Weed Control Gets More Complicated

Jim Martin Extension Weed Scientist

Photo: Mike Smith 8-21-2013

HERBICIDE RESISTANT WEEDS IN KYRESISTANT BIOTYPE RESISTANT BIOTYPE

SMOOTH PIGWEED

• PS II (1987) * • ALS (1992) • PS II + ALS (2000)

ITALIAN RYEGRASS • ACCase (2004) • ALS (2013)

COMMON RAGWEED • EPSP (2006)JOHNSONGRASS

• ACCase (1991) • ALS (2006)

WATERHEMP • EPSP (2010)

MARESTAIL • EPSP (2002)

PALMER AMARANTH • EPSP (2010)

COMMON CHICKWEED • ALS (2013) ?

* YR of Discovery Based on Confirmation in Lab or Field Tests

Pay attention to weed size

Source: Loux 2011

Factors to Consider on Marestail Control in Soybean

• Application Timing: – Fall + Spring – Spring

• Utilize Alternative Chemistries to Limit Risk of Developing ALS Resistance.

• Flumioxazin (Valor products)• Metribuzin• Saflufenacil (Sharpen, Verdict)• Glufosinate (Liberty)• 2,4-D

• Manage Populations in Fallow Areas

Impact of Spray Volume and Weed Size on Waterhemp Control with Liberty and Prefix in LL Soybean

6.5" Tall 8.5" tall0

102030405060708090

100

10 GPA 15 GPA 20 GPA

6.5" Tall 8.5" tall0

102030405060708090

10010 GPA 15 GPA 20 GPA

a

bc c

Liberty 29 oz/A Prefix 2.33 pt/A

aa

Hancock CO 2013

Comparing Preemergence Herbicides (Waterhemp Control & Soybean Injury

Soybean Injury (%)

Waterhemp Control (%)

Authority MTZ 18 oz/A 0 100Boundary 3 pt/A 0 100Valor XLT 5 100Zidua 0 100Fierce 7.5 100

Hancock County Ratings at 3 weeks after Planting LL soybeans 2013

Soybean Injury With Soil-Residual Herbicides(2 Weeks After Application)

Valor SX Authority MTZ

Valor XLT Authority First

Authority Assist

Sencor0

2

4

6

8

10

12

14

16

18

20

Alone Plus Warrant

Warrant Alone

Fulton Co 2013

Crop

Inju

ry (%

)

Palmer Control With Soil-Residual Herbicides(7 Weeks After Application)

Valor SX Authority MTZ

Valor XLT Authority First

Authority Assist

Sencor0

10

20

30

40

50

60

70

80

90

100 Alone Plus Warrant

Fulton County 2013

Cont

rol

%

Warrant

Shading Impacts Palmer Emergence

Fallow (5-16-13)

Wheat 7” Row (5-16-13)

Wheat Skip Row (6-20-13)