A new bio-rational fungicide formulation of potassium bicarbonate for horticultural crops, vines and ornamentals Dr Jean-Pierre Laffranque and Dr Steve W. Shires

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A new bio-rational fungicide formulation of
potassium bicarbonate for horticultural crops,
vines and ornamentals Dr Jean-Pierre
Laffranque and Dr Steve W. Shires
INTRODUCTION
APPLE SCAB (Venturia inaequalis)

• Two field trials in Belgium in 2002 and two in
  Austria in 2004
• Standard reference product Captan at 1000 g
  a.i./ha and Kresoxim-methyl at 100 g a.i./ha
• A total of 10 or 11 sprays were applied at 7 to
  12 days intervals.

• Potassium bicarbonate is a naturally occurring
  inorganic salt found in soil, water, sediments,
  plant and animal tissues.
• Registered by both CODEX and the EU as a food
  additive, classified as GRAS (Generally
  Recognised As Safe) in the USA.
• Indistinguishable from natural potassium and
  bicarbonate, therefore exempt from residue
  tolerances (MRLs) in USA.
• Mode of action related to osmotic and pH effects
  on fungal hyphae and spores, non site specific,
  therefore resistance is extremely unlikely.
• Research to find a formulation that gives
  optimum spreading and penetration carried out by
  Cornell University and Church Dwight Co. Ltd
• Soluble powder formulation containing 85
  potassium bicarbonate, is now registered and
  commercialised in the USA, and is being developed
  in Europe under the brand name of Armicarb 85SP.

RESULTS

• High crop selectivity
• High scab infestation
• Potassium bicarbonate activity similar to
  standards (Fig. 3).

VINE POWDERY MILDEW (Uncinula necator)

• Reference products Captan and Kresoxim-methyl
• Untreated check incidence Fruits 100
  Leaves 100

• 13 field trials were conducted in Austria (2),
  France (5), Spain (1) and Switzerland (5) in 2003
  and 2004.

STRAWBERRY POWDERY MILDEW (Sphaerotheca macularis)
Apples

• 10 trials were conducted in France (7), Belgium
  (2), Spain (1)
• Strawberries were grown under plastic.
• Application rates for potassium bicarbonate were
  between 2125 to 4250 g/ha.
• Two to eight sprays at one week intervals

• Potassium Bicarbonate application rate 4250 g
  a.i./ha in Austria and Switzerland 5100 g
  a.i./ha in France and Spain
• 3 to 10 applications at 8 to 14 day intervals
• Comparison with standard reference products
  Sulphur at 10 kg a.i./ha Spiroxamine at 250 g
  a.i./ha Penconazol at 25 g a.i./ha

Grapes infected with powdery mildew
RESULTS
RESULTS on Vine Powdery Mildew

• Crop selectivity was excellent in all trials
• Potassium bicarbonate gave good control in all
  French trials where natural substrate was used
• In Spain potassium bicarbonate was superior to
  the standard sulphur and in Belgium it was
  superior to myclobutanil but inferior to
  kresoxim-methyl (Fig. 4)

• Crop selectivity was generally good, although
  moderate phytotoxicity observed in two trials
  that had been sprayed twice within two days
• Potassium bicarbonate at 4250 and 5100 g a.i./ha
  provided good control of powdery mildew (Figs. 1
  and 2)
• Overall efficacy was numerically but not
  statistically slightly lower than the standard
  products
• French trials confirmed that potassium
  bicarbonate performs best when applied
  preventatively

Untreated check incidence Leaves 72
CONCLUSIONS

• The recently developed 85SP formulation of
  potassium bicarbonate provides commercially
  acceptable control of some key diseases.
• In vines, potassium bicarbonate applied at 4250
  to 5100 g a.i./ha gave similar or only slightly
  reduced control of powdery mildew compared with
  the standards.
• In apples, 3825 to 4250 g a.i./ha of potassium
  bicarbonate gave similar control of scab on
  fruits but slightly inferior on leaves compared
  with the standards.
• In strawberries, 2125 to 4250 g a.i./ha provided
  high powdery mildew protection
• Potassium bicarbonate is a naturally occurring
  inorganic salt and the concentrations used in
  agriculture are unlikely to have any adverse
  effects on man or the environment.
• Exemption from residue tolerances have been
  granted in the USA and a similar request has been
  made to the European authorities.
• Other trials ongoing in Europe are demonstrating
  interesting efficacy against powdery mildew in
  vegetables (e.g. cucurbits) and Botrytis in vines.

Efficacy trial on Cucumbers Powdery mildew
(Erysiphe cichoracarum)
ab a
a a
ab a
a a

• Reference products Penconazol or Spiroxamine
• Untreated check severity (pest pressure)
• Bunches 33 Leaves 51

Formulated potassium bicarbonate at 3 kg/ha
Untreated check severity (pest pressure) Bunches
51 Leaves 27
Untreated check