Irrigation cut-off date affects growth, frost damage, and yield of jojoba

Flower bud injury resulting from freezing temperatures has been a major problem in jojoba (Simmondsia chinensis (Link) C. Schneid.) production. A 3-year field study, which began with 4-year-old plants, evaluated the effect of three irrigation treatments on growth, flower bud survival, seed yield, seed weight, and seed wax concentration of six clones. After 3 years, irrigation cut-off dates of late May (dry treatment) and early September (medium treatment) resulted in reduced plant height and width compared to irrigating through November (wet treatment). Flower bud survival and seed yields were very low in the first year for all treatments. In the second and third years, bud survival for most clones, even at -8C, was greatly improved by withholding water in the fall. In December of the second and third years, plants in the medium and dry plots had lower leaf water potential than those in the wet plot. In the second year, plants in the medium and dry plots had seed yields that were 3.5 times higher and wax yields that were were 2.3 times higher than plants in the wet plot. In the third year, the medium treatment had the highest seed and wax yields. Average seed weight and seed wax concentration were generally highest for plants in the wet plot where seed yields were low. Withholding irrigation from jojoba in the fall appears to improve flower bud survival and seed and wax yields following cold winters. Jojoba is a new industrial crop being grown commercially in hot arid and semiarid regions of the southwestern United States. The primary product of this evergreen shrub is a unique liquid wax contained in the seed. This wax is used as a natural base for a wide range of cosmetic products, has heat-resistant lubricating proper- ties, and is potentially useful in the chemical industry. Several factors limiting jojoba production have become appar- ent, including the use of low-yielding genotypes, cold injury to flower buds, and a lack of information on suitable cultural prac- tices. Most of the early plantations were established from seed or seedlings collected from female plants in the wild, and these populations typically have a low percentage of high seed producers (Yermanos, 1983). This problem is being overcome to some extent