In North America, the invasion of foreign forest tree diseases has caused tremendous losses. Examples are chestnut blight, white pine blister rust, and Dutch elm disease. The latter is insect borne. The importance of injurious insects that might come from abroad also is clearly recognized. However, the insects are outside the scope of the present consideration.
Epidemic diseases are much more serious for forest trees than for comparable agricultural crops.
If a field of wheat should be destroyed, something else could be planted the next year. Furthermore, with some of the root and butt rot organisms another danger appears. Such pathogens may develop in an apparently innocuous way in the nurseries. Thus, dangerous disease organisms may be distributed with the nursery stock throughout the areas used for reforestation. His trip was financed by the University of Wisconsin.