Study on Control of Leucaena leucocephala (Lam.) de Wit in Okinawa

Leucaena leucocephala is an exotic tree plant causing trouble in Okinawa. To control this tree in standing condition, some holes were made at the trunk base (up to 50 cm from soil surface) with an electric driller and glyphosate solution (100%) was injected. The diameter of the trunks was around 4 cm at 10 cm from soil surface. Trunks of some trees were cut at 10 cm from soil surface. One milliliter of glyphosate solution was taken for each cm of the tree-diameter as a standard. The treatments were: (1) 4 ml glyphosate was injected into each tree with whole trunk (11 whole trees), (2) 12 ml glyphosate was injected into each tree with whole trunk (12 whole trees) and (3) 4 ml glyphosate was injected into each tree without trunk (8 trees without trunks). All trees withered 21 days after glyphosate injection into the trees without trunks. Around 27 and 92% of trees withered when 4 ml and 12 ml of glyphosate was injected into each tree with whole trunk, respectively. All trees withered 56 days after glyphosate injection in all treatments. The results of this study indicate that Leucaena leucocephala could be controlled in standing condition with glyphosate application.要注意外来植物のギンネムは沖縄県内で繁茂している．そのギンネムを立木の状態で制御するために，電動ドリルで樹幹根本付近に穴を開け，グリホサート(glyphosate)イソプロピルアミン塩液剤原液を注入した． 地際から10cmの株経(cm)と同量(ml)を注入する除草剤標準区(11株)，除草剤の量を標準区の3倍注入する除草剤3倍区(12株)および伐採後に標準区と同量の除草剤を注入する伐採・標準区(8株)に分け比較検討した．供試ギンネムの地際から10cmの株径は4.0cm程度であった．除草剤注入3週間後の伐採・標準区はすべての株で枯死，除草剤3倍区91.7%，除草剤標準区27.3 ％ が枯死と判定された．除草剤注入8週間後には，すべての区において枯死していた．このことからギンネムを立木の状態でグリホサートイソプロピルアミン塩液剤原液を注入することにより制御できることが明らかになった