Bending stress, modulus of elasticity, shearing stress and specific shearing energy were determined for sunflower (Heliantus annus L.) stalk. The bending forces were measured by a cantilever test in the field at different moisture contents and the bending stress and the modulus of elasticity were calculated from these data. For measuring the shearing forces, the stalk specimens were severed by using a computer aided cutting apparatus. The specific shearing energy was calculated by using the area under the shearing force versus displacement curve. The bending tests were conducted at four different moisture contents. The bending stress decreased as the moisture content increased. The average bending stress value varied between 37(.)77 and 62(.)09 MPa. The modulus of elasticity in bending also decreased as the moisture content and diameter of stalks increased. The average modulus of elasticity varied between 1251(.)28 and 2210(.)89 MPa. The shearing stress and the specific shearing energy were also determined at five moisture contents according to the stalk regions. The results showed that the shearing stress and the specific shearing energy increased as the moisture content increased. The maximum shearing stress and specific shearing energy were 1(.)07 MPa and 10(.)08 mJ mm(-2) respectively. Both the shearing stress and the specific shearing energy were found to be higher in the lower region of the stalk due to structural heterogeneity. (c) 2005 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.