UMASS Landscape Update

Pioneer Valley (Amherst)

General Conditions: 

We’ve rounded into the second half of June, and the summer solstice is upon us, marking the longest day of the calendar year. The Pioneer Valley experienced more clouds than sun over this past reporting period with mostly mild temperatures. While scattered showers occurred throughout the tri-counties, accumulations over the past week generally ranged from 0.5–1”.

What’s notable is the near perfect conditions for disease development on June 17 and June 18 with high temperatures hovering between the upper 60s to 70s, dewpoints at or just below ambient air temperature, and a steady mist to light rainfall. Many plant pathogens require free moisture on plant surfaces for spore production, spread and germination, and we can expect many new infections will have developed during this period.

Soil moisture remains good and there’s been only limited need to water this growing season. That said, keep a close eye on recent transplants to ensure the root zone is properly wetted.

The primary task right now is weeding beds and closely scouting plants for any symptoms and signs of disease and insect feeding. The long-term forecast calls for high temperatures in the upper 90s and our first heat wave of the summer. Overall, the landscape remains lush with new growth due to the mild temperatures and abundant rainfall. Many trees and shrubs with indeterminate growth habits, such as red maple (Acer rubrum), eastern hemlock (Tsuga canadensis), and crabapple (Malus sp.), continue to push new growth.

Pests/Problems:

Foliar anthracnose diseases are locally abundant on oak (Quercus), maple (Acer), sycamore (Platanus), and an array of other deciduous trees and shrubs.

Iris leaf spot, caused by the fungal pathogen Cladosporium iridis, is very bad on certain iris cultivars right now. Bearded iris (Iris germanica) is generally more susceptible to infection compared to Siberian iris (I. siberica).

Arborvitae needle blight, caused by Phyllosticta and Pestalotiopsis, is widely present on trees damaged during this past winter. Prune and discard as many blighted shoots as possible to reduce inoculum in the canopy. Adult arborvitae leafminers (Argyresthia spp.) are active right now. Infested plants will have numerous dead shoot tips that will also be infected by the fungal pathogens mentioned. Shaking infested plants will often reveal the adults as they scatter and quickly return to the plant. 

Nick Brazee, Plant Pathologist, UMass Extension Plant Diagnostic Lab, reporting from Amherst.