Effects of implanted and injected pesticides and fertilizers on the survival of Adelges tsugae (Homoptera: Adelgidae) and on the growth of Tsuga canadensis

Studies in a forest of eastern hemlock, Tsuga canadensis (L.) Carriere, in Connecticut showed that Mauget injections of bidrin and oxydemetonmethyl and CSI implants of acephate in May caused significant mortality of the spring generation of hemlock woolly adelgid, Adelges tsugae Annand, present at that time (93-98%) and significant mortality of the subsequent summer generation 5 mo later (60-88%). Injections and implants of fertilizer (alone or in combination with pesticides) significantly enhanced the survival of the adelgid generation present at the time of treatment and significantly reduced the effectiveness of the pesticides. However, survival of the subsequent generation of A. tsugae 5 mo. after treatment was no higher on fertilized hemlocks than on untreated controls. Because the survival of A. tsugae is inversely density-dependent, the higher adelgid mortality on fertilized hemlocks after 5 mo. probably reflected the higher population densities on those trees that resulted from enhanced adelgid survival during the previous generation. Hemlock growth and foliage color were not improved by either method of fertilization. On the contrary, fertilized trees produced significantly less new growth and showed greater adelgid-induced injury after 14 wk than did the untreated hemlocks because of the increased adelgid densities. The greatest biomass of new growth was produced on hemlocks in which injections or implants of pesticides had significantly reduced adelgid population densities. Injected and implanted pesticides and fertilizers were readily translocated throughout the crown of these lightly infested hemlocks regardless of their size and age. However, the ability of hemlocks to translocate these materials may become severely impaired as trees become more heavily infested and more severely injured by A. tsugae.