UMASS Landscape Update

Pioneer Valley (Amherst)

General Conditions: 

The first half of August was hot, humid, and dry across most of the tri-counties. The recent cool down on August 18, courtesy of a large Canadian air mass (without any wildlife smoke), ushered in pleasant temperatures and low humidity.

Scattered showers have occurred on several days during this reporting period, but they have been isolated and fast-moving. Two bands of heavy rainfall did provide some moisture for southern Hampden County (August 13) and western Franklin County (August 17). But for the rest of us it’s been scraps at best. Symptoms of drought stress are abundant across the UMass campus. Numerous trees, shrubs, and perennials have wilted leaves, scorched leaf margins, chlorotic foliage, early leaf drop (especially river birch and serviceberry), and upper canopy dieback. Large swaths of brown and dead turfgrass are visible as well. Bark mulch has taken on that almost hydrophobic quality where water sheets off and it takes considerable watering to absorb through to the underlying soil. Rain during the time of writing (August 20) will hopefully provide some relief.

There’s an abundance of late summer colors with black-eyed Susan (Rudbeckia), cardinal flower (Lobelia), sunflower (Helianthus), Gladiolus, and Dahlia in full bloom. Panicle hydrangeas (Hydrangea paniculata) are in peak flower across the landscape. These durable and dependable plants tolerate drought conditions very well and have few associated pests and pathogens. The wide range of cultivars available provides a variety of sizes and forms, and some are magnets for pollinators, drawing a large volume and diversity of insects.

Pests/Problems:

Late summer and early autumn is the time when many beech leaf disease nematodes are migrating from infested leaves to buds, where they will overwinter and feed. Any minor rain event and light wind is sufficient to disperse the nematodes to nearby beech trees.

Spider mites have been an issue for certain plants all season and they thrive during extended dry periods. If chemical control is used, make sure to use a miticide and avoid broad spectrum insecticides (e.g. bifenthrin) that can also kill non-target, beneficial insects.

Asian jumping worms (Amynthas agrestis) are quite active right now and easily disturbed from the organic layer of infested soil. Groups of robins (Turdus migratorius) have been observed digging and disturbing garden beds to capture and feed on jumping worms. In some cases, significant amounts of mulch and organic matter have been disturbed by their activity.

Late season foliar diseases continue to appear, but none are as striking as lilac leaf blotch, caused by Pseudcercospora. Some large plantings of common lilac (Syringa vulgaris) are badly diseased with brown and shedding foliage. 

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