March 17, 2016 – Kenosha News

Question: At a recent program on emerald ash borer, the speaker made the claim that adult emerald ash borers emerge when the black locust trees bloom. I found this quite interesting and was wondering if there are other unique occurrences similar to this. K.K.

Answer: The call of the chorus frogs, the trumpting of the cranes, and the appearance of the red-winged black birds along with warmer temperatures indicate the impending arrival of spring. Recording when these annual biological events occur is part of a branch of science called phenology, the study of periodic plant and animal life-cycle events influenced by seasonal changes and climatic conditions.

Aldo Leopold, naturalist and author of Sand County Almanac, was one of the first phenologists in Wisconsin. The data he collected in the 1930’s – 1940’s in Sauk County has been compared to data collected more recently in the same area by his daughter, Nina Leopold Bradley, indicating some species are changing behaviors in response to climate change.

Phenological records are used as guides for planting vegetable gardens and for scouting insect pests. The information they provide is useful in pest management programs since it assists in targeting the proper time to apply controls during the most susceptible life stage of pests. The growth and development of insects are directly related to temperature and weather conditions making them perfect candidates for phenology based predictions.

The growth stages of common lilac, Syringa vulgaris, are routinely used for phenological observations…

  • Plant cole crops, spinach, carrots, and beets when the first leaf of lilac emerges.
  • When lilacs are in bloom, plant bean, squash, and cucumber seeds.
  • Watch for pine sawfly activity when lilacs are blooming.

Other horticultural suggestions based on phenology are:

  • Plant peas when forsythia blooms.
  • When wild cherry trees bloom, asparagus is ready to harvest.
  • Plant tomatoes when Lily-of-the-Valley is in full bloom.
  • Apply crabgrass preventer to lawns when forsythia blooms.
  • Plant potatoes when the first dandelion blooms.
  • When the first flowers of chicory open, Japanese beetles begin feeding. Also at this time, apply control measures to prevent damage from squash vine borers.
  • Adult apple maggots appear when Canada thistle blooms.

Although these guidelines seem more like folklore than phenology, many seasoned gardeners adhere to them. Plant scientists prefer to rely on a measurement of heat accumulation called growing degree days, to estimate timing of certain events. Either way, signs of spring are welcome after a Wisconsin winter.


Kenosha County UW-Extension LogoJeanne Hilinske-Christensen, M.S., is the Consumer Horticulture Educator for Kenosha County UW-Extension.