Reducing inoculum – Lab trials

Posted on by Better Bananas

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

Posted on by Better Bananas

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

Posted on by Better Bananas

Plants symptoms and causes

Plants kink, bend or fall over

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

Plants turn yellow and die

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

Small and stunted plants

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

Stem shatters

Click here to view the stem shatters symptoms and causes.

Internal stem discolouration

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

Green leaves dropping

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

Leaves bunching at top of plant

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

Stages of leaf spot disease

Posted on by Better Bananas

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. 

ns

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.

ns

Corm smelly, rotting or discoloured

Posted on by Better Bananas

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

Posted on by Better Bananas

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. 

Roots discoloured internally

Posted on by Better Bananas

Roots discoloured internally

Burrowing nematode, other nematodes

Cause: Burrowing nematode Radopholus similis feeding on the cells in the root cortex. Many species of nematodes in the soil also parasitise the roots of bananas.


Solution: Nematodes other than burrowing nematode are not usually a problem in the tropics. Check a random sample of roots over the whole field to determine the extent of the problem and if a nematicide treatment is necessary.

Damaged roots or no root hairs

Posted on by Better Bananas

Damaged roots or no root hairs

Note burnt root tips.

Fertiliser burn, drought or water-logging, poor drainage, air burn, soil compaction.

Cause: There are several causes of root tip burn. They include fertiliser burn from too much fertiliser or poor placement; aluminium or manganese toxicity caused by low soil pH; and soil drying out or staying too wet for too long. As well as these causes, air burn or soil compaction can cause root hairs to be lost. 


Solution: Determine the cause with soil and tissue analyses. Broadcast fertiliser evenly and at recommended rates. Watering heavily to leach salts out of the root zone can alleviate problems of excess fertiliser. Maintain soil pH between 5 and 6 and avoid planting in areas with poorly drained soils. 

Note chewed roots.

Greyback cane beetle

Cause: Chewing by larvae (cane grubs) of Dermolepida albohirtum. 


Solution: Correct timing of insecticide application is crucial. The chemical must be applied when larvae are close to the surface between November and January. 

 

Note lumps (galls) within roots and missing root hairs.

Root-knot nematode

Cause: Meloidogyne spp. Root-knot nematode invades the root when young. When mature the females form special feeding cells that appear as galls within the roots. 


Solution: Root-knot nematode is not usually an economic problem to banana production in the tropics. Most mature banana plants with adequate irrigation and fertilising can compensate for any damage. Root-knot nematode may become a problem in very young plants, or on very sandy soils.