous stain Cold temperatures
Mesophyll collapse Unknown
Oleocellosis Physiological
Postharvest pitting Physiological
Puffing Physiological
Rind breakdown Physiological
Rind staining Physiological
Rind stipple of grapefruit Environmental
Rumple of lemon fruit Unknown
Shell bark complex Unknown - (viroid?)
Sooty mold (superficial, not pathogenic) Capnodium

C. citricola
Capnodium sp.

5 All-Natural Garden Fungus Treatments.

Natural Garden Fungus Treatments

I’ve been gardening for more than 40 years. I’m particularly fond of vegetable gardening, although my wife is an avid gardener with flowers and decorative plants. Both of us, though, have confronted the challenge of various forms of fungus growing on leaves, and we’re both very hesitant about any chemical sprays. As a result, we’ve looked for and found organic and natural solutions.

There are more than 10,000 species of fungus in North America. Most present themselves as mushrooms, but a good many are mold. The fungus that affects plants is actually a form of mold. It appears as a white, powdery coating on leaves and quickly spreads. This is due to the way that a fungus reproduces: spores.

Spores are, essentially, microscopic seeds. They are about the size of a grain of pollen. Thus, a fungus can spread easily as the spores are carried on the wind. And that can be a real problem.

A fungus might first show up as a mold growth on cucumber leaves, but the spores will happily spread the fungus to other plants in the garden, and eventually to flowers and even trees in the yard.

One year I had a small orchard of apple trees annihilated by a fungus. By August the leaves had turned yellow and half of the leaves were on the ground. I didn’t lose any trees, but there were few apples and little growth that year.

Here are five natural garden fungus treatments:

1. Trim affected leaves and plants.

Keep an eye on your yard and gardens, and the minute you see a leaf affected by what appears to be a fungus, cut the leaf at the base of the stem. If the entire plant seems affected, you may have to remove the entire plant.

Do not throw the affected leaves or vines in the compost heap. It’s nice to believe that the heat of a compost heap will effectively kill the fungus, but some spores will always find themselves on the top of the heap. The problem is that as you incorporate your compost into your garden or yard, you are spreading the spores. Either burn the leaves or place them in a plastic garbage bag and throw them out with the garbage.

2. Hydrogen peroxide.

Add one ounce of hydrogen peroxide to nine ounces of water, and pour the solution into a spray bottle. After removing any affected leaves, spray the surrounding plants and the affected plant with a liberal, misting spray of the solution. The hydrogen peroxide will kill and prevent further fungal growth. If you’re a bit squeamish about applying hydrogen peroxide to your fruits or vegetables, then you can use this approach on flowers and other decorative plants and use the next approach for your vegetable garden.

Keep an eye on the weather, however. After any rain, you likely should reapply the solution.

3. Acetic acid.

Sounds scary, doesn’t it? But in case you didn’t know, acetic acid is vinegar. Most store-bought vinegar has a 4 to 5 percent solution of acetic acid.

Vinegar is, in fact, a highly powerful, natural antiseptic. Combine the vinegar with an equal measure of water and put into a plastic spray bottle. Some people prefer the vinegar approach to hydrogen peroxide, but you can apply both to your plants if you want a little extra insurance.

Protect your garden produce with these natural garden fungus treatments.

I prefer this approach for vegetables and fruits. It’s easy to rinse off the vinegar before eating any fruit or vegetable. Reapply after a rain.

4. Baking soda.

Combine one quart of water with one teaspoon of baking soda. Add a half teaspoon of canola oil and a splash of dish soap and shake the bottle. Apply the same way as either the hydrogen peroxide treatment or the vinegar treatment.

One note: If you apply the vinegar solution to your leaves immediately followed by the baking soda solution, you may see some foaming. I’ve done this intentionally a couple of times to see if it was more effective, but there was nothing to indicate the combination was better than either one individually.

5. Change your garden location.

The simple fact is that a fungus doesn’t like bright sun. It prefers the cool shade of trees or other plants to grow and spread. Your garden location will be somewhat protected from fungus if it’s in full sun all day. My problem is that my current vegetable garden was started in bright sun and raised beds 30 years ago since then, the surrounding trees partially shade it at times.

When to Go on High Alert

Certain weather factors encourage the rapid growth of fungus on plants. Humidity is a primary culprit. After any rain and especially a fog, be on the lookout for the sudden appearance of any fungus on your plants. It can take only a few days for the fungus to grow.

So, can you eat food with fungus? The answer is yes and no. Most fungus only affects the leaves of plants, not the fruits. If the tomatoes, cucumbers or squash look like they’re not affected, then just make sure to give them a good rinse in cold, running water. If they smell like mildew, toss them in the garbage.

Green, leafy vegetables are another story. A fungus causes a leaf to rapidly decompose. You’ll notice two things if you try to rinse some spinach, kale or lettuce that’s been affected by a fungus. For one, the leaves may dissolve in your hands as you rinse them. Worse, they may smell and taste like mildew. If a leafy vegetable is affected, toss it in the garbage.

Hopefully you won’t have a serious problem with fungus in your yard or garden this year, but if so, you now have the tools to battle it. Happy gardening!

What advice would you add? Share your tips in the section below:

Citrus Leaf Miner

Citrus leafminer (Phyllocnistis citrella) tunnels through the young leaves of citrus trees which creates silvery lines. Finally, it curls the leaf into a shelter and pupates within. This can severely distort the leaves, but mature trees are not likely to be seriously damaged. To protect young trees, spray new growth thoroughly with Searles Pest Gun .

Two-spotted Mite

Two-spotted mite (Tetranychus urticae) affects ornamentals, fruit trees and some vegetables. Affected leaves have a mottled appearance or can be bronzed or shrivelled. Leave them to natural predators, but if the problem is severe, spray Searles White Oil .

Bronze orange bug on citrus

Watch out for these brightly coloured bronze orange bugs on citrus trees and flowers. They suck the sap from young stems and damage new growth. They give off a bad-smelling substance when threatened so its best to spray them with an approved insecticide to control their numbers.

Fruit Fly on citrus

The Queensland fruit fly is common in the warmer times of the year. After mating, the female lays her eggs under the skin of the fruit. When the maggot-like larvae hatch, they burrow deeper into the fruit causing it to rot. Searles Fruit Fly Trap is an effective reusable trap to monitor and control fruit fly activity around vegetables, particularly tomatoes, and around citrus trees. It contains a wick that attracts male fruit flies, traps and kills them, stopping the breeding cycle.

Gall wasp on citrus stems

Small female wasps lay her eggs inside the branch of citrus when the weather starts to warm up in spring. By summertime new tiny wasps escape from the swollen growth leaving the branch deformed. The citrus gall wasp does not directly kill the citrus tree but when repeated attacks occur it severely deforms the tree branches inhibiting normal growth. If you see lumps starting to appear cut the branch off promptly and remove the affected branch away from the tree.

Scale on citrus

Scale found on the leaves and stems of citrus is from sap-sucking insects laying their eggs underneath the protection of a hard waxy dome shell. Once the immature ‘crawlers’ hatch they spread and multiply rapidly. Severe infestations can lead to branch dieback, leaf drop and yellowing of the leaves. Control red scale, white and pink wax scale with an organic oil spray Searles Ecofend Natural Solutions Fruit & Garden . Some soft scale, such as white wax scale and black scale secrete a sticky like substance ‘honeydew’ which then attracts the fungus sooty mould and ants to the plant. The ants protect the scale from predators, letting them proliferate even further. Treat the ants first.


Melanose is a fungus that can multiply quickly in wet weather. Little dark brown, raised spots appear on immature leaves, twigs and fruit. In severe infestations, Melanose can cause fruit disfigurations and wood rot. Remove dead wood from your citrus where the spores lay and spray with Searles Copper Oxychloride when fungus is first sighted.

More details on melanose

Large citrus butterfly caterpillar

The small and large citrus butterfly caterpillar can strip citrus trees of their leaves and produce a strong foul odour when disturbed. This smelly, spiky and unattractive caterpillar will turn into a beautiful butterfly. If infestation is severe, spray tree leaves and branches with a natural Pyrethrum insecticide. Alternatively, you can handpick them and squash them if you can handle the smell.

Citrus Diseases

Symptoms on fruit and leaf.

Symptoms on leaf (top surface).

Symptoms on leaf (bottom surface).

Soft brown decay at the stem end of a Meyer lemon fruit.

Leaf symptom - variegation as a result of chimera mutation on Valencia orange leaves.

Chimera on orange rind (fruit).

Segmented coloration on fruit as a result of mutation.

Leaf lesions on Red grapefruit cultivar.

Leaf lesions on Red grapefruit cultivar.

Leaf lesions on Red grapefruit cultivar.

Leaf lesions on Red grapefruit cultivar.

Leaf lesions on Red grapefruit cultivar.

Hard spot form of citrus black spot on fruit.

Citrus Black Spot symptoms are frequently numerous and irregularly distributed on the fruit peel.

Pycnidia in center of lesions on fruit.

False melanose form of citrus black spot on fruit.

Early virulent form of citrus black spot on fruit.

Cracked spot form of citrus black spot on fruit.

Advanced stage of a hard spot lesion showing a tan center and the brick-red raised border on fruit.

"Freckle spot" symptom type or "early virulent spot". Reddish or colorless spots on fruit lacking a halo which are a sign of heavy infection.

Close up of "freckle spot" symptom type or "early virulent spot" on fruit. Reddish or colorless spots lacking a halo which are a sign of heavy infection.

"Virulent spot" symptom type. Fusion and expansion of many lesions covering part of the surface of heavy infected fruit giving a lathery appearance.

"Cracked spot" symptom type on fruit. Lesions with cracked surface and irregular margins.

Close up of "Cracked spot" symptom type on fruit. Lesions with cracked surface and irregular margins.

Symptom on green fruit that can become hard spots later in the season.

Symptom on green fruit that can become hard spots later in the season.

"Hard spot" symptom type on fruit. This is the most typical symptom of CBS. Usually appears between the beginning of yellow coloration and maturity.

"Hard spot" symptom type on fruit. This is the most typical symptom of CBS. Usually appears between the beginning of yellow coloration and maturity.

"Hard spot" symptom type on fruit. This is the most typical symptom of CBS. Usually appears between the beginning of yellow coloration and maturity.

Early stage of hard spot symptoms on fruit. Note green tissue surrounding the lesions.

Longitudinal section of a hard spot lesion on fruit.

Water-soaked ring on leaf lesion.

Concentric circles found on leaf lesions.

Close-up of lesions on front of grapefruit leaf.

Yellow halo surrounding leaf lesion.

Leaf lesions on grapefruit, top view.

Leaf lesions on grapefruit, bottom view.

Leaf lesions on grapefruit, chlorotic halo.

Whole leaf symptoms on top and bottom of grapefruit leaves.

Fruit lesion with center cracking Photo by Jeffrey W. Lotz, Florida Dep. of Ag. and Consumer Services,

Fruit, leaf, and stem canker lesions.

Typical leaf, stem, and fruit symptoms on grapefruit.

Symptoms on sweet orange fruit.

Xanthomonas campestris pv. citri infection on fruit of Citrus unshiu (satsuma) showing crater-like lesions.

Symptoms on fruit (grapefruit).

Stem canker caused by Xanthomonas campestris pv. citri on Citrus natsudaidai.

Xanthomonas campestris pv. citri on stem of Citrus sp. outer layer of bark removed to show brown lesions.

Leaf symptom - chlorotic flecking on young leaves.

Leaf symptom - chlorotic flecking and warping on leaves.

Leaf symptom - gondol like leaves with inverted cupping on young leaves.

Leaf symptom - distorted, puckered both young and old leaves.

Leaf symptom - wrinkled/curled leaves with some bumpy areas.

Leaf symptom - distorted and warped mature leaves with nutrient deficiency.

Leaf symptoms on Red Blush grapefruit leaves. Courtesy EcoPort (, Kersting U.

Leaf symptoms of CCDV on leaves of Minneola tangelo. Courtesy EcoPort (, Kersting U.

The first symptom of citrus chlorotic dwarf on a leaf of a rough lemon seedling after inoculation. Note the notch on the left margin of the leaf, which is symptomatic for this disease. Courtesy EcoPort (»

Tree symptom on Fremont mandarin on sour orange rootstock 10 weeks after inoculation. Control is on the left. Courtesy EcoPort (, Kersting U.

Leaf symptoms - typical bent tip symptoms of CCDV on leaves of sour orange seedling. Courtesy EcoPort (, Kersting U.

A close-up of the v-notch on a leaf of a citrus chlorotic dwarf inoculated rough lemon seedling. Courtesy EcoPort (, Kersting U.

Leaf mottle and tip notches on rough lemon 10 weeks after inoculation with CCDV. Courtesy EcoPort (, Kersting U.

Common citrus scab on sour orange leaf. Note the scabby areas at the tip of the conical formations.

Close-up of scabby areas at the tip of conical formations on leaf.

Common citrus scab on sour orange leaf.

Early stage of common citrus scab on sour orange leaf.

Early stage of common citrus scab on sour orange leaf.

Advanced stage of citrus scab on sour orange.

Tree exhibiting irregular (off season) flowering.