Agriculture Reference
In-Depth Information
brought to the surface to desiccate during dry weather. Simply removing the
leaves is ineffective because they quickly regrow from the well-supplied root
crown. Burial may be an effective control strategy if the storage organ is
severely fragmented.
Most nonwandering species without taproots (e.g., Plantago major ) are
easily controlled by tillage (Table 4.2). In this regard, Poa annua , which com-
monly perennates (Law, Bradshaw & Putwain, 1977), is an exception that
proves the rule. This species is notoriously hard to kill with shallow tillage
methods because soil clings to the dense root mat (Bates, 1948). However,
when clumps are successfully broken up, the fragments often die quickly.
Since most nonwandering weeds without taproots have a rosette growth form
with small storage reserves and limited capacity for stem elongation, burial is
often highly effective.Consequently,these species are rarely problem weeds in
tilled systems.
Various strategies exist for mechanical management of perennial weeds.
Which approach is most effective against a particular species depends on the
growth and stress response characteristics of the weed. Effectiveness of all
these strategies is improved by understanding the growth cycle of the weed.
How the timing of tillage affects the growth of perennial weeds
The effect of tillage on a perennial weed varies depending on the phe-
nology of the species relative to the timing of tillage. In general, a perennial
weed in a seasonal climate is most vulnerable to damage shortly after reserves in the per-
ennating organs have been converted to new shoots .
In a series of studies in southern Sweden, Håkansson & Wallgren
(Håkansson, 1963, 1967, 1969 a ; Håkansson & Wallgren, 1972 b , 1976) found
that although Allium vineale , Sonchus arvensis , and Agropyron (Elytrigia) repens
perennate by different means,all were most susceptible to damage by burial at
the point when their perennating organs reached minimum mass.For A.repens
this occurred when three to four leaves had formed on the new shoots - just
prior to initiation of tillers and new rhizomes (Håkansson 1967; Håkansson &
Wallgren 1976).In Sweden the three-to-four leaf stage was reached in late May
for undisturbed plants, but in warmer climates overwintering leaves may
resupply rhizomes before the new growth reaches this size.Majek,Erickson &
Duke (1984) similarly found that A.repens in New York was most susceptible to
tillage in early May, just before formation of new rhizomes.
For Allium vineale , maximum susceptibility to tillage due to depletion of
stored reserves occurred primarily in the spring following autumn germina-
tion of bulbs and was difficult to induce by cultural practices.In contrast,pro-
vided Agropyron repens and S. arvensis were metabolically active, fragmentation
Search WWH ::




Custom Search