Water is going to be the primary carrier of your agricultural chemicals. It will have the job of delivering pesticides to the plant, fungal spores or insect to achieve the goal of protecting your vines. Water quality is determined by chemical properties such as pH (measure of acidity and alkalinity) and the level of inorganic minerals present (water hardness as determined by level of minerals such as calcium, magnesium, potassium, etc.…). Pesticides can be sensitive to water chemistry and quality. Some are affected by high pH. At various levels above a pH of 7 certain pesticides can undergo alkaline hydrolysis. Alkaline hydrolysis breaks down the parent pesticide molecule into charged or ionic molecules (cations and anions). In this form a pesticides’ ability to perform can be altered. Uptake through the plant leaf, inability to bind at its target site, and in the ionic form binding with hard water minerals or charged soil sediment that may occur in spray water are a few critical events that can be influenced by alkaline hydrolysis.
Benefits of maintaining optimum pH for the pesticide molecule:
A whole or non-ionic chemical is also considered lipophilic or fat loving. A leaf cuticle has a large waxy portion that is also lipophilic. This lipophilic, whole or non-ionic, pesticide is more soluble in the waxy cuticle tissue and therefore moves more rapidly into the leaf. For pesticides whose mode of action is to interfere with a plant biochemical process or be made available to sap sucking insects, rapid movement into the leaf and plant cells is critical.
Hydrolysis is considered the beginning of a pesticide’s breakdown or degradation. At a certain pH level a formulated product can remain stable for a period of time after which hydrolysis will begin. The published half-life of a pesticide can give you the optimum pH for the solution and information on how long it can last at that level. The half-life of a pesticide is defined as the length of time required for 50% of the pesticide’s active ingredient to breakdown.
In general, insecticides are more sensitive to high pH and alkaline hydrolysis than fungicides and herbicides.
There are certain classes of pesticides that are also sensitive to acid hydrolysis (low pH). These seem to be fewer than those sensitive to alkaline hydrolysis but it is best to be aware of a chemical’s behavior when subjected to either condition.
Key points to remember:
- Determine the pH of your spray water prior to adding the pesticide. Check it several times a year.
- Determine the hardness of your water. Only knowing the hardness may not necessarily keep you safe. The pH level determines the amount of ions in solution which can be tied up by hard water minerals. For accurate hardness reading take a water sample to a local lab.
- Check the pesticide label or MSDS for optimum pH level (or ask your PCA or manufacturer rep).
- Use a quality pH adjuster and buffering agent to bring your pH to the necessary level before adding your chemical (usually between 6.0 – 7.0).
- Use a clean spray water (soil sediments can bind some pesticides).
- Know the half life of the chemical (check the MSDS or ask your PCA or manufacturer rep).
- The longer the chemical sits in solution, the more opportunity to degrade. Try to mix up only what you can spray that day.
- Spray the mix as soon as possible.
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