This document discusses organic weed management techniques for farmers. It outlines that organic farming uses vegetation management to improve soil, prevent degradation, and enable crop production. Weeds managed include intentionally planted cover crops and cash crops as well as naturally occurring plants. Common organic weed control methods include prevention practices like using organic mulches, cultural techniques like timed planting, and mechanical practices like cultivation. The document also describes a study comparing different planting systems and cover crops for managing weeds and their effects on squash yields over multiple years. Results found that black plastic mulch consistently produced the highest yields while other tillage techniques worked better depending on planting dates and weather conditions. Overall, the document emphasizes using integrated, preventative practices and mechanical removal through cultivation for organic

1. Organic Weed Management
Jim Shrefler, Extension Horticulturist
and
Merritt Taylor, Professor of
Agricultural Economics
Oklahoma Cooperative Extension
Service

2. Watermelon Trial - June 27

3. Watermelon Trial - July 10

4. Organics and Weed Management
Is there a quick guide to organic weed
control?
Is it good to have weeds on your farm?
Do organic growers just need to learn to
accept weeds?
Is learning to control weeds an ongoing
process?
Will there ever be an “organic”
Roundup?

5. Organics and Weed Management
Organic farming systems use
vegetation management to:
– Improve soil
– Prevent soil loss and degradation
– Enable production of field crops, forage
and produce

6. Organics and Weed Management
Organic farming systems use
vegetation management to:
– Improve soil
– Prevent soil loss and degradation
– Enable production of field crops, forage
and produce

7. Organics and Weed Management
Vegetation that is managed
may include:
– Intentionally planted annual and
perennial cover crops
– Annual and perennial cash crops
Forages; Small Fruits
– Naturally occurring plant species
May include many species
Some may be considered “weeds”
Annuals and Perennials

8. Perennial Weeds
May or may not have
abundant seed production
May survive the winter via
roots or rhizomes
May or may not be woody
plants
Include grasses, broadleaf
and sedges

9. Annual Weeds
Generally produce
abundant seeds
May be cool or warm
season plants
Are adapted to disturbed
environments
Have varied life cycle
durations
Seed may persist for years

10. Organic Weed Management
Practices
Various farm practices may
contribute to weed management
– Carefully timed planting of cover
crops
– Prevention of the introduction of
undesirable plant species or
cultivars
– Carefully timed planting of cash
crops
– Prevention and removal of
undesirable weeds in cash crops

11. Organic Vegetables in
USA South Central Plains
Weeds pose a big
challenge to all
growers
With organics,
normally manageable
issues   major
concerns
– e.g. annual grasses

12. Weed Control Methods for
Organic Vegetables
Prevention
Cultural / Management
Soil preparation
Exclusion
Mechanical
Pruning / mowing / flaming
Chemical
Allelopathy

13. Prevention
Avoid Introducing new
weeds
– Organic mulches
– Manures
– Moving contaminated
equipment
– Irrigation water
– Moving soil

14. Prevention
Watch for new weeds
that appear
– Do not allow them to go to
seed
– Seed may persist for many
years
– If perennial, watch for
regrowth from vegetative
propagules

15. Cultural / Management

16. Allelopathy
Organisms that
release “chemicals”
that inhibit growth of
other organisms
May be while the plant
is alive or during its
decomposition
Certain varieties of
cereal rye are an
example

17. Application
methods
Crop safety
Efficacy
Preemergence Weed Control
Corn Gluten Meal
Onions
Summer Squash


18. Soil Preparation
Use sound practices
that do not harm soil
Eliminating all “green”
can be a good starting
point

19. Exclusion
Barriers that
prevent weeds
from establishing
Plastic mulch
Landscape fabrics
Carpet scraps
Organic mulches

20. Mechanical
Cultivation, hoeing,
hand removal
Labor intensive
Proper equipment
makes a big difference!

21. Cultivation for Weed Control in
Organic Vegetables
For some crops, such as
cucurbits, cultivation has
limitations
Vining growth habit
Shallow roots
Wet soil conditions may
preclude effective
cultivation

22. Pruning / mowing / flaming
Anything the gets above
ground parts of weeds
– Grazing
– Flaming
– Mowing
– String trimmers
We will see some
examples later

23. Chemical
Synthetic chemicals are not allowed in
organics
– Glyphosate, 2,4-D, “Poast”
Natural weed control “chemicals” are
being developed
– Vinegar
– Plant extracts, oils
– These are “burn down” products
– A natural “Roundup” is not yet available

24. Postemergence Herbicides for
Organics

25. Integrated Management

26. Opportunities
Rye – a common winter cover crop
Rye has been shown to suppress
germination / establishment of weeds
Various practices could be used to
establish vegetables following a rye
cover crop

27. Objectives
Compare field preparation / planting
system practices for:
– Impact on squash productivity
– Weed incidence and removal costs
Compare treatments for production cost /
economic benefit relationships

28. Materials and Methods
2004
Soil – Bernow fine sandy loam
Field history
– 2 year fallow
– Abundant crabgrass and tumble pigweed
Soil test and apply nutrients with poultry
litter in autumn
Beds – 6 foot centers
Sow „Elbon‟ Rye

30. Materials and Methods
2005
Divide field  3 planting dates
– May, June and July
Mow cover crop, prepare plots and plant
Transplant Zucchini squash „Revenue‟
– Spacings: Rows 1.8 m and plants 0.77 m
Drip irrigation
Weeds – count and hand hoe
Harvest squash over about 3 weeks

32. Treatment Advance
Procedures
At Plant
Procedures
Conventional Mow, Rework Rototill
Black plastic M+R; Plastic Nothing
Stale seedbed M+R Burn
Mow M M
Mow & Burn M M+Burn
Shallow till M Till (2-5 cm)
St & Burn M Till+Burn
Treatments

34. Response Variables
Squash Yields:
– Impact on squash productivity
Number of marketable fruit
Weed incidence
– Annual weeds
Weed removal requirements
– Hoeing time

35. Squash Yields*
First Planting Date
0
20
40
60
80
conven plastic stale seedbed mow mow & burn shallow shallow &
burn
Fruitperplot
* Harvest period of 3 weeks
LSD (0.05)=15.4

36. Squash Yields*
Second Planting Date
0
40
80
120
160
conven plastic stale seedbed mow mow & burn shallow shallow &
burn
Fruitperplot
* Harvest period of 3 weeks
LSD (0.05)=23.6

37. Summary – Squash Yields
Plastic mulch best with May planting
Any tillage, especially at-planting tillage,
was better than no tillage with June and
July plantings
– * conventional and shallow tillage were
comparable

38. Crabgrass
First Planting Date
0
400
800
1200
1600
2000
conven plastic stale
seedbed
mow mow & burn shallow shallow &
burn
3 weeks 5 weeks
Plants/m2

39. Crabgrass
Second Planting Date
0
400
800
1200
conven plastic stale
seedbed
mow mow & burn shallow shallow &
burn
2 weeks 4 weeks
Plants/m2

40. Crabgrass
Third Planting Date
0
100
200
300
400
conven plastic stale
seedbed
mow mow & burn shallow shallow &
burn
1 week 5 weeks
Plants/m2

41. Summary – Crabgrass
Crabgrass response to treatments varied
with planting dates
For PD1 and PD2 – greatest early
emergence with conventional and/or stale
seedbed
PD3 – appreciable emergence in all
except plastic and non tilled plots

42. Conclusions
The optimum system may depend on
planting date
– Plastic always produced greater or comparable
yields
– Weed patterns will probably differ across dates
Shallow and conventional tillage yields
were comparable
– Are there benefits to shallow tillage?

43. Interesting results in 2005
Plastic mulch always best
with early planting
Weed control results varied
with dry (2006) and wet
(2007) conditions
Predictability as a weed
control tactic is questionable
Results Over 3 Years

44. In Summary
Learn your weeds
Strive to prevent new
weed infestations
Learn and apply good
management practices
When all else fails –
Keep on Hoeing!