Trees’ and insects’ growth and development are dependent on environmental factors like temperature (heat), light and humidity. Because insects are cold-blooded, temperature has the greatest effect on insect development rates.Development rate increases as temperature increases up to a point. In the temperature range from 10 to 30 degrees, development rate changes almost linearly with increasing temperature. At very low temperature there is no development, and at very high temperature development is stunted.
Since temperature influences tree growth in a similar manner to insects, development of the various growth stages in the tree is dependent on temperature. Each stage of tree development requires a certain amount of heat units before growth to the next stage will occur. This measure of accumulated heat over time is known as physiological time. For instance, remember the cool, rainy late-winter/early-spring weather we recently had? This year’s cherry blossom’s in DC went from 2/28/2011 (green color in buds) to 3/29/2011 (peak bloom).Last year’s cherry blossoms only went from 3/14/2010 (green color in buds) to 3/31/2010 (peak bloom) because it was warmer earlier – so developmental growth speeded up – and left us with less time to enjoy the blooms.
For many years, growers have observed the arrival or development of a partlcular insect pest with flower bud or leaf development and have timed the applications of sprays in the spring. This is an indirect use of physiological time. Using these natural timers are most useful early in the growing season when tree growth stages are readily observable. However, making accurate predictions on insect life stages throughout the growing season are needed. This is done by measuring degree-days of the insects in question.
What are degree days? Entomologists have determined lower threshold temperatures and degree-day totals for the life stages of many insects by studying their development in the field and the laboratory. The lower developmental threshold for a species is the temperature below which development stops. The upper developmental threshold is the temperature at which the rate of growth or development begins to decrease. Phenology models are then developed and used to predict various events or lifestages of an insect. This is useful for tree and shrub care companies because it gives a general timetable for when to treat insect pests during the correct stages to be effective.
Mother Nature is full of surprises! If you find your insect pest populations are out of control this season and damaging your trees and shrubs, contact Wood Acres Tree Specialists for a consultation. It takes years to grow a beautiful tree or shrub specimen – don’t let it be disfigured or destroyed in one season.