General Conditions: Spring color continued this past week due to the cooler temperatures and rain. Mid-week, however, the weather warmed up with a high of 84 degrees on May 17th in Hanson, with more warm weather forecast for May 18th. Hanson received 2.10 inches of rain and soils are moist. The following plants are, or remain, in full bloom: Aesculus hippocastanum (Common Horsechestnut), Cercis canadensis (Eastern Redbud), late blooming magnolias, Magnolia fraseri, Rutgers hybrid dogwoods (Stellar series), Weigela florida ‘Versicolor’, Wisteria floribunda (Japanese Wisteria), Calycanthus floridus (Common Sweetshrub), Malus sp. (apples, crabapples), Halesia sp., Cornus florida (Flowering dogwood), Daphne x burkwoodii 'Carol Mackie', Daphne tangutica, Viburnum ‘Eskimo’, Viburnum setigerum, Viburnum plicatum f. tomentosum (Doublefile file viburnum), Syringa vulgaris (Common Lilac), Aristolochia durior (Dutchman's pipe), Fothergilla major (large Fothergilla), Fothergilla gardenii (dwarf Fothergilla), Kerria, Vaccinium corymbosum (highbush blueberry), Rhododendron ‘Olga Mezitt’, Lonicera tatarica (invasive), Cytisus scoparius (Scottish broom, Ilex x meserveae, Camassia sp., Persicaria bistorta ‘Superbum’, Corydalis lutea, Tiarella cordifolia (Foam Flower), Buglossoides purpurocaerulea, Geranium sp., Convallaria majalis (Lily-of-the-valley, Epimedium sp., Cypripedium parviflorum (Yellow Lady’s Slipper), Trillium sp., Galium odoratum (Sweet Woodruff), Brunnera macrophylla, Asarum canadense, Polygonatum sp. (Solomon's Seal), Stylophorum diphyllum (Wood Poppy), Phlox subulata, Phlox stolonifera, Phlox divaricata, Arisaema dracontium, Arisaema ringens, Arisaema sikokianum and other Arisaema sp.(Jack-in-the-pulpit), Euphorbia polychroma, Pulmonaria sp., Doronicum sp., Ajuga, dwarf bearded Iris, Saruma henryi, Lamiastrum galeobdolon, Lamium sp., Aurinia saxatilis (Basket of Gold), Dicentra spectabilis, Lunaria annua (honesty or money plant), Mertensia virginica (Virginia bluebells), Helleborus foetidus, Violets, Aquilegia sp. (Columbine) Myosotis sylvatica (Forget-me-not) and Vinca minor.
The following plants are ending bloom: Kwanzan cherry, Spiraea prunifolia f. simplicifolia (Bridalwreath Spirea), Pieris floribunda (Mountain Pieris), Chaenomeles speciosa (Common Floweringquince), Exochorda racemosa and Glaucidium palmatum.
On the down side, the wet weather continued to interrupt mowing and landscape operations and mosquitoes are active and thriving; on the up side, the drought is now officially over and hopefully the rain, and more rain, will activate Entomophaga maimaiga, the fungus which could help reduce the gypsy moth caterpillar population. If using a preventative grub management product that contains Chlorantraniliprole (AceleprynTM, GrubExTM), it is best applied before the end of May; follow the directions on the label before applying
Pests/Problems: The cool weather has kept not only plant growth in check but has also delayed insect development. Winter moth caterpillars continue to feed and most are in 3rd instar. Winter moth caterpillar numbers appear significantly lower than in past years. It has been difficult to find many when scouting, however, they are out there and were found in higher numbers on roses and Japanese maples, feeding between leaves they had webbed together. (632 growing degree days (GDD) at Base 40).
Gypsy moth caterpillars are present in high numbers on a wide range of plant material, especially oaks and reports continue to come in of the caterpillars ‘ballooning’ or floating through the air this past week. Gypsy moth caterpillars were also found feeding on the undersides of rose foliage and creating ‘window-pane’ damage (usually a sign of roseslug sawfly). Now is a good time to manage gypsy moth caterpillars while they are small and before they do significant damage. Products containing Spinosad are effective on small caterpillars as well as larger caterpillars; do not apply to plants in bloom. Most gypsy moth caterpillars observed were in 2nd instar. Driving through Plymouth County revealed many oak trees with dead branches or trees that are completely dead. Dr. Joe Elkinton’s staff (UMass, Amherst) reports that many oak trees in certain areas of Wompatuck State Park, Hingham, MA, are completely dead; last year’s defoliation, followed by the severe drought, most likely factoring into to their decline and/or death.
The bright green, azalea sawflies are active on deciduous azaleas and can be difficult to see at first. These caterpillar-like sawflies feed on the edge of the leaf and work their way in, towards the midrib and can cause significant foliar damage. Sawflies are not lepidopteran caterpillars (butterflies & moths) and Bt (Bacillus thuringiensis) is not effective on sawfly larvae.
Monitor for roseslug sawfly which may cause significant damage to rose foliage, if left untreated. (See the Insect section of the Landscape Message).
Continue to monitor pines for European pine sawfly larvae which can decimate the new growth if not managed early. Deer tick nymphs are active and will remain active for several months. The tiny, poppy-seed size nymphs are difficult to see and it is this stage that is usually most responsible for the transmission of Lyme disease.
Lily leaf beetle adults remain active on true lilies and egg-laying has begun. Monitor the undersides of the foliage and look for the feces-covered larvae. Prune the foliage and destroy the eggs, when possible. Products that contain Spinosad are effective on the larvae but not on the adults. Hand-pick and destroy the adults when possible, or manage with a labeled insecticide. Read and follow the directions on the label.
Monitor the undersides of azaleas for azalea whitefly, and manage if found. The following insects and/or pests are also active: Eastern tent caterpillar, European pine sawfly; hemlock woolly adelgid; spruce spider mite; Elongate hemlock scale; azalea sawfly; black flies, carpenter bees, ants, wasps, snails, slugs and dog ticks. Beneficial insects are also active. We've had just enough wet weather to foster development of foliar diseases of susceptible conifers, dogwood and crabapples. Dandelion are ending bloom and setting seed. Euonymus alatus (burning bush), barberry, veronica, garlic mustard, ground ivy, violet, and chickweed remain in bloom.