Recent pathogens of interest seen in the UMass Extension Plant Diagnostic Lab:
Verticillium wilt and foliar anthracnose infection (caused by Colletotrichum) of a mature sycamore maple (Acer pseudoplatanus). Tree is approximately 60-years-old and has been present at the site for nearly as long. Symptoms of decline have been visible for several years now and include shoot and branch dieback, peeling and shedding of bark and premature leaf drop. Tree resides in a residential lawn with sandy soils in full sun with periodic lawn watering providing some supplemental water. Verticillium invades through the roots and spreads systemically throughout the host. Chronic infections lead to the upper canopy dieback and a buildup of inoculum in the host and surrounding soil.
Decline of eastern hemlock (Tsuga canadensis) due, in part, to infestations of the elongate hemlock scale (Fiorinia externa) and the hemlock rust mite (Nalepella tsugifoliae) coupled with infection by the opportunistic cankering pathogen Phomopsis. Five trees are approximately 40-years-old and were planted at the site as young saplings. Until 2012, the trees were subject to four annual applications of horticultural oil to control HWA. At that time, the needles were chlorotic and appeared to be suffering from oil burn. Oil application ceased and the trees recovered over the past several years. However, in late 2015 and early 2016, two of the trees began shedding large volumes of needles. Based on the submitted sample, the insect pest infestations are not severe, but some of the symptoms were clearly associated with the scale and mite feeding. Phomopsis was abundant on declining and dead shoots. Overhead watering is used and the subsequent wetting of the canopy is likely facilitating disease development. It’s likely that some abiotic stress, perhaps winter injury or drought stress depending on the volume of water provided, is also associated with the premature needle shedding.
Edema on Chinoides rhododendron (Rhododendron ‘Chinoides’). Plant is three-years-old and nursery grown with overhead watering. This summer, chlorotic spots developed on the surface of the leaves while on the abaxial side, brown-colored, raised blisters developed. Edema is a physiological disorder that develops when there is an imbalance between water uptake from the roots and transpiration of water from the foliage. Essentially, the plant roots take up water at a rate faster than what the canopy can use for physiological processes and transpiration/respiration. The calluses are enlarged leaf cells that continue to divide and then rupture. The condition is not threatening to the overall health of the plant as long as corrective action is taken, which often only requires reduced watering.
Needle blight of Hinoki falsecypress (Chamaecyparis obtusa) caused by Phyllosticta and Pestalotiopsis. Tree was approximately 6-7’ tall at the time of planting in 2010. It was planted in the understory of a forest at the edge of a residential property and receives minimal sunlight. Phyllosticta and Pestalotiopsis have become a destructive combination of foliar pathogens on arborvitae and to a lesser degree, falsecypress. Interior needles on lower canopy branches often harbor the highest populations but these fungi can also be found causing a shoot tip blight in the upper canopy on Thuja and Chamaecyparis. Trees injured from excessive pruning, drought and winter/free damage are more susceptible to needle blight diseases.
Report by Nick Brazee, Plant Pathologist, UMass Extension Plant Diagnostic Lab, UMass Amherst.