OREGON STATE UNIVERSITY
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Make sure new stands are well established and approximately 10 to 12 inches (25 to 30 cm) tall before grazing. This can occur in as little as 45 days after seeding. Plants are established when they have three or four leaves and are not easily pulled out of the ground. Test this by pulling on newly established plants. If they resist your pulling, livestock won't be able to remove plants by grazing.
Proper management precautions should ensure maximum yield of high-quality forage, rapid regrowth, and stands capable of living beyond one season. These objectives can be achieved by safeguarding the regrowth mechanisms of annual ryegrass as described below.
In early spring, annual ryegrass is in the vegetative stage. During the vegetative stage, the apical meristem (which generates new leaves) is safely below defoliation height (at approximately 0.5 inch; 1 cm above ground level). See Figure.
While annual ryegrass is in the vegetative stage it shows no sign of seed head development. The plant is composed of leaves and no stems are evident.
In the vegetative stage, allow annual ryegrass to grow to 8 to 12 inches, graze to 2 to 6 inches, and provide three to five weeks for recovery.
During this stage the apical meristem is elevated in an "un-telescoping" manner to a position vulnerable to removal by grazing or mechanical harvest (see figure). The consequence of removal of the currently vegatative meristem, which is generating new leaves, is the loss of leaf generating capacity from this tiller. New tillers initiated from crown buds will not appear for 4 to 10 days following defoliation at this growth stage. Grazing or harvesting at this stage will result in no forage available until new tillers are initiated and have time to grow to a height suitable for removal.
When annual ryegrass plants are in the elongation stage, delay harvest until new tiller buds are available for regrowth.
The presence of tillers ready for regrowth will be evident when you examine the base of the plant and see new bud shoots ready to grow.
Transition to the reproductive or flowering stage in annual ryegrass does not require any cold temperature (vernalization) induction. Flowering can occur when daylengths are greater than 9 to 11 hours.
Progress toward seed head development is easily monitored by splitting a shoot lengthwise with a sharp blade and examining the apical meristem for signs of seed head development (see figure).
When culms are allowed to develop past the early-jointing stage (to the late jointing to early boot stage), basal (crown) buds will develop in the root zone. These basal buds produce a second cycle of tillers (new plants), which assure vigorous regrowth.
The best insurance for vigorous regrowth after the vegetative stage is to remove livestock before the growing points of elongating stems (culms) are raised to the grazing height. These pastures may be safely grazed again when plants have reached the boot to early heading stage (late transition) because new buds will have had time to develop.
Delaying defoliation until boot stage or the early heading stage will minimize the delay of regrowth of new vegetative tillers. You can tell when shoots reach the boot stage due to the swelling in the sheath of the flag leaf (the smallest and terminal leaf on the culm) (see previous figure).
Annual ryegrass regrowth is slower than for perennial ryegrass. It may take 3 to 4 weeks or more before the crop is ready for regrazing. Allow regrowth to attain a height of 4 to 10 inches (10 to 25 cm) before defoliation.
Since annual ryegrass has no low temperature induction requirement for flowering, it may progress through the developmental stages toward flowering anytime daylength exceeds 9 hours. The length of time to flowering is affected by environmental and management factors. High temperature and water stress speed the progression toward flowering. Removal of stresses through adequate supply of soil water, nutrients (particularly N), and moderate defoliation management will extend the vegetative period.
For green chop, silage, or hay production, allow plants to reach the boot to early heading stage. Under silage or green chop management, four to six harvests are common. With hay production, three or four harvests are obtained.
Following each grazing or mechanical harvest cycle, assure that adequate N is available for rapid growth. This can be accomplished by fertilizing with nitrogen at 50-75 lb/a (56-84 kg/ha), or if previously manured, from N already in the soil.
Maximum high quality and rapid regrowth of annual ryegrass will occur when defoliation is delayed until tillers are allowed to progress through the elongation and transition phases - allowing regrowth tillers to be ready to regrow rapidly. This progression takes 1 to 2 weeks from the time tillers initiate the elongation phase. Stressed plants (high temperature and/or limited water conditions) will progress more rapidly through the progression, while plants growing under optimum conditions will progress through the stages more slowly.
In summary, defoliate annual ryegrass plants while they are in the vegetative stage or the late boot to early heading stage, but avoid severe defoliation when they are in the elongation to early transition stage.