approach -hoe, hoe, hoe, or try herbicides However, before beginning on
the herbicide approach it must be stated that with increases- in the price of
herbicides, and awareness of associated problems including weed tolerance,
hoeing and spot-spraying should be a more common practice.
The weed problem is such that one in ten
seed crops are
rejected or downgraded because of weeds. This is a massive mortality rate.
Seventy-five percent of all rejections and downgradings are because of weeds;
they are a major
in seed production. Wild oats are a major contributor
to the problem, also soft brome (also known as goosegrass) particularly when
over-threshed; bearing this in mind headers should be adjusted to’ keep awns
that reach Seed Testing, wild oat contamination results in 5.5% of perennial
crops being rejected and
1% of annual
rejected. If ‘undesirable’ weeds, of which thirteen are specified, are found within
a seed crop, financial penalties ensue. The undesirable weeds include barley
grass, wild oat, and winged and nodding thistle.
An analysis of 1800 seed lots using Ministry of Agriculture and Fisheries’
seed testing records indicate that after dressing 77% of all
contain goosegrass, 40% contain hair grass
poa, 35% contain chickweed and 29% contain field madder.
The range of herbicides actually registered for use in seed crops is
extremely small. In
United States unregistered products cannot be used;
that are registered for use in grass seed crops four are for broad-leaf weeds
and two are for wild oats,
there are no chemicals registered for use against
grass weeds, which are the major problem in grass seed
(ethofumesate) is very effective but very expensive at over $200
it is not considered to be economic. Preliminary trial results for TCA (one of the
oldest herbicides) or TCA dalapon mixtures (e.g.,
are promising in terms
of being able to control annual grasses, but the chemicals are unregistered (and
now unavailable). Furthermore, most research work has been done in the North
Island. As environmental conditions do influence the effect of herbicides they
should be applied only in small amounts initially (i.e., on test strips) in order to
avoid the possibility of destroying the crop.
Test strips of the herbicide at
different rates and times will allow the grower to get a feel of the chemical in his
Many broad-leaved weeds are developing a tolerance to common
herbicides such as 2,4-D and MCPB. On grass seed crops most of the
hormone sprays registered for cereals can generally be used safely (but
dicamba cannot be used on
seed crops without detrimental effect).
Non-hormone sprays cannot generally be used (e.g., Glean used on
seed crops can result in severe damage).
Eighty to 90% of
seed crops are sown with white clover.
Although this practice may reduce the amount of nitrogen required by the crop,
it creates limitations in terms of what herbicides may be used. Most sprays that
will tackle problem weeds such as nodding thistle and yellow gromwell will be
extremely damaging to the clover.
order to have a more flexible spray
programme clover should not be sown with
seed crops. A further
consideration is that white clover is extremely competitive, and it probably
decreases seed yield from the
more than one year old (e.g., tall fescue, cocksfoot and second year
crops). Atrazine is used widely in Palmerston North but it is an unpredictable
chemical and results can be spectacularly good or bad it is very easy to
destroy a crop completely. The. chemical works because the crop is deeper
rooting than the weeds that are being sprayed out. Atrazine, simazile and
diuron are root-absorbed. When a small dose of chemical is applied, shallow
roots absorb more than deep roots, thus tall fescue, which is deep rooting, can
survive. Atrazine is applied in late autumn/early winter when low light intensity
means the plant is less active than otherwise but soil moisture is present to
activate the chemical. Use of these products must be timed with irrigation or
to coincide with rain (they can even be applied during rain) so that the chemical
is washed off the leaf into the soil. If allowed to sit on the, leaf for a long time,
particularly when morning dews are followed by bright, sunny days, crop
damage and even crop failure will occur. Thus the products are difficult to use
effectively and require
For instance on light sandy soils atrazine
rates must be reduced considerably. In fact, as atrazine water solubility is 40
ppm and simazine water solubility is only 5 ppm, simazine is safer to use on
killed. The difficulties with atrazine use cannot be over-stressed. In Oregon,
where the product was developed, an uncommon winter drought (which meant
that spray was not washed off leaves) resulted in 70% of the
being damaged. Since then the registration for use of Atrazine and Simazine
crops has been withdrawn in Oregon, This has resulted in problems
with maintaining quality of grass seed, and in increased research on alternative
is a serious problem in tall fescue and can be in
or Hoegrass-atrazine mixtures has been effective in
cocksfoot and the mixture has proved more effective than
Atrazine can be effective if the timing is right. Kerb has been used successfully
is not a recommended chemical. Alloxol or Fusilade can
used on Chewings fescue as they kill almost all other grasses.
control in tall fescue is very difficult and 100% control is impossible to achieve.
However, the correct use of atrazine can
In all this it should be remembered that planning a crop and herbicide
rotation can alleviate some build-up in a weed problem. Ultimately this forward
planning can reduce expenditure on chemicals and increase profitability.
Talking about the use of fertilisers in seed crops opens up a
there is much divergence of opinion. Many of the problems lie in interpreting
worked upon. This was particularly the case in early nitrogen (N) trials as the
residual N status of the soil was not known.
In general it is possible to say that autumn N applied to first year
does not result in increased seed yield but does produce winter grazing for
sheep. No more than
of the total N for a seed crop should be applied
in the autumn. Spring N is important for increased seed yield.’ It should be
applied in the
to four week period between the period of
and stem elongation. A split application is not necessarily important in terms
of increased seed yield, but does spread the risk in terms of leaching loss (in
the event of high rainfall). Elongation is controlled by photoperiod and, to a
lesser extent, temperature.
This means that calendar date can be used to
determine when N should be applied: For
is late flowering and N should be spread later.
flowers much later and so N can be delayed. Applications of N after
flowering are not generally effective but may increase thousand seed weight.
The estimated total N requirements for a seed crop is 130 kg ha” (equal
to 280 kg urea ha“). The amount applied as fertiliser should be the difference
between soil N and 130. Traditionally, Oregon and Denmark have used more
N and achieved higher seed yields than New Zealand. Over recent years more
nitrogen has been used in New Zealand, too, and more growers are taking soil
tests to give them an indication of residual N.
In general the type of N that should be used is the cheapest. However
it should be remembered that there are limitations-to the use of urea particularly
on very dry soils or if soil temperatures are above 15°C (when volatilisation
Potassium is removed from seed crops in large quantities and so growers
must be aware of their soil type.
Fifty percent potassic serpentine super
matches losses in seed crops more closely than ordinary super, but in most
cases potassium and phosphorus applied to seed crops do not result in
increased seed yields,
Soil acidity is not usually a problem in seed production except with prairie
grass; the biggest problem is overliming leading to trace element deficiencies,
e.g., in zinc.