Almond (Prunus dulcis Mill.) cultivars vary in tolerance to cold with flowers at pink bud more tolerant than at full bloom or than small nuts. Branch samples 60 cm long with 30-100 blossoms or nuts were cut, sprayed with water, and artifically frozen. Subsamples were removed after exposure to 4 to 6 successively lower temperatures for 30 minutes. After 48 hours of ambient temperatures, flowers or small nuts were sectioned and examined for visual evidence of injury. Of the early cultivars, `Peerless', is most sensitive at full bloom and `Sonora' is most hardy. `Sonora' is especially hardy at pink bud. `NePlus Ultra' is intermediate. Of the mid-blooming cultivars, `Carmel' is most sensitive to cold while `Nonpareil' is most tolerant. `Price' is intermediate. The late blooming cultivar, 'Mission' is most sensitive while 'Padre' and 'Butte' appear similar. This study compared several popular new cultivars to older industry standards.
Joseph H. Connell and Richard L. Snyder
Neil V. O'Connell, Craig E. Kallsen, Richard L. Snyder, Blake L. Sanden, Paul W. Giboney, and Mark W. Freeman
Many citrus growers are hesitant to plant cover crops, particularly perennial types, because of possible increased frost hazard. To quantify the increased risk, temperature relations over a 3-year period were compared between areas in a `Valencia' orange orchard with and without a partial perennial cover crop. The partial perennial cover crop consisted of a mowed perennial planting along the double drip line hoses, and an annually fall-replanted unirrigated strip of groundcover in the middle between the tree rows. This partial perennial cover crop increased the frost hazard compared to uncultivated bare ground even when wind machines were operating.