Evapotranspiration (ET) is a term used to describe the amount of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and water bodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through its leaves. Evapotranspiration is an important part of the water cycle and can be used by farmers to estimate crop water loss and to schedule efficient irrigation events. For step-by-step instructions on how to use ET data for scheduling irrigations, click here.

Powdery Mildew Index Presence of powdery mildew on wine grapes adversely impacts fruit quantity and quality. According to the University of California, powdery mildew appears on leaves as chlorotic spots on the upper leaf surface. Signs of the pathogen appear a short time later as white, webby mycelium on the lower leaf surface. As spores are produced, the infected areas take on a white, powdery or dusty appearance. On fruit and rachises the pathogen appears as white, powdery masses that may colonize the entire berry surface. Black to brown web scarring can be seen on mature fruit, which represents former colonies. Symptoms of powdery mildew infection include red blotchy areas on dormant canes. Once initial infection occurs, ideal temperatures for growth of the fungus are between 70° and 85°F. Temperatures above 95°F for 12 continuous hours or longer cause the fungus to grow more slowly. The powdery mildew index assesses the risk of disease development by relating it to air temperature and predicts the need to spray to protect the vines.

Water Quality Water quality plays an important role in determining irrigation practices used for satisfying crop water demand. For growers within RCWD's service area, water quality parameters such as total dissolved solids (TDS) and chlorides are of particular importance for avocado growers. TDS refer to any minerals, salts, metals, cations, or anions dissolved in water, and excessive TDS levels can require additional water to be applied in order to maximize crop production. Likewise, excessive levels of chlorides in irrigation water can reduces yield and leaching is required for mitigating yield reductions due to chloride toxicity.

Sources:
WikiPedia - Evapotranspiration: link
FAO Irrigation and Drainage Paper No. 56 - Crop Evapotranspiration: