Agriculture Reference
In-Depth Information
Emerging technologies that may in future improve non-herbicidal weed
management include the application of machine vision to the guidance of inter-
row steerage hoes (Melander
et al.
, 2005) or to robotic weeding machines, for
which progress has been made in distinguishing leeks from weeds (Grundy
et al.
,
2005). It has been found that drilled onion leaves need to have a height of 10 cm
or more before they can withstand current methods of mechanical intra-row
weeding without excessive crop damage (Melander
et al.
, 2005). In this context,
it should be possible to give drilled alliums a size advantage over weeds by
accelerating their emergence and early growth through the use of seed priming
and starter fertilizers (see Chapter 6).
Another intriguing idea is to restrict soil cultivation to night-time so that
exposure to daylight during cultivation does not break the dormancy of light-
sensitive weed seeds. Seed dormancy is another process that can be influenced
by phytochrome, which was mentioned in relation to the control of bulbing in
Chapter 4. In one experiment, dark cultivation reduced weed emergence in an
onion crop by 50%, but in the next year there was no effect; the reasons for the
difference were not understood (Melander
et al.
, 2005).
The majority of arthropod pests of alliums are insects, but there are also some
mites. Some of these pests damage a wide range of crops. For example,
cutworms - soil surface-dwelling caterpillars of certain moths, which eat
through the bases of crop plants, sometimes demolishing row upon row of
young plants. Other pests are more specific to alliums and are highly adapted to
locating and parasitizing them; most emphasis will be placed on these allium
specialists here. The pests of alliums were comprehensively reviewed by Soni
and Ellis (1990), and they give an extensive bibliography of original research.
More recently, Lorbeer
et al.
(2002) have reviewed the literature on monitoring
and forecasting of allium crop pests.
The number of severe pests is small and it is important to realize that pest
numbers are kept in check by a wide range of diseases, predators and parasites,
and that many of the latter two control agents are themselves insects or
arachnids. Therefore, insecticidal chemicals should be targeted as specifically
as possible at pests, to minimize the damage to beneficial species. Insecticides
should be applied when monitoring or predictions based on knowledge of pest
biology show a build-up of economically damaging numbers. Use of insecti-
cides should be complementary to other techniques of pest control, including
cultural methods, resistant cultivars and the introduction or encouragement
of natural enemies.
This is illustrated by the 'integrated pest management' (IPM) methods used
to control thrips, onion fly and leek moth described below. Resistance to many
insecticides has developed in thrips and onion fly, the two most important allium
