contents
The problem
Spectrum of activity
Which two?
Addition points
Safety
Measuring fungicide performance
Quality control

We at Tantec have been working on this problem, and have come to the conclusion that at least two fungicides are needed.

Spectrum of Activity
This is the phrase used to determine how many moulds a fungicide can kill when used at low doses.  If it is just a few, then it has a limited spectrum of activity.  If a fungicide can kill many or most moulds, then the spectrum of activity is large.  Unfortunately, no fungicide can kill all moulds.

We measure spectrum of activity by the MIC laboratory test. This is short for Minimum Inhibitory Concentration.  The stages of the test are :

• Prepare culture agar (sterile) in a number of containers.
• To each container, add a different strength of the fungicide being tested.  For example, we might add 5 parts per million, then 10, 20, 30, 40, 50, 60 etc.
• Pour the agar onto sterile petri dishes and let it set.
• Add the fungus being tested to each dish.
• Culture it at 25 to 30°C,  and see how much fungicide it takes to stop it growing.
• Carry out this test many times for many different fungicides and for many different moulds, and a picture slowly builds up.

We can then say that a certain minimum amount of fungicide will stop a specific mould.

There are five main fungicides used in Australia and New Zealand that we have tested.

1. 30% TCMTB   2-(Thiocyanomethylthio)benzothiazole
2. 50%  MBT  (sodium mercaptobenzothiazole)
3. A phenol blend  (sodium salts of ortho phenyl phenol plus para chloro meta cresol)
4. 10% OITZ (octyl isothiazolone)
5. 50% carbendazim

Note : We did not test TCP (sodium trichlorophenate) since it is not acceptable in many world markets, and probably should not be used.

For example :  to stop the troublesome mould called Trichoderma viride Tantec’s test results show we can use any one of the following.

1. 40 parts per million of TCMTB product
2. 160 ppm of MBT product
3. 160 ppm of OITZ product
4. 40 ppm of phenol blend
5. 5 ppm of carbendazim product

So carbendazim is best against Trichoderma viride. Should we all use carbendazim as the preferred fungicide, and ignore the rest? No, because carbendazim is weak against some other moulds.  For example Penicillium alternaria. It is much better to add insurance by using two fungicides.

Which Two?
At Tantec, we recommend that a primary fungicide be selected, and this be supplemented by a secondary dose with (preferably) carbendazim.  The selection of carbendazim is based on a great deal of experience and an awful lot of test work.

Which primary fungicide?
From the list of five above, consider the following.

1. TCMTB is probably the most potent and most broad spectrum, and most cost effective.  However, it fails to work well in many tanneries.  If previous experience shows it works well in your plant, it is a logical choice as primary fungicide.
2. OITZ performs similarly to TCMTB.  If TCMTB fails, then there is a good chance that OITZ will fail also.
3. After the above two, the lower cost product will be MBT. It often works very well when TCMTB and OITZ fail.
4. The phenol blend should be seen as a last resort since it is the most expensive.

1. It is very potent.
2. It has a very wide spectrum of activity.
3. It is low in human toxicity. In  Australia and New Zealand it is registered and approved for spraying onto fruit trees.
4. It is low in cost.

1. If your plant can use TCMTB successfully, then the most cost effective treatment will be a blend of Thiostop (30% TCMTB) and Carbostop (50% carbendazim).
2. If your plant cannot use TCMTB successfully, then we recommend a blend of Mercostop ( 50% MBT) and Carbostop.

Thiostop at 0.075% plus Carbostop at 0.03%
Mercostop at 0.2% plus Carbostop at 0.03%

Addition Points
Thiostop needs to be added slowly,  Add when pH is low - into pickle, tannage or rinse. Do not add within 30 minutes of tanbase addition.

Mercostop should be added into high pH.  Best is with salt before acid addition just prior to pickling.  Run for 30 minutes before adding acid. However, this material is quite forgiving and is often added successfully at other points.

Carbostop should be added where pH is low (less than 6.5).

 Safety
All handling of chemicals should be done with caution, following correct procedures to minimize risk.

While most modern fungicides are not highly toxic, many are harmful if they contact delicate tissue.  The most sensitive tissue in the human body is the lungs.  Breathing fungicide dust, or spray droplets, may be harmful.  Avoid spraying fungicide solutions, and wear proper filter masks if dust is around.

Wear full protective clothing when handling fungicides (or other chemicals).  This includes :

• Gloves which fit well and are made of chemical resistant material
• Eye protection that fits
• Overalls and boots.
• Filter masks if handling powders.

• If breathed, get to fresh air
• If in eyes flush with fresh water, holding eyelids open, for 15 minutes.
• If on skin, wash off with water, or soap and water.
• Get to a physician

Measuring Fungicide Performance
There are two basic methods that are widely used.

1.  Petri dish method.  A sample of treated leather is placed on a sterile disc that sits on nutrient agar in a petri dish.  The agar is inoculated with various mould species, and the whole thing incubated for about 90 days.  The number of days the leather remains mould free is a measure of  how resistant the treatment is to mould.  This has the disadvantage that it takes a long time.

2. The Tantec method - the Tropical Chamber.  An insulated cabinet is kept warm and moist, with air gently circulating.  Mould from a wide range of  sources such as mouldy leather, or mouldy spore count plates is introduced into the chamber.  Samples of treated leather are placed in the chamber.  Mould grows very quickly on under-treated samples.
The main disadvantage of this system is that it tends to make phenol treated samples perform less well than they do outside the chamber.

If you run a leather fungicide trial, ask us to test your results for mould resistance.

When we do this, we ask that you send at least ten samples per treatment, cut to 110 by 70 mm in size, and labeled with a simple letter such as A, B, C etc so we cannot see what the treatments are.  Results are reported as the percentage of sample covered by mould after six weeks in the chamber.
 

 

Example of a real trial result. Untreated control   Borderline treatment   Positive control   Phenolic treatment   Mercostop/Carbostop

50% 1.3% 0.3% 5.3% 0.1%


Quality Control
The tropical chamber can be used on a regular and routine basis to monitor mould resistance.  Our customers often send samples for this quality test. Sample size of 110 by 70 mm and three samples per batch.

In addition, as part of routine service, we do :

• in plant spore counts
• MIC tests on local moulds
• Microscopy
• Defect analysis
• Training of staff
• Tests of bacteria degradation, preservative performance and similar.
• Anything else that is relevant

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