1. Banana Disease Huang Jiang Hua 2008-5-1

2. Banana bunchy top disease  Banana bunchy top virus (BBTV) is a threat to bananas  BBTV is diagnosed by identifying symptoms of diseased  plants or by submitting a banana leaf sample to test for the banana bunchy top virus.  Diseased plants should be destroyed properly

3. Banana bunchy top disease  Banana bunchy top disease continues to be the main pest concern for banana growers across the state. The disease is caused by the banana bunchy top virus (BBTV). The banana aphid, Pentalonia nigronervosa, is the insect vector of the banana bunchy top virus. Continued spread of BBTV is a significant threat to banana industry.

5.  Disease Identification:  Bunchy top disease is diagnosed by symptom identification or by a lab test for the virus. Banana bunchy top disease

6.  Insect Control: Controlling aphids is essential to reducing the spread of BBTV. Aphid populations may increase during the spring or during warm, dry weather, and they can often be found on suckers. Homeowners can apply insecticidal oils or soapy water to kill banana aphids. It is a violation to apply this diazinon product on fruit bunches or plants bearing fruit.

7. Banana bunchy top disease  Disease Prevention: To minimize the spread of BBTV, all infected plants and their mats must be destroyed with an approved herbicide. Destroying infected plants with Roundup Ultra Max can help reduce the spread of BBTV. Fruits must be removed before treatment. Aphids on infected plants should be killed with soapy water, insecticidal oils, or an approved insecticide before injecting Roundup Ultra Max into a hole made at the base of the stem. Do not immediately cut the plants—the foliage is needed to move the herbicide throughout the plant.  Allow injected plants to dry completely before moving them off your property.

8. Banana bunchy top disease  Routine Monitoring: Commercial and neighborhood banana plantings should be monitored for BBTV symptoms.

9. Banana bunchy top disease  Alternative Host Management: Control banana aphids on all known alternate hosts such as ginger, heliconia, and taro.

10. Banana bunchy top disease  Fresh Start: Backyard and new growers should avoid planting bananas until they can verify that their planting material is free of BBTV. Only BBTVfree plants should be used for planting.

11. Banana bunchy top disease  Prevent Contamination: Prevent the spread of BBTV by not transporting banana plants around your island or to other islands in the state.

12. Banana leaf spot  Introduction  Leaf spot or yellow Sigatoka, caused by the fungus Mycosphaerella musicola, is a very serious disease in tropical banana growing areas. Another form of the disease black Sigatoka, Mycosphaerella fijiensis, is a major threat to the industry. This note describes how yellow Sigatoka spreads and the important cultural and chemical strategies that you can use to control it.

13. Banana leaf spot  About leaf spot disease  The leaf spot fungus produces two types of spores: sexual ascospores and asexual conidia.  Ascospores are produced within the tissue and are forcibly ejected into the air currents. They can be carried over long distances and are responsible for spread of the disease into new plantings, new plantations and within the plantation. Ascospore infection results in tip spotting of younger leaves. Ascospores are only produced during warm moist conditions and are generally absent or in low numbers during winter and dry spring periods.  Conidia are produced on the leaf surface and disperse in droplets of water, so their spread is only over short distances, generally within a plantation. Conidial infection usually results in line spotting or scattered spotting over the entire leaf.

14. Banana leaf spot  Effects of leaf spot on production  Sigatoka leaf spot affects not only the banana leaves, but also bunch weight and fruit quality. Leaf spot will severely reduce yield when less than six viable leaves remain at harvest. Leaf spot will also cause early maturity and premature ripening of fruit. Bananas from leaf spot infected plants can ripen in the field. Field-ripe bunches harbour fruit fly and are unmarketable. Even unripe fruit from affected bunches are unsaleable, because they are likely to ripen in transit to market.

15. Banana leaf spot  Development of symptoms  Development of leaf spot symptoms can be divided into five distinct stages from the minute yellowish-green speck to the fully mature spot. The various stages are shown in the poster Yellow Sigatoka available from the DPI office at South Johnstone.  With massive infections several stages are skipped, the leaf tissue dies rapidly (burns) and large areas of the leaf turn brown and then grey.

16. Banana leaf spot  Stage 1 (speck/dot) :Yellowish green specks less than 1 mm long.  Stage 2a (early streak) :Specks become 3 - 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.

17. Banana leaf spot  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.

22. Banana leaf spot  Controlling leaf spot  Leaf spot is very difficult to control under hot wet conditions. An integrated disease management program involving both cultural and chemical measures is required for effective control.

23. Banana leaf spot  Cultural control practices  Cultural practices aim to reduce spore levels in the plantation and to reduce humidity levels around the leaves. Diseased leaf tissue (source of spores) should be removed (deleafing) regularly throughout the year. Deleafing hooks are available to deleaf banana plants. Every effort should be made to remove all diseased tissue during the dry season so those plantations are 'clean' with the onset of the next wet season.

24. Banana leaf spot  Banana blocks should be designed to ensure all water is rapidly removed and air flow is not limited. Avoid planting bananas in wet areas or near areas of permanent water. Planting densities should be reduced in disease-prone areas. This will improve spray coverage and increase air flow in the plantation, which allows quicker drying of the leaves.

25. Banana leaf spot  Chemical control practices  The fungicide program should include protectant and systemic type fungicides and oil should be included in all sprays.  Protectant and systemic fungicides  Three fungicide groups are used on bananas.

26. Banana leaf spot GroupActive ingredients Trade name Group Y protectants Dithiocarbama tes Dithane, Mancozeb Group C systemics DMITilt, Folicur, Bumper

27. Banana leaf spot  Protectant fungicides must be applied before infection while systemic fungicides can stop or arrest the fungus after it has infected the leaf. Petroleum oils can arrest infection up to about two weeks after it has entered the leaf, whereas some systemic fungicides can kill infections up to the speck or early streak stage (stages 1 and 2a). Systemic fungicides, however, cannot prevent development of the disease if applied later than the late streak (stage 2b) or early spot (stage 3) stages.

28. Banana leaf spot  Application frequency  Application frequency can be based on disease development monitored by competent consultants, on weather conditions or by the calendar on a regular schedule. Monitoring systems have been developed and various forms are used by consultants. With time-based (calendar) systems, sprays should be applied at:  10 to 14 day intervals during the wet season  extended to two to three weeks during winter  extended to three to four weeks during the dry spring period  reduced to two to three weeks before the next wet season.

29. Banana leaf spot  Targeting the chemical applications  Fungicides should be aimed at the younger leaves as these are most prone to infection. As the leaf ages, new infections are less though earlier infections will continue to develop. Aerial application is widespread in the banana industry as it allows large areas to be sprayed rapidly, when weather conditions permit. It is also highly effective for airborne ascospore infections.  During the cooler and drier periods, however, conidia are the main means of spread and these are produced within the canopy. Conidia mainly move downwards with dew or irrigation water, and under- canopy applications of fungicides are more effective for these infections.

30. Banana leaf spot  Preventing chemical resistance  Repeated applications of systemic fungicides to severely diseased leaf tissue can lead to resistance to the fungicides in the leaf spot population. When a leaf spot fungus population becomes resistant (or less sensitive) to a particular systemic fungicide, do not use a fungicide from that group of fungicides until that particular population of leaf spot has been controlled.  Strategies to reduce this resistance have been developed and presented in a DPI&F poster. The key points include:  not using a chemical-only program; (Cultural practices are essential.)

31. Banana leaf spot  limiting the use of systemic fungicides; (Use them when conditions are most conducive to infection, not when symptoms are most obvious.)  not applying systemic fungicides to heavily disease plants; (Deleaf diseased leaves before applying the systemic fungicide.)  observing systemic-free periods and monitoring the sensitivity of the leaf spot population. (If a shift in sensitivity is detected, do not use systemic fungicides until the shift is reversed.)  Leaf spot control is costly and can contribute significantly to the costs of production. Twenty to twenty-five sprays are generally applied each year.