UMASS Landscaping Update

Pioneer Valley (Amherst)

General Conditions:

As May winds down, it really feels like summer across the Pioneer Valley. The landscape is lush with new growth and varying textures. The graceful layering of hemlock branches with lime green new growth contrasting with the dark older needles is one of the highlights of late May. Warm to hot and sometimes humid weather characterized this past reporting period. From 5/21 through 5/26, high temperatures crested in the middle to upper 80s with lows in the lower 60s. Recent summers have been very hot and humid in the valley and this season is starting off on a similar path. Bands of heavy rain and gusty winds gave most of the region a good soaking on 5/27, replenishing soil moisture in the upper horizons. Accumulations between 1–2” were recorded at several stations in western and central Franklin, Hampshire and Hampden counties. The eastern half of the tri-counties didn’t fare as well, with totals around 0.5”. The driving rain and strong winds overburdened some branches heavy with new growth and toppled many irises across the UMass campus. Black flies and mosquitoes are abundant, swarming and biting.

Pests/Problems:

Beech leaf disease, caused by the non-native foliar nematode Litylenchus crenatae ssp. mccannii, continues to be the most serious landscape and forest disease issue we’re currently facing. This disease will have a transformative impact on northern hardwood forests where beech is a primary component. When infestations are minor, the interveinal banding and convex cupping on the foliage can be nuanced. However, once the nematode becomes established, populations typically increase dramatically the following year. Serious infestations result in heavily banded, thickened, distorted and undersized foliage. Canopy thinning and dieback often begins in the lower half of the canopy and spreads upwards.

We have entered the time of year when symptoms of white pine needle damage are most severe. Older needle browning and shedding has or will soon reach its zenith for diseased trees. While not a lethal disease for eastern white pine, needle blights are a chronic stress that stress and weaken trees, making them susceptible to other diseases, insects and abiotic injury, such as drought.

Azalea sawfly larvae (Amauronematus azaleae) and fruitworm caterpillars (Orthosia sp. - suspected) were found on a variety of dwarf rhododendrons and azaleas. The azalea bark scale (Eriococcus azalea) was also found on a Korean azalea (Rhododendron yedoense var. poukhanense) and because the infestation was minor, the scales were manually crushed and removed. Their white, waxy outer coating makes them easy to find.

Exobasidium gall is starting to appear on susceptible azaleas and rhododendrons. Prune and remove the galls as they appear. Despite their ubiquity, rhododendrons and azaleas can be challenging to properly transplant from containers. Their fibrous roots become extremely dense, and the bark is very easily scraped away on the root flare. This makes disentangling the primary lateral roots or exposing the root flare a delicate matter. But circling and girdling roots must be addressed for plants to thrive. If rhododendrons and azaleas that have been established for several years are languishing, excavate the root flare to determine if girdling roots are present. Prune and remove as necessary.

Damage caused by larvae of the European pine shoot moth (Rhyacionia buoliana) was recently observed on eastern white pine (Pinus strobus ‘John’s Find’) and mugo pine (Pinus mugo). Infested candles were elongated but were brown and drooping, having been hollowed out by larval tunneling. The larvae are brownish in color with a black head and were found inside the dead shoots.

Defoliating caterpillars (ID unknown) were observed on Delphinium and lily leaf beetle (Lilioceris lilii) larvae are now present on a variety of lilies (Lilium). The bright red adult lily leaf beetles contrast strongly with the green lily leaves, making them easy to capture. The larvae, meanwhile, are coated with a “fecal shield”, which is a strange and yet effective adaptation to avoid predation.