Trials conducted in Tulare County (reported in accompanying article) have demonstrated that the walnut aphid has a profound influence on walnut production and quality. Observations on infested trees during 1969 showed that honeydew accumulations on developing nuts had a phytotoxic effect on husk tissue which resulted in killing surface cells (photo 1). These turn black and together with subsequent sooty mold aggravate sunburn, since dark surfaces have the capacity to absorb more heat. It was also noted that sooty mold developed through the whitewash deposits. This situation of dark husk surfaces due to honeydew (photo 2) compounded by sooty mold accumulation (photo 3), was studied in relation to the sunburn problem of walnuts grown in interior valleys.