Dewberry (Rubus sp.) is a serious weed in commercial cranberry production. It spreads quickly, reduces yield, crowds out cranberry vines, and is very difficult to control with current methods. Flame cultivation (FC) may offer a non-herbicide option for management of this weed. Our preliminary work with hand-held FC has shown that relatively short exposures with an open flame torch can decrease dewberry biomass. This research aimed to identify the best timing and application recommendations for the practical use of FC for dewberry control in cranberry cultivation by testing various treatment timings and frequencies. The field work was combined with a study on the seasonal patterns of carbohydrate reserves in untreated dewberry plants improve treatment timings. Results showed that all FC treatments were equally effective at reducing the quantity of dewberry stems within the year of treatment, and aboveground biomass a year after treatment. Root carbohydrate reserves decrease after plants resume growth after winter dormancy until they have achieved full leaf expansion, after which time reserves increase until plants enter dormancy in the fall. The outcome of this study has the potential to reduce environmental and health risks by reducing chemical inputs, and to increase crop productivity by providing weed control. Information generated by this study was disseminated to the cranberry growers via bogside workshops, newsletters, and Extension meetings.
Cranberries (Vaccinium macrocarpon Ait.) are produced in the Northeast region in Massachusetts, New Jersey, New York, Maine, and Rhode Island and are important agricultural commodities for these states. Cranberry is a woody perennial crop that can remain productive for decades and competition for resources between cranberries and weeds can depress cranberry farm yields, resulting in large annual crop losses. The majority of problematic weeds are also long-lived perennials like dewberry (Rubus spp.) which spread quickly, reduces yield, crowds out cranberry vines, and are difficult to control with current methods. In a recent survey of Massachusetts cranberry growers, approximately 80% reported having dewberry present on their farms. The majority reported the weed as “difficult to control”, and rated currently available control methods as only “somewhat effective” (Ghantous and Sandler 2010).
Renewed interest in reducing chemical inputs into cranberry systems has provided the motivation to evaluate methods, such as flame cultivation (FC), as potential nonchemical options for weed control. Also known as thermal weeding, FC exposes plants to brief periods of high temperature that causes the water in the plant tissue to expand rapidly, rupturing plant cells and leading to necrosis (Daniell et al. 1969). Various FC methods have been used successfully in annual crops as both a preemergence and postemergence weed control (Diver 2002), but few scientific reports have been published on the use of FC on perennial weeds in a woody perennial crop system.
Perennial plants rely on stored sugars and starch, known as nonstructural carbohydrates (NSC), for survival during periods when respiration exceeds carbohydrate assimilation such as during dormancy and when resuming growth after dormancy (Kozlowski 1992; Loescher et al. 1990). There is evidence that fire can be used as a tool to deplete NSC and control woody species in forest management (Richberg 2005), and this can reduce weed size and vigor, and renders them more vulnerable to mortality (Kays and Canham 1991; Loescher et al. 1990).
Our preliminary work with hand-held FC tools has shown that a single mid-July exposure with an open flame tool can reduce both dewberry shoot and root biomass (Ghantous et al. 2012), but the efficacy of FC treatments to woody weeds may be impacted by the timing and frequency of treatments as they relate to the specific carbohydrate cycles of targeted woody weeds. Dewberry roots are woody structures and a sink for nonstructural carbohydrates (NSC), and there might be a window of time in which dewberry plants will be more impacted by FC exposure.
The objectives for the current study were to determine if seasonal timing and frequency of exposure with a handheld, propane-fueled flame cultivator would differentially reduce dewberry stem length and biomass, both in the year of and the year following treatment and to evaluate whether FC treatments were altering the ratio of NSC in dewberry roots by using high-performance liquid chromatography (HPLC) to study relative amounts of sugars and starch. Our other objective was to follow the seasonal changes in levels of NSC within the roots of dewberry plants at different phenological growth stages to determine if changes occur in predictable patterns.
1. Objective: Conduct a 2-year replicated on-farm study in the summer of 2011 utilizing hand-held FC for control of dewberry to investigate the effects of frequency and seasonal timing of FC applications. Qualitative measurements of stem number and length will be taken periodically, and aboveground biomass samples will be collected at the conclusion of the study to evaluate treatment effects.
Completed: The experiment was established on a cranberry farm in East Wareham, Massachusetts in June of 2011. Plots 0.25 m x 0.25 m were established on bog edges were dewberry plants were growing. Qualitative measurements of dewberry stem number and lengths of stems were made for each plot on June 23, 2011. Plots were randomized within each replicate, received one of seven different treatments with an open flame handheld cultivator (no treatment, a single treatment in June, July or August, or two treatments June/July, June/August, or July/August). All treatments were replicated 5 times. End-of-season measurements of dewberry stem number and lengths of stems were made September 26, 2011 and September 28, 2011.
Plants within each plot were re-measured in June 2012. All aboveground biomass was collected from each plot June 19, 2012. Samples were then dried and weighed to assess biomass.
2. Objective: Analyze carbohydrates in root samples from dewberry plants treated with FC in a 2010 experiment (root samples to be collected in 2011) and in the proposed 2011 experiment (Objective 1, root samples to be collected in 2012) to gather quantitative data on how FC treatments affects the amount of dewberry reserve carbohydrates.
Completed: Roots from plants treated in 2010 were collected on June 27, 2011. Approximately 6-cm sections of roots 1 cm in diameter or larger were dried and ground according to the proposed protocol. They were analyzed with HPLC in April 2012.
Unfortunately, roots from the 2011 experiment (Objective 1) did not meet the minimum diameter requirement (> 1cm), which had been established for suitability for HPLC analysis. In addition to the 2011 experiment conducted under this grant contract, an identical experiment was conducted on dewberry plants that had been cultivated in an area adjacent to a cranberry production area. Roots from this experiment were collected, dried and ground. These roots were analyzed with HPLC in June 2013 in place of the roots from the experiment in this grant contract, but provided similar information on the impact of the FC treatments on dewberry reserve carbohydrates.
The results of HPLC analysis from 2010/2011 samples and 2011/2012 samples were statistically analyzed to test for differences in dewberry reserve carbohydrates between the different FC treatments in June 2013.
3. Objective: Conduct a replicated study of two untreated dewberry populations to determine seasonal variations of stored carbohydrates in dewberry. Due to the destructive nature of root sampling, areas need to be identified were dewberry are growing without cranberries present, but in conditions similar to those found on a commercial farm. One site will be an area adjacent to a commercial cranberry farm, and the other at area at the UMass Cranberry Station. This information will be used to refine FC timing, so that treatments are administered at the time when seasonal reserves are known to be the lowest.
Completed: Root samples were collected from two sites at five collection dates in 2011 based on dewberry phenological stage: bud break, full leaf expansion, flowering, fruit ripe, and onset of dormancy. Four entire plants were excised from each site at each sampling time. Approximately 6-cm sections of roots 1 cm in diameter (the minimum size needed for the protocol) or larger were dried and ground according to the proposed protocol. Root samples were analyzed with HPLC in April 2012.
Although not within the scope of the original grant proposal, we had the time to repeat this study again in 2012. The samples were analyzed with HPLC in June 2013, and the results of HPLC analysis from 2011 and 2012 samples were then statistically analyzed for seasonal and phonological trends in dewberry reserve carbohydrates June 2013.
Objectives 1 and 2: Conduct an on-farm study utilizing hand-held FC for control of dewberry to investigate the effects of frequency and seasonal timing of FC applications. Analyze carbohydrates in root samples from dewberry plants treated with to gather quantitative data on how FC treatments affects the amount of dewberry reserve carbohydrates.
The experiment on the effects of timing and frequency of FC treatments on dewberry was conducted on a commercial cranberry farm in East Wareham, MA. It was arranged as a randomized-complete-block design with seven treatments blocked by replicate to account for differences in growing conditions across the production area. Treatments were replicated five times. Plots (0.5 x 0.5 m) were located in areas where dewberry was visibly present and plots were placed over areas that were visually assessed to have uniform weed coverage at each site. Treatments were applied over the center of each dewberry plot. Plots received either a single exposure (June, July or August) or two exposures (June/July, June/August, or July/August) or no treatment. A FC exposure was a 9 s / 0.25 m2 exposure from a handheld, propane-fueled flame cultivator (Weed Dragon vapor torch; Flame Engineering, LaCrosse, KS 67548). Water was applied to all plant foliage and soil with a hand-held watering can for 10 s before and after FC treatments to minimize risk of fire.
Quantitative measurements of dewberry stem number and length were taken periodically using a ruler to measure the length of each main stem from its origin at the ground (the crown) to the tip, but did not take into account branching of the stems. The total numbers of crowns present and the total number of stems in each plot from all crowns were counted. Baseline measurements were made prior to June treatments, at the end of the growing season prior to the onset of dewberry dormancy (as denoted by initiation of leaf color change), and again the following June. The lengths of all individual stems for each plot were added to together to calculate cumulative stem length (CSL). One year after study initiation all aboveground dewberry biomass was harvested using hand-held pruners and placed into paper bags. All aboveground biomass samples bags were placed into an oven at 60 degrees C for a minimum of 3 d. Dry biomass was determined by weighing each sample.
Carbohydrate concentrations can be dependent on the root diameter, so a 1-cm diameter size criteria was selected for this study (Wargo 1976). The majority of root samples from this site were smaller than the 1-cm diameter size criteria, so they were not used for HPLC analysis. In addition to the 2011 experiment conducted under this grant contract, an identical experiment was conducted on dewberry plants that had been cultivated in an area adjacent to a cranberry production area. Roots from this experiment were collected, dried and ground. These roots were analyzed with HPLC in June 2013. Root samples from a previous experiment on a commercial farm (plants treated in 2010 and roots collected June 2011) were also analyzed.
Samples were washed, cut into small pieces using a razor blade, placed into paper bags, and dried in an oven at 60 C for 1 wk until a constant weight was maintained for dry matter determination. These samples were then ground in a Wiley mill (Thomas Scientific, Swedesboro, NJ) to pass through a 2-mm screen and used for high performance liquid chromatography (HPLC) analysis to determine concentrations of sucrose, glucose, fructose, and starch that collectively represent NSC (Botelho and Vanden Heuvel 2005).
Objective 3: Conduct a replicated study of untreated dewberry populations to determine seasonal variations of stored carbohydrates in dewberry.
Several sites with groups of dewberry plants were identified on cranberry farms in areas located adjacent to production areas in East Wareham, MA were sampled in 2011. Site 1 did not have sufficient amounts of dewberry plants for a second year of sampling so 2012 samples came from Site 2 and Site 3, also in East Wareham, MA.
Dewberry root samples were collected at five distinct phenological stages in the dewberry life cycle: initial bud break, full leaf expansion, flowering, fruit maturity, and after the onset of dormancy as indicated by leaf color change and senescence. The use of phenology to select sampling time has been used in other weed studies that measured NSC (Bhowmik 1994; Tworkoski 1992). Dates of dewberry phenology varied slightly by year, and variation was likely due to normal variability in environmental conditions (2011 : Bud break 4/20, full leaf expansion 5/24, flowering 6/13, fruit maturity 8/1, dormancy 11/14; 2012 : Bud break 4/2, full leaf expansion 5/11, flowering 6/5, fruit maturity 8/1, dormancy 10/24).
At each collection, four plants (each plant was considered a replicate (Cyr et al. 1990)) per site were excavated using shovels and rakes to remove entire plants with intact roots from the soil. Plants were transported with their roots in a container of water to the lab, where they were immediately processed. Samples were prepared as described above.
The project was structured as a research project and as such, our target audience was initially limited to the growers who provided farm space on which we could do the work. More growers were reached by various Extension programs and activities (discussed in Section 8).
Stem length measurements made in the fall approximately 3 months after FC treatments showed that dewberry plants exposed to any treatment had significantly less CSL than untreated plants. Treatments did not statistically differ from one another, but two treatments did reduce CLS more than a single treatment (Fig 1). Dewberry aboveground biomass collected the year after treatments showed similar effects. All treated plants had less aboveground biomass than untreated plants, and treatments did not differ from one another. Two treatments did not reduce biomass more than a single treatment.
Carbohydrate analysis of dewberry root samples collected the year after FC treatments showed that the ratio of structural to non-structural carbohydrates was not significantly affected by treatments. The sampling of roots occurred at the conclusion of the study 1 yr after the initiation of the study. Roots were not sampled at other times because it is a destructive process, would have affected the plants, and likely confounded treatment effects. It is possible that significant differences in dewberry root carbohydrate ratio existed among treatments closer to the time of treatments, but that these differences disappeared within the year between treatments and root sampling.
Although a single year of FC treatment may not eradicate dewberry, it can reduce the biomass and slow the spread of this weed, which competes with cranberry plants. All timings and frequencies of FC treatments were able to significantly reduce the fall CSL and biomass of dewberry plants. Data from the Garden Area indicated that two treatments may be more effective than a single treatment at reducing overall dewberry biomass. A single June treatment was the least effective at reducing cumulative stem length at all sites and shoot biomass. Growers have some flexibility in the timing of FC treatments, and could administer FC at their convenience (i.e., around other farm activities or cranberry growth stage) without sacrificing weed control efficacy.
Root carbohydrate in untreated populations of dewberry plants varied significantly between different growth stages of the dewberry plants (Fig 2 and 3). Total nonstructural carbohydrates (TNC, which are the sum of starch and soluble sugars) levels declined between bud break and leaf expansion, while starch did not decrease in this period. This indicates that plants were primarily using sugars to support growth until leaves were fully expanded to produce new carbohydrates through photosynthesis. After full leaf expansion, soluble sugar levels remained similar until dormancy and always ended the season at lower levels than those measured at bud break. In contrast, starch always began the season lower than soluble sugars and, and increased significantly between the time of fruit maturity and onset of dormancy. This indicates that plants accumulated starch for long-term storage to support energy needs through the winter.
Our recommendation for timing dewberry controls which damage above ground dewberry plant parts (mowing pastures, flame cultivation of individual plants, etc.) during the time when TNC are low, yet when plants have will not have time to fully replenish depleted root reserves prior to the onset of dormancy. This window of time would roughly coincide with fruit maturity.
This work will help to support agricultural sustainability by demonstrating that chemical alternatives for weed management can be successfully employed on cranberry bogs to control dewberry, and also helping to inform growers about the most effective time to target these weeds. This information on timing will be applicable to other weed control techniques such as pulling or digging out the weeds, clipping plants, or even some types of herbicide applications. Flame cultivation has the potential to reduce environmental and health risks by reducing chemical inputs, and to increase crop productivity by providing more effective weed control.
Education & Outreach Activities and Participation Summary
• Recommendations for using FC for dewberry management were included (authored by H. Sandler) in the 2011 UMass Chart Book Weed Management section. p. 24. Recommendations to use FC to manage dewberry, rushes, and Japanese knotweed, and in combination with late water floods were published in the 2012 and 2013 UMass Chart Book Weed Management section, pp. 24, 29, 32, 60 and 24, 28, 33, and 61, respectively.
• K. Ghantous presented information and results related to FC to growers and industry representatives at the 2012 and 2013 annual UMass Cranberry Research Update Meeting held in January of each year at the Plymouth Radisson, Plymouth, MA. Approximately 250 growers attended each year.
• FC option for weed control was included in the UMass Cranberry Station IPM message on July 18, 2013.
• K. Ghantous demonstrated FC torches and procedure to approximately 15 growers at a bogside workshop June 21, 2013 at the UMass Cranberry Station.
• During the 2013 season, several growers borrowed our FC torches to manage weeds on their own farms prior to making a FC purchase on their own.
• K. Ghantous gave oral presentations on the efficacy of flame cultivation for weed management at the 2011 and 2013 North American Cranberry Researchers and Extension Workers (NACREW) Conference in Wisconsin Dells, WI and Quebec City, Quebec, respectively.
• K. Ghantous presented a paper on the effects of timing and frequency of flame cultivation treatments on dewberry at the Joint meeting of the Weed Science Society of America and Northeast Weed Science Society (NEWSS) Annual Meeting, Baltimore, MD. February 2013.
• K.Ghantous gave a presentation on the timing, duration and type of flame cultivator affects weed response in cranberry at the Northeastern Weed Science Society meeting, Baltimore, MD. January 2011.
Since the conclusion of the project, several cranberry growers have expressed interest in trying FC to manage weeds on their farms. Some have borrowed the FC torches and used them on their farms, and have had positive results. Several have indicated that they are going to buy their own torches or may like to borrow ours again in 2014.
Areas needing additional study
The results of the root carbohydrate study suggest that TNC levels are the lowest at full leaf expansion, which happened in May. This was a month before our first FC treatment timing. It is possible that a treatment during this time may differ from treatments at later times. A future study could be designed to test this earlier timing.
Although no differences were found for root carbohydrate ratios a year after FC treatments, it is possible that significant differences in dewberry root carbohydrate ratio existed among treatments closer to the time of treatments, and that these differences disappeared within the year between treatments and root sampling. A future study would benefit from a larger sample population that would allow for non-repetitive sampling throughout time to better study the carbohydrate dynamics after FC injury.
Future projects could look the effects of two successive years of FC treatments. Many perennial cranberry weeds require multiple years of treatment. In addition, herbicide use on the experiment area was prohibited. It is possible that herbicides may weaken dewberry plants and make them more susceptible to FC, or conversely that FC may weaken dewberry plants and make them more susceptible to herbicides. This synergistic effect is also an area of potential future work.