Hazelnut Abscission is Delayed by Simulated Drift of 2,4-D

2,4-D is commonly used for sucker control in hazelnut (Corylus avellana L.). However, the use of 2,4-D for sucker control has been implicated in delaying natural abscission in hazelnut. Hazelnuts naturally abscise and are collected from the orchard floor. Delays in abscission may reduce nut quality due to the onset of the rainy season, increasing mold and mud in the nuts. The effect of basal-directed applications of 2,4-D on hazelnut abscission, yield, and quality was assessed. In the first study, four basal-directed applications of 2,4-D (1.06 kg ae ha-1) did not affect hazelnut abscission, yield, or quality compared to glufosinate (1.1 kg ha-1) or manual pruning. In a second 3 yr study, a single yearly simulated drift of 2,4-D to the tree canopy at 0.06 and 0.6 mg L-1 increased the growing degree d (GDD) requirement from 50 to 141 to reach 50% hazelnut abscission, compared to nontreated. This is the equivalent of 5 to 15 calendar d. No effect was observed in the third yr of the study when the simulated drift was not performed. No differences in abscission were observed with basal-directed applications of 2,4-D at rates up to 4.4 kg ha-1 when applied four times each season during all 3 yrs of the study. Simulated drift reduced hazelnut yield by up to 37% and reduced the percentage of marketable nuts during one yr of the study. No effect on average kernel weight was observed. However, 2,4-D drift did delay hazelnut abscission, highlighting the importance of drift control measures.