Plant Phenological Indicators

Phenology is the study of periodic occurrences in nature and their relation to weather. The growth of plants is, in part, a response to an accumulation of heat units. Some examples of growth stages of plants that can be correlated to heat units include bud swell, leaf emergence/expansion, stages of flowering, or elongation of new growth (conifers). Specific plant growth stages can be correlated to certain life stages of insects and mites. Length of day, other environmental factors, and different cultivars may affect specific events in a plant's development so that correlations of plant phenology are not as precise as the use of growing degree day information. Using plant phenological indicators is useful in establishing monitoring times and is more accurate than referring to calendar dates to time a particular management strategy. An example of the use of a plant phenological indicator would be the correlation of egg hatch of gypsy moth with the bloom of shadbush or serviceberry (Amelanchier). Donald Orton's book Coincide contains many observations on relationships of plant phenology and some key arthropod pest life stages. It is available from Labor of Love Conservatory, 468 South President Street, Unit #103, Carol Stream, IL 60188, phone: 630-668-8597.

Data collection and observations of growing degree days and plant phenological indicators in Pennsylvania are currently being conducted by an applied group of arborists, nurserymen, landscape managers, and Penn State Cooperative Extension educators. This organization was originally known as the Southeast Pennsylvania IPM Research Group. It is now known as the Penn-Del IPM Research Group. Additional information regarding this group's activities can be obtained by calling 610-489-4315.