UMASS Update

Pioneer Valley (Amherst)

General Conditions: 

As we approach the autumn equinox (September 22), the 2025 growing season is winding down. Fall color is starting to appear on scattered trees, such as sugar maple (Acer saccharum) and red maple (A. rubrum). This incredible stretch of weather we’ve enjoyed over the past month continues with plentiful sun, mild temperatures, low humidity, and cool nights.

What has also unfortunately continued is the lack of regular rainfall, aside from a powerful and damaging thunderstorm on September 6. Gentle overnight showers both preceded (September 4 – 5) and followed (September 6 – 7) this serious storm event that tore through the Pioneer Valley. Strong winds brought down trees and power lines across several towns, most notably in southern Hampshire and Hampden Counties. A stunning 1.7” of rain was recorded during a 45-minute period at the Easthampton gauge. Total accumulations from September 4 to September 7 thunderstorms ranged from 0.8 - 2.3” with the highest amounts in southern Hampden County. While this rainfall was badly needed, the ferocity of the storm resulted in tremendous runoff with washouts and localized flooding.

Still, a good deal of rain was absorbed but ultimately this was not enough to alleviate the dry conditions across the region. Drought classifications have worsened, with the northern half of Franklin County now in moderate drought (D1) according to the U.S. Drought Monitor (at the time of writing). Soils in full sun are very dry, and many trees and shrubs are shedding older foliage due to drought stress. But the burst of rainfall and cooling temperatures have improved turf grasses in many landscapes.

Outdoor water use restrictions by town can be found here. Continue to irrigate trees and shrubs on regular intervals, while avoiding overwatering. As a rule of thumb, newly planted deciduous hardwoods should receive supplemental water until they are completely dormant for the season (sometime in October), while conifers should be watered through November.

Pests/Problems:

Elm anthracnose (Stegophora ulmea) is widespread again this year and the leaf yellowing caused by this disease can be mistaken for Dutch elm disease flagging. Several mature red oaks (Quercus rubra) across the UMass Amherst campus have severe oak spider mite (Oligonychus bicolor) infestations this year due to the dry weather. More importantly, these oaks are also suffering from Tubakia leaf blotch (Tubakia spp.) and oak anthracnose (Apiognomonia errabunda) with significant premature leaf shedding in some cases. 

Septoria leaf spot (Septoria) of birch is causing many forest and landscape birch to prematurely shed their leaves. Lilac leaf blotch (Pseudocercospora) continues to defoliate common lilac (Syringa vulgaris) across the region. Powdery mildews are abundant on a range of perennial and woody plants. Continue to scout for adult spotted lanternflies (Lycorma delicatula) and their egg masses on containers, stone, outdoor furniture, along with a range of other outdoor objects.

The drought stress that many trees are currently experiencing will only exacerbate the decline of beech (Fagus) infested by the beech leaf disease nematode (Litylenchus crenatae ssp. mccannii). The impact of drought stress should be considered when evaluating the efficacy of BLD treatments next season (foliar sprays and injections).

Ensure that mature rhododendrons and azaleas receive a thorough soaking of the root zone sometime in October, if we don’t experience more regular rainfall. This will help to reduce drought stress entering dormancy and hopefully lessen the impacts of winter injury.

With the dry weather, mushrooms and conks of wood-rotting fungi have been fewer and farther between. Berkeley’s polypore (Bondarzewia berkeleyi), black-staining polypore (Meripilus sumstinei), and reishi (Ganoderma sessile) have been observed recently so continue to scout large oaks and other hardwoods for their presence.

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