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Ministry of Agriculture

About Pesticides

Enhancing Effectiveness

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Pesticide Sprays and Water pH  

The pH of water can adversely affect the performance of some pesticides 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, conversely, are most effective when mixed in acidic water. This break down 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 frequently from any water source 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 as well as pH of water from reservoirs can change over time.

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

Product Optimum pH Half Life / Time for 50% Hydrolysis
Insecticides
Admire 7.5 Greater than 31 days at pH 5 - 9
Agri-Mek   Stable at pH 5 - 9
Ambush 7 Stable at pH 6 - 8
Apollo   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
Belmark 6 Stable in acid condition
Carzol 5 Not stable in alkaline water; use within 4 hours of mixing.
Cymbush   pH 9 = 35 hrs
Cygon 5 pH 9 = 48 min; pH 6 = 12 hrs; pH 4.5 = 20 hrs
Decis   no data
Diazinon 7 pH 5 = 2 wks; pH 7 = 10 wks; pH 8 = 3 wks; pH 9 = 29 days
Dipel 6 Unstable in pH above 8
Endosulfan   70% loss after 7 days at pH 7.3 8
Foray 48B 6 Unstable in pH above 8
Guthion   pH 9= 12 hrs; pH 7 = 10; days; pH 5 = 17 days
Imidan 5 pH 8 = 4 hrs; pH 7 < 12 hrs; pH 5 = 7 days
Kelthane 5.5 pH 9 = 1hr; pH 7 =  5 days; pH 5 = 20 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
Mitac 5 pH 9 = 1.5hrs;  pH 7 = 15hrs;  pH 5 =  35 hrs
Morestan 4.5 pH 9 = 4hrs;  pH 7 = 80 hrs;   pH 4.5 = 10 days
Pounce 6 pH 5.7 to 7.7 is optimum
Pyramite   Stable at pH 4 9
Ripcord   pH 9 = 35 hrs;  more stable pH below 7
Sevin XLR 7 pH9 = 24 hrs;   pH 8 = 2-3 days; pH7 = 24 days; pH6 = 100 days.
Sniper   See Guthion
Spinsosad 6 Stable at pH 5 7; pH 9 = 200 days
Thiodan 6.5 70% loss after 7 days at pH 7.3 to 8
Zolone 6 pH 9 = 9 days; stable pH 5 - 7
Fungicides
Aliette 6 Stable at pH 4.0 to 8.0
Bravo 500 7 Stable over wide range of pH
Captan 5 pH 8 = 10 min;  pH 7 = 8 hrs;  pH 5 = 32 hrs
Dithane DG 6 Most stable at pH 5.5 to 6; pH 5 9 = 1- 2 days
Equal   Incompatible with calcium products
Funginex   Stable to pH 10 or 11
Ridomil   pH 5 9 = more than 4 weeks
Rovral   Chemical breakdown could take place in high pH
Senator   Do not combine with products that are high alkaline
Topas   Stable from pH 5 9
Herbicides
Ignite 5.5  
Laredo 5.5  
Poast 7 Stable in pH 4.0 to 10
Roundup 5 - 6  
Touchdown 5 - 6  
Wrangler 5 - 6  
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Adjuvants 

Adjuvants are materials that are added to the spray tank mix to enhance the activity (performance) of a pesticide, or to change the characteristics of a spray mixture. There are many different types of adjuvants, including surfactants (wetting agents, or spreaders), stickers, extenders, plant penetrants, compatibility agents, buffers or pH modifiers, drift retardants, anti-foaming agents and thickeners.

Refer to the pesticide label for recommendations on the use of adjuvants. Many labels have specific recommendations.  Some pesticides may benefit from the addition of an adjuvant, while others may be adversely affected.  Most pesticides products are already formulated with adjuvants by the manufacturer, and it may not be necessary to add anything else.