High humidity and temps in Early September

Some intense late season heat and humidity has kept summer alive and well in the Pioneer Valley. Heat index values in the upper 90s were expected from 9/5 through 9/7 with high humidity expected to continue through 9/10 with minimal relief from scattered thunderstorms. The tri-counties experienced two rain events over this past reporting period on 8/25 and 8/30. Accumulations from these two storms ranged from ~0.75” to 2”, with Franklin County receiving the higher totals. Subsurface soil moisture remains good but the uppermost soils in exposed, sunny locations are drying out. Established trees and shrubs have ample soil moisture as we endure this blast of early September heat. However, recently transplanted trees and shrubs should be closely monitored to maintain good moisture in the root zone. Prior to the heat, there were some pleasant late summer days with daytime temperatures in the 70s and lows in the 50s.   

Pests/Problems:

The elm zigzag sawfly (Aproceros leucopoda) was recently detected in both Hampden and Berkshire Counties. This non-native pest is capable of defoliating elms; more information, including links to photos, can be found at https://ag.umass.edu/landscape/fact-sheets/elm-zigzag-sawfly and info from MDAR on where to report suspected finds at http://www.mass.gov/news/dcr-announces-that-elm-zigzag-sawfly-has-been-confirmed-in-massachusetts(link is external)

. A distinctive symptom of infestation is the zig-zag pattern of defoliation made by the sawfly larvae. Feeding occurs between the primary leaf veins (interveinal). At present, elms may also have scattered defoliation in the canopy from Japanese beetles (Popillia japonica). This ubiquitous pest also feeds on interveinal leaf tissue, but the primary and secondary veins remain intact, giving infested leaves a skeletonized appearance. As badly injured as Japanese knotweed (Polygonum cuspidatum) was after the 5/18 frost, it’s currently basking in full flower with no lingering effects. The season-long activity of Asian jumping worms (Amynthas agrestis) is very conspicuous right now and beds harboring these invasive pests may need additions of organic matter (compost, bark mulch, leaf mulch, etc.) to compensate for its rapid breakdown. Hawthorns in shaded settings on the UMass campus are almost completely defoliated from Entomosporium leaf spot. Horsechestnuts appear awful, as they always do this time of year, due to Guignarida leaf blotch. Early color change continues for scattered hardwoods, especially for sugar maples with abundant seed in the canopy. Mast years for maples can result in undersized foliage and for trees with maple anthracnose, foliage may be shed prematurely. Diplodia and Botryosphaeria canker are very abundant on a range of different hardwoods and conifers at this time, especially crabapples. Pear trellis rust (Gymnosporangium sabinae) was observed on a pear (Pyrus communis). This disease is characterized by large, orange-yellow leaf spots on the upper leaf surface with tan-colored, gall-like tissue on the underside that can be confused with insect activity. The black-staining polypore, Meripilus sumstinei, has been located around the base of deciduous hardwoods. Its presence does not indicate serious root or lower trunk rot is present. Spruce spider mites (Oligonychus ununguis) were found on lower and interior canopy needles of Norway spruce. The abundant rainfall this season likely suppressed outbreaks this season (heavy rain easily washes spider mites from infested needles), but new populations can quickly develop during dry periods in the autumn season.