weed control with herbicides in alaska: some concerns control and herbicide... · weed control with...

Weed Control with Herbicides

in Alaska: Some Concerns

Steven Seefeldt

Mean Farm Size in the USA

100

200

300

400

500

1850 1870 1890 1910 1930 1950 1970 1990

Acre

s

Year

Weed Control is the Key

• 1731 – Jethro Tull wrote Horse Hoeing

Husbandry

– Plant crops in rows

– Use horse drawn hoe to weed

– Use fertilizers (horse manure) to enhance

crop growth

• He developed farm equipment, started

research, and wrote widely

• By early 1970’s was a band with a flute…

Weed Control Classification

• Physical

• Cultural

• Biological

• Chemical


• Physical

• Hand pulling and

hoeing

• Fire

• Flame

• Tillage/Disturbance

• Mowing and

Shredding

• Chaining and

Dredging

• Flooding

• Mulching and

Solarization


• Cultural

• Prevention

• Crop rotation

• Competition

• Smother crops

• Living mulches

and cover crops

• Harvesting


• Biological

• Grazing

• Mycoherbicides

• Allelopathy


• Chemical

• Herbicides

Pesticides

• Herbicides

• Fungicides

• Insecticides

• Rodenticides

• Biocides

• Etc.

Toxicology

• Caution

• Warning

• Danger

Before the scientific method and

hypothesis testing

What did hunter gathers do?

One Several Dinner

Tasty Tasty Filling


One Several Dinner

Tasty Tasty Filling

Tasty Tasty Stomach

ache


One Several Dinner

Tasty Tasty Filling

Tasty Tasty Stomach

ache

Stomach Dead Still Dead

ache

Log-logisitic equation

y=C+

D = Upper limit C = Lower limit b = Related to slope I = Dose giving 50% response

D-C 1+exp[b(log(x)-log(I ))] 50

50

Seefeldt et al. 1995

Dose-response curve

0.01 0.1 1 10 100 0

20

40

60

80

100

Herbicide Dose

Perc

en

t of contr

ol Upper limit (D=100)

I50

Lower limit (C=4)

Treatment comparison

0.01 0.1 1 10 100 0

20

40

60

80

100

Herbicide Dose

Perc

en

t of contr

ol Upper limit (D=100)

I50

Lower limit (C=4)

I50

Factors affecting pesticide fate

Volatilization Photodecomposition Plant uptake

and removal

Microbial degradation

Absorption

Chemical degradation

Leaching

Runoff

How do herbicides kill plants?

• Basically it is a chemical reaction

2,4-D Roundup

Paraquat Garlon Glean

What Roundup (glyphosate) does

Chorismate is

turned into one of

the three aromatic

amino acids

What Roundup (glyphosate) does

Sheep + Plateau

Plateau only Sheep only

Control

Biological + Chemical

Physical + Chemical

Fate of Herbicides

• The half life

• The time it takes to lose half the herbicide

Fate of Herbicides

• The half life


• For 10 day half life

• Day 0 100%

• Day 10 50%

• Day 20 25%

• Day 30 12.5%

• Day 40 6.3%

• Day 50 3.2%

• Day 60 1.6%

Fate of Herbicides

• The half life


• For 10 day half life

• Day 0 100%

• Day 10 50%

• Day 20 25%

• Day 30 12.5%

• Day 40 6.3%

• Day 50 3.2%

• Day 60 1.6%

Herbicide fate

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Days

% o

f h

erb

icid

e

Fate of Herbicides

• Photo-decomposition (treflan)

Fate of Herbicides


• Adsorption (paraquat)

Fate of Herbicides



• Plant metabolism (tolerant versus

susceptible plants)

Fate of Herbicides




susceptible plants)

• Chemical (soil and weather dependent)

Fate of Herbicides




susceptible plants)

• Chemical (soil and weather dependent)

• Microbial decomposition (most important)

Environmental Influences

• Soil pH – it depends on the herbicide

• Soil organic matter – adsorbs herbicide

• Clay – adsorbs most herbicides

• Soil chemistry – hard to separate microbes

• Cold – slows breakdown

• Dry – slows breakdown

Fate of Triclopyr

Results: Delta Junction CRP

0-5 cm

15-15 cm

15-30 cm

Soil froze about

110 DAT and

thawed about

276 DAT

A comparison of herbicide extraction

from the soil and a bio-assay

0

20

40

60

80

100

120

0.01 0.1 1 10

Triclopyr concentration (kg ai/ha)

Bio

mass a

s p

erc

en

t o

f co

ntr

ol

1 DAT 3 DAT

7 DAT

21 DAT

35 DAT

283 DAT

365 DAT

Fate of 2,4-D and Glyphosate

• Similar to triclopyr with normal breakdown

rates in the growing season, but cessation

when soils freeze

Aminopyralid and Clopyralid

Use in Alaska • Control of invasive weeds

• Spot spraying for perennial sowthistle

• Control of orange hawkweed and narrowleaf

hawksbeard in pastures and hay fields

Background

• Aminopyralid and Clopyralid

– Both are synthetic auxins

• Auxin is a plant hormone

– Involved in cell division

– Involved in cell growth

• Auxins move in the phloem to the growing points

Background

• Aminopyralid and Clopyralid

– Both are synthetic auxins

• Auxin is a plant hormone

– Involved in cell division

– Involved in cell growth

• Auxins move in the phloem to the growing points

– Both control orange hawkweed and

narrowleaf hawksbeard

Background Clopyralid

• Discovered 1961

• Sold in 1978 in Europe

• Sold in 1987 in US

• Curtail, Stinger, Confront

Background Clopyralid

• Discovered 1961

• Sold in 1978 in Europe

• Sold in 1987 in US

• Curtail, Stinger, Confront

• Now off patent

• Post emergence in pasture, rangeland,

and CRP

• Half life 12-70 days – microbial

Background Aminopyralid

• Sold as Milestone

• Still on patent

• Expensive

• Sold about 2005

Background Aminopyralid

• Sold as Milestone

• Still on patent

• Expensive

• Sold about 2005

• Used in rice, pastures rangeland, ROW,

wheat, oil palm, and rubber plantations

• Half life 25 to 35 days (averages)

• Photodegradation then microbial

Orange Hawkweed Study

• Five sites, Talkeetna and

Homer

• Plots 6 x 30 feet

• Three herbicides at three

rates (1, ½, and ¼ the full

rate plus a control)

• Three replications of each

of the above treatments

• Randomized complete

block

2007 Field Trials

Pre-treatment Measurements:

• Two ¼ x ¼ m sub-plots per plot

• % cover estimates of orange

hawkweed, grasses, and forbs

Post-treatment Measurements:

• Rate plots visually based on

herbicide damage, 0% (no damage)

to 100% (dead) after three weeks

• End of season harvest ¼ x ¼ m

sub-plots and separate by cover

type

• Rate plots visually the following year

Visual Injury - Milestone

0

10

20

30

40

50

60

70

80

90

Perc

en

t in

jury

0.125 0.25 0.5 1

Herbicide rate (1 = 0.12 kg/ha)

C

A A

B

The Work in Homer, AK

Control area

Biomass harvest Milestone 1x

Visual Injury - Transline

0

10

20

30

40

50

60

70

80

Perc

en

t in

jury

0.25 0.5 1

Herbicide rate (1 = 1.1 kg/ha)

B

AB

A

Impact on Grasses

0

50

100

150

200

250

300

350

Perc

en

t d

ry w

eig

ht

0.125 0.25 0.5 1

Herbicide rate

Milestone Redeem Transline

Impact on Other Plants

Milestone Redeem Transline

----------------- % injury -----------------

Dandelion 100-72 98-83 81-73

Clover 100-53 100-80 73-57

Yarrow 25 100-50 70-50

Geranium 0 100 -

Some Label Restrictions

Example of Injury, Raised Beds

Marigolds Potatoes Tomatoes

Injury 2 Years After Spot Spray

Unexpected Injury, Potatoes

Carry Over Research Design

H1 H2

H3 H4

H5 H6

• Six treatments

– Control

– Glean 75DF (0.33 oz/A)

– Ally 60DF (0.1 oz/A)

– Banvel (3 fl oz/A)

– Stinger (0.33 pt/A)

– Milestone (7 fl oz/A)

• Applied the summer of 2011

Carry-Over Weed Injury – Palmer

Weed Control Aminopyralid Clopyralid

Plants per meter square

Chickweed 48 2 74

Corn Spurry 89 3 166

NL Hawksbeard 668 0 11

Dragonhead 24 0 1

Lambsquarters 54 1 27

Pineapple Weed 8 0 0

Shepherd’s Purse 504 0 11

Total 1,395 6 290

Dose-Response Research Design 1X glean

0.5X glean

0.25X glean

0.125X glean

0.062x glean

No herbicide

Barley Canola Potato Lettuce Carrot Kale Nocrop

Visual Injury – Dose Response

Aminopyralid Clopyralid

Potato Response Above Ground

0

20

40

60

80

100

0 0.06 0.125 0.25 0.5 1

% o

f co

ntr

ol

Aminopyralid dose (1 = 7 fl oz/A)

Delta

Fairbanks

Palmer

0

20

40

60

80

100

0 0.06 0.125 0.25 0.5 1

% o

f co

ntr

ol

Clopyralid dose (1 = 0.33 pt/A)

Visual Injury – Crop + Weed

Aminopyralid Clopyralid

The Weed as a Bio-assay

• Can we use weeds to estimated herbicide

residuals?

• What are potential problems?

0

10

20

30

40

50

60

70

80

90

100

0 0.06 0.125 0.25 0.5 1

% o

f c

on

tro

l

Aminopyralid rate (1 = 7 fl oz/A)

Delta

Palmer

Milestone D

Milestone P

Potato

Crepis

Potato Response Below Ground

0

5

10

15

20

0 0.06 0.125 0.25 0.5 1

Po

tato

harv

est

(lb

)

Aminopyralid dose (1 = 7 fl oz/A)

Delta Palmer

0

5

10

15

20

0 0.06 0.125 0.25 0.5 1P

ota

to h

arv

est

(lb

)

Clopyralid dose (1 = 0.33 pt/A)

Is there Herbicide in the Tuber?

Is there herbicide in the tuber?

• Tubers were sent to the Montana

Department of Agriculture Laboratory at

Montana State University to extract the

herbicide

• Dr. Rick Boydston with ARS in Prosser,

WA funded the work ($150/sample)

Extraction Results

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 0.06 0.125 0.25 0.5 1

Am

ou

nt

ex

tra

cte

d (

pp

m)

Aminopyralid rate (1 = 7 fl oz/A)

Delta

Palmer

Is that Herbicide Herbicidal?


Aminopyralid


clopyralid

Conclusion

• Aminopyralid and clopyralid management

– Their residues are in the plant and soil

– They pass through ruminants unchanged

– They will accumulate in potato tubers

– Some plants are more sensitive than others

– There are potential bioassays

– Half lives are currently unknown

Conclusion

• Other herbicides

– In the growing season several herbicides

breakdown at rates estimated in the literature

– When soils are frozen herbicide breakdown

ceases

– Therefore, overall herbicide half-lives are

extended in Alaska, particularly in the interior

Questions

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