Incidence of Internal Decay in American Elms (Ulmus americana) Under Regular Fungicide Injection to Manage Dutch Elm Disease
Nicholas J. Brazee and Robert E. Marra
Abstract: Fungicide injection is regularly performed to prevent and manage Dutch elm disease (DED) of American elm (Ulmus americana). In an effort to better understand the effects of long-term fungicide injection on tree health, sonic tomography (SoT) and electrical-resistance tomography (ERT) were used to nondestructively determine the incidence and severity of internal decay in the lower trunk of American elms in suburban and urban settings. Overall, 253 sonic and electrical-resistance tomograms were generated from 210 American elms. Sampled trees were partitioned into two fungicide injection groups: (1) regular injection; and (2) irregular injection or no known history of injection. Among all American elms, the incidence of internal decay in the lower trunk was 30% (63/210) with a mean percent decay, as determined by SoT, of 39%. Based on Chi-square analysis, there were no significant differences in the frequency of elms with decay by injection history (P = 0.799). Mean percent decay was significantly different by dbh class (P = 0.005) and while linear regression demonstrated a positive correlation between percent decay and dbh, most of the variability went unexplained (R2 = 0.182). For elms with decay, there was a significantly higher frequency of trees in the lowest decay class (< 25% of the cross section) compared to the highest decay class (> 75% of the cross section). The results suggest that the wounding associated with regular fungicide injection does not increase the likelihood of internal decay and that American elms exhibit a low frequency and severity of internal decay.
Keywords: Incidence of Internal Decay in American Elms (Ulmus americana) Under Regular Fungicide Injection to Manage Dutch Elm Disease