Front Range Seed Analysts
1992 Seed Forum Volume 6 Number 4
Basic Seed Treating for the Laboratory
Part 1. In-house disease control during the germination test
by Russ Elliott, Bio-Tech, USDA/ARS-NSSL
Seed analysts may find cause to treat seeds in the laboratory
for the following three reasons:
1. to reduce the effects of fungi on seedling development during
the germination test (in-house purposes).
2. to comply with a seedsman's/farmer's request to supply a treated
vs. untreated germination or vigor test (paired test), additionally a lab
may want to voluntarily treat lots showing significant disease/deterioration
and report this along with the untreated germination for the client's benefit.
3. for research purposes such as treating seed for field trials,
etc.
This article will deal with reason number 1. The latter 2 situations
will be discussed in a later SEED FORUM article.
Seed can be accurately treated in the lab in virtually
any amount desired using the information on the treatment container label,
some metric/english unit conversion factors, and some inexpensive equipment.
Please note that chemical rates may vary depending on the farmer's needs,
therefore it would be wise to check with the chemical representative, seedsman,
etc. to verify the rate desired. The treatments used in this article are
for example purposes only and do not represent an endorsement of any kind.
Again, consult your chemical rep or seedsman.
Equipment:
-scale (accurate to 0.001 grams)
-glass jars with lids, to be used as treating containers (select sizes
which, when filled with the seed to be treated, are approx. 1/4-1/3 filled
with seed-this allows adequate room for the shaking/rolling action needed
to combine seed + treatment and obtain an even, uniform coverage)
-plastic gloves, dust mask, ventilation for safety purposes
Conversion Factors
1 oz.= 28.35 grams
1 lb.= 453.6 grams
Methods and Example:
For simplicity and convenience it is recommended that a dust type fungicide (not to be confused with a wettable powder type) be used such as the 'planter box' or pre-sowing treatments used by farmers at the time of planting by mixing the treatment directly in with the seed at the planter box. Presently, the NSSL is using Terra-Coat SD-205 (Terraclor Super X) which is an example of a 'planter box' type product.
Example: Treat 400 seeds of sorghum prior to planting for a germination
test using the label rate of SD-205 for sorghum (label rate = 2 oz. per
100 lbs. seed)
- weight of 400 seeds = 7.27 grams
- to calculate: SD-205 @ 2 oz./100 lbs. seed
2 oz. = 56.70 grams
100 lbs. = 45,360. grams
therefore:
(cross multiply and divide using the converted units)
56.70 gms. SD-205 = ? amt.
SD-205 needed
45,360. gms. seed
7.27 gms. seed to be treated
56.70 X 7.27 = 412.209
412.209 = 0.009 grams SD-205 needed
45,360
to treat 400 seeds.
However, there will be chemical loss to the interior sides of
the treating container. As a rule of thumb, 2% extra treatment is
added to compensate for this loss. So technically, 0.0092 grams would
be added (Admittedly, this is difficult with such a small amount.)
When using a new, clean treating container, the container should be 'pretreated'
by initially adding an equivalent amount of clean untreated seed (wheat
works well) plus an equivalent amount of treatment, treating this seed,
and discarding. This will coat the sides of the treating container
with a thin layer of treatment and avoid future chemical loss when treating.
Subsequent use of the container using the same chemical will not require
the pretreatment.
Place 400 seeds in small jar, add 0.009 grams of SD-205, cap
jar, and shake or roll until the seed is evenly treated and there is little
or no chemical remaining visible on the sides of the treating container.
The moral of the story: a very little treatment goes a long
way. There seems to be a basic human tendancy towards the idea
that "if a little is good, then more will be better." In the
field of pesticide application (including seed treatments) nothing chould
be further from the truth. Treatments can have adverse (phytotoxic)
effects on seed which typically begin during the imbibition stage of germination.
It should be noted that this type of in-house seed treating,
using only one 'blanket' treatment on all types of seed to control disease
during a germination test, does not represent the real world. Its
primary use is in assessing viability regardless of the effect disease
may have on germination and should never be used to represent a "treated
seed germination result" to a seedsman/farmer as in most cases he will
be using different treatments and rates.
In the next issue of the seed forum, the methods used to duplicate
commercial seed treatments (typically 'slurry' or liquid applications)
in the laboratory will be discussed. This upcoming article will address
the seedsman's request to supply a treated vs. untreated germination or
vigor test with the treatments and rates he will be using (or contemplating
using) in his operations.