UMASS Update

Pioneer Valley (Amherst)

General Conditions: 

It was an extremely wet and humid week in the Connecticut River Valley as we settled into the month of May. Scattered showers and thunderstorms unleashed a staggering amount rainfall from 5/2 through 5/6, with totals ranging from 2–6”. The eastern half of the tri-counties saw lesser totals (2–3”) while the hill towns in western Hampshire and Franklin counties had the highest amounts (~4.5”). Powerful bands of damaging thunderstorms snapped and uprooted numerous trees on Saturday, 5/3. With ambient air temperatures near 80°F and dew points that day in the mid-60s, it felt very much like summer. Pollen levels have been high but the regular rainfall over the past week has subdued dispersal.

Woody and non-woody plants are heavy with new growth and soils are wet to saturated. It’s been an impressive spring for magnolia, redbud, and now crabapples. While many rhododendrons suffered serious cases of winter injury, cultivars in the PJM group have really showed their hardiness, with virtually no dieback.

Mosquitoes continue to emerge in growing numbers and that trend will surely continue with the pooling rainfall. The long-term forecast (at the time of writing on 5/7) calls for another round of heavy rainfall. Low-lying areas of the valley prone to flooding are doing just that.

Pests/Problems:

Presently, many plants are appearing robust and disease free during these early weeks of the growing season. But multiple days of heavy rainfall as new shoots and foliage develop can stimulate a variety of common diseases for landscape ornamentals. In the coming weeks, closely monitor for symptoms of anthracnose, shoot blight and twig cankering diseases, and leaf spot and blotch diseases. Fire blight could be locally abundant with the rain, occurring while apples and pears were in full bloom.

Proper scouting must be conducted very close to the plants to properly assess disease and insect symptoms. Many issues are masked by viewing from a distance. Continue to prune and discard dead twigs and branches from trees and shrubs throughout the landscape. Interior canopies often harbor dead twigs that can allow cankering fungi like Phomopsis and Botryosphaeria to linger in plant canopies.

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