The influence of fertilization, phloem restriction, irrigation, microbes, and ethephon on pecan shuck disorders in Texas

Typescript (photocopy).Shuck disorders are a common production problem of Texas pecan producers. The shuck disorders observed in this study were not caused by stem end blight or shuck dieback. The principal shuck disorders studied were called sticktights. Four types of sticktights were observed: green, water stress, west Texas, and north Texas. All were characterized by poor kernel development. Three fertilization systems were evaluated: traditional ground applications, foliar sprays, and repeated ground applications. Traditional ground rates included a standard 112, high 224, and a very high 448 kg N/ha. Foliar sprays supplied 134, 79, or 11 kg N/ha plus some micronutrients. The repeated ground application gave a total of 400 kg N/ha. The high (224 kg N/ha) and foliar (134 kg N/ha) rates had the least number of sticktights. Lower (11, 79, and 112 kg N/ha) and higher (400 and 448 kg N/ha) rates had the most sticktights. The custom foliar spray failed to increase tissue nutrient levels although the Harvest Plus spray did increase the leaf micronutrient contents. There was a strong positive correlation between yield and sticktights. The sutures had more Ca and less K than the area between the sutures. There was a net movement of P, K, Ca, Mg, Cu, Mn, and Mo away from the sutures at shuck split. Trunk and limb clamps had a negative effect on tree growth with little effect on pecan quality and sticktights. An increase in carbohydrates and C/N ratio was not detectable which was attributed to feedback inhibition. Four irrigation frequencies were examined: weekly, 3 week, tensiometer, and no water. Significant differences in the tree water stress were found between the treatments, although no correlations were found between levels of stress and sticktights. The tensiometer treatments had the least sticktight percentage followed by the 3 week, weekly, and no water treatments respectively. In a microbe study, isolations from pecan shucks with sticktight symptoms yielded Phoma sp., Coniothyrium sp., Stemphylium sp., Alternaria sp., and yellow and white bacteria. Alternaria inoculations failed to cause sticktight symptoms. Trunk injected ethephon advanced shuck opening, although leaf drop was severe in some cases. The critical time for ethephon injections to influence shuck opening was at the shuck/nut separation stage