Influence of Bravo fungicide applications on wood density and moisture content of Swiss needle cast affected Douglas-fir trees

Abstract

Wood density, moisture content, tracheid width and cell wall size were examined in trees from plots that were sprayed for 5 years with chlorothalonil (Bravo ®) fungicide to reduce the impact of Swiss needle cast (SNC) and from trees in adjacent unsprayed plots. The unsprayed (more heavily diseased) trees had significantly narrower sapwood, narrower growth rings, lower sapwood moisture content, and narrower tracheid cell wall thickness than did the sprayed (less heavily diseased) trees. Moreover, unsprayed trees had altered earlywood density—earlywood width relationships, higher latewood proportion, and higher overall wood density than the sprayed trees. We hypothesize: (1) that the decreased moisture content of diseased trees results from their poor carbon economy resulting in insufficient energy (photosynthate) to reverse sapwood embolisms, and (2) SNC decreases wood density relative to growth rate.