Foliar treatments against horse chestnut leaf miner (Cameraria ohridella)

Kestenov moljac miner (Cameraria ohridella) najznačajniji je štetnik divljeg kestena (Aesculus hippocastanum), koji je sastavni dio europskih parkova. Štetnik se redovito javlja u velikim populacijama i čini značajne štete na listovima. Suzbija se tretiranjem lišća (folijarno) ili ubrizgavanjem insekticida u deblo (endoterapeutska metoda). Rad prikazuje rezultate pokusa suzbijanja kestenovog moljca minera tretiranjem krošanja divljeg kestena gradskih parkova. Pomoću leđnog motornog orošivača tretirana su stabla viša od 15 m. Korišteni su regulatori rasta kukaca, imidakloprid, spinosad i Bacillus thuringiensis, uz utrošak škropiva od 3 l po stablu. Najbolji rezultati u suzbijanju kestenovog moljca minera postignuti su tretiranjem listova u dva navrata (razmak između dvije aplikacije približno 43 dana) s insekticidom imidakloprid (91.4–97,2 % učinkovitosti) i regulatorima razvoja kukaca – diflubenzuron (89,5–94,9%), heksaflumuron (84,6–96,3 %), metoksifenozid (85,6–94,9 %) i lufenuron (85,8–94,4%). Nije zabilježena statistički značajna razlika u učinkovitosti suzbijanja gusjenica kestenovog moljca minera nakon jednokratne primjene imidakloprida (88,9–97,7 %) i diflubenzurona (85,9–95,3 %) u odnosu na dva tretiranja istim insekticidima u jednoj vegetaciji. Učinkovitost spinosada bila je značajno niža (67,4–89,3 %), dok je učinkovitost pripravka na osnovi B. thuringiensis bila još niža, neovisno da li je provedeno tretiranje samo s B. Thuringiensis (30,3–87,1 %) ili je primijenjen B. thuringiensis u kombinaciji s imidaklopridom (52,4–91,6 %).Horse chestnut leaf miner (Cameraria ohridella) is the most important pest of horse chestnut (Aesculus hippocastanum), common tree in European parks. The pest regularly develops high populations of larvae which damage leaves. It could be controlled with foliar spraying or with trunk injections of insecticides (endotherapeutical method). The paper presents results of in-city trials with foliar treatments against horse chestnut leaf miner’s larvae. Knapsack mist-blower was used for insecticides application (dates of applications are presented in Table 2) on trees higher than 15 m. Insect growth regulators (IGRs), imidaclopride, spinosad and Bacillus thuringiensis (Table 1) were applied with liquid rate of 3 l per one tree. Each year, leaves were examined five times; each time 400 leaves were examined for each trial variant and numbers of mines per leaf were counted and statistically analyzed. The best results were achieved after two applications in one season (with average period between two applications of 43 days) with imidaclopride (91.4–97.2 % efficacy) and insect growth regulators (IGRs) – diflubenzuron (89.5–94.9%), hexaflumuron (84.6–96.3 %), methoxyfenozyde (85.6–94.9 %) and lufenurone (85.8–94.4 %). Single application of imidaclopride (88.9–97.7%) and diflubenzuron (85.9–95.3 %) did not achieved statistically different efficacy in horse chestnut leafminer control than two applications in one season. Efficacy of spinosad (67.4–89.3%) and combination of B. thuringiensis and imidaclopride (52.4–91.6 %) did not satisfy. Even lower efficacy was achieved after two applications of B. thuringiensis in one season (52.2–83.7 %) and after single application in one season (30.3–84.7 %) (Table 8). In this period untreated control trees were infected with average of 22.4 –84.2 larvae/leaf (Tables 3–7), depending on date of examination. Results of those five-year trials results show that is possible to protect horse chestnuts if foliar insecticides application is provided in period of first generation’s larvae hatching. The most suitable insecticides were insect growth regulators (IGRs), while imidaclopride is not appropriate in urban area due to its high toxicity. B. thuringiensis provides very good initial protection, but it has very poor residual effect so it is advisable to apply B thuringiensis twice or more times in one season (Tables 3–8)