Written by Bob Beede (UCCE Kings County, Emeritus) and David Doll (UCCE Merced) Tests of winter applied kaolin clay or calcium carbonate-based materials intended to either reflect solar radiation or diffuse it continue.  Results from David Doll, UCCE Farm Advisor, Merced County, and Valley Orchard Management, showed an increase in chill portion accumulation and a 200 to 250 pound increase in CPC yield over untreated trees when kaolin-clay was applied prior to the 2015 season. More can be found here.  The data thus far suggests that spraying these materials to mitigate the negative effects of warm winter temperatures does not assure you of a normal crop, but it might prevent NO crop! This past winter, Carl Fanucchi and Bob Beede collaborated with ORCAL, the company which manufactures ultra-fine, dry ground calcium carbonate, which is marketed in liquid form as Mask® and Diffusion®. They performed UNREPLICATED screening trials in two locations; one in Buttonwillow, and the second east of Highway 99 on Pond Road.  The screening trials included single and double applications applied January 12 and February 12.  A December treatment was planned, but the field could not be accessed.  Flower bud temperatures were monitored in treated and untreated areas using tiny thermocouples inserted into the buds without causing their death.  The resulting data showed bud temperatures were reduced by as much as 100F, and the rate of heating during the morning hours was also slower.  Calculations indicate that the January treatment increased chill portion accumulation by about 13%, due to the lower bud temperatures.  Weekly rating of the treatments for bud break and bloom were also performed.  The treated trees emerged more evenly, and the second treatment of Diffusion applied in February delayed development by four to five days.  The single January treatment developed at about the same rate as the untreated.