1. Introduction
  2. Development of HML32
  3. Recommended fungal spray programme based on HML32
  4. Registration and safety information
  5. Research and trials
  6. Other technical publications/papers to assist


HML32 is a manufactured formulation of Protectorhml and food grade potassium bicarbonate.

It is formulated because, as noted below, a tank mix of these two products does not produce acceptable efficacy. Likewise, many other adjuvants would also not ‘activate’ potassium bicarbonate in a tank mix.

HML32 is registered as a fungicide for botrytis and powdery mildew control on wine grapes by the Ministry for Primary Industries – Agricultural Chemicals Veterinary Medicines Group (ACVMG) – registered number P8633.

HML32 is also certified as a ‘permitted’ fungicide by BioGro for use on organic properties.


Five seasons of study document the transition from hand spraying to grower machine spraying with all the associated variables.

Season 1 (2010/2011)

Like many things that are discovered in life, something that starts as one thing ends up something else.

In the case of HML32, in the 2010/2011 season (the first season), what began as a simple efficacy trial on grapes for powdery mildew ended up with several treatments showing remarkable resistance to botrytis, sour rots, with enhanced maturity (higher brix, thickened skins and enhanced colour), in what was a highly challenging season.

The properties of Protectorhml are explained in this website. Protectorhml is pure potassium soap. The properties of potassium bicarbonate, as with carbonates of potassium and other metals have also been well researched. They are known to require activation by a suitable adjuvant (Note: Many common sticker/spreaders do not activate potassium bicarbonate). Once ‘activated’ their main pesticide use is as an eradicant for powdery mildew infections. Their previous known efficacy on botrytis is not rated highly, if at all.

Season 2 (2011/2012)

The second season, (2011/2012), went the way of a tank mix of the ingredients and 28 grower machine sprayed studies using elevated water rates. There were two water rate regimes and 2 potassium bicarbonate rates compared to grower’s best chemical regime. There was also complex hand sprayed studies. The season was again highly challenging for diseases, botrytis in particular. An effective transition between the two seasons was not made. There was in places a lack of powdery mildew efficacy, setting up a botrytis scenario - likewise many of the previously measured differences between treatments in both hand sprayed and machine sprayed studies did not repeat themselves.

Season 3 (2012/2013)

Changes were made. The third year of study, (2012/2013), reverted to a pre-formulation of ingredients as had been used in initial season. There were 24 grower machine sprayed studies comparing what is now HML32, with HML32 containing an elevated level of potassium bicarbonate and grower’s best chemical regime. Standard water rates (none were low) were used and wettable sulphur was added to all machine sprayed applications which began pre-flowering and finished at veraison. There was also complex hand sprayed studies. Powdery mildew for the most part was very well controlled. Botrytis was not a major challenge in most places but when it did appear efficacy was virtually the same as grower chemistry. HML32 efficacy on botrytis was better when potassium bicarbonate was not elevated. Of importance – while the disease pressure did not make testing more robust, ‘the measurable indicators’ that were found in the first season’s study were present again.

Season 4 (2013/2014)

Hence, in the fourth season (2013/2014), it was a planned low key commercial release within New Zealand through the distributor Farmlands Horticulture. Growers were asked to target areas of low to moderate botrytis challenge only.

To complement grower use, there were specific studies, both hand sprayed and machine sprayed in both Hawke’s Bay and Marlborough. Some of that material is reported within.

In general, growers who used HML32 all season were pleased with the results achieved in respect of botrytis, and where performance was compared to grower’s chemical regime, the results were similar. There were some issues arising with incompatibility with other chemicals.

The greatest benefit was seen by growers who used HML32 in combination with low doses of copper for powdery mildew control and eradication (report is available below). In Gisborne, Hawke’s Bay and parts of Marlborough, the 2013/2014 season was one of very high powdery mildew pressure.

In addition, under ‘Other technical publications/papers to assist’ there is an independent screening trial undertaken by Farmlands Horticulture, Hawke’s Bay. They screened many powdery mildew products and others, used by grape growers, for their eradicative/curative efficacy on powdery mildew infections. Products were included on the basis of grower use – not label claim. They included such combinations as a common surfactant with potassium bicarbonate, phosphoric acid and molasses, reduced oil rates with surfactants etc.

Season 6 (2015/2016)

Two separate hand sprayed trials for powdery mildew prevention and eradication were undertaken this season containing HML32 treatments in different combinations with sulphur, copper and potassium bicarbonate. The trials were assessed 'blind' by independent experts.

The trials contained various products that were under development of which HML Silco (potassium silicate) is looking like a very promising additive.

Both trials confirmed the efficacy of HML32 and Sulphur for Powdery Mildew prevention and HML32, Copper and Potassium Bicarbonate for Powdery Mildew eradication.

Other learnings from the 2016 Eradication Trial are:

  • If you can only manage one eradication spray, due to lack of resources, increase the rate of metallic copper to 67 - 90 g/100L; Don't add sulphur to the eradication spray as it reduces its efficacy
  • Eradication provides significant forward protection. Prevention sprays can be subsequently resumed at normal timings

Season 7 (2016/2017)

A machine sprayed trial was undertaken on a 3 ha Chardonnay block in Hawke’s Bay to compare the efficacy of three product combinations against a chemical standard. The three combinations were HML32, sulphur and copper fungicide, HML32, sulphur and HML Silco, and HML32 with HML Silco (no sulphur).

The trials were assessed 'blind' by independent experts.

The trial confirmed that HML Silco was an effective replacement for copper and that HML32 and HML Silco was able to achieve reasonable efficacy without sulphur in the programme.

It is noted that the chemical standard was not as robust as it could have been due to one of the chemical product not have claims for powdery mildew so it is likely that the chemical standard would not have been statistically different from the HML32, sulphur, copper fungicide treatment and the HML32, sulphur and HML Silco treatment.

Recommended fungal spray programme based on HML32

Based on what we learnt over 2010-14, and over more recent years with the use of the HML Silco adjuvant, we have developed a fungal spray programme using HML32 as a base for the prevention of both powdery mildew and botrytis. More information on this Cover spray programme can be found here or view it in pdf form below.

View the Powdery Mildew and Botrytis Prevention Spray Programme for 2017-18

The programme is still based on powdery mildew control as a priority. Powdery mildew is a prime cause of winery rejection of crop. It causes a musty off flavour in wines and is a precursor to botrytis and sour rots. In addition, the challenge of powdery mildew is now higher in modern times because of the ‘sexual stage’ of the organism. This provides spore release at the most potentially damaging times, over the flowering and post flowering period when the current crop is most susceptible.

The fungal spray programme uses Protectorhml, HML32, HML Silco and HML Potum, in combination with sulphur and copper fungicides. HML32 must always be used with Sulphur to provide a robust powdery mildew preventative programme.

For susceptible varieties, or where there was higher pressure in the previous season, spray intervals should be tightened.

The focus of the programme is prevention but the product combinations provide eradicative/curative properties as well which is critical to a modern spray programme.

As the mode of action is contact, application technique and coverage are key to achieving maximum efficacy. Effective ‘covers’ and reasonably tight spray intervals are important during times of high growth, likewise the replacement of ‘cover’ after significant rain events. Simple things such as alternating the spraying direction to reduce ‘shadows’ count towards well controlled disease.

'Prevention is far cheaper and easier than cure'.

View a list of distributors.

Registration and safety information

Research and trials

Other publications and papers that may assist