Pesticide Sprays and Water pH

The pH of water can adversely affect the performance of some pesticides in the spray mixture soon after mixing. Leaving the spray mixture in the tank overnight or for the day due to inclement weather can result in some pesticides breaking down. The result is less chemical applied and less control than expected.

pH is the measure of acidity or alkalinity of solutions. A scale of 0-14 is used to indicate whether the solution is neutral (7), acidic (0 – 6) or alkaline (8 – 14). Most pesticides break down faster in alkaline water, and generally are most effective when mixed in acidic water. The break down of pesticides is caused by a reaction called alkaline hydrolysis and this reaction is affected by pH. In most cases the pesticide is broken down to non-toxic forms. pH affects many organophosphate and carbamate insecticides. The table below lists some pesticides for which information is available on their sensitivity to water pH. The half-life values may not be valid when two or more pesticides are mixed.

Check the pH of the spray water from any water source frequently throughout the season. Use indicator paper or a pH meter to check water pH. If tank mixing another pesticide or nutrient product, check the pH after the products have been thoroughly mixed and adjust pH accordingly. Sprays containing lime or lime sulphur and fixed-copper fungicides should not be acidified. Algae can change water pH and pH of water from reservoirs can change over time.

Always read the label for any precautions with respect to alkaline water. Apply pesticides soon after mixing in the spray tank and avoid mixed pesticides left in the spray tank overnight.

Optimum
PRODUCT	pH	Half Life/ Time for 50% Hydrolysis (Breakdown)
Insecticides
Acramite	<7	pH 9 = 2 h; pH 7 = 20 h; pH 5 = 5.5 days
Actara	4	pH 4 = 16 wks; pH 7 = 5 wks;
Admire	7.5	Greater than 31 days at pH 5 - 9
Agri-Mek	6 - 7	Stable at pH 4 – 7.5
Apollo	6 - 7	pH 5 = 10 days; pH 7 = 34 hrs; pH 9.2 = 4.8 hrs
Assail	5 - 6	Unstable below 4 and above 7
Avaunt		Stable for 3 days at pH 5 – 10
Calypso		Stable pH 5 - 9
Carzol	5	Not stable in alkaline water; use within 4 hours of mixing.
Cygon	5	pH 9 = 48 min; pH 6 = 12 hrs; pH 4.5 = 20 hrs
Dipel	6	Unstable in pH above 8
Entrust	7	Stable at pH 6 - 9
Envidor	5 - 7	pH 4 = 63 days; pH 7 = 31 days; pH 9 = 5 days
Foray 48BA	6	Unstable above pH 8
GF-120 NF	7	Stable pH 6 - 9
Imidan	5	pH 8 = 4 hrs; pH 7 < 12 hrs; pH 5 = 7 days
Lagon	5	pH 9 = 48 min; pH 6 = 12 hrs; pH 4.5 = 20 hrs.
Malathion	5	pH 9 = 5 hrs; pH 8 = 19 hrs; pH 8 = 3 days; pH 6 = 8 days
Matador	6.5	Stable pH 5 – 9
Pyramite		Stable at pH 4 – 9
Rimon	5 - 7	pH 9 = 100 days
Sevin XLR	7	pH9 = 24 hrs; pH 8 = 2-3 d; pH7 = 24 d; pH6 = 100 d.
Success	6 - 7	Stable at pH 6 – 9
Fungicides
Aliette	4	Stable at pH 4.0 to 8.0
Bravo 500	6 - 7	Stable over wide range of pH; pH 9 = 38 days
Captan	5	pH 8 = 10 min; pH 7 = 8 hrs; pH 4 = 32 hrs.
Dithane DG	6	Most stable at pH 5.5 to 6
Elevate	5.5 – 6.5
Equal		Incompatible with calcium products.
Funginex	7	Stable to pH 10 or 11
Ridomil	5 - 7	pH 9 = 88 days
Rovral		pH 7 = 1-7 days; pH 9 = < 1 hr.
Senator	4.5 – 7.5	Do not combine with products that are high alkaline.
Topas		Stable from pH 5 – 9; use within 12 to 16 hrs.
Herbicides
Devrinol	5.5 - 7
Gramoxone		Not stable in pH above 7
Ignite	5.5
Laredo	5.5	Avoid pH above 7
Poast	3 - 4	Stable in pH 4 to 10
Princep	5 – 7	pH 4.5 = 20 days; pH 5 = 90 days; pH 9 = 24 days
Prowl	5	Stable from pH 5 - 10
Roundup	5 – 7.5	Avoid pH above 7
Touchdown	5 - 7.5	Avoid pH above 7
Wrangler	5 - 6	Avoid pH above 7

Questions, comments, or concerns can be emailed to [email protected].