How do pesticides that are growth regulators work

It is the concentration of soluble alkalis in a solution. Alkalinity establishes the buffering capacity of water and affects how much acid is required to change the pH. Both alkalinity and pH must be considered when adjusting the pH of water. Forty-eight greenhouse businesses in Massachusetts participated in a two-year water quality project that includes having their irrigation water tested. The first test results performed in spring 04, showed that thirty-seven growers had water with pH greater than 7.

Growers that had irrigation water with alkalinity that measured within the target range of 40 ppm were able to manage the pH of their growing media by using fertilizers that had either a basic or acidic reaction depending on the needs of the crops. Acid injection for managing growing media pH was not recommended for these growers. The water tests helped growers to customize their fertilizing practices. Although the pH and alkalinity of the water was acceptable for irrigation, the pH of the water was too high to be used for mixing some pesticides and growth regulators.

Water pH is a critical factor in the effectiveness of many pesticides and growth regulators. Many materials work best when mixed in water that is acidic while a few perform best in a neutral or higher pH.

P esticides such as organophosphates, synthetic pyrethroids, carbamates, chlorinated hydrocarbons, the growth regulator ethephon and others undergo a chemical reaction, called hydrolysis that causes them to break down in water with a pH greater than 7.

The more alkaline the water, the more rapidly the pesticide breaks down. The hydrolysis can be very fast when the pH of the water is greater than 8 and 9. For every unit increase in pH, the rate of hydrolysis increases 10 times. Some pesticides begin to break down as soon as they are combined with water with high pH.

For example, if a spray tank is allowed to stand several hours or overnight before the contents are used, as much as 50 percent of the active ingredient may be lost. Options for finding the optimum pH range is by reading the pesticide or growth regulator label or contacting the company technical representative.

If the product label says to avoid alkaline water or materials, the spray mixture will benefit by adjusting the pH to 6. Many manufacturers provide information on the rate at which their products hydrolyze.

Below are some examples of pesticides and optimum pH range of the water used for mixing. If you do not need to inject acid into your irrigation system and your water pH is above 7. Buffering agents prevent pesticide hydrolysis during mixing and storage in the tank. Buffering agents should not be used with pesticides containing fixed copper or lime such as copper sulfate, or lime sulfur. Copper is more soluble under acid conditions, and will damage plants.

How much buffering agent to use will depend on the water pH. Although they are rarely fatal for adult insects, they can prevent reproduction, egg-hatch, and molting from one stage to the next. Many IGR products are mixed with other insecticides that kill adult insects. IGRs are generally low in toxicity to humans. If you have questions about insect growth regulators, or any pesticide-related topic, please call NPIC at am - pm PST , or email us at npic ace.

NPIC provides objective, science-based information about pesticides and pesticide-related topics to enable people to make informed decisions. For example, for an insect to grow, it must molt shed its external skeleton or shell and produce a new, larger one. Some IGRs prevent the insect from forming this new protective shell, which leads to its death. Many insects undergo a dramatic metamorphosis change in form during their life cycle.

For instance, a caterpillar spins a cocoon and changes into a pupa, which then changes into a butterfly or moth — a remarkable transformation!!! There are IGRs that disrupt this change in form, preventing the pupa from becoming an adult insect — breaking the life cycle. Since IGRs disrupt processes like an insect metamorphosis, which do not occur in animals such as mammals including humans, dogs and cats , birds and fish, they have a larger margin of safety than conventional insecticides.