Weed control & Crop Tolerance to Broadcast Flaming as Impacted by Time of Day

Stevan Knezevic

et al.

University of Nebraska

“Our Flame Weeding Team”• Agronomy Department & Haskell Agricultural Lab:

– Dr. Stevan Knezevic & Dr. Jon Scott (Weed Technologist)

– Santiago Ulloa (PhD student) & Dr. Avishek Datta (Post Doc)– Heverton Teixiere, Andray Domingous, Claudio Costa, Jaymo Nato, Sidnei (Brazil)

– Pierre Marteau (France), Robert Leskovsek (Slovenia),

– Dr. Goran Malidza, Igor Elezovic, Strahinja Stepanovic (Serbia)

• Department of Mechanical Engineering:– Dr. George Gogos and Chris Bruening (PhD student), Brian Nelson, (MS)

Jared Miller and Dustin Simpson

• - Organic producers: Liz Sarno, Mike Ostry, Larry Stanislav, Randy Fendrich, Gerald Humlicek, Paul and Dan Huenefeld , Mark Ramaeker

IntroductionIntroduction • Variability in flaming efficacy has been observed following early Variability in flaming efficacy has been observed following early

or late day flaming applications. or late day flaming applications.

• The variation in leaf relative water content (RWC) at various The variation in leaf relative water content (RWC) at various times of day times of day is thought to contribute to this differential is thought to contribute to this differential response.response.

• Leaf RWC is a ratio of the amount of water in the leaf tissue at Leaf RWC is a ratio of the amount of water in the leaf tissue at

sampling compare to when fully turgidsampling compare to when fully turgid. .

ObjectivesObjectives To describe DOSE RESPONSE CURVES for time of To describe DOSE RESPONSE CURVES for time of

day as influenced by propane rates on 4 species day as influenced by propane rates on 4 species ((green foxtail, velvetleaf, soybean and maize) ..

To select PROPANE dose from the curve to:To select PROPANE dose from the curve to:- Minimize crop injury - Minimize crop injury

- Maximize weed control- Maximize weed control

Greenhouse Study:

- 4 flaming times: 6AM, 10AM, 2PM and 6PM- 4 propane rates: 0, 30, 60 and 90 kg/ha- 4 species: green foxtail, velvetleaf, soybean and maize

- Air Temp, Rel-Hum. light and RWC were recorded at treatment application

- RWC was measured @ procedure modified from Barrs and Weatherley (1962)

- It is a function of the relative water content (RWC)- RWC is the ratio of the water volume in a leaf to the maximum water volume of the leaf at full turgor.- Typically, RWC is high in the AM and lower in PM hours

RWC during day timeRWC during day time

All plant species presented the lowest RWC around All plant species presented the lowest RWC around 6 to 9 hours after sunrise6 to 9 hours after sunrise

Results:

Green foxtail flamed with 90kg/ha (~ 18GPA)

Control 6am 10am 2pm 6pm

Velvetleaf flamed with 90kg/ha (~18GPA)

Control 6am 10am 2pm 6pm

Plant injury at different rates as Plant injury at different rates as influenced by time of dayinfluenced by time of day

0 2 4 6 8 10 12 14

0

20

40

60

80

100

Green foxtail visual injury

Hours after sunrise

Vis

ua

l in

jury

(%

)

30kg/ha60kg/ha90kg/ha

Lower limit= 48

Upper limit= 82

ED 50= 9 (3pm)Slope= -13

Dose (kg/ha)

Regression parameters

- B C D IED50 (and time of day) ED90 (and time of day)

30 -23 23 55 12 (18h or 6PM) 13 (19h or 7pm)

60 -22 15 37 12 (18h or 6pm) 10 (16h or 4pm)

90 -13 48 82 9 (15h or 3pm) 10 (16h or 4pm)

Dose (kg/ha)

Regression parameters

-B C D IED50 (and time of day) ED90 (time of day)

30 -40 43 75 10 (16h or 4PM) 11 (17h or 5PM)

60 -25 50 75 11 (17h or 5PM) 12 (18h or 6PM)

90 - 13 71 98 8 (14h or 2PM) 9 (15h or 3PM)

0 2 4 6 8 10 12 14

0

20

40

60

80

100

Velvetleaf visual injury

Hours after sunrise

Vis

ua

l in

jury

(%

)

Lower limit= 71

Upper limit= 98

ED 50= 8 (2pm)Slope= -13

Flame weeding is more effective if conducted in the Flame weeding is more effective if conducted in the afternoon, but crop injury will be higher, regardless of the afternoon, but crop injury will be higher, regardless of the propane rate.propane rate.

Practical implicationsPractical implications Flaming could be done around the noon time in order to Flaming could be done around the noon time in order to obtain the obtain the maximum weed control maximum weed control with the with the minimum crop minimum crop damage.damage.May not be always possible with large fieldsMay not be always possible with large fields

ConclusionsConclusions