Alfalfa yellows was first studied in the 1950’s in Central Washington as a new problem. The study ended in the mid-sixties as researchers found no disease organism or plant nutrient deficiency associated with alfalfa yellows and no information was published from these early studies. Excessive subsoil moisture, due to seepage from water ditches and/or over-irrigation, was thought to cause alfalfa yellows. Alfalfa yellows symptoms are: Leaves are light green to yellow and distorted, especially terminal leaves. In severe cases, stunted plants may be only several inches tall. Alfalfa yellows symptoms may be confused with symptoms of other growth problems, such as bacterial wilt. The alfalfa yellows have been observed in all cuttings except the first. This study’s objective was to find a nutrient deficiency and/or soil moisture characteristic that may be associated with alfalfa yellows. Four locations were studied in Central Washington: three in 1996 and one in 1997. Two replications of a "non-affected" (green plants) site adjacent to an "affected" (yellow plants) site were studied at each location. Each site was approximately 20 feet X 20 feet. Soil and plant samples were taken from each site on the date when alfalfa growth was at least 12-15 inches tall. Sixty stems were collected from 30 plants. Soil cores were collected to a depth of 8 inches at all locations with the exception of one location where cores were 12 inches. Soil moisture cores were collected in one-foot increments to 3 feet to measure plant available water (1/3 and 15 bar) and actual moisture content. All samples were tested at the University of California DANR Laboratory at Davis, California. No significant differences were found between affected and non-affected sites for soil and plant nutrients. Soil moisture, expressed as "percent of field capacity", was significantly higher in the affected areas in the second and third foot depths. Soil moisture in the top foot was higher in the affected sites, and was not significantly different than the non-affected sites. This study’s results show that control of alfalfa yellows can be done by distributing water so that affected areas receive less-than-normal water and non-affected areas receive the same or more water. While water management is easy on fields with clear boundaries between affected and non-affected areas, most affected fields have these areas intermixed. For intermixed areas, check the amount and depth of soil moisture in non-affected areas before reducing applied water across a field. If water application is reduced to help control yellows in affected areas, non-affected areas must maintain equal production as before with less water. For this to happen, non-affected areas must have adequate soil moisture to 3 feet or more. If soil moisture is adequate to maintain production in non-affected areas, reducing water application rates by one-half or more may eliminate the alfalfa yellows caused from excessive subsoil moisture.

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