Seed Treatment - Crop and Soil Science

Seed Treatment
Thomas G Chastain
CROP 460/560 Seed Production
Why Treat Seed?
• Prevent infection or predation of
seeds and seedlings by pests
resident on seed or in the soil.
• Improve stand establishment -Stand establishment is the most
important event in crop
production; there are no
management practices to
improve a poor stand. Optimum
plant stands are related to the
crop’s ability to compete with
weeds and is important in
determining yield.
• Low pesticide dosage -- pesticide
is applied directly to the target in
very small dosages, not
throughout the environment.
Direct-seeding wheat
(John Mc Manigal photo)
Seed Treatment and Disease
• Seed treatments can be used to
control diseases such as dwarf
bunt in wheat.
• Dwarf bunt is a seed
replacement disease that
reduces yield, baking quality,
and international marketing
opportunities and dwarfs the
crop’s tillers. The spores
contaminate good seed that are
not replaced by the fungus.
• Seed treatment fungicide and
resistant cultivars can be used
to control dwarf bunt disease in
wheat.
Wheat spike with seed replaced by dwarf bunt balls (top), bunt ball slightly crushed to reveal
spores within (bottom left), and spores (bottom right) TG Chastain photos
Seed Treatment and Disease
• Seed treatments are
effective in improving
stand establishment.
• Metalaxyl seed treatment
is effective in controlling
damping off disease in
perennial ryegrass.
Perennial ryegrass treated as seed with 1.5 oz.
metalaxyl (left), treated with 0.75 oz metalaxyl
(middle), and not treated (right).
Seed Coating
• Seed treatment is often referred
to as seed coating, although the
two following processes are
better classified as seed coating.
• Film-coated Seed -- Seed retains
original size and shape. Coating
may contain pesticides, biological
agents, colorants. Polymer
coating reduces dust-off losses.
• Pelleted Seed -- Size and/or
shape of seed is changed to
increase planting efficiency. Seed
pelleting material may contain
colorants, pesticides, etc.
Lettuce seed (left), pelleted lettuce
seed (right) TG Chastain photo
Types of Seed Treatments
• Systemic vs. Protectant -- A
protectant is a substance that
protects a seed or seedling against
infection or predation. A systemic is
a substance that translocates
internally to protect the seed and
seedling. Some systemics can kill
the pest within the host and so have
a curative effect.
• Broad-spectrum chemicals affect
more pests than narrow-spectrum
chemicals.
• Combinations of compounds are
common. Benefits of combinations
include broader range of activity,
reduced cost, and lessened chance
for development of resistant pests.
Downy mildew of alfalfa - disease that can
be controlled by seed treatment (Paul
Koepsell photo)
Types of Seed Treatments
1. Fungicides - Carboxin, metalaxyl
2. Insecticides - Lindane, chlorpyrifos
3. Plant Growth Regulators
4. Herbicide Safeners Benzacetonitrile
5. Micronutrients
6. Animal Repellants - Methiocarb
7. Osmotic Agents
8. Biological Agents
9. Seed Disenfestants - Hot water,
Hot vegetable oil, Hot sodium
hypochlorite
Covered smut of barley (top – OSU
Extension photo), wireworm (bottom –
Ken Gray photo)
Seed Treatment Formulations
• Dusts
• Wettable Powders
• Water Dispersable Granules
• Emulsifiable Concentrates
• Flowables
Black leg of cabbage – seed of Brassica family
crops should be treated to prevent this
disease (OSU Extension photo)
Seed Treatment Components
• Active ingredients
• Inert diluents
• Dye, Colorants
• Solvents - some may be
phytotoxic, eg. Xylene
• Stickers
• Wetting agents
• Emulsifiers
• Film coating
Sweet corn seed - treated and colored (left), and
untreated (right) TG Chastain photo.
Phytotoxicity Testing
• Seed treatments must control the
pest and not affect seed germination
and establishment of the crop.
• Curative Dose = the lowest dose
required to kill the pest.
• Toxic Dose = the threshold dose
causing injury to the seed as
measured by a seed germination test.
• The target dose must fall within a
range of potential dosages that
optimize stand establishment yet will
control the pest.
• Combinations with other pesticides
may increase phytotoxicity to seed.
Germination testing of treated pea seed (top), field
testing wheat seed for treatment efficacy and crop
safety (bottom) TG Chastain photos
Seed Treatment Equipment
• Rotary Seed Treater -- Batch
treaters, cement mixer - use
wettable powders and dusts.
• Slurry Treater -- Continuous type
treater - use wettable powders,
other formulations
Batch treater (top), slurry treater
(bottom) – Gustafson photos
Seed Treatment Equipment
• Liquid Treater -- Continuous
type treater
• Mist Treater -- Continuous type
treater
Continuous flow rotary treater (top), Mist-o-matic
mist treater (bottom) – Gustafson photos
Seed Treatment License Requirements
• Grow and Treat Own Seed -- No
license is needed as there are
no restricted-use seed
treatments. If pesticide is
restricted, then a private
applicators license is required.
• Purchase and Treat Seed -- No
license is required at this time.
If pesticide is restricted-use,
then a commercial applicators
license and seed treatment
endorsement is required.
• Custom Treat Seed -- Need
commercial applicators license
and seed treatment
endorsement.
Direct-seeding wheat
John Mc Manigal photo
Safety Considerations
• Treatments must be applied in
ventilated facilities
• Workers need to wear protective
clothing -- respirators (dust mask,
half or full mask, etc.), earplugs,
gloves, eye protection, protective
suit, foot wear cover
• Workers need to wash thoroughly
after treatment
• Observe storage and disposal
requirements for the treatment
material -- use returnable bulk
tanks or barrels, haul rinsates to
approved disposal site
• Observe seed labeling
requirements
Tips for Successful Seed Treatment
• Read label -- use recommended
dose and combinations
• Calibrate treater
• Observe safety precautions
• Obtain germination tests
• Keep accurate and complete
records