FURTHER EXPERIMENTS ON CONTROL OF SUCKER GROWTH IN HAZELNUTS (CORYLUS AVELLANA L.) WITH NEW ESTERS OF 1-NAPHTHYLACETIC ACID

The well known plant growth regulator 1-naphthylacetic acid (NAA) has been employed for sucker control in many fruit tree species. Esters of NAA are also active in sucker control. In the hazelnut (Corylus avellana L.), which is known to have a strong suckering tendency, the elimination of suckers is performed either mechanically (at a high cost) or with chemical herbicides. Following previous research in which new esters of 1-naphthylacetic acid were tested, six other new esters, derived from NAA and primary linear alcohols with 6-11 carbon atoms, were suspended in deionized water with the wetting agent Tween 20 (1% w/w) and sprayed at concentrations of 0.25%, 0.5% and 1.0% (w/w) till runoff. Three replicates were arranged in a randomized block design and treatments applied to 0.1-0.2 m long herbaceous suckers of ‘Tonda Gentile delle Langhe’ trees. Sucker control was evaluated 4, 11 and 30 days after treatment using a wilting index. After 4 days at the doses of 0.25 and 0.5% undecyl 1-naphthylacetate produced a significantly lower effect than hexyl and octyl derivatives. At 1% no differences were detected. After 11 days at 0.25 and 0.5% there were no significant differences between the tested esters, while at 1% the decyl derivative had a lower effect than heptyl. After 30 days no differences were detected between the compounds; all produced complete wilting. The compounds with a shorter chain produced a quicker action. Although the six compounds at the same concentration (by weight) showed similar effectiveness, it must be stressed that the undecyl derivative has fewer moles/L than the hexyl derivative of 21%. None of the compounds caused phytotoxic effects on the plants or changed nut quality or the yield of the trees.