IRRIGATION CUTOFF DATE AFFECTS GROWTH, FROST DAMAGE, AND YIELD OF JOJOBA

Flower bud injury resulting from freezing temperatures has been a majo r problem in jojoba [Simmondsia chinensis (Link) C. Schneid.] producti on. A 3-year field study, which began with 4-year-old plants, evaluate d the effect of three irrigation treatments an growth, newer bud survi val, 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 heigh t and width compared to irrigating through November (wet treatment). F lower 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 plo t. In the second year, plants in the medium and dry plots had seed yie lds 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 tre atment had the highest seed and wax yields. Average seed weight and se ed 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 newer bud survival and seed and wax yields fo llowing cold winters.