Management: Balance for Success
Boron (B) deficiency can reduce profits in
almond production for several reasons:
. Low nut set
. Excessive nut drop
. Malformed nuts
. Undesirable vegetative growth
Boron deficiency is found in many areas of North America. In California, it occurs on some soils in the northeast, along the eastern and western edges of the Sacramento Valley, and on some sandy soils in the northern and eastern side of the San Joaquin Valley. Boron deficiency may be widespread in the eastern San Joaquin Valley and may be a problem in any orchard on sandy soils and/or where irrigation water is low in B.
Moderate B deficiency of almonds (or other tree fruit and nut crops) does not produce recognizable leaf symptoms, but is characterized by low nut set and excessive nut drop. The lack of crop often results in excessive vegetative growth. In the almond variety “Peerless”, brown gummy areas develop in the endocarp with gum extruding to the surface of the nut (photo and upper inset). Necrotic areas also develop. The embryos in these injured nuts usually abort and the nuts drop in Mayor June, sometimes resulting in the loss of the entire crop. Other varieties may blossom, but nuts may fail to set and spurs develop a non-productive "yellow twig" symptom. 'Mono'(lower inset) and 'Peerless' varieties may produce partial or malformed nuts as seen in the bottom row. In the case of severe B deficiency, the terminal and sub terminal leaves on water-sprouts and other vigorous shoots develop tip scorch.
Tissue analysis of almond leaves is not a good indicator of tree B status because B is highly mobile and as a result leaves do not accumulate it to any great extent. The most sensitive indicator of B status is the hull, though leaves can be used to determine severe B deficiency. Hull or leaf samples (10 per tree or more) can be collected at harvest from around the periphery at a height of 6 feet. Comparison samples from good and poor areas should be taken.
Soil applications of B can occur al any lime, but should always be performed with caution as high rates may be toxic. Foliar B should be applied al early post harvest, which is more effective than spring or dormant sprays. Sprays at hull split may also be effective, but have not been sufficiently tested.
"Information and photos provided by Dr. Patrick Brown. Associate Professor, Department of Pomology. University of California, Davis.
THIS IS ONE OF A SERIES 01 publications on Plant Problem Insights, a service 01 the Potash & Phosphate Institute (PPI), 655 Engineering Drive, Suite 110, Norcross, GA 30092-2843. Phone (770) 447-0335. Reference #95251. Item # 40-4042. PI-42
