These studies will evaluate tactics for flame-weeding as an early-season option for weed control in soybean. The first objective will evaluate the effectiveness of flaming weed seed on or near the soil surface. Seeds of Palmer amaranth or smooth pigweed will be placed in flats containing a sterilized mix of field soil and potting soil at 0, 0.5, 1, and 1.5 inches below the soil surface. Flats will then be flamed for 1 to 5 seconds. Data from objective 1 will be used to inform two standard flaming rates for the second objective. The second objective will evaluate flame-weeding as an integrated tactic for early season weed control (Table 1). The study will undergo conventional tillage immediately prior to planting to prepare a clean seedbed and stimulate weed germination. All plots will be flamed within 24 hours of planting (at planting). Subsequent flaming will occur one or two more times using a shielded, hand-held flamer when weeds reach 3 inches in height. Integrated treatments of flaming and cultivation will also be included as well as flaming followed by cultivation only treatments.

1. Determine the dose (time of exposure to flaming) and depth of burial needed to control weeds pre-germination.
2. Evaluate flame-weeding as integrated tactic for early-season weed control.

Objective 1: Weed emergence will be recorded from each flat 3, 7, and 14 DAT. Seedlings will be removed at each counting date.

Objective 2: Individual plots will be divided into treated and untreated sections in order to evaluate differences in weed emergence, weed control, and crop injury. Weed species and density will be assessed using two 0.25 m2 quadrats prior to each application timing, and 2 weeks after each application. Weed control and crop injury will be visually evaluated on a 0 to 100% scale (0 = no control, 100 = complete control) at the aforementioned rating dates.

All trials will be conducted as small-plot replicated trials. Data will be analyzed in a statistically sound procedure, based on the design of each study. Field treatments will be replicated at two different sites and greenhouse studies will be repeated twice.

Research will be highlighted via social media posts and on field tours at the University of Maryland Wye Research and Education Center. Reports of this study will be summarized online in University of Maryland Agronomy News and used to develop weed control recommendations. At the completion of the trials (individual objectives), fact sheets will be prepared based on the study findings.

Update:
A greenhouse study was conducted to evaluate pigweed seed mortality and depth of burial (objective 1). This study was repeated twice. A field study was conducted to evaluate flame weeding alone, or as an integrated tactic with cultivation (objective 2). The field study has been completed at the first site, and is ongoing at the second site. Results from both the greenhouse study and first field study were presented at the Maryland Commodity Classic on July 27, 2023.

View uploaded report

Update:
A summary article for the project was written for the November 2023 edition of University of Maryland Extension's Agronomy News. Data from the project was presented at the annual meeting of the Northeastern Weed Science Society.

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View uploaded report 2

Updated June 5, 2024:
No new information to report as of Feb 1. Attached is a copy of the abstract and presentation that was given at the 2024 Northeastern Weed Science Society Meeting.

View uploaded report

Early season weed control can be difficult in organic production systems. Many organic farmers rely on tillage and in-row cultivation to manage weeds. However, these tactics can have negative effects on soil quality; accelerating soil erosion and surface runoff, and reducing organic matter content. Flame weeding is a non-chemical tactic that has been shown to control several broadleaf weed species. Greenhouse and field studies were conducted to determine the effects of flame weeding on early season weed control. The greenhouse study evaluated the depth of seed burial (0, 0.5, 1, 1.5 inches below the soil surface), and amount of flame exposure (speed of flaming unit; 1, 2, 3 mph) needed to kill weed seeds. Results showed that smooth pigweed emergence was reduced when seed was buried deeper in the soil profile (1 to 1.5 cm). However, there were no clear patterns related to flame exposure, indicating that flame-weeding cannot be used successfully for preemergence control of this and similar species. The field study was conducted in two organic soybean fields in Caroline and Kent counties in Maryland. All plots received a flame treatment prior to soybean emergence followed by no additional treatment, one sequential flame treatment, two sequential flame treatments, a cultivation treatment, or a cultivation treatment followed by an additional flame treatment after weeds reached a height of at least 3 in. Each flame-weeding treatment was conducted at two speeds, 1 and 2 mph. At 5 weeks after planting at the Kent County site, pre-flaming followed by 2 sequential flame treatments reduced overall broadleaf weed density, compared to preemergence-flaming alone and preemergence-flaming followed by 1 sequential flame treatments. However, cultivation treatments caused the greatest reduction in early season weed density. Similarly, cultivation treatments caused the greatest reduction in early season Palmer amaranth density at the Caroline County site. These results indicate that although flame-weeding has some effect on reducing early season weed density, it does not provide acceptable, long-term weed control in organic soybean. This may be due the variability in weed emergence among individual species. Further research should evaluate timing of flame-weeding treatments for optimum effectiveness on individual species.

Starting clean or weed-free is the key to any good weed control program, especially when dealing with herbicide-resistant weeds such as Palmer amaranth. Many conventional, soil-active (residual) herbicides are available that effectively control many of these weeds. However, control is more complicated in organic systems: 1) where effective residual herbicides are not an option, and 2) when weeds may germinate at different times throughout the growing season.

Flame weeding is a non-chemical tactic that has previously been evaluated to control several grass and broadleaf weed species (Cisneros and Zandstra 2008; Sivesind et al. 2008) in multiple cropping systems including corn (Stepanovic et al. 2016a) and soybean (Stepanovic et al. 2016b). The majority of this research has evaluated the effects of flame weeding on emerged weeds. However, Gallant (2013) reported that flaming “popped” redroot pigweed seeds post-dispersal. Furthermore, certain seeds such as those of horseweed (marestail) and Palmer amaranth tend to germinate from shallower depths in the soil profile, and may be more readily controlled by flaming on or near the soil surface.

Cultivation/tillage is a tactic used in both conventional and organic farming to prepare a seedbed for planting. It too can be effective in controlling emerged weeds, but this tactic can also bring weed seeds to the soil surface and stimulate weed germination. Growers may use this aspect to their advantage by implementing the stale seedbed tactic - a weed management practice in which weed seeds just below the soil surface are allowed to germinate only to be killed by repeated cultivation prior to planting the cash crop. However, additional cultivation often leads to additional weed emergence and cannot be used when the soil is too wet. Flame weeding may aid in this practice by eliminating emerged weeds when cultivation is not an option. In general, flaming will only burn the top couple millimeters of soil leaving weeds buried deeper in the soil intact.

We hypothesize that integrating flame weeding with the stale seedbed approach will improve control by 1) stimulating weed emergence for early flaming postemergence, 2) burning weed seed on or near the soil surface, and 3) minimizing soil disturbance and additional weed germination.