Plant Pest Phenology

Plant Pest Phenomena – a Fresh Phenological Perspective

Plant and insect activity rely on moderate temperatures; a temperature of 50 F is the starting point for growth and development.  In the northeast, we generally reach daily temperatures averaging in the 50s sometime in April (or oddly this year, in May)!  Buds swell, plants flower, and insects emerge from their winter diapause.  Hemlock woolly adelgid being the exception; they are active in the winter months.  Spring has arrived and it’s time to plant, enjoy the bursting buds and bloom, and to consider the pesky if not sometime persistent issue of pests in the garden.

Temperatures drive change in plant development – bud swell, bud burst and flowering; these events are plant phenology. Concurrent with plant growth and flowering is insect activity; the two go hand in hand.  Given this, we can use the phenomenon of phenology as a clock to help guide insect management decisions.

The top ten insect pests that we’ll consider here (in this installment) are: Eastern tent caterpillar, Hemlock woolly adelgid, Gypsy moth, Aphids, Cankerworms (inch worms), Birch leafminer, Spotted Lanternfly, Emerald ash borer, Cottony maple scale, and Japanese beetle.

Scout for Eastern tent caterpillar (look for tents in branch crotches of cherry trees) and Gypsy moth in late March to early April when red maple, forsythia, and PJM Rhododendrons are in full flower.  This is also a good time to treat for Hemlock woolly adelgid which are active in the cool weather months. In early April, when crabapple, Japanese cherry, and serviceberry bloom, look for aphids and inchworm activity.  Aphids often make their presence known by excreting honey dew making surfaces sticky, while Cankerworms (inchworms) damage new leaves by consuming them.  Late April to early May, eastern redbud, common lilac, and Korean viburnum bloom; it’s time to think about treating for Birch leafminer and to scout for Spotted Lanternfly egg hatch.  First instar nymphs of Spotted lanternfly drop from trees onto grasses to feed on tender foliage; this is a good time to consider a “drop zone” treatment.  Some of the trees that Spotted Lanternfly overwinter on include Ailanthus altissima (Tree of Heaven), red maple, black walnut, birch, and sycamore.  In mid to late May, Emerald ash borer begin to emerge.  Look for black locust bloom, as well as mock-orange, black cherry, red horsechestnut, and weigela flowering as indicators to treat to protect ash trees. In mid to late June, first generation of Cottony maple scale and Japanese beetle adult emergence are expected.  The phenological indicators include oakleaf hydrangea, Greenspire linden, northern catalpa, mountain laurel, and common elderberry.  Cottony maple scale makes it presence known by dripping honeydew, whereas Japanese beetle adults go to work on skeletonizing a large number of host species including roses, lindens, grapevines, apple, and cherry.


When considering treatments, whether by foliar spray or by tree injection, always read and follow the label instructions. If you need assistance in determining how best to treat a plant pest problem, email or call us here at Arborjet.  We’ll be very happy to help!