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
Introduction
• Variability in flaming efficacy has been observed following early
or late day flaming applications.
• The variation in leaf relative water content (RWC) at various
times of day is thought to contribute to this differential
response.
• Leaf RWC is a ratio of the amount of water in the leaf tissue at
sampling compare to when fully turgid.
Objectives
 To describe DOSE RESPONSE CURVES for time of
day as influenced by propane rates on 4 species
(green foxtail, velvetleaf, soybean and maize).
 To select PROPANE dose from the curve to:
- Minimize crop injury
- 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 time
All plant species presented the lowest RWC around
6 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
influenced by time of day
100
100
80
80
60
40
29 kg ha
43 kg ha
87 kg ha
20
0
0
2
4
6
8
10
12
60
40
1
20
1
1
0
14
0
6
8
10
Soybean
Velvetleaf
100
80
80
60
40
0
0
6
8
10
Hours after sunrise
12
14
14
12
14
40
20
4
12
60
20
2
4
Hours after sunrise
100
0
2
Hours after sunrise
Injury (%)
Injury (%)
Green foxtail
Injury (%)
Injury (%)
Corn
0
2
4
6
8
10
Hours after sunrise
Green foxtail visual injury
100
30kg/ha
60kg/ha
90kg/ha
Upper limit= 82
Visual injury (%)
80
Slope= -13
ED 50= 9 (3pm)
60
Lower limit= 48
40
20
0
0
2
4
6
8
10
12
14
Hours after sunrise
Dose
(kg/ha)
Regression parameters
-B
C
D
IED50
30
-23
23
55
60
-22
15
90
-13
48
(and time of day)
ED90 (and time of day)
12
(18h or 6PM)
13 (19h or 7pm)
37
12
(18h or 6pm)
10 (16h or 4pm)
82
9
(15h or 3pm)
10 (16h or 4pm)
Velvetleaf visual injury
Upper limit= 98
100
Slope= -13
ED 50= 8 (2pm)
80
Visual injury (%)
Lower limit= 71
60
40
20
0
0
2
4
6
8
10
12
14
Hours after sunrise
Dose
(kg/ha)
Regression parameters
-B
C
D
IED50
30
-40
43
75
60
-25
50
90
- 13
71
(and time of day)
ED90
(time of day)
10
(16h or 4PM)
11
(17h or 5PM)
75
11
(17h or 5PM)
12
(18h or 6PM)
98
8
(14h or 2PM)
9
(15h or 3PM)
Conclusions
 Flame weeding is more effective if conducted in the
afternoon, but crop injury will be higher, regardless of the
propane rate.
Practical implications
 Flaming could be done around the noon time in order to
obtain the maximum weed control with the minimum crop
damage.
May not be always possible with large fields