Banana Black Leaf Streak Disease in Hawaii -Symptoms and Integrated Management
Scot C. Nelson, University of Hawaii at Manoa, College of Tropical Agriculture and Human Resources, December 2007
Note: this is an unpublished draft of some relevant information about banana black leaf streak disease in Hawaii and its integrated management. It is intended for use by banana farmers and crop advisors. The article is based largely on the author's experience with banana cultivation in Hawaii. Any questions or comments about this article should be directed to Dr. Scot C. Nelson (snelson@hawaii.edu).
Black leaf streak, also known as Black Sigatoka, was first recorded in 1964 from Fiji. This fungal disease of banana has since spread to most of the banana growing regions of the world and is regarded as one of the most important constraints on banana production worldwide. The disease is particularly important where growers cultivate monocrops of banana and cannot afford to use chemical fungicides for disease control.
Black leaf streak can cause extensive defoliation. Yields are reduced, and fruit from affected plantations is prone to premature and uneven ripening. Because banana bunch weight is a function of the number of healthy leaves at flowering, it is critical to manage the crop and the disease so that an acceptable quantity and quality of fruit is harvested.
2. Disease occurrence and significance in Hawaii:
3. Disease symptoms and progression:
The first symptom of black Sigatoka is minute, chlorotic flecks that appear on the undersurface of the third or fourth fully expanded leaf. The flecks develop into narrow (1-2 X 10-20 mm) rusty brown streaks and often have truncated ends and sides that are sharply limited by the leaf veins. During early stages, the streaks are visible only from the lower surfaces.
On some cultivars, and on very young plants (suckers) the streaks are less defined and have diffuse margins
The color of the lesions or streaks intensifies to dark red, brown, or black, sometimes with a purple tinge, and they become visible on the upper surfaces
The streaks enlarge, becoming fusiform or elliptical, and darken to give the characteristic black streaking of the leaves. Conspicuous yellowing of adjacent leaf tissue may also occur.
The lesions dry to light gray with definite dark brown or black borders and often have narrow, yellow transition zones between the borders and the green leaf tissue.
When disease severity is very high, large areas of the leaf may become blackened and water-soaked. As with yellow Sigatoka, the spots on juvenile leaves are oval or rounded and are often surrounded by a conspicuous yellow margin.
In extreme cases, all leaves can be destroyed before the bunch is mature, and the bunch may fall from the plant.
Black leaf streak disease symptoms on banana (Musa spp.) in Hawaii
Figure 1. The first symptom of black Sigatoka is minute chlorotic flecks on the undersurface of the third or fourth fully expanded leaf. The flecks develop into narrow rusty brown streaks and often have truncated ends and sides that are sharply limited by the leaf veins. On some cultivars, the streaks are less defined and have diffuse margins. During early stages, the streaks are visible only from the lower surfaces.
Figure 2. Symptoms of black leaf streak disease on young banana suckers (above) differs from the symptoms on mature plants. On suckers, streaks rarely form; instead there are circular leaf spots ranging in color from black to brown to grayish, depending on the stage of plant and lesion development.
Figure 3. Symptoms of black leaf streak disease on young banana suckers (above) differs from the symptoms on mature plants. On suckers, streaks rarely form; instead there are circular leaf spots ranging in color from black to brown to grayish, depending on the stage of plant and lesion development.
Figure 4. On some varieties such as Cavendish types, leaves of young banana suckers naturally have maroon- colored blotches (above) that should not be mistaken for symptoms of black leaf streak disease. These blotches are naturally occurring on young plants and are not present on leaves of older plants.
Figure 5. On mature banana leaves where triazole fungicides or translaminar fungicides are used to control black leaf streak, lesions appear first at the leaf midrib as the fungicide moves within tissues to distal parts of the leaves.
Figure 6. On mature banana leaves where triazole fungicides or translaminar fungicides are used to control black leaf streak, lesions appear first at the leaf midrib as the fungicide moves within tissues to distal parts of the leaves.
Figure 7. There is always a significant amount of yellowing of affected banana leaf tissues before they turn various shades of brown and gray.
Figure 8. In areas of high rainfall, necrotic banana leaves turn very dark in color as the dead tissues becomes waterlogged.
Figure 9. Hundreds of smaller black leaf streak lesions coalesce to form large, blighted ares on banana leaves.
Figure 10. Stagnant air and high humidity in the banana canopy favor the development of black leaf streak disease.
Figure 11. Ascospores of the pathogen, Mycosphaerella fijiensis, form in perithecia formed within the tan-colored centers of lesions.
Figure 12. The recommended IPM practice for managing the disease in Hawaii stipulates that this leaf should be removed from the plant, as it has more than 50% of the leaf area covered with black leaf streak disease. Large farms hire workers to move through field weekly, removing heavily diseased leaves from the plant and placing the upper leaf surface facing down upon the ground to minimize spore discharge into the atmosphere.
Figure 13. Grasses and weeds around banana plants should be kept under control, otherwise if they are tall there is a lot of humidity created in the banana canopy, which favors infection and disease development.
Figure 14. Even where fungicides are applied regularly at banana plantations, if the environment is very favorable for disease development plants may be largely defoliated before harvest, reducing bunch weight and fruit quality.
4. Causal organism: biology and life cycle:
Black leaf streak disease is caused by the fungus Mycosphaerella fijiensis (anamorph is Pseudocercospora fijiensis). The life cycle of the pathogen is depicted below.
Conidia of the fungus form soon after the collapse of tissues in lesion centers. Conidiophores may emerge singly or in small groups directly from the stomata, or they may form in fascicles on dark erumpent stromata. Conidiophores are pale to olivaceous brown, often lighter at the tips, sometimes have a basal swelling, and are straight or variously bent. The terminal conidiogenous cell is paler and sometimes geniculate and has one to four conspicuous, slightly thickened conidial scars. Conidia are subhyaline, straight or slightly curved, have one to 10 septa, and are obclavate or cylindrical obclavate. The base is typically truncate and has a conspicuously thickened hilum. Conidia form more abundantly on the lower surfaces of the lesions but are sometimes found on the upper surfaces. Spermagonia develop as the tissues within the lesions collapse. They are amphigenous but are generally more abundant on the lower leaf surface, are semierumpent through stomata, obpyriform. Spermatia are cylindrical or bacilliform. Under moist conditions, a mass of spermatia may extend above the ostiole. Occasionally, single conidiophores may be associated with spermagonial initials. Numerous aerial hyphae sometimes extend from the rim of the ostiole, appearing superficially like immature conidiophores. Perithecia are submerged, dark brown, globose, slightly erumpent, and have a papillate ostiole. Asci are bitunicate, biseriate, eight spored, and obclavate. Paraphyses are absent. Ascospores are hyaline, fusiform, clavate, biseriate, two celled, and slightly constricted at the septum. Mature perithecia are found most abundantly in lesions in leaf tissue that has recently died (text for this paragraph was adapted from Agrios, George N. 2005. "Banana Leaf Spot or Sigatoka Disease", pp. 459-460 In: Plant Pathology (5th Edition). Elsevier Academic Press).
Life cycle of Mycosphaerella fijiensis in relation to banana and development of black leaf streak.
Figure 15. From: Agrios, George N. 2005. "Banana Leaf Spot or Sigatoka Disease", pp. 459-460 In: Plant Pathology (5th Edition). Elsevier Academic Press.
5. Disease Cycle and Epidemiology:
Conidia and ascospores both have roles in the spread of the disease. Conidia form readily under conditions of high humidity, especially if there is a film of free water on the leaves. The principal means of dispersal are rainwash and splash. These spores are not readily detached by wind. Conidia are associated mostly with local spread of the diseases and are important during periods of high humidity, frequent heavy dews, and intermittent showers. Maturation of perithecia requires saturation of the dead leaf tissues for approximately 48 hr. Ascospores are the primary means of dispersal over longer distances within plantations and into new areas and are the main means of spread during extended periods of wet weather. They are forcibly discharged through the boundary layers o(the leaves and are readily disseminated by air currents. Because M. fijiensis produces relatively few conidia, ascospores are considered to be more important in the spread of black leaf streak. Infection occurs on the youngest leaves of the plant during and immediately after unfurling. Older leaves are not readily infected. Spores germinate on the leaf surfaces, and the fungus undergoes a period of epiphyllic growth for up to 6 days before it produces a stomatopodium and penetrates the leaves. Successful infection is promoted by extended periods of high humidity and the regular presence of free water on the leaves.
Most infections occur on the lower surfaces of the leaves. The first symptom, chlorotic flecks, appears about 15-20 days after infection. The period between the appearance of flecks and the development of streaks and subsequently of necrotic spots varies according to the cultivar and the severity of infection. After a susceptible cultivar is heavily infected, there is rapid evolution of symptoms from streaks to spots (10-15 days), often accompanied by extensive leaf death. On a cultivar with a high degree of resistance, symptom evolution is very slow and may not progress to the spot stage until natural senescence of the leaves occurs. The youngest leaf with spots on a plant and the number of leaves between the first leaf with a streak and the first leaf with a spot are commonly used as measures of severity of infection and disease tolerance by the host (text for this paragraph was excerpted from Agrios, George N. 2005. "Banana Leaf Spot or Sigatoka Disease", pp. 459-460 In: Plant Pathology (5th Edition). Elsevier Academic Press).
6. Disease Management:
The principal objective of black leaf streak disease management is to promote rapid and healthy plant growth in order to achieve a sufficient number of disease-free leaves by the time a banana plant flowers and begins to develop a bunch. Generally, the more healthy (disease-free) leaves are present at time of flowering, the better are the banana bunch yield and fruit quality.
a. Cultural management of banana black leaf streak:
To achieve the optimum control of banana black leaf streak, growers in Hawaii strive to integrate cultural and chemical control measures. Following are the common cultural control methods used by banana farmers in Hawaii:
Sanitation (known as "de-trashing") is the practice of regularly removing severely diseased banana leaves from the banana plant. Banana fields are scouted weekly to identify diseased leaves with >50% of the leaf area destroyed by black leaf streak. Either the diseased portion is cut off or the entire leaf is cut off. De-trashers use a sharp, curved, serrated knife or blade that is attached to a long pole, such as bamboo. Reaching up into the canopy with this too, the diseased portion of the leaf is served or the entire leaf is severed at the petiole. The benefits of de-trashing include: (1) removal of fungal spores from close proximity to the youngest, apical leaves of the plant; (2) increased air flow in the canopy; (3) reduced relative humidity in the canopy; (4) more efficient use of fertilizers; (5) better penetration of spray applications into the banana canopy and more effective fungicide spray applications; (6) reduced premature or precocious ripening (diseased leaves emit ethylene gas, which can ripen fruits in the field prematurely). Ideally, severed banana leaves should be placed top-side down on the ground, so that most of the ascospores of the pathogen are discharged into the soil rather than into the atmosphere. Do not allow banana leaves to die and hang down from the plant. All dead leaves should be removed, as they can harbor M. fijiensis!
De-suckering (known as "pruning") is the removal of unwanted banana suckers from each production unit. Pruning is done bi-annually or annually at we-managed farms. Suckers arise from the mother plant. A mother plant and her set of suckers of various ages is referred to as a "mat" of plants, which is the production unit. In Hawaii, efficient banana production is realized when the production until consists of one mother plant bearing fruit, one plant that is nearing maturity but has not yet flowered, and one or two smaller suckers with only a few leaves. Any additional plants in the production unit is considered unthrifty and a waste of fertilizer and resources. Therefore, the suckers must be pruned. "Directional pruning" is the selection certain suckers to retain in the field. If growers strive to select suckers to retain that are on the side of the mother plant that is in the direction of the plant row, then the line of plants will all "walk" in the same direction over the years, preserving the integrity of the roads in the field. In the case of black leaf streak disease management, the benefits of pruning include: (1) increased air flow in the canopy; (2) reduced relative humidity in the canopy; (3) more efficient use of fertilizers; (4) better penetration of spray applications into the banana canopy and more effective fungicide spray applications
Choice of planting location. Avoid planting bananas in bowl-like depressions in the landscape, and in areas with poor drainage or heavy clay soils. Good water drainage in field will reduce disease levels greatly by minimizing relative humidity and moisture.
Planting geometry and spacing. Single-row or double row planting systems allow best fungicide coverage for bananas and have superior air flow and reduced relative humidity levels in the canopy. More roads per acre (between rows) within a banana field will help it dry out more quickly after a storm. Regardless of planting geometry, growers in Hawaii strive to achieve about 650 - 700 planting units per acre; any more than that creates disease control problems. Wind management is another issue. A North-South orientation of roads in Hawaii is preferred. And, when spraying fungicides, do not go with wind when spraying, rather it is best to go across the wind to minimize drift over the applicator. Therefore, with a North-South orientation of roads in the field, spray applicators can take advantage of the trade winds to avoid or minimize exposure to the chemicals.
Variety selection. Of the two most commonly planted commercial banana varieties in Hawaii (Cavendish types, and dwarf Brazilian "apple"), the dwarf Brazilian is more tolerant or is less affected by black leaf streak disease.
Weed control. Tall weeds (especially grasses) create high humidity in the plant canopy, which favors black leaf streak disease.
Choice of mist blower. Fan sizes for tractor-drawn mist blowers come in different sizes. Experience in Hawaii indicates that 31-inch-diameter fans provide superior disease control than 28- inch-diameter fans.
Use of spray adjuvants. It is important to use a "spreader sticker" such as Latron B to enhance fungicide coverage of leaves and adhesion to leaf surfaces.
Weekly scouting and disease records. Well-managed farms scout field weekly to estimate disease severity or "youngest leaf spotted." Thus provides a quantitative record how effective the disease control program is and also when to apply the next fungicide application, and can also help to detect the possible emergence of fungicide resistance in the pathogen population.
Chop up plants after harvest. A few seconds spent chopping up harvested plants (especially the leaves chopped off the fallen plants) can help to speed up the decomposition of the plants, which should reduce the viability of the fungal population.
Figure 16. One- or two-row planting geometries (with tractor roadways separating each two-row set) are most efficacious for managing black leaf streak disease in Hawaii. The objective is to achieve about 700 plants or production units per acre in this intensive style of farming.
Figure 17. A worker thinning out the plant population (a practice referred to as "pruning"). This is done perhaps twice per year in a field to ensure efficient use of fertilizers and to optimize black leaf streak disease management by increasing air flow in the field and reducing relative humidity in the plant canopy.
Figure 18. After pruning, chop up the downed plants if possible to speed up their decomposition.
b. Plant nutrition:
It is very important to maintain adequate level of banana plant nutrition in order to minimize the effects of black leaf streak disease. Undernourished plants are more susceptible to infection and also succumb more rapidly to disease. The objective is to have banana plants growing as quickly and possible, to "outgrow" the effects of the disease as symptoms "climb up" the plant. In Hawaii, banana growers try to produce plants with at least 10 healthy (disease-free) leaves at time of flowering, because after flowering there are no more leaves produced.
Crop logging is the monitoring of soil and banana tissue data over a period of time to help the grower make better decisions on the type, rate, and interval of fertilizer applications. Crop logging for banana consists of selecting banana leaf samples for tissue analysis. Here is the crop logging procedure for Hawaii: (1) Select a plant(s) that is(are) almost ready to flower. This could be a randomly or arbitrarily selected plant or a plant from a problematical part of a field; (2) Select the third leaf from the top of the plant for tissue analysis; (3) From the center of the leaf and ajacent to the leaf midrib, cut out rectangular pieces of leaf, about 2 " x 4" each; (4) Submit the tissue to the University of Hawaii at Manoa,College of Tropical Agriculture and Human Resource, Agricultural Diagnostic Service Center (UH-CTAHR ADSC). The advantages of crop logging include: (1) the practice provides a quantitative basis of decision making; (2) it allows early detection of problems; (3) one can verify suspected problems and interactions; (4) the practice can result in improved banana yield and quality; and (5) fertilizer use patterns are optimized.
Figure 19. Crop logging methodology. Tissue rectangles are removed from the 3rd banana leaf from the top of a plant just before flowering and submitted for analysis. After the analysis has been completed, the nutrient values obtained my be compared with the optimum ranges for bananas in Hawaii provided in the table below.
Table 1. Recommended levels of elements in banana leaf tissue in Hawaii.
Element
Symbol
Range (suggested)
NITROGEN
N
2.8 – 3.1%
PHOSPHOROUS
P
0.18 – 0.20%
POTASSIUM
K
3.2 – 3.5%
CALCIUM
Ca
0.6 – 1.0%
MAGNESIUM
Mg
0.3 – 0.6%
SULFUR
S
0.22 – 0.25%
IRON
Fe
50 – 100 ppm
MANGANESE
Mn
30 – 100 ppm
COPPER
Cu
10 – 15 ppm
ZINC
Zn
25 – 40 ppm
BORON
B
15 – 25 ppm
Table 2. In addition to quantitative data, nutritional problems can diagnosed by observing the various symptoms associated with nutrient deficiencies of bananas.*
Deficient element
Symptoms
Notes
Nitrogen
Generalized chlorosis (more yellowing on older leaves); rose-colored tints on petioles and leaf sheaths; stunting; rosetting; slender pseudostem; small petioles and leaves; reduced life span of leaves; notable reduction in yield.
Banana is more sensitive to a lack of nitrogen than any other element; problem is compounded by dense stands of weeds or grass.
Potassium
Rapid yellowing of oldest leaves which then turn orange and dry up; leaves become tattered and fold downward; crumpled leaves; poorly filled bunch
Responds well to potash applications
Magnesium
Marginal chlorosis of lowest leaves; violet-colored marbling of petioles; fruit may have defective flavor and not ship well.
Magnesium sulphate can alleviate the symptoms.
Calcium
General dwarfing; reduced leaf length; reduced rate of leaf emission; leaves are undulated; tissue near midrib thickens, may turn reddish-brown
Fields should be limes periodically; calcium nitrate can help to correct this deficiency.
Iron
General interveinal chlorosis of young leaves; retarded plant growth; small bunches
Apply iron compounds to soil; foliar sprays of iron compounds can relieve symptoms temporarily.
Zinc
Rosetting and stunting; chlorotic, strap-shaped leaves; leaf chlorosis ion stripes or patches; abnormal bunch and hand characteristics
Problem may be more severe in sandier areas.
Sulphur
Leaves are chlorotic and reduced in size with a thickening of secondary veins; undulating leaf edges; necrosis along edge of lower leaves
Sulphate fertilizers can correct this problem (e.g., ammonium sulphate, potassium sulphate and magnesium sulphate)
Boron
Chlorotic streaking oriented perpendicular to and crossing the primary veins; leaf malformation; interveinal chlorosis
Deficiency can develop over time in mature banana fields in Hawaii
*Reference: Stover, R.H. 1972.Banana, plantain and abaca diseases. Commonwealth Mycological Institute, Kew, Surrey, England. 316
Element requirements for high-production banana farming in Hawaii*:
Element (pounds per acre per year)
Nitrogen (300-650)
Phosphorous (60-120)
Potassium (600-700)
*Expert farmers' recommendations for high-rainfall banana cultivation.
Fertilizers. Primary fertilizer sources for banana production in Hawaii: (1) "Banana Special" (13-3-37), general N-P-K fertilizer, about 200 lbs/acre/month; (2) Urea (sulfur-coated or poly-coated); (3) Potash, KSO or KCL; (4) Lime, dolomite (fields limed to pH 5.5 - 6.5 up to twice per year; (5) Borax, Solubor; (6) Zinc sulfate; (7) Sulfur
Figure 20 .13-3-37 ("Banana Special") is applied at about 0.35 pounds per "mat" (banana plant or production unit) per month.
c. Chemical management (fungicides):
Table 3. Fungicides registered for banana in Hawaii (2006). Products in bold font are effective for controlling banana black leaf streak in Hawaii. They are all commonly used, either alone (and in rotation) or in various tank-mix combinations. The triazole fungicides (febuconazole, tebuconazole) are reported to be the most effective. As systemic fungicides, the triazole fungicides provide the longest duration of disease mitigation after application, but also pose a risk for the development of fungicide resistance if they are overused.
Fig. 21. Hand-held type of mist-blower for applying fungicides to banana plants.
Figure 22. Tractor-mounted blower for applying fungicides to banana plants.
Figure 23. Operating the mist blower in a banana field in Hawaii for black leaf streak control. Fungicides must be sprayed on a regular basis in high-rainfall areas for high-yielding banana cultivation.
Choice of mist blower. Fan sizes for tractor-drawn mist blowers come in different sizes. Experience in Hawaii indicates that 31-inch-diameter fans provide superior disease control than 28- inch-diameter fans. Backpack mist blowers provide inferior coverage as compared with tractor-drawn mist blowers, machetes.
Use of spray adjuvants. It is important to use a "spreader sticker" such as Latron B to enhance fungicide coverage of leaves and adhesion to leaf surfaces.
7. Scouting and record keeping:
At large banana farms, scouts monitor for black leaf streak disease levels weekly. Then, fungicide spray applications are scheduled based upon the data collected. Shown below is an international disease rating scale used by some farmers. The idea is to scout fields regularly looking for plants of the same age (to be determined by the farmer, although plants pre-flowering are best) and gathering and recording disease information, usually on a sheet of paper on a clipboard. Some farmers simply collect data on "youngest leaf spotted" (youngest leaf showing symptoms, based on the idea that if young leaves become heavily diseased, then bunch yield and fruit quality will be very low.
8. Tools and Equipment:
High-production banana farms use the following tools and equipment to manage black leaf streak disease in Hawaii: Tractors, mist blowers (28" or 32" inch diameter fans), personnel protective equipment for spraying, pruning shovels or blades, de-trashing knives and poles, disease scouting sheets.
9. Managing or preventing fungicide resistance:
Fungicide resistance occurs when a product is no longer effective at controlling a disease due to a shift in the genetics of the target organism. Fungicide resistance is a consequence of (1) natural selection (increase in naturally resistant spores are favored frequent sprays) or (2) pathogen genetics (mutation, sexual recombination/reproduction). It can be a very serious problem where fungicide resistance develops in a plant pathogen population.
Types of Fungicide Resistance: (1) Single-step, major gene (one type of gene mutation is responsible; there is a sudden and marked loss of effectiveness; there are clear-cut sensitive and resistant populations; the developed resistance tends to be stable in the pathogen population); (2) Progressive, multiple genes (a number of genes are involved in a stepwise fashion; there is a gradual observed decline in control; there is a range of sensitivity in the pathogen population; the population reverts to more sensitive population with less intensive use of product).
Phenomena Associated with Fungicide Resistance: (1) Cross-resistance (the resistant population automatically and simultaneously becomes resistant to other products that have similar chemical relationships or mechanisms); (2) Multiple resistance (resistance occurs when a population develops separate mechanisms of resistance to more than one product; resistance arises from independent mutations selected from exposure to each of the products); (3) Negative cross-resistance (a rare condition in which change in resistance in one product results in sensitivity to another).
Resistance mechanisms: (1) Altered target site (target site for fungicidal actions experiences mutation which allows escape); (2) Metabolic and altered metabolic pathways (for example, demethylation inhibitors such as are present in the triazole fungicides febucionazole and tebuconazole.
In Hawaii, the primary risk of fungicide development in banana crops is where triazole fungicides (e.g., Enable and Elite) are used repeatedly.
Preventing Resistance Development in Fungi:
- Do not use product in isolation: Apply the product(s) as: (1) a mixture with one or more different fungicides; or (2) as a component in a fungicide rotation. Do not alternate or tank mix with fungicides to which resistance has already developed in your population.
Examples of tank mixtures:
Dithane + Oil
Abound + Enable or Elite (triazoles)
Dithane + (triazole)
All of the above plus Latron 1956 which “dries hard”
Manex II + Superior 70 oil
Example of block spraying program rotation. This program was developed by the Hawaii banana industry for prudent use of the effective triazole fungicides, Elite or Enable.
Jan 16 – Mar 1 non-triazole (Dithane, Oil, Abound)
Mar 2 – May 31 triazole (Enable, Elite)
Jun 1 – Sep 30 non-triazole (Dithane, Oil, Abound)
Oct 1 – Jan 15 triazole (Enable, Elite)
- Apply only when necessary (or just before) and restrict application numbers.
Disease monitoring (Example: DITHANE M-45): “DITHANE M-45 fungicide is a broad-spectrum, protectant fungicide. If not applied on a routine protectant spray schedule, crop should be scouted on a weekly basis. Fungicide application should be made at the recommended label use rate and spray schedule, at first sign of disease, report of disease in the area, or during environmental conditions favorable for disease development.”
Fungicide Label Directions for ABOUND (azoxystrobin) resistance management : “Do not apply more than 2 sequential sprays of ABOUND Flowable before alternating with a fungicide that has a different mode of action. Do not make more than 8 applications of ABOUND Flowable or other stroliburin fungicides per acre per year.”
Fungicide Label Directions: ENABLE 2F resistance management: “Do not apply more than 8 times (0.72 lbs. Active) per acre per year.”
Fungicide Label Directions: ELITE Resistance Management: There are no specific recommendations printed on the label, but please follow same instructions as for ENABLE 2F, as both are in the same class of fungicides (triazoles).
- Maintain recommended dose:
Use enough water to get thorough coverage. Set spray equipment to get good coverage (amount, rate of travel through field). Use of LATRON surfactant to spray solutions will improve performance. A typical tank mixture and spray rate for controlling black leaf streak disease in Hawaii using contact ("protectant"), surface-acting fungicides is as follows. One could also add a triazole fungicide at the recommended rate:
12 gallon per acre mix consisting of the following:
Figure 3. Symptoms of black leaf streak disease on young banana suckers (above) differs from the symptoms on mature plants. On suckers, streaks rarely form; instead there are circular leaf spots ranging in color from black to brown to grayish, depending on the stage of plant and lesion development.
