Severe Water Stress Can Increase Stick Tight Levels

Severe water stress, poor quality irrigation water with high boron levels and the fungal disease hull rot all cause stick tight nuts.

Anticipating severe water stress as their almond crops matured, some growers chose to harvest early and avoid potential problems with stick tight nuts.

Franz Niederholzer, UCCE orchard systems farm advisor in Yuba and Sutter counties, said growers who were short on irrigation water were applying just enough to keep the crop growing until harvest.

Severe water stress, poor-quality irrigation water with high boron levels and the fungal disease hull rot all cause stick tight nuts, those that are not easily shaken from the tree at harvest.

Extremely dry orchard conditions where not enough energy is delivered to the nuts causes them to remain attached at harvest. In the case of boron toxicity due to poor-quality ground water, gumming occurs and the nuts do not shake off. Where hull rot infections occur, generally later in the harvest season, there can be an increase in the number of stick tight nuts.

Research and demonstration trials conducted by many UC specialists and farm advisors have shown that mild water stress during the early hull split period can reduce hull rot and improve nut removal. Excessive stress will lead to defoliation or increased numbers of stick tight nuts. Moderate stress is the target for avoiding stick tights.

“A number of factors can contribute to stick tights, but it depends on specific conditions in that block of almonds,” Niederholzer said.

Mummy shakes will generally dislodge stick tights after harvest when (hopefully) wetter conditions will add weight to them.

Stick tights represent a crop loss that growers have to pay for twice, Niederholzer noted.

If not removed from the tree, stick tights can serve as an overwintering site for navel orangeworm (NOW). UC IPM guidelines recommend not more than two per tree on average, but in high NOW pressure regions, one stick tight per five trees is the goal.