Agriculture Reference
In-Depth Information
noxIouS WEEd SEEd ExAMInATIon And oTHEr buLk ExAMS
An examination for noxious weed seeds may be made in addition to the AOSA purity test. Many people
consider the noxious weed seed examination to be a part of the purity test. Others separate the two by refer-
ring to them as the “purity working sample” and the “noxious weed, or bulk working sample.” The size of
sample for the noxious weed examination varies depending on the seed size of species being examined,
but it is generally about ten times the amount examined in the purity test, or approximately 25,000 seeds
(AOSA). The noxious weed seed test provides very important information needed for determining whether
a seed lot may be legal for sale in different states and countries. Since noxious weed lists vary from state
to state and among different countries, a sample may need to be analyzed for the occurrence of noxious
weed seeds for the particular state or area of interest or it may be analyzed as an all-state noxious weed seed
test. Other examinations such as sod quality, Undesirable Grass Species (UGS), and Crop and Weed (CW)
are also frequently performed on the bulk sample. ISTA rules do not recognize the term “noxious weeds”;
however, ISTA has a similar test called “Determination of Other Species by Number” that is also based on
a sample size of 25,000 seeds.
It is important that seed merchandisers be familiar with noxious weed lists of those states or countries
in which they are selling seed. Thus, every seed laboratory should have this kind of information available.
One valuable source of this information is in the “Seed Trade Buyers Guide,” published annually by the
American Seed Trade Association. Similar information can be found on the Internet. Examples of websites
that have useful information regarding noxious weed lists are: (1) www.ams.usda.gov/seed which includes:
Federal noxious weed lists, and (2) the website for noxious weed list of Australia: http://www.weeds.org-au/
noxious.htm.
Since the noxious weed seed test involves the examination for only certain kinds of weed seeds, it is
usually performed faster than a routine purity test. The automatic or semi-automatic inspection station can
be used for this examination. In general, the time required to complete the noxious weed exam depends on
the proiciency of the seed analysts.
The percentages of pure seed, other crop seed, inert matter, and weed seed, a listing of contaminat-
ing species found in the purity analysis, plus a statement of the noxious weed seeds present are typically
included on the test report (Fig. 4.8). This information is, in turn, used to label the seed lot from which the
sample was drawn.
PurE SEEd
With few exceptions, the deinitions for pure seed and other crop seed units are the same in the AOSA rules.
All seed samples, regardless of kind, contain numerous seeds which are either broken, cracked, shriveled,
diseased, injured by insects, or abnormal in some way that can make their classiication as inert matter or
crop seed dificult.
broken and Cracked Seeds
This is one of the easiest and perhaps the most common rule the analyst will use in performing a purity
analysis. However, seeds of different species characteristically break in different ways. Seed of small grains
such as barley, rye, and sometimes wheat, tend to break transversely along rather straight and clean lines
and the half-seed rule is easily applied. Fragments need not contain the embryo to be considered pure seed
but must consist of more than one-half the original size. This can be determined by aligning the fragments
in question along with several unbroken kernels on the working surface for direct comparison. Broken
kernels that are dificult to determine even when lined in a row may be divided equally 1/2 to crop and 1/2
to inert matter. This method of determination employs the
quick method
in contrast to the so-called
strong
method
used earlier by European analysts who attempted to predict if a fragment was capable of growth
