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Internal dormancy was shown to occur in western ironweed (Vernonia baldwinni Torr.) and leafy spurge (Euphorbia esula L.) in late summer and fall. Time required for emergence and extent of growth were important indicators of dormancy. Dormancy is apparently broken naturally in the field by low soil temperatures.
Perennial weeds capable of vegetative reproduction comprise, as a group, some of our most serious weed problems. Eradication is difficult where new top growth can be produced repeatedly from underground buds. A time honored control method involves the cutting of all top growth with special tillage implements each time sufficient new growth has been produced. In this way food reserves in the root system of the weed are slowly depleted until all growth stops. Root systems of most creeping perennial weeds are supplied with numerous buds on either the crown, lateral roots or rhizomes. Removal of the top growth of such plants with either chemicals or tillage results in the activation of a small percentage of the available buds and new top growth is produced. The new growth thus produced tends to prevent further bud activation presumably through the maintenance of auxin levels unfavorable for growth of these buds. This phenomenon is often referred to as apical dominance. Food depletion of the root system would be faster if more buds could be stimulated to active growth prior to each cycle of top growth removal.
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