Evaluation of fungicides for control of Sphaeropsis shoot blight of red pine nursery seedlings

A nursery study was conducted to evaluate possible chemical alternatives to the fungicide benomyl for control of shoot blight caused by Sphaeropsis sapinea (Fr.:Fr.) Dyko & Sutton in Sutton on red pine (Pinus resinosa Ait.). Replicated plots of seedlings in their first or second growing seasons were treated either weekly or biweekly with one of the following materials (or combinations): benomyl; thiophanate-methyl; mancozeb thiophanate-methyl + mancozeb; chlorothalonil; copper; myclobutanil; myclobutanil + thiophanate-methyl; water (control). Plots were located in three complete blocks at increasing distances from an inoculum source, diseased trees in a red pine windbreak. Percentages of seedlings affected by shoot blight were determined by examination in late fall. Analyses of variance indicated significant treatment and block effects (p < 0.0001) on disease incidence. The most effective materials applied either weekly or biweekly to seedlings of either age were the systemics benomyl and thiophanate-methyl, and the protectant chlorothalonil. In spite of fungicide application, incidence of disease was generally much higher in plots within the block closest to the red pine windbreak and lower in plots further from this windbreak. Results confirm the desirability of integrating chemical and cultural practices for control of Sphaeropsis shoot blight in conifer nurseries.