Flame Burning for Weed Control and Renovation with Strawberries

9 Flame Burning for Weed Control and Renovation with Strawberries Principal Investigator Dr. David Wildung University of Minnesota North Central Research and Outreach Center 86 East Hwy 69 Grand Rapids, MN 55744 8-7-47 Itasca County Project Duration 999 to 00 ESAP Contact Jean Ciborowski, 65-97-7 Flaming a row of strawberries Keywords strawberry, flame burning, flame cultivation, weed control Project Summary Weed control is a major limiting factor in the production and longevity of strawberry plantings. It is expensive and, when poor, greatly reduces yield and the aesthetics of harvest. Currently, weed control is most often accomplished through the use of herbicides. Since strawberries are considered a minor use crop by chemical companies, strawberry herbicide choices have been greatly reduced, leading to the need to find alternative weed control systems. In addition, many consumers want pesticide free food and strawberry production has one of the highest rates of pesticide residues of conventionally grown fruits and vegetables. Certainly anything the industry can do to reduce pesticide applications will greatly enhance the image to the public. Making strawberry production systems more sustainable will benefit both the producer and the consumer as well. Dave s project looks at flame cultivation for weed control in newly established strawberry plantings and flame burning at strawberry renovation for weed control and reducing cultural practices in existing plantings. Project Description Strawberry flame burning has two potential areas for success: first for weed control in newly established plantings and second for weed control and reducing cultural practices in renovation of existing plantings. Flame cultivation in the growing strawberry row is made difficult due to the extremely succulent leaf habit of the strawberry plant and the often uneven growth of the plant in the row as it produces runners and new daughter plants. However, with protective shields flame cultivation may be possible especially early in the establishment season when new weed growth is at its greatest and the strawberry plants are their smallest. Early season flame cultivation could be done with speed and effectiveness. For renovation, strawberry plantings are typically mowed, (often with foliage removed for disease control) rototilled, fertilized and herbicide is applied. Directed flame burning over the top of the row could reduce or eliminate any one or several of the normal cultural practices currently being used. For renovation, the succulence of the strawberry leaf may be beneficial because fast flame burning could be accomplished, fast enough to kill the strawberry foliage and weeds without damaging the strawberry crown, destroying needed organic matter or starting mulch fires in the planting. Much of the work done on this project was conducted in 997 and 998 with funds from LCMR and the North American Strawberry Growers Association project grants, which were completed in 998 and 999. Because of the way strawberries grow, crop burn treatments applied during one season will not affect crop production until the next season. Therefore, much of what is reported here was started with funds from one grant and completed or will be completed with ESAP grant money. The project is being done at each of the three locations described below: North Central Research and Outreach Center (NCROC). The Center is located in Grand Rapids and the project is being done in the horticultural plot area. GREENBOOK 000 ENERGY AND SUSTAINABLE AGRICULTURE PROGRAM MINNESOTA DEPARTMENT OF AGRICULTURE

9 FRUITS AND VEGETABLES WILDUNG Lavalier Berry Farm. A commercial strawberry and blueberry pick-yourown farm. The farm sells ready picked fruit. It is located on County Road 44 about five miles southeast of Grand Rapids. There are approximately four acres in strawberry production. Luneyberries Berry Farm. A commercial strawberry pick-your-own farm. This farm also sells ready picked fruit. It is located nine miles west of Grand Rapids on County Road 6. The Lunemanns have seen their strawberry acreage expand every year and currently have over five acres in production. Two propane burners were built by NCROC staff for this project. The first, built in 997, was used in small plot situations. It was built on wheels so that it could be pulled from plot to plot and cost $40 to build. The second can be used in larger production situations. It is tractor mounted, has two burner heads that can be adjusted up and down or in or out, more controls to regulate flame, a bar in front of the unit that pushes thick strawberry foliage down for better flame penetration during burn renovation, a 0 lb propane tank, and cost $500 to construct. Weed burning in newly established strawberry plantings was done on NCROC plots in 997, 998, and again in 999. Burning was done at two to four week intervals as necessary or at a stage when cultivation would normally occur. Burn treatments were compared to standard cultivation and hand weeding. In addition, burn treatments were discontinued after June, July, August, September or October to evaluate weed regrowth potential and its effect on yields. The cultivar Kent was used for these studies. Field plot burn studies at renovation were begun at NCROC in 997, two grower sites were added in 998 and expanded in size in 999. The treatment mix varied slightly at each location depending upon each grower s standard renovation practices. Treatments at NCROC were selected to compare traditional renovation to burning and using burning to replace one of the normal renovation practices - mowing, herbicide use and/or tilling. The cultivar Kent was used for studies at NCROC and at one grower site. Glooscap was used at the second grower s farm. Each treatment plot was a single row ten (NCROC) or fifteen (grower sites) feet long. Standard planting, spacing, fertilization and pest management practices were followed at all locations. Results and Observations Strawberry vigor, percent plant stand, and leaf spot disease ratings were taken in fields before or following burning and during the fruiting season. Vigor and leaf spot ratings were on a one to nine rating scale with nine being most vigorous or no leaf spot. Grass and broadleaf weed control was evaluated on a one to nine rating scale with nine being best and one being no weed control. Crop yield and fruit size were taken each year following the burn treatments. Burn Weed Control in New Plantings at NCROC. Burning to control weeds in new plantings was not as effective as normal cultivation and hand weeding. While yields were much better in 999 than in 998, they were still significantly less compared to hand weeding and cultivation treatments. Production was reduced 9% in 998 with the best burn treatment compared to the worst hand weed treatment (9,6 lb/a compared to 7,47 lb/a); in 999 the difference was 4% (4,08 lb/a compared to 0,74 lb/a). Plant stand was also significantly less in burn treatments compared to hand weeding both years. Strawberry fruit size, percent early harvest (amount of fruit that is harvested during the first three harvests of the season) and plant vigor were not affected by burning. During both seasons, the longer into the season burning was done the better production was. The worst of the burn treatments was when burn cultivation was discontinued in June, July or August. Season long burn cultivation resulted in the best yields being produced. Burning, while not as effective, was less labor intensive and costly than hand weeding. Strawberry burn weeding in new plantings can be done, but may not be totally successful due to the strawberry plants susceptibility to flame, the plants architecture (runner growth out of the row), and inability to control weeds in the strawberry row with burning. Some level of weed control is possible with burning, but it is not as good as hand weeding. It is also impossible to burn weeds that develop within the strawberry plant canopy itself. These weeds have to be hand weeded. This factor is responsible for the reduction in total yield and plant stand we observed in the burn treatments. Burning is useful in killing weeds outside the strawberry plant canopy or between strawberry rows. The value of burning for weed control in new plantings has to be balanced closely with the cost of weeding in traditional weed management programs. Burn Renovation in Established Plantings. Burn renovation treatments in 998 at NCROC emphasized replacing various steps in the traditional renovation system with burning (Table ). Since grassy weeds were most prominent, Poast herbicide was used in combination with the renovation treatments. Three treatments included mowing after burning to determine if removing this stubble would allow plants to regrow faster. Strawberry plant growth and production in 999 for all burn treatments was equal to, and in most treatments was greater than, the traditional renovation treatment (Mow- Till-Poast) (Table). No negative effects from burn renovation were evident. At each cooperator location, burning replaced one or several traditional cultural practices the grower used at renovation. By fall, significant reduction in leaf spot was observed in the burn treatments (Tables and ) at both locations. At one farm Glooscap did not show any vigor or stand differences (Table ) while at the other farm Kent GREENBOOK 000 ENERGY AND SUSTAINABLE AGRICULTURE PROGRAM MINNESOTA DEPARTMENT OF AGRICULTURE

9 was significantly more vigorous in the burn treatments (Table ) compared to traditional renovation. Weed control was good at both farms on all treatments. During harvest, vigor and stand ratings were equal for all treatments at both farms (Table and ). Leaf spot ratings, while not statistically significant, were better on all burn treatments compared to traditional renovation at both locations. Production and berry size varied at both locations. Table. Strawberry Burn Renovation - NCROC - 998 Weed Control Stand Leaf 998 Renovation Vigor (%) Spot Grass Broadleaves Treatments 7/7/99 7/7/99 7/7/99 7/7/99 7/7/99 Burn-Mow-Poast 8.6 90 5.7 8. 7.7 Burn-Mow-Till 8.6 77 5. 7. 7. Burn 8.6 8 6. 7. 7. Burn-Till-Poast 8.7 90 5.8 8.0 7.7 Burn-Mow-Till-Poast 8. 79 6. 7.7 8.0 Burn-Poast 8.5 8 6.4 8. 6.7 Mow-Till-Poast 8. 77 5.4 7.8 6.9 Burn-Till 8.5 7 6. 6.6 6.7 LSD 5% NS NS NS 0.7 NS Treatments: Mowed 7/9/98; Burned 7/0/98; Mowed after burning 8//98; Poast applied 8/9/98 Cultivar Kent 5 replications Vigor: Scale of -9, where = dead and 9 = best vigor; Leaf Spot: Scale of -9, where = heaviest and 9 = no leaf spot; Weed Control: Scale of -9, where = heaviest weed infestation and 9 = no weeds present In 999, burn renovation treatments were repeated at both grower locations on a larger scale using 0.6 A and 0. A respectively. By fall, no growth differences were noted except for reduced leaf spot infection where burning was used. Yields will be taken at each location in 000. Strawberry fruit yield, berry size, and percentage early harvest have not been reduced by burning compared to traditional renovation practices (Tables 4, 5 and 6). At two of three locations, Lunemann s and NCROC, fruit yield has been greater following burn renovation. In some cases there has been an increase in plant vigor and less leaf spot after burn renovation. Burn renovation appears to reduce leaf spot development. The same situation that makes flaming difficult in new strawberry plantings appears to aid flaming for strawberry renovation. Strawberry foliage and weed growth is especially vulnerable to flaming. Burn renovation is fast and Table. Strawberry Burn Renovation Lavalier Farm - 998 Vigor Stand(%) Leaf Spot 999 Weed Control 998 Renovation Treatments 0/0/98 7/0/99 0/0/98 7/0/99 0/0/98 6/7/99 Grass Broadleaves Mow-Till-Devrinol 7. 7.4 88 78 5.0 6. 7. 8. Burn-Till-Devrinol 7.7 7. 9 77 7.0 7. 7.7 9.0 Burn-Till 8.0 7.4 94 77 7. 7. 7.0 8.7 Burn 7.0 7.5 78 77 7.0 7.7 6.0 9.0 LSD 5% NS NS NS NS 0.6 NS NS NS Treatments: Mowed 7/8/98; Burned 7/6/98; Cultivar Glooscap replications Vigor: Scale of -9, where = dead and 9 = best vigor; Leaf Spot: Scale of -9, where = heaviest and 9 = no leaf spot; Weed Control: Scale of -9, where = heaviest weed infestation and 9 = no weeds present Table. Strawberry Burn Renovation Lunemann Farm - 998 998 Vigor Stand(%) Leaf Spot 999 Weed Control Renovation Treatments 0//98 7/9/99 0//98 7/9/99 0//98 6/8/99 Grass Broadleaves,4-D-Mow-Till 7.0 8.7 6 9.7 7.7 9.0 7.,4-D-Burn-Till 8. 9.0 7 96 6.7 8.0 9.0 8. Burn-Till 8.7 8.9 77 96 6. 8.0 8.9 8. Burn 8. 8.9 70 9 6. 8.0 8.8 7. LSD 5% 0.9 NS 0.0 NS.0 NS NS NS Treatments:,4-D 7//98; Mowed 7/9/98; Burned 7/9/98; Tilled 7//98; Cultivar Kent replications Vigor: Scale of -9, where = dead and 9 = best vigor; Leaf Spot: Scale of -9, where = heaviest and 9 = no leaf spot; Weed Control: Scale of -9, where = heaviest weed infestation and 9 = no weeds present GREENBOOK 000 ENERGY AND SUSTAINABLE AGRICULTURE PROGRAM MINNESOTA DEPARTMENT OF AGRICULTURE

94 FRUITS AND VEGETABLES WILDUNG Table 4. Strawberry Burn Renovation Yield NCROC - 999 998 Renovation 999 Yield Size Treatments lb/0 lb/a Grams/Berry Burn-Mow-Poast.8,90 8.88 Burn-Mow-Till.,5 9.4 Burn.,8 9.7 Burn-Till-Poast.0,98 9.8 Burn-Mow-Till-Poast 0.6,540 8.70 Burn-Poast 0. 0,995 8.4 Mow-Till-Poast 8.5 9,6 8.64 Burn-Till 8.4 9,70 8.8 LSD 5% NS NS NS Cultivar Kent 5 replications 999 Picking season: 6/8/99 to 7/6/99 (6 harvests) Table 5. Strawberry Burn Renovation Yield Lavalier Farm - 999 998 Renovation 999 Yield Size Treatments lb/0 lb/a Grams/Berry Mow-Till-Devrinol. 4,55 8. Burn-Till-Devrinol 0.4,9 7.8 Burn-Till.,0 9.6 Burn.6,58 9. LSD 5% NS NS NS Cultivar Glooscap replications 999 Picking season: 6/0/99 to 7/9/99 ( harvests) Table 6. Strawberry Burn Renovation Yield Lunemann Farm - 999 998 Renovation 999 Yield Size Treatments lb/0 lb/a Grams/Berry,4-D-Mow-Till 6. 7,576 7.,4-D-Burn-Till 9.8,587 8.8 Burn-Till 7.0 8,499 8. Burn 8. 9,798 4.6 LSD 5% NS NS.0 Cultivar Kent replications 999 Picking season: 6/0/99 to 7/4/99 (5 harvests) weeding and cultivating compared to $.85 for flame burning and cultivating). Their propane cost was estimated at $.05/00 linear feet for row. The economics of strawberry burning systems are still being determined, but improves as the machinery is modified and the operators gain experience. Our experience indicates that burning may have some beneficial effects while not affecting strawberry plant health and production. Flaming offers an exciting alternative in a strawberry renovation management program to reduce cultural operations and especially herbicide use. Management Tips. Flame cultivation is a very different approach and concept for most producers so each producer needs to evaluate it on their own farm.. Small hand burners can be purchased at most hardware stores and offer farmers an opportunity to try burning systems on a small scale.. Burning weeds in a new planting can be challenging. When the burner is working correctly it is difficult to see the flame in daylight. Since strawberry plants are so succulent, it is easy to burn and injure the foliage. In addition, it takes several minutes to see burn damage to the strawberry plants so considerable strawberry foliage injury can occur before flame and shields are properly adjusted. However, with careful direction of the flame and proper shielding it can be done effectively. does not destroy organic matter or injure strawberry plant crowns. Initially there was concern about starting straw mulch fires. This risk was minimized by carrying a hand sprayer of water to extinguish whatever fires started. Such fires can be further minimized by burning after rain or irrigation, burning when the humidity is high, or, in the total management system, tilling to incorporate the straw mulch and narrow the row before burning. The cost of flame burning may be lower than many mechanical or hand weeding operations. Back pack flame burners for smaller operations cost less than $50. Larger units such as those used for field crops range in cost from $400 to $700/ row. With these types of units it has been estimated that it costs about $6/A for propane, considerably less than the pesticides they could replace. Using a backpack flame burner, some growers have reduced weed control costs by three-fourths on onions ($7.00 for hand 4. The longer into the summer burn weeding is done, the better production is the following year. 5. Periodic burning for weed control in new plantings does not give as good a weed control as hand weeding and cultivation. 6. Strawberry burn renovation looks promising, potentially reducing cultural operations and herbicide use while not hurting yield. In some cases, reduced GREENBOOK 000 ENERGY AND SUSTAINABLE AGRICULTURE PROGRAM MINNESOTA DEPARTMENT OF AGRICULTURE

95 leaf spot and greater plant vigor occurred following burning. 7. Flame weeding probably was less expensive than traditional hand weeding and cultivation. The economics of burn renovation need to be evaluated further and burner modifications and operator experience should improve operations to the point where the economics will be comparable to traditional renovation practices. Cooperators Stuart Lavalier, Grower, New Hope, MN Mike and Carol Lunemann and family, Growers, Cohasset, MN Keith Mann, Research Plot Coordinator; Kay Sargent, Scientist; Carol Cooper, Junior Laboratory Technician; U of M NCROC, Grand Rapids, MN Flame weeder at work in berries Project Location Contact David Wildung for directions to field plots. Other Resources Flame Engineering, Inc., West Hwy 4, P.O. Box 577, La Crosse, KS 67548, 800-55-469 Peterson, Jean, and Al Sterner, 890 Hwy, Delano, MN 558, 6-97-05. Jean and Al have been using flame weeding for several years and are always very helpful in providing their ideas and encouragement. In fact, it was one of their MDA Field Days that inspired us to pursue this project. Wildung, D.K., K. Sargent, and K. Mann. (999). Flame burning for weed control and renovation with strawberries. Report to North American Strawberry Growers Association. Ten pages. Wildung, D.K., K. Mann, and K. Sargent. (000). Flame weeding in strawberries. In, Proceedings of the Upper Midwest Regional Fruit and Vegetable Conference (pp 5-55) and Proceedings of the 000 Illinois Small Fruit Strawberry School, University of Illinois, Mt. Vernon, IL, pp 95-04. Dave at field day GREENBOOK 000 ENERGY AND SUSTAINABLE AGRICULTURE PROGRAM MINNESOTA DEPARTMENT OF AGRICULTURE