Control of sucker growth in hazelnut with esters of 1-naphthylacetic acid

A known plant growth regulator 1-naphthylacetic acid (NAA) has been employed for sucker control in many tree fruit species. Esters of NAA are also active in sucker control. In hazelnut (Corylus avellana L.), which is known to have a strong suckering tendency, the elimination of suckers is done either mechanically (at high cost) or with chemical herbicides. Five esters, derived from NAA and primary linear alcohols with 1-5 carbon atoms, were suspended in deionized water with wetting agent Tween 20 (1% w/w) and sprayed at concentrations of 1% and 0.5% (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 2, 10, and 30 days after treatment using a wilting index. The persistence of sucker control was evaluated by counting, 3 months after the treatments, the number of the new suckers that grew in the treated zone. All products at both doses produced a quick response (within two days) and complete wilting after 30 days, but no evident effect was detected on the controls (1% Tween 20). The number of new suckers was severely reduced (0-4 per replicate) in comparison to the control (5-24 suckers). None of the compounds caused phytotoxic effects on the plants or changed nut quality or yield of the trees.