Pesticide sprays consist of at least 95% water. Water quality plays an important role in pesticide performance. The following issues may indicate a compatibility problem with pesticides and spray water quality: - Pesticide does not work at labeled rates; - Difficulty mixing sprays or clogging of nozzles; - Inconsistent pest control observed in fields or plots; - Pests seem resistant to a new pesticide active ingredient, or - Crops are lower quality or lower yielding. Understanding how water quality characteristics such as pH, water hardness, turbidity, and total suspended solids affect the adsorption and persistence (half-life, storage time) of a pesticide can help pesticide applicators reduce or eliminate compatibility issues and improve pesticide effectiveness

Mixing two or more pesticide products can allow for the treatment of several pests at the same time, improve pesticide performance, and ultimately saving time and money. However, physical and chemical tank mix incompatibilities can occur when combining two or more pesticides. Physical incompatibility is the failure of pesticide products to stay uniformly mixed and can result in layering, products settling out of solution, or clumping. A chemical incompatibility is the result of a chemical reaction between pesticide products. A chemical incompatibility is less visible and can be harder to detect. This publication focuses on basic factors that influence product compatibility (agitation speed and method, water temperature, mixing order, carrier type, and chemical formulations) and summarizes best mixing practices to address these factors.

Spray water problems may arise due to water quality and management decisions. Certain aspects of water quality can reduce the efficacy of the pesticide as well as affect how the pesticide interacts with the plant surface or targets pests. Evaluating and testing spray water chemistry can help identify water quality problems that might otherwise be overlooked. This publication will examine possible solutions to spray water problems, including the use of adjuvants and other additives to enhance pesticide performance.