Agriculture Reference
In-Depth Information
do not think potential sales justify the costs of testing to meet the modern
regulations. Consequently, there is something of a crisis for vegetable growers,
including allium producers, in that they must rely on a diminishing range of
herbicides. A number of useful products have ceased to be available to UK onion
growers, including alloxidim-sodium, sethoxydim, aziprotryne, chlorbufam,
cyanizine, methazole, prometryn and sodium monochloroacetate (Grundy
et
al.
, 2003). In the extreme scenario this could make it impossible to grow some
crops economically. A more insidious danger is that reliance on a smaller range
of herbicides is likely to increase the risk of weeds evolving tolerance to
compounds that are applied repeatedly without alternation with herbicides
having a different mode of action. In order to overcome these difficulties, trials
are ongoing to find newer herbicides that are effective in vegetable alliums and
to provide data to gain approval for their use. In the UK, this work is carried out
by a development organization funded by growers (Knott, 2005). Given the
critical need for good weed control in bulb onion crops and the need for multiple,
low-dose treatments, with risk of crop damage and each needing favourable
weather conditions for spraying, if onions genetically modified to be resistant to
glyphosate or glufosinate were available and acceptable (see Chapter 3), weed
control would probably be simplified and improved.
Herbicide recommendations for garlic are similar to those for bulb onions
(University of California, 2007) - as are those for salad onions, but particular
care must be taken to avoid herbicide damage to leaves, which can make the crop
unsaleable (Grundy
et al.
, 2003). Leeks also need a similar herbicide programme
to that for onions, often including split-dose applications starting from the one- to
three-leaf stage. Since leek leaves funnel liquids towards the junction of blade and
sheath, there is less run-off than with onions and they are more sensitive to post-
emergence herbicides. They also collect more pesticide residue than onions, and
this restricts use of some chemicals (Grundy
et al.
, 2003). Minimum intervals
between the final herbicide spray and harvest are specified by regulatory
authorities to avoid significant residues on the produce, and some supermarkets
impose additional restrictions on herbicide use by their suppliers.
Cultural and mechanical weed control
In recent years public concerns about pesticide usage have given impetus to
research on the improvement of non-herbicidal methods of weed control.
Governments have banned some herbicides formerly used, particularly those
found to be contaminating water supplies and, at the same time, have funded
research on 'integrated' crop weed control methods to try to reduce the need
for herbicides.
In many countries there is an expanding market for 'organic' produce that
must be grown without the use of herbicides, and research on non-chemical
weed control is relevant here. Producing alliums without herbicides is
particularly difficult given their weak competitive ability against weeds. Time
