Foliar applied urea improves freezing protection to avocado and peach

Abstract

The effect of foliar applied urea on freeze hardiness was evaluated under orchard and laboratory conditions. Freezing injury and senescence of avocado ( Persea americana Mill.) cv. ‘Hass’ leaves in the orchard was inversely correlated to N content. Three foliar applications of 2% low-biuret urea caused a 26% nitrogen enrichment of leaves. Consequently, leaf freezing hardiness was increased and senescence retarded. Urea-treated leaves were 2.5 times more tolerant to freezing than untreated leaves, at the same level of senescence. The freeze protection effect of foliar-applied urea was confirmed using potted plants of the cultivar ‘Fuerte’ under controlled conditions. Potted avocado plants treated with 2% low-biuret urea, gradually cooled, and exposed to −2 °C for 4 h, were significantly more hardy than control plants. Foliar application of 10% low-biuret urea to peach ( Prunus persica L.) cv. ‘Maravilha’ shoots before flowering, 3 days before frost occurrence, increased the freezing hardiness and survival of the reproductive organs. The protective effect of foliar-applied urea on peach flower buds in spring decreased gradually as bud development progressed.