Greenhouse, Nursery, and Landscape - Spray Water pH

Spray water pH can have great effects on the pesticides that you use. The following is an article on the subject.

Improving the effectiveness of pesticide applications is critical to reducing the number of total applications made (saving time and money), helping to prevent pest resistance problems, and limiting the damage to the environment. Growers may attribute ineffective applications to pest resistance, the product they used, or the rate at which it was applied. However, they often overlook the fact that the pH of their water may be at the root of the problem. The effectiveness of many chemicals is greatly influenced by pH. Take time to run a pH test before you mix up your PGR or pesticide.

Most products work best when mixed at acidic pHs of 6.0 or lower. Chemicals can experience a degradation process called hydrolysis at higher pH's; these include the organophosphates, synthetic pyrethroids, carbamates, chlorinated hydrocarbons, and ethephon growth regulator. Every unit increase in pH represents a tenfold increase in the rate of hydrolosis. Buffering agents such as pHase 5, Buffer P.S., and Buffer Extra Stength can be added to adjust the pH of the water in the spray tank before mixing. Buffering agents should not be used with products containing fixed copper or lime (copper becomes more soluble at low pH). Caution: adding too much buffering solution can be phytotoxic to plants.

The Ohio State website www.floriculture.osu.edu has an article called Spray Solution pH with great links to lists of products that can’t be used with buffering agents and the optimum pH ranges of many common insecticides, fungicides, growth regulators, and herbicides. You can also check the product label or with a company technical representative to see if there is a suggested pH range. Most growers who use florel know that the pH of the water should be low, but did you know that it should be pH 3.0? If you use B-Nine, the pH of the water should not be alkaline (higher than pH of 7.0). The azadirachtin products (Azatin or Ornazin) are very sensitive to high pH levels. How about Fungicides? The pH for Maneb and Manzatet should be pH 5.0 -6 for optimal effectiveness.

From the February 10, 2006 edition of the Greenhouse TPM/IPM Weekly Report by the University of Maryland Cooperative Extension.