Evaluate Winter Wheat Seed Quality Prior to Planting
By Laura Sweets
There were a number of stresses on the wheat crop this growing season.
Hot, dry conditions were a problem in many areas of the state. Barley
yellow dwarf was quite widespread ćAnd the incidence of loose smut was
higher than usual during the 2006 season. Therefore, if growers are
saving seed to plant, it is critical that they pay special attention
to testing the viability of their wheat seed in 2006.
The first step is to clean the wheat seed. It is important that wheat
seed be cleaned to remove small and damaged seed and to eliminate weed
seeds. Removing small and damaged seed will not only aid in crop
establishment it will also provide a more uniform wheat seedling
stand. Removing small and damaged seed will also increase the
thousand-kernel weight (TKW), which serves as a measure of seed
quality. Wheat seed lots with TKW values greater than 30 grams tend to
have increased fall tiller number and seedling vigor.
The next step is to perform a germination test. Germination tests can
either be completed at home or by sending a sample to the Missouri
Seed Improvement Association. A home test can be performed by counting
out 100 seeds and placing them in a damp paper towel. Place the paper
towel into a plastic bag to conserve moisture and store in a warm
location out of direct sunlight. After five days count the number of
germinated seeds that have both an intact root and shoot. This will
give the grower an estimate of percent germination. It is important to
choose random seeds throughout the entire seed lot and conduct at
least five 100 seed counts. The Missouri Seed Improvement Association
also performs a germination test. The test requires one pound of seed
and costs $12.00. For details email
MOSEED@AOL.com or check the
Missouri Seed Improvement Association Website at
http://www.moseed.org/.
If germination is below 85 percent it is
important to increase the seeding rate to compensate; however seeding
any wheat with a germination test below 80percent would not be
recommended.
The next step is to decide whether a fungicide seed treatment is
necessary. A number of fungicides are labeled for use as seed
treatment fungicides on winter wheat. These seed treatment fungicides
protect germinating seed and young seedlings from seedborne and
soilborne pathogens. Seed treatment fungicides will not improve
germination of seed that has been injured by environmental factors and
will not resurrect dead seed. A correct assessment of the cause of
poor seed quality or poor germination rates is the first step in
deciding if a seed treatment fungicide is necessary.
As mentioned before loose smut was more common than usual in Missouri
wheat fields during the 2006 season. Loose smut is obvious as heads
emerge from the boot. All portions of the head except the rachis are
converted to masses of dusty black spores. Spores produced on smutted
heads are wind carried to adjacent plants in the field and infect
those plants through the flowers. Later in the season loose smut is
not as obvious as most of the spores on the smutted heads have been
dislodged by wind and rain leaving only the bare rachis of the plant.
The fungus which causes loose smut survives within the embryo of the
wheat seed. The fungus survives as dormant vegetative strands within
the embryo. This infection is not visible to the naked eye and will
not be picked up in the standard germination test. If infected seed is
planted and germinates, the fungus also begins to grow within the
plant, and at heading, the fungus is at the growing tip and produces
smut spores where the grain kernels should be. If seed from a field
that has a "small" amount of smut in one season is used for seed, the
field planted with that seed may have a substantially higher level of
smut.
Management of loose smut is through the planting of disease-free seed
or the use of a systemic fungicide seed treatment (see accompanying
table of wheat seed treatment fungicides). Growers with considerable
loose smut should consider seed treatment on this grain next year, if
grain is to be used for seed. In wheat, infection levels of 2 percent
or greater would indicate that seed treatment would be economic.
Laura Sweets
573-884-7307
