Stages of leaf spot disease

Stages of leaf spot disease

Stage 1 (speck/dot)

Yellowish green specks less than 1 mm long.

Stage 2a (early streak)

Specks become 3 to 4 mm x 1 mm long streaks, increase in length and turn yellowish.

Stage 2b (late streak)

Streaks darken to a rusty brown.

Stage 3 (early spot)

Streaks broaden to a spot. They become longer and wider, with indefinite margins, which may be water-soaked in appearance and darken to brown. 

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Stage 4 (Brown spot)

Spots have definite dark brown edges, the centre becomes sunken and is sometimes surrounded with a yellow halo. Conidia are produced on the surface. 

Stage 5 (mature spot)

The sunken centre of spots turns grey and is surrounded by a dark brown to black border, sometimes with a yellow halo. Ascospores are produced within the grey central area of the mature spots.

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Tattered or holey leaves

Tattered or holey leaves

Inset: close-up of the feeding beetles.

Greyback cane beetle

Cause: Feeding by adults of Dermolepida albohirtum. Damage is seldom severe, but extensive feeding on older leaves of bunched plants can lead to sunburnt fruit.
Solution: There are no recommended foliar chemical treatments as these will interfere with biological control and will result in serious mite infestation. This will be more damaging and costly than greyback cane beetle damage.
Feeding on the young cigar leaf results in 'shot hole' type damage as the leaf unfurls. Inset: close-up of the feeding beetles.

Swarming leaf beetles

Cause: Leaf feeding of large numbers of adult Monolepta australis or Rhyparida spp. beetles. They swarm in spring and summer.
Solution: Damage is sporadic and no specific treatment is required.
Cluster caterpillars and damage caused to leaf.

Cluster caterpillar

Cause: Young larvae of Spodoptera litura feeding in groups on either the top or bottom of leaves, leaving the opposite side intact. Large larvae are solitary.
Solution: Damage is sporadic and most often concentrated on the tender leaves of plant crops. Fruit damage is usually restricted to a  few isolated bunches and seldom requires specific treatment. 
Inset: close-up of rolled leaf.

Banana skipper

Biosecurity Alert

Cause: Larvae of Erionota thrax feed on the leaf blade and strip and roll it to form a shelter in which the larva develops. In heavy infestations, the entire leaf lamina is destroyed, leaving only the midrib.
Biosecurity: This leaf pest has not been found in Australia or Torres Strait Islands but is well established in Papua New Guinea. It is widely distributed throughout China, India, South East Asia, Mauritius and Hawaii. Report all suspicious outbreaks to Biosecurity Queensland immediately (13 25 23).

Grasshopper

Cause: Feeding by grasshoppers Valanga spp.
Solution: The damage is mostly cosmetic as plants will rapidly compensate for any leaf loss. It is usually only a problem on young plants, especially on new plant crops. No treatment is required.

Wind

Cause: Strong winds tearing the leaf lamina.

Solution: Retaining existing vegetation or planting specific windbreak trees can reduce the damage caused by strong winds.

Discoloured leaf petioles

Discoloured leaf petioles

Note vein flecking in the leaf petiole caused by banana streak virus.

Banana streak virus

Cause: The banana streak virus (BSV).
Solution: Do not take planting material from infected plants. Eradicate infected plants where symptoms are observed.
Note vein flecking in the leaf petiole caused by banana bunchy top virus.

Bunchy top

Cause: The banana bunchy top virus (BBTV) which is spread on infected planting material and by the banana aphid, Pentalonia nigronervosa. BBTV is not present in tropical Australia, and movement of planting material is controlled by legislation.

Solution: There is no cure for this disease and all infected plants must be eradicated. Outbreaks must be reported to your state primary industry authority.
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Pink discolouration of the petioles first appears on the older leaves but all leaves quickly become affected.

Nitrogen deficiency

Cause: Insufficient nitrogen available for the plant due to inadequate fertiliser applications or leaching and gaseous loss of the nitrogen fertiliser applied.
Solution: Appropriate application of nitrogen fertiliser. You need to know your soil type, climate, past fertiliser program, and soil and leaf analysis results when determining the fertiliser rate.

Yellow leaves

Yellow leaves

Bunchy top

Cause: The banana bunchy top virus (BBTV) which is spread on infected planting material and by the banana aphid (Pentalonia nigronervosa). BBTV is not present in tropical Australia, and movement of planting material is controlled by legislation.
Solution: There is no cure for this disease and all infected plants must be eradicated. Outbreaks must be reported to your state primary industry authority.
More info:
Yellowing appears first on the older leaves but all leaves quickly become affected.

Nitrogen deficiency

Cause: Insufficient nitrogen available for the plant due to inadequate fertiliser applications or leaching and gaseous loss of the nitrogen fertiliser applied.
Solution: Appropriate application of nitrogen fertiliser. You need to know your soil type, climate, past fertiliser program, and soil and leaf analysis results when determining the fertiliser rate.
Yellowing starts in the oldest leaves.

Potassium deficiency

Cause: Reduced availability of potassium for plant uptake. Enhanced by leaching losses of potassium and/or inappropriate fertilisation.
Solution: Appropriate application of potassium fertiliser. Knowledge of your soil type, climate, past fertiliser program, and soil and leaf analyses need to be considered in determining fertiliser rate.
Leaf margins of the older leaves remain green and the area between the leaf margin and the midrib yellows.

Magnesium deficiency

Cause: Reduced availability of magnesium for plant update. Usually due to inappropriate fertilisation causing an imbalance.
Solution: Appropriate application of magnesium fertiliser. Knowledge of your soil type, climate, past fertiliser program, and soil and leaf analyses all need to be considered in determining fertiliser rate.

Water-logging

Cause: Poor soil aeration which reduces root function and leads to water and nutrient stress.

Solution: Depends on soil type and situation but usually involves surface and subsurface drainage works.

Panama disease (Fusarium wilt)

Biosecurity Alert

Cause: The fungus Fusarium oxysporum f. sp. cubense which is a soil-borne organism. It is spread in water, soil and planting material. It enters the plant through the roots, and blocks the conducting tissue within the plant resulting in wilting, yellowing of leaves, splitting of pseudostem and death of the plant.
Solution: There is no cure for affected plants. Use only approved planting material and do not plant in previously infested areas.
Biosecurity obligation: Panama is a notifiable disease and you must report any suspicious plants. If you suspect Panama disease you must notify Biosecurity Queensland immediately (13 25 23).
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Yellowing of leaves caused by Bacterial corm rot.

Bacterial corm rot

Cause: The bacteria Pectobacterium spp. (formerly known as Erwinia spp.) which are widespread in most soils. Plants that are stressed from heat or lack of water during the dry season can succumb to bacterial invasion during the early part of the wet season.
Solution: There is no cure for infected plants. Avoid stress conditions. Ensure adequate moisture levels are maintained during the dry season.

Spots on leaves

Spots on leaves

Early stage
Later stage

Leaf spot (yellow Sigatoka)

Cause: The fungus Pseudocercospora musae (formerly known as Mycosphaerella musicola). Early stages of development appears as light yellow streaks 1 to 2 mm long. Streaks enlarge in time to become spots. 

Solution: Ensure the leaf spot management program is carried out effectively. The program should include cultural (deleafing, drainage) and chemical (fungicides, oils, application timing, coverage) practices. 

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Early stage
Later stage

Black Sigatoka

Biosecurity Alert

Cause: The fungus Paracercospora fijiensis (formerly known as Mycosphaerella fijiensis). In the early stages of development, black Sigatoka appears as rusty red streaks up to 5 to 15mm. These symptoms are more obvious on the underside of leaves. Streaks enlarge over time to become spots.

Solution:
If you suspect black Sigatoka you must notify Biosecurity Queensland immediately (13 25 23). It is a notifiable disease and you must report any suspicious plants.

Biosecurity:
Importation of all banana material (fruit, leaves, planting material) is prohibited without approval. A biological barrier is now established, reducing the number of susceptible bananas between the Torres Strait/Papua New Guinea,  where the disease exists and the Far North Queensland banana production areas. 
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Banana leaf speckle symptoms are mainly seen on the underside of the leaves.
Tropical leaf speckle on the underside of leaf.

Leaf speckle

Cause: Several fungi including Mycosphaerella musae (banana leaf speckle or common speckle), and Ramichloridium spp. (tropical leaf speckle) can produce a range of symptoms. These fungi are spread by wind in moist weather and are more tolerant of cool conditions than the leaf spot fungus. 

Solution: The leaf spot management program normally provides control of speckle. If better control is needed, apply fungicides by ground rig which targets the underside of leaves. 

Commonly seen surrounding leaf spot lesions or along the leaf margin.

Cordana leaf spot

Cause: The fungus Cordana musae. Large numbers of spores produced on the underside of lesions are spread during wet windy weather. The fungus mainly enters the leaf through injuries. It is common on plants weakened as a result of water-logging or drought. 

Solution: The leaf spot program provides adequate management of cordana leaf spot.

Southern cordana leaf spot

Cause: The fungus Cordana johnstonii. This disease is present in the tropics and  distribution is limited. It is frequently seen on unsprayed Ducasse plants, and in areas of high elevation under cooler weather conditions. Lesion size is significantly smaller than Cordana musae, approximately 10 by 15 mm. As with Cordana musae, spores form abundantly on the underside of leaves on mature lesions.

Solution: The leaf spot control program should manage this disease.

Close-up of banana rust lesions

Banana rust

Cause: The fungus Uredo musae. A disease with limited distribution, it is seen within plantations near tree lines and buildings which reduce spray coverage. Banana rust occurs predominantly on older leaves. Therefore fungicide applications should be applied via ground rig.

Solution: The leaf spot program should provide adequate management of rust.

Herbicide drift

Cause: Spray drift of contact herbicides such as paraquat onto the plant.

Solution: Avoid spray drift onto leaves. Affected plants should grow out of the symptoms.

Mite damage

Cause: Feeding by the banana spider mite, Tetranychus lambi, or the two-spotted mite, Tetranychus urticae, causes tissue to die, resulting in bronzed areas under leaves. 

Solution: Treatment is usually not necessary because predatory beetles Stethorus spp. maintain adequate natural control. If these beetles are not present and monitoring results show the level of damage is severe, treat with an appropriate miticide. Ensure adequate coverage to the underside of leaves.

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Transparent scale

Cause: The scale insect Aspidiotus destructor sucking nutrients from the leaf cells. 

Solution: Natural predation by beetles, parasitism by wasps and oil sprays used for leaf spot help to suppress scale. For small outbreaks, cut off affected leaves. Avoid the use of foliar sprays that will interfere with natural control agents. Specific insecticide treatments are not recommended or required.

Inset: close-up of the white trail and the whitefly.

Spiralling whitefly

Biosecurity Alert

Cause: The insect spiralling whitefly (Aleurodicus dispersus). The white adults and nymphs occur on the underside of the leaf. The name comes from the white trail in which the eggs are laid. Its sap-sucking reduces vigour, and the production of honeydew supports the growth of sooty mould which can cover fruit and leaves. 

Biosecurity: Report all suspicious symptoms immediately to Biosecurity Queensland (13 25 23)

More info:

Curled or distorted leaves

Curled or distorted leaves

Spike leaf

Cause: A temporary shortage of calcium caused by rapid growth. Most common in spring and early summer.
Solution: Avoid sudden bursts of growth by using regular, light fertiliser applications. A foliar application of calcium nitrate at 10 g/L in early spring will reduce the problem.  
Left: damage to leaf. Note twists in leaf tip. Right: close-up of damage. Note the cracked and raised veins.

2,4-D damage

Cause: Spray drift of 2,4-D onto green parts of the plant.
Solution: Take efforts to avoid spray drift onto leaves. Plants should grow out of it. 

Tissue-cultured off-type

Cause: A genetic abnormality that occurs in tissue-cultured plants.
Solution: Destroy affected plants and set additional following suckers on nearby plants.

Banana streak virus

Cause: The banana streak virus (BSV). The streaks or flecks on leaves become progressively darker with age and the leaves may die. Symptom expression is sporadic. Symptoms of cucumber mosaic are similar.

Solution: Do not take planting material from infected plants. Eradicate infected plants where symptoms are observed.

Leaves with dead edges or patches

Leaves with dead edges or patches

Manganese toxicity (dead patches)

Cause: Excess manganese in the plant due to the presence of manganese nodules in the soil profile and water-logging.
Solution: Confirm the diagnosis with a leaf analysis. Improve soil drainage and soil structure. Avoid planting bananas in poorly drained soils.

Salt toxicity (dead edges)

Cause: A build-up of salt in the plant from high soil or water salinity.
Solution: Confirm the diagnosis with tissue or water analysis. Water heavily to leach salt out of the root zone. Seek alternative sources of water. Avoid excessive applications of fertilisers containing chloride.

Mites (dead edges)

Cause: Feeding of the banana spider mite Tetranychus lambi, or the two-spotted mite, Tetranychus urticae on the underside of leaves. Severe outbreaks are usually the result of poor insecticide management which has destroyed beneficial insects.
Solution: Treat with an appropriate miticide. Ensure adequate coverage to the underside of the leaves.

Water stress (dead patches)

Cause: Severe water stress during hot, dry periods.
Solution: Apply more water during periods of high demand. Water scheduling devices help to plan irrigation. 

Herbicide damage

Cause: Spray drift of contact herbicides such as paraquat onto the plant. 
Solution: Avoid spray drift onto leaves. Affected plants should grow out of the symptoms. 

Streaks on leaves

Streaks on leaves

Variegation

Cause: A genetic abnormality that occurs in tissue-cultured plants. 

Solution: Destroy affected plants and set additional following suckers on neighbouring plants. 

Banana streak virus

Cause: The banana streak virus (BSV). The pale streaks or flecks on the leaves become darker with age. Symptoms of cucumber mosaic virus are similar.

Solution: Eradicate infected plants and set additional following suckers on neighbouring plants. Do not take planting material from infected plants.

Zinc deficiency in young tissue culture plants.

Zinc deficiency

Cause: Insufficient zinc available to the plant. 

Solution: First confirm the diagnosis with a leaf analysis test. Apply zinc fertiliser at the rate recommended on your analysis result. 

Note dark green flecks develop along the veins of the leaves, producing a ‘dot-dash’ pattern which ‘hooks’ into the midrib from the leaf blade.

Bunchy top

Cause: The banana bunchy top virus (BBTV) which is spread in infected planting material and by the banana aphid, Pentalonia nigronervosa. BBTV is not present in tropical Australia, and movement of planting material is controlled by legislation. 

Solution: There is no cure for this disease and all infected plants must be eradicated. Outbreaks must be reported to your state primary industry authority.  

More info:

Cucumber mosaic virus

Cause: Cucumber mosaic virus (CMV). This virus has a wide host range and can be spread to bananas by aphids. 

Solution: Disease incidence is sporadic and generally low. Control measures are not warranted. Do not take planting material from infected plants.

October to November streak

Cause: A physiological disorder of unknown cause which generally occurs during October and November. 

Solution: There is no known cure. Plants will grow out of it. 

Chlorotic patching

Cause: A physiological disorder that indicates the plant is suffering stress. It usually occurs in spring and can be related to water-logging.

Solution: Determine the exact cause of plant stress. Check for corm or root damage from banana weevil borer or nematodes.

 

Colours on leaves

Colours on leaves

Sooty mould (blackened leaves)

Cause: A fungus growing on the honeydew secretions produced by insects such as      aphids, scales and bugs.

Solution: Natural control by parasites and predators usually provides adequate            control of these pests. Chemical sprays specifically to reduce insects which promote honeydew and sooty mould are seldom required.

Juvenile plants (red-purple blotches on leaves)

Cause: The juvenile stage of young Cavendish bananas and some other varieties usually has red-purple blotches on the leaves. This is normal.

Solution: No control is needed and plants grow out of this symptom.

 

Mite damage (bronzed leaves)

Cause: Feeding on the banana spider mite, Tetranychus lambi, or the two-spotted mite, Tetranychus urticae, on the underside of leaves.

Solution: Treatment is usually not necessary because predatory beetles Stethorus spp. maintain adequate natural control. If these beetles are not present, and monitoring results show the level of damage is severe, treat with an appropriate miticide. Ensure adequate coverage to the underside of leaves.

More info: