1. Heath Sanders Area Extension Agronomy Specialist March 20, 2019
Coffee Shop Talk
Heath Sanders
Area Extension Agronomy Specialist
March 20, 2019

2. 180-Day Rainfall

3. Discussion/Updates
Pasture Weeds
Musk Thistle, Prairie Threeawn,

4. Causes for Weeds in Pastures
Poor stand of adapted forage
Inadequate fertility
Improper harvesting
Overgrazing
DROUGHT
Soils and climate
Invasive weeds
There are a number of causes for weeds in pastures but usually the root of the problem is overgrazing or poor harvest management. This year a drought in the southern portion of the state caused the overgrazing that will end in a heavier than usual weed population this spring.
Overgrazing leaves less residue which means less weed suppression due to shading when the annual weeds are germinating in the spring.
Musk Thistle is an example of an invasive weed.

5. Thistles in Oklahoma Native-not a major threat Introduced “Invasive”
Wavyleaf
Yellowspine
Tall
Yellow
Introduced “Invasive”
Bull
Musk
Scotch
Distaff
Canada

6. Musk Thistle - Recognizing The Plant
Unique Characteristic -
Does not have hair (pubescence) between the spines. I.E., smooth leaves and stems. Leaf margins often silvery
Bull
Musk
Scotch

7. Musk Thistle
Biennial - 2 years to mature or can act like an annual in OK.
Germinate in fall
Overwinter as rosette
Bolt and produce seed in the spring
Deep rose to violet or purple in color
Aggressive
Germinate Anytime
10,000-20,000 Seed Per Plant
Continuing to germinate for 5 years
Livestock Do Not Graze Infested Areas

8. Integrated Management Approach for Musk Thistles
Prevention
Mechanical
Chemical
Biological

9. Prevention Thistles spread by movement of seed-contaminated Hay Wind
Water

10. Prevention Do not allow thistles to produce seed
If present, avoid the use of hay and feed from infested areas
Destroy plants before they produce seed

11. Mechanical Control Some flowers can still produce seed
Tillage or Mowing
Cut Below The Crown
Spade or Garden Hoe
Mow to suppress seedhead production
Close to the ground as possible
Some flowers can still produce seed

12. Chemical Control Good moisture Actively growing 60o F + temperature
Before seedheads are mature.
Always read and follow the herbicide label

13. Chemical Control Fall (Oct. and Nov.) Spring (Mar. - April)
Applications to rosette plants
Before plant starts bolting
Spot treatments

14. Chemical Control 2,4-D, Weedmaster 2 pt./A Grazon P+D
2-4 pt/ac
Weedmaster 2 pt./A
Rosette-Bolt
Grazon P+D
2 pt/ac rosette
3-4pt/ac late season, bolting-bud
Cimarron Max rate I
Pasturegard 3 pt./A
GrazonNext 1.5/2 pts/ac
Always read and follow herbicide labels

15. Biological Control
The use of natural enemies to reduce populations once area is infested
Thistle head weevil and rosette weevil
Advantages
Low cost
Non-target organisms are unaffected
Adjoining infested areas will attract the control agent
Requires little effort once established
Can be used with other methods

16. Biological Control
Head weevil – lays eggs on the bracts of newly emerged flower heads
When eggs hatch, larva make their way to the young seed of the head
Feed and destroy musk thistle seed
Head weevil

17. Biological Control Rosette weevil –smaller than head weevil
Feeding of the rosette weevil can lead to less competitive multiple stemmed plants, that produce seed or destruction of the growing point
Rosette weevil

18. “Weevil Roundup” 1-2 per year in Oklahoma
Alfalfa Co.
Okfuskee Co.
Both head and rosette weevils are collected
From bolted plants
Take and release them
Within 48 hours

19. Prairie Threeawn

20. Prairie Threeawn Other names Annual short grass
“Old-field threeawn”, “ticklegrass”, “wiregrass”
Annual short grass
Can establish easy under adverse conditions
Undesirable forage, unpalatable, difficult to chew, very low quality, seeds can cause eye problems
Referred to as a “indicator” grass
On range sites that are heavily eroded, routinely overgrazed, or lacking nutrients

21. Fertility Critical lacking nutrient is (P) Phosphorus
(DAP)
100lb/ac of DAP in most cases will meet P needs for the year and possibly start building some residual
Manures, chicken litter have sources of P too
Bermudagrass pasture- recommend fertilizing according to soil test
Encourage Bermuda stands to thicken and cover

22. Fertility Native Pastures
Don’t usually recommend fertilizing but, in this situation get a soil test
Apply some P if needed
Graze instead of haying
Use lighter stocking rates
Allow for rest period later in growing season
Feed hay or put troughs out in the worst three awn areas in the winter
Will take time to recover, didn’t happen overnight

23. Prescribed Fire Fall fire before December has proven to be effective
This is essentially destroying the seed before they reach the soil
Fire Timing
Threeawn
Perennial Grasses
Western Ragweed
Unburned
74%
21% 5%
Spring (4/27)
84%
14% 2%
Fall (11/8)
76% 7%
This Prairie Threeawn (PTA) study by Kstate occurred over 5 years on multiple native sites. The average PTA infestation was ~75%.
The use of a spring fire encouraged the increase of PTA density and as such is not recommended when PTA is dominate in the landscape. However, they found that a fall burn, after killing frost but before December drastically reduced the prevalence of PTA in following years. The researchers noted this is due to the nature of PTA holding its seeds until approximately December, where the fire is able to fully consume most seeds produced in the current year.
Fall fire in November!
Study conducted by Kansas State University ( ).

24. Chemical Control
No good herbicide options labeled for the control of threeawn
Glyphosate, (non-specific) can be applied at 8 oz/ac in bermudgrass field but not native pastures.
No labeled herbicide in native pastures

25. Private Applicator Certification
Required for use of Restricted Use Pesticides on owned or leased farms
New packets available at the county Extension office
Current Cycle expires 12/31/2018
Next Cycle will expire 12/31/2023
Open Book Test
CEU’s not applicable

26. Questions?