Many say mix the paint 50:50 with water but Alan posted a Cornell study on GW in 2012 http://forums.gardenweb.com/discussions/1439988/painting-tree-trunks that I base my treatments off of http://nysipm.cornell.edu/\/grantspgm/projects/proj06/fruit/kain.pdf. I always use interior undiluted white latex paint though exterior is fine to as long as it’s water based and plain paint. Here is another North Carolina State University expert confirming this method http://articles.extension.org/pages/60831/should-i-paint-apple-tree-trunks-to-prevent-sunscald#.VkkRbTZdHIU