Until maturation, a juvenile plant is insensitive to environmental conditions that later promote flowering. During induction, physiological changes take place in the plant that prepare a plant to initiate floral development.
Two types of induction exist: 1) low-temperature induction called vernalization and 2) photoperiodic induction. Vernalization takes place in the growing point, while photoperiodic induction occurs in the leaves.
Cool-season grasses have a vernalization requirement as the first prerequisite for flowering. The most effective vernalization temperatures are 32 to 50 F. This is a reversible process, with "devernalization" taking place at high temperatures.
Short days can substitute for vernalization in some grasses, including perennial ryegrass and colonial and creeping bentgrass.
Warm-season grasses have no vernalization requirement.
Photoperiodic induction involves the production of a flowering stimulus in the leaves and its translocation to the stem apex during certain day lengths. Cool-season grasses are long-day plants that flower after exposure to day lengths greater than a critical number of hours.
Warm season grasses are predominantly short-day plants in which flower induction occurs when days are shorter than a critical number of hours. Some warm-season grasses are day-neutral plants that flower irrespective of day length or other requirements.
All grasses have a transition phase during which time the vegetative shoot apex is transformed into a floral bud. During this phase the sheaths of flowering shoots elongate raising their respective leaf collars to the extent that the leaf could be severed by grazing or cutting below the meristematic zone. This malpractice may seriously reduce the number of leaf blades in the recovery growth.
If the shoot apex remains a part of the stubble, the central stem will continue growth producing a naked seed stalk. This effect is called "denuding" because many of the flowering stems are indeed naked.
Such regrowth is unpalatible and plant hormones associated with seedhead development tend to suppress growth of aftermath shoots. If seedheads are not consumed they should be clipped to trigger growth of aftermath shoots at an early date.
Intensive defoliation during the transition phase presents still another hazard. By this stage internode elongation may have raised the shoot apex to a vulnerable height. This meristem represents the currently active regrowth mechanism, if it is destroyed (decapitated), there will be no further production from the shoot. Recovery growth depends largely on an alternative under-ground regrowth mechanism (basal buds in the crown zone).
Management precautions are needed during the transition phase because of the exposure of regrowth meristems caused by culm development. These exposed meristems are located in the collar at the base of the blade and the shoot apex. The latter is easily found by splitting a shoot lengthwise. The developing segmented culm will terminate in the meristematic shoot apex and appear as a feathery frond.
Grazing systems should be designed which provide for the preservation of these exposed meristems until such time as basal buds located in crown tissue have produced new shoot initials. These new shoot initials are normally well developed by the late boot stage. This marks the time for intensive grazing or mechanical harvest for optimizing yield and promote rapid regrowth.
With simple forage mixtures, one or two grasses with a companion legume, care should be taken during the transition phase of the dominant grass because culm development has elevated the meristematic zone of the shoot to a position where it could be removed. If an alternative underground regrowth mechanism is not yet ready to function, weeds and companion legumes may become predominant due to slow recovery of the desired grass. This vulnerability prompts grazers to seed a more complex forage mixture in order to spread the risks associated with untimely grazing or mowing. A defoliation system which is unfavorable to one grass may be beneficial to an associated grass. But proper management of the desired grasses means a simple mixture can be successful.
Graze desired grasses in the vegetative phase and carefully watch for signs of transition into reproduction. Graze unwanted grasses when they are in transition.