Agriculture Reference
In-Depth Information
Environmental concerns have led to increased governmental regulation of
pesticide use in recent years. As a result, the costs have increased of proving the
safety and efficacy of pesticides and of registering them for use on specified
crops. In addition, there has been a requirement for older pesticides to be tested
to modern standards and re-registered if their use is to continue to be permitted.
It is now uneconomic for manufacturers to register pesticides for use on
anything other than the major arable crops where the areas planted generate
sufficient demand to recover registration costs. In these terms the allium
vegetables, in common with other vegetables, are minor crops. Various schemes
have been instigated in different jurisdictions whereby growers themselves, or a
combination of growers and public bodies, finance the testing and registration
of pesticides for use on these 'minor crops'. In the UK, uses for minor crops are
granted by 'Specific off-Label Approvals' (SOLAs), and the costs of testing and
registering for these are borne out of a research and development levy on
growers. By this process it is possible to provide growers with a range of
appropriate pesticides that allows them to continue production of vegetable
crops economically (Chapman, 2000; Knott, 2005).
Weed control is absolutely vital for vegetable allium production. Research on
the topic was reviewed by Rubin (1990) and Bosch-Serra and Currah (2002).
All aspects of weed control in vegetable crops were reviewed in depth by
Grundy
et al.
(2003), and this account owes much to their work.
Effects of weed competition
Vegetable allium crops are easily outcompeted by weeds, especially when
directly seeded rather than grown from transplants or sets. The slow
germination, low relative growth rate (RGR) and low, upright leaf canopy of
alliums that never approaches total light interception, are innate features of
these crops that make them weak competitors for light (see Table 4.5 and Fig.
4.1). The shallow, relatively sparsely branched root system is also ill-adapted to
compete for water and nutrients against weeds (see Figs. 2.15 and 2.16). As an
example, the poor competitive ability of leeks for light compared with celery,
which has a higher seedling RGR and more horizontal foliage - and the
consequences of these features for the suppression of groundsel (
Senecio
vulgaris
) in these crops - is illustrated in Fig. 5.1 and Table 5.1 (Baumann
et al.
,
2001). Ample water and nutrients, the elimination of all weeds but groundsel
and the prevention of pests and diseases ensured that the effects shown in Fig.
5.1 and Table 5.1 resulted solely from light competition between the crops and
this weed.
