When spring is close but still elusive, the gardener’s heart yearns for any sign of the coming season. That sign may come as a sound, such as the call of a male red-winged blackbird as he establishes his breeding territory, or maybe a whiff of skunk’s scent from underneath the front porch. The first snowdrop in bloom gives us hope, when days are still gray and cold, that spring can’t be far off.
For me, the first sure sign of spring came this year on March third. On a hike along the banks of the Tuscarawas River, my husband and I heard the calls of several male red-winged blackbirds and counted 10 turkey vultures soaring overhead. As the last of the snow melted in our backyard (at least I hope it’s the last), a dozen yellow crocuses lifted their heads in bloom. It’s still too early to plant, mulch, or even walk on the sopping-wet lawn, but it’s not too early to plan and dream.
I used to feel swept up by spring, caught in a whirlwind of blooming plants and emerging pests. Brief spikes in temperatures would bring plant after plant into bloom all in a rush, followed by a seemingly endless sequence of insect pests. My head would spin as I tried to keep up with the pace.
Over the years, I’ve learned to jump onto the runaway train that is spring unfolding, and enjoy the ride. Much of my enjoyment now comes from an appreciation of phenology, the study of recurring natural events and their relationship to weather and climate. The sequence of events remains consistent from year to year. While the pace of the sequence may change depending on the weather, with a warm spring bringing on a fast progression of bloom, the sequence of flowering and insect emergence remains consistent from year to year.
Gardeners can use this sequence to anticipate plant and pest activity in the garden. Since the development rate of both insects and plants is determined by temperature, plant events can be used to predict insect emergence and time pest management strategies. Dr. Dan Herms, professor of entomology at Ohio State University in Wooster, has compiled a biological calendar based on years of observation of plant and insect activity at Secrest Arboretum in Wooster (www.oardc.ohio-state.edu/gdd). By entering an Ohio ZIP code, gardeners can use this calendar to pinpoint development events in their region.
For the purposes of this calendar, first bloom is defined as the first individual flower opening to expose its reproductive structures, and full bloom as the point when one out of 20 flowers is still in bud.
On a cluster of lilac flowers, for example, first bloom means one of the small individual flowers has opened.
Eastern tent caterpillar egg hatch and border forsythia first bloom: This caterpillar forms silky nests in tree crotches in spring. The pest overwinters as a crusty gray egg case attached to tree branches; the eggs will hatch in spring when forsythia shrubs begin to bloom.
Eastern tent caterpillars feed on tree leaves, returning to their nests to avoid predation by birds. Black cherry, crabapple, apple, plum and cherry are favorite tree hosts.
This pest can be managed by removing silken nests as they are formed in branch crotches, by applying Bt for caterpillars (a naturally derived insecticide) when caterpillars are young, or with traditional labeled insecticides including soaps and oils. Good product contact is essential, since the insects are protected inside their silken webs.
European pine sawfly egg hatch and Callery pear first bloom: European pine sawfly overwinters as eggs, laid in needles last year. The needles have yellow bands where eggs have been laid, and can be removed if noticed in winter.
Once the eggs hatch, around the time flowering pear comes into bloom, the larvae begin to feed on needles. The young larvae are unable to eat all the way through the needle; they leave brown strips of uneaten tissue. These brown needles, just under this year’s new growth, help to detect early presence of this pest.
Larvae will strip the plant’s older needles, leaving new needles untouched, giving the plant a “poodle cut” look. Sawflies are easily killed when small with horticultural oils, insecticidal soaps, or traditional insecticides, or simply knock them into a bucket of soapy water.
Viburnum leaf beetle egg hatch and Koreanspice viburnum full bloom: This invasive pest damages viburnum shrubs by eating leaves. In spring, beetle larvae hatch out of eggs laid in twigs the previous fall and begin to chew through leaves.
Shrubs can be defoliated by larval feeding. Beetles pupate in the soil, then emerge as adults in summer. The adults can again defoliate the shrubs.
Local populations can build up quickly, since each adult female can lay up to 500 eggs in twig ends. Pest populations can be reduced by pruning twigs with egg damage right now, before new leaves emerge. Other options include pruning off twig tips with egg scars in fall after leaf drop, treating with systemic insecticide applications in fall, or applying foliar insecticides to protect leaves in spring before larvae emerge.
Pine needle scale egg hatch and common lilac full bloom: Pine needle scale attacks a wide range of pine hosts, most notably Scotch and mugo pine. Scale is an insect pest that damages plants by removing plant sap.
This scale overwinters as eggs, protected underneath the dead female scale. Juvenile scale, called crawlers, are the active stage of this pest. At the time when common lilacs are in full bloom, the crawlers hatch from the eggs.
Scale can spread in the crawler stage, moving by wind or sometimes birds or mammals. Once in their new location, the crawlers settle, insert their mouthparts, and begin to form protective armor over their bodies.
This armor protects scale from most insecticides. Pine needle scale can cause significant damage over time by removing plant sap from the needle tissue. A second and sometimes third generation can be produced in only one season. Crawlers are easy to kill with insecticidal soaps or horticultural oils if these products are applied in the week following egg hatch.
Bagworm egg hatch and Japanese tree lilac first bloom: This caterpillar pest is most easily seen in the winter, before leaves and flowers have emerged. Brown, cone-like bags can be found hanging from twigs and branches of conifers and deciduous trees.
Around the time of the first bloom of tree lilac, the eggs will hatch, with 500 to 1000 juvenile caterpillars emerging from each egg-laden bag. The young caterpillars spin a silken thread and are carried by the wind to new plants. Larvae eat plant leaves, using the leaves to build bags around themselves. On evergreens, bagworms can cause damage.
Insecticidal soap, horticultural oils or Bt for caterpillars can be used to control young larvae. These products are best applied about 10 days after hatching to be sure all caterpillars are destroyed.
Japanese beetle adult emergence and littleleaf linden first bloom: The adult stage of this pest feeds on over 400 plant species, including rose, willow, linden, grape, apples and cherries. Adults damage plants by eating the leaf tissue between veins.
The adults emerge from the ground around the time littleleaf Lindens come into bloom. Since the first beetles to arrive in the garden send out a congregation scent to attract other beetles, hand-picking adults as soon as they’re observed can reduce overall damage.
Gardeners can expand upon and personalize this biological calendar by tracking plant and pest activity in their own gardens, and penciling these observations into the sequence. This results in a customized biological calendar featuring bloom events from an individual garden, with a sequence that remains consistent year after year. For many gardeners, an understanding of phenology opens a window onto the patterns of a wider natural world, a window that once open, never closes.
Denise Ellsworth directs the honeybee and native pollinator education program for Ohio State University. If you have questions about your garden, call her at 330-263-3700 or click on the Ask Denise link on her blog at www.osugarden.com.