Our vineyard manager discusses the process of vineyard shoot thinning (suckering) in the spring. The number of grapevine shoots removed is based on the quantity of fruit the viticulture team wants each vine to yield and desired air flow in the vine canopy to combat disease.
http://blog.jordanwinery.com/2010/06/suckering-rainy-spring-means-extensive-grapevine-shoot-removal/.