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 |
