1. Introduction
  2. Development of HML32
  3. New Zealand Registration and safety information
  4. Research and trials
  5. 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 (ACVM) – registered number P8633.

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

HML32 is EPA registered in the USA, along with state registrations in California and others.

HML32 is registered in Australia as HML 32 and has ACO organic certification. It is not yet in the Australian Market.


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

A large replicated hand sprayed Enhanced Maturity and Botrytis trial was also undertaken over January to March 2016 involving HML32 and HML Silco.

Undertaken on Chardonnay, Merlot and Syrah in Hawke's Bay (Triangle), the objective was to determine the most effective application timing to achieve enhanced maturity effects, and also effects on late season Slip Skin and Botrytis.

There were three sets of treatments (HML32 and HML Silco sprayed once, HML32 alone sprayed once and HML32 alone sprayed twice 10 days apart). Treatments were applied every 5 days from the lag phase (approximately 13 January 2016) and continued through veraison to harvest. All trial field data was assessed ‘blind’ by an independent expert.

Significant improvement in resilience to botrytis (both expressed as bunch botrytis or slip skin) was achieved through applications at the same particular timing that produced significant‘enhanced maturity’ effects. For more information about the enhanced maturity and botrytis results and the timing of the applications, click here

Watch this video to see the difference that applications of HML32 at particular timings make to markedly reduce end of season slipskin infection in the trial.

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.

Season 8 (2017/2018)

Another large handsprayed trial was undertaken on the 3 ha Chardonnay block that was used the previous season. This trial confirms the efficacy of HML32 and sulphur particularly when used with the HML Silco adjuvant.

It also indicates that HML Silco improves the efficacy of the Protector/Sulphur mix against powdery mildew, making it a less expensive spray round for the early season applications.

Use of HML32 around flowering

The label recommendation is to apply HML32 with sulphur plus additives just before flowering and when flowering is complete. If flowering is protracted and cool or wet, and there is a desire to apply additional cover, use Protectorhml at 2% concentration instead of HML32.

New Zealand Registration and safety information

Research and trials

Other publications and papers that may assist