UMASS Landscape Update

Pioneer Valley (Amherst)

General Conditions: 

Cool conditions prevailed yet again this past reporting period as we approach the midway point of May. Low temperatures in the 30s were recorded throughout the tri-counties on May 8, 9, 12, and 13, but the long-term forecast indicates a big warmup is on the horizon.

Despite the cold nights, verdant new growth and flowering is everywhere right now, and the number of garden tasks to tackle is limitless. Redbuds (Cercis canadensis) had a fantastic showing this year but are now fading out. One important factor to consider when selecting redbud stock is its place of origin. Nursery material grown in the south may not have the same level of winter hardiness as trees grown from more northern latitudes.

A multi-day rain event is forecasted at the time of writing, which should help to water in new plantings and replenish soil moisture levels that have been good so far this spring. Based on long term measurements (>6 months), the U.S. Drought Monitor continues to show the entire tri-counties in either abnormally dry (D0) or moderate drought (D1) conditions. The forecasted rain and warming temperatures should favor mosquitoes and black flies.

Pests/Problems:

American beech (Fagus grandifolia) and European beech (F. sylvatica) across the UMass campus are mostly exhibiting very low levels of beech leaf disease due to treatments in 2025. Trees in the forest, however, are not doing well, but the full extent of the damage won’t be apparent for a few more weeks as new growth develops (or does not).

Conifer needle blights will soon be taking center stage. Spruce (Picea) needles are elongating and can be readily infected by both Rhizosphaera and Stigmina. White pine candles continue to elongate and from late May to late June, older and infected needles will be yellowing / browning and shedding from the canopy. This can give pines an extremely thin appearance until the current season’s growth matures.

Now is a good time to scout for the wood-rotting fungus Kretzschmaria deusta. The primary hosts are European beech (Fagus sylvatica) and sugar maple (Acer saccharum). Another wood-rotting fungus that produces fruiting bodies in the spring is Cerioporus squamosus (Dryad’s saddle). If possible, avoid any insecticide and fungicide applications to plants about to flower or those in full flower. For some diseases, such as fire blight (Erwinia amylovora), flowering coincides with peak infection, making the avoidance challenging. But a growing body of literature reveals that fungicides can be very damaging to pollinators by disrupting key physiological processes. A summary of the specific impacts can be found on the Xerces Society website.

Nick Brazee, Plant Pathologist, 

UMass Extension Plant Diagnostic Lab

, reporting from Amherst.