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Alternative host research

Can weeds and ground covers host Panama disease?

The soil borne fungus Fusarium oxysporum f.sp. cubense (Foc) which causes Panama disease can survive and persist in the soil for years in the absence of banana plants. Weeds and ground covers that co-habit banana plantations can act as alternative ‘host’ plants. In this context, a host is defined as a plant in which the fungus can survive, often without obvious disease symptoms apparent.

By understanding what other species are capable of hosting Foc, it may change weed and ground cover management in areas infested with Panama disease. Keeping disease inoculum low is key to minimising spread to non-infected areas, and in the long term may play an important role in growing bananas in the presence of the disease.

So far, two complementary research efforts using Panama disease race 1 (R1) and subtropical race 4 (SR4) have begun to help our understanding of what weeds and ground cover species are capable of hosting Foc. This research has led to further trial work currently underway, including:

  • Understanding how Foc behaves within alternative hosts and whether it reproduces and has the ability to increase inoculum levels.
  • Publication of a guide that gives an overview of the plant species regularly observed in banana plantations and their ability to host Foc.
  • Investigation of weed and ground cover species in the Northern Territory using Panama disease tropical race 4 (TR4).

More information on trials...

This research was funded as part of the Fusarium Wilt Tropical Race 4 – Biosecurity and Sustainable Practices project (BA14013). This project was funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland Department of Agriculture and Fisheries and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

Guide to crown end rot identification

Guide to crown end rot identification

Thielaviopsis musarum (commonly known as Chalara).

  • Rot extends beyond the crown and into the fruit (rapid development).
  • Usually limited to a few clusters.
  • Occurs randomly and mostly reported during winter and spring.
Thielaviopsis musarum

Fusarium equiseti-incarnatum species complex.

  • Gives a fuzzy/fluffy appearance on cut crown surface.
  • Usually causing cosmetic damage but incidence is often reported as high.
  • Reported to be worse during summer/spring. 
Fusarium equiseti-incarnatum species complex

Musicillium theobromae

  • Appearance not as fuzzy/fluffy as the above organism.
  • High incidence reported.
  • Reported to be worse during summer/spring.
Musicillium theobromae

Colletotrichum musae

  • Limited fungal growth apparent and sometimes orange spore masses are observed.
  • Rot can extend below the crown.
  • Low incidence reported.
Colletotrichum musae

Please note...

The above information is a guide only, as multiple organisms may be involved and simultaneously cause symptoms.  

If you notice any crown end rot symptoms or want further information, contact the better bananas team at betterbananas@daf.qld.gov.au or 13 25 23. 

This work is funded as part of the Cause and management of crown rot of banana project (BA13011). This project is funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland Department of Agriculture and Fisheries and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

Reducing inoculum – field trials

Field trials - reducing inoculum

The use of high rates of urea to reduce disease inoculum levels of plants infected with Panama disease has been investigated. Researchers have looked at the effect of applying urea to both the soil surface surrounding infected plants as well as infected pseudostems.

Two field trials conducted at Duranbah in New South Wales used a site infested with Panama disease race 1. In the first field trial, Dwarf Ducasse plants showing symptoms of Panama disease race 1 were cut off at ground level. The growing point was then gouged out and a 1 m2 area was treated around each plant.  All gouged corms were treated with 200 g of urea and the 1 m2 areas around the plants were treated with either:

  • urea (1 kg/m2) and covered with black plastic
  • urea (1 kg/m2), watered in (10 L) and covered with black plastic
  • urea (1 kg/m2), Basamid® (500 g/m2), watered in (10 L) and covered with black plastic
  • plastic only
  • untreated.

Soil samples were taken from the treatment areas 6 and 15 days after the treatments were applied. The soil was analysed to determine the ammonium content in surface (0-5 cm) and subsurface (5-15 cm) soil and the populations of Fusarium oxysporum in the subsurface samples (5-15 cm). 

Trial showing 1 m2 plots covered with black plastic.
Black plastic used to prevent runoff and contain breakdown gasses.

So what happened under these treatments?

As expected the ammonium levels were significantly greater in the soil treated with urea. As a result the number of Fusarium oxysporum spores in the soil (including the strain that causes Panama disease race 1) measured by the number of colony forming units (cfu) was significantly reduced. 

The table below shows the levels of ammonium (ppm) in the soil 6 and 15 days after treatment application. 

Means in each column with the same letter are not significantly different at 5% level (P<0.001). For example at 15 days after treatment at surface depth (0-5 cm) there was no significant difference between untreated and plastic. However, there was a significant difference between urea and all the other treatments (15 days at surface depth 0-5 cm).

Table showing ammonium levels in the soil 6 and 15 days after treatment application.

The graph below shows the significant reduction in cfu under the urea treatments. 

Levels of Panama disease race 1 in the soil measured 6 and 15 days after treatment application.

The second field trial investigated the method of cutting up infected pseudostem material and placing it into bags with urea. To test this technique Dwarf Ducasse plants infected with Panama disease race 1 were cut into 15 cm length and placed inside heavy duty plastic garbage bags. Some of the bags included 1 kg of urea and some bags contained no urea. After 6 weeks pieces of vascular tissue were plated out to determine the survival of the fungus. There was no recovery of the fungus that causes race 1 in any of the bags which were treated with urea. There was some reduction in survival of the fungus in the untreated bags, but the pathogen was still recovered.  

Bags of infected pseudostem. Bags either contained urea or had no urea.
Close-up of infected pseudostem treated with urea.

So what does this all mean...

These field trials confirm that the current method for dealing with infected plants does significantly reduce the amount of inoculum in banana paddocks infested with Panama disease.

For more information about this work contact the better bananas team: 
betterbananas@daf.qld.gov.au or 13 25 23.

This trial was funded as part of Biosecurity Queensland’s Panama TR4 Program and the Fusarium Wilt Tropical Race 4 – Biosecurity and Sustainable Practices project (BA14013). This project (BA14013) was funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland Department of Agriculture and Fisheries and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

Reducing inoculum – Lab trials

Lab trials - reducing inoculum

To reduce disease inoculum levels, researchers have investigated the practice of using high rates of urea on the soil surface immediately surrounding infected plants.

Lab trials at South Johnstone used a soil bioassay with spores of Fusarium oxysporum f.sp. cubense (Foc), the fungus that causes Panama disease race 1. This was used as surrogate for tropical race 4. The inoculated soil was treated with one of the following treatments:
  • ‘control’ – no urea or lime treatment
  • urea (rate equal to 0.5 kg/m2)
  • lime (rate equal to 0.5 kg/m2)
  • both lime and urea (rate equal to 0.5 kg/m2).

Interestingly, Foc was not recovered from soil that was treated with urea and the urea/lime combination. Foc was however recovered from soil treated with lime only, proving the application of lime on its own as ineffective at reducing inoculum levels.

Back: Jars of inoculated soil with different treatments. Front: Samples showing fungal development of control (far left) and lime (third from left) treatment.
Results of lab trials showing recovery of Foc from control and lime treatments, while no recovery of Foc was observed for the urea and urea and lime treatments.

Outcomes...

Lab trial results have shown that both urea and the combination of urea and lime at the specified rates are effective at killing the spores that cause Panama disease race 1.

Further lab investigations

Further trial work has evaluated the effectiveness of lower application rates of urea as well as chemical alternatives that are suggested to be toxic to Foc. The same bioassay using soil in jars was used to determine the effectiveness of the following treatments:
  • potassium chlorate @ 4, 8 and 16% (w/v)
  • sodium nitrite at 200, 400 and 800 ppm
  • nitrite at 200 and 400 ppm
  • lower rates of urea (rate equal to 0.031, 0.062, 0.125, 0.25 and 0.5 kg/m2). 

These investigations showed that urea applied at 0.062 kg/m2 or greater prevented Foc recovery from soil. All the other chemical alternatives were not effective at reducing the recovery rate of Foc

Results of lab trials showing urea applied at greater than 0.062 kg/m2 was the only effective treatment in preventing Foc recovery from soil.

Additional trials have investigated the effectiveness of different urea rates (between 0.031 and 0.062 kg/m2) and further explored alternative sources of ammonium. This time the effect of urea, ammonium nitrate + potassium hydroxide and aqueous ammonia were assessed. The trial showed that ammonia (NH3) from any source that produces a concentration equal to or above 2500 ppm was effective at preventing Foc from being recovered from the soil.

So what does this all mean?

These lab trials show the current methods for dealing with infected plants using urea (1 kg per square metre) would significantly help in reducing the amount of inoculum in infested banana paddocks. The trials further show that ammonia, rather than other gasses produced during the breakdown of urea, is likely to be responsible for the toxic effect on the fungus.

For more information about this work contact our better bananas team on 13 25 23 or email: betterbananas@daf.qld.gov.au

This trial was funded as part the Fusarium Wilt Tropical Race 4 – Biosecurity and Sustainable Practices (BA14013) project, which was funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland Department of Agriculture and Fisheries and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

Reducing inoculum from plants infected with Panama disease

Reducing inoculum from plants infected with Panama disease

A key aspect of managing Panama disease tropical race 4 on an infested property, is the implementation of practices to reduce the amount of inoculum (number of spores) entering the soil. The management of infected plants via a careful and thorough destruction protocol is one of the most crucial of these practices. 

The current method requires infected plants to be cut up and placed into large plastic bags with 1 kg of urea to accelerate the breakdown of the fungus and plant tissue. Urea is then evenly applied to the soil surface at a rate of 1 kg per square metre around the infected stools, and 200 g of urea is also applied to each gouged corm. The entire treated area is then covered with heavy plastic to prevent runoff and to contain the breakdown gasses which help kill the fungus. 

Lab and field trials conducted to validate this method, have showed the application of urea at this rate can significantly reduce inoculum levels. 

See below for details of the lab and field trials:

Due to strict biosecurity conditions this research has been conducted using Panama disease race 1 as a surrogate for Panama disease tropical race 4.

Black plastic in field trial, used to prevent runoff and contain breakdown gasses (Duranbah, New South Wales).
Urea application to ground around infected plants and to gouged corm (Duranbah, New South Wales).

Please note...

Due to the extremely high rates of urea used for this technique, the strategy is ONLY utilised to treat confirmed detections of Panama disease on properties where a Notice of presence of Panama disease tropical race 4 is in effect.

Plants

Plants symptoms and causes

Click here to view the plants kink, bend or fall over symptoms and causes.

Click here to view the plants turn yellow and die symptoms and causes.

Click here to view the small and stunted plants symptoms and causes.

Click here to view the stem shatters symptoms and causes.

Click here to view the internal stem discolouration symptoms and causes.

Click here to view the green leaves dropping symptoms and causes.

Click here to view the leaves bunching at top of plant symptoms and causes.

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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Corm smelly, rotting or discoloured

Corm smelly, rotting or discoloured

Panama disease (Fusarium wilt) (discoloured)

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). 

More info:

The rotting corm has a strong odour.

Bacterial corm rot (smelly, rotting, discoloured)

Cause: The bacteria Pectobacterium spp. (formerly known as Erwinia spp.) that are common soil inhabitants. Plants that are stressed during the dry season can succumb to invasion during the wet season. 


Solution: No chemical treatments are available. Ensure adequate moisture levels are maintained during the dry season and provide good drainage during prolonged wet seasons.

Moko disease (discoloured)

Biosecurity Alert

Cause: The bacteria Ralstonia solancearum race 2. Moko is a soil-borne disease and is spread with soil, in water, on implements, in planting material and by insects from flower to flower. The infection enters the plant through the roots and spreads through the host, blocking conducting tissue and resulting in plant yellowing, wilting and death.


Solution: There is no chemical control for Moko. All plants plus an adequate buffer zone around the diseased plants must be destroyed. The area must be quarantined and only non-host plants grown.  

Biosecurity obligation:
If you suspect Moko disease you must notify Biosecurity Queensland immediately (13 25 23). 

More info:

Note discoloured edge of corm.

Burrowing nematode (discoloured)

Cause: Burrowing nematode feeding in the banana corm. Planting nematode-infected corm pieces is the most common method of spread to new areas.


Solution: Do not use banana corms with visible signs of nematode damage as planting material.  

Tunnelling in corm

Tunnnelling in corm

Severe infestation reduces plant vigour and the tunnelling allows the entry of rot organisms, which result in faster corm breakdown.

Banana weevil borer

Cause: Tunnelling by larvae of Cosmopolites sordidus.


Solution: Use stem baits to establish the severity of the infestation. If necessary treat with an appropriate chemical. Follow label directions regarding application method and timing to maximise the effectiveness of the treatment.