Relationship of leaf necrosis and defoliation to phosphorus and potassium concentrations in selected tissue and to certain fruit quality parameters of pecan

Pecan [Carya illinoinensis (Wangenh.) K. Koch] trees developed necrotic areas in the leaves late in the growing season. July samples indicated that leaf P (0.114% DW) and K (0.62% DW) were low, but other elements were within accepted sufficiency ranges. Relationships between leaf P and K concentrations with nut quality and return bloom were determined. Trees were rated for leaf necrosis 1 October using a 1 (none)–5 (severe) scale. Fruit were harvested and analyzed for weight/nut, kernel weight, and kernel grade. Leaflet pairs collected 1 October from fruit bearing shoots were analyzed for N, P and K. Return bloom was determined on branches that bore fruit the previous year. Necrosis ratings were positively related to leaf N and negatively correlated with weight/nut; kernel, shuck and leaf P concentrations; and kernel and leaf K concentrations. Leaf, kernel and shuck P concentrations were positively correlated with weight/nut and percentage number 1 kernels. Leaf K was positively correlated with return bloom and weakly negatively correlated to weight/nut. Phosphorus was the primary element limiting fruit development and K shortage substantially reduced return bloom. Data support minimum pecan leaf standards in July for fertility recommendations of 1.0% K and 0.14% P.