Fruits and Vegetables Wildung 111 Flame Burning for Weed Control and Renovation with Strawberries ries Principal Investigator Dr. David Wildung University of Minnesota North Central Research and Outreach Center 1861 East Hwy 169 Grand Rapids, MN 55744 218-327-4711 Itasca County Project Duration 1999 to 2001 ESAP Contact Jean Ciborowski 651-297-3217 Project Summary Weed control is a major limiting factor in the production and longevity of strawberry plantings. It is expensive and, if weeds are not controlled, they can greatly reduce 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. Making strawberry production systems more sustainable will benefit both the producer and the consumer. Dave WildungJs project looks at flame burning for weed control in newly established strawberry plantings and flame burning at strawberry renovation for weed control and reducing cultural practices in existing plantings. 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. 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: Keywords flame burning, strawberry, weed control 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 at their smallest. j j North Central Research and Outreach Center (NCROC), Grand Rapids, MN. Lavalier Berry Farm, near Grand Rapids, MN. A commercial strawberry and blueberry pickyour-own and ready picked fruit farm. There are approximately four acres in strawberry production. Flame weeder at work in berries
112 Fruits and Vegetables Wildung j Luneyberries Berry Farm, near Grand Rapids, MN. A commercial strawberry pick-your-own and ready picked fruit farm. The Lunemanns currently have over five acres in production. Two propane burners were built by NCROC staff for this project. The first, built in 1997, was used in small plot situations. It was built on wheels so that it could be pulled from plot to plot and cost o140 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 the flame, a bar in front of the unit that pushes thick strawberry foliage down for better flame penetration during burn renovation, a 30 lb propane tank, and cost o500 to construct. In 2000, the second unit was further modified with larger burner heads, three portable 30 lb propane tanks, a better hose and control system, and a better system for containing heat over the strawberry row. Weed burning in newly established strawberry plantings was done on NCROC plots in 1997, 1998, and again in 1999. 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 bentj was used for these studies. Field plot burn studies at renovation were begun at NCROC in 1997, two grower sites were added in 1998 and expanded in size in 1999. The treatment mix varied slightly at each location depending upon each growersj standard renovation practices. Treatments at NCROC compare traditional renovation to burning and using burning to replace one of the normal renovation practices - mowing, herbicide use, and/or tilling. The cultivar bentj was used for studies at NCROC and at one grower site. GlooscapJ was used at the second growerjs farm. Each treatment plot was a single row ten feet long. Standard planting, spacing, fertilization, and pest management practices were followed at all locations. Results Strawberry vigor, percent plant stand, and leaf spot disease ratings were taken in fields before and following burning and during the fruiting season. cigor and leaf spot ratings were on a 1 to 9 rating scale with 9 being most vigorous or no leaf spot. Grass and broadleaf weed control was evaluated on a 1 to 9 rating scale with 9 being best and 1 being no weed control. Crop yield and fruit size were taken each year following the burn treatments. F+$"'=##)'C4"-$40'."'P#9'30("-."%,'(-'PCEMC<$ Burning to control weeds in new plantings was not as effective as normal cultivation and hand weeding. The 1999 weed cultivation burns were done on a larger scale, even so, results in 2000 (Table 1) were similar to 1998 and 1999 results. The hand weeded control produced 11,278 lb/a of berries while burn cultivated plots produced 6,201 and 6,894 lb/a (about 60m of the hand weeded control). In the 1999-2000 study, leaf scorch from flame burning was significantly less in the burn cultivated plots. Plant stand was also less in burn treatments compared to hand weeding. Strawberry fruit size, percent early harvest 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 August. Seasonlong burn cultivation resulted in the best yields being produced when burn cultivation was used. Burning, while not as effective, was less labor intensive and costly than hand weeding. Table 1. Burn Weed Control in New Plantings - 2000 Growth and Production )=064F0;4 Hand weed Burn All Season Burn Until 8/15 '"h 10.4 6.3 5.7 2.4 S>03: + 11,278 6,894 6,201 2,591 5=2>4 D>T0 ^FL 5=2>4 13.5 12.2 R V6=3< Q6=P014 18 15 11 #L''!""" Kent planted in 1999 and burn cultivated or hand weeded during the 1999 season. Early Season: 6/30-7/6/00 (3 Harvests), Total Season 6/30-7/20/00 (7 Harvests) 8.9 R D46;: 80 71 Burning weeds in new plantings 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 plants. In addition, it takes several minutes to see burn damage to the strawberry plants so considerable plant injury can occur before flame and shields are properly adjusted. As the plants grow, both flame and shields need to be adjusted away from the plant canopy. Strawberry plant and runner growth can be uneven in the row and burning will quickly kill any strawberry 76,06O D?7=?@ 6.8 7.5 0.2 B=76:,06P01 ^=61101 7.6 7.1 U00:1 7.5 7.5
runner outside the shield. This problem was reduced by using a small metal finger in front of the shield that moved the runners into the strawberry row before the flame could damage them. It is also impossible to burn weeds that develop within the strawberry plant canopy itself. These weeds have to be hand weeded out. This factor is probably most responsible for the reduction in total yield and plant stand we observed in the burn treatments. F+$"' E#"4:(-.4"'."'!,-(/0.,7#) 30("-."%,< Burning studies in 1997 resulted in a slight increase in strawberry plant vigor, no change in plant stand, less leaf spot, larger fruit size and greater fruit production than the control, which was renovated in the traditional way. Given these promising results, the 1998 burn renovation treatments emphasized replacing various steps in the traditional renovation system with burning. Since grassy weeds were most prominent, Poast herbicide was used in combination with the renovation treatments. Strawberry plant growth and production in 1999 for all burn treatments was equal to, and in most treatments was greater than, the traditional renovation treatment (Mow- Till-Poast). No negative effects from burn renovation were evident. Broadleaf weed control was equal to or better than the traditional renovation treatment while grass weed control was significantly better in the treatments where Poast herbicide was used. The 1999 burn renovation treatments were similar to the 1998 treatments except that Devrinol was used in place of Poast herbicide. In the fall of 1999, it was observed that in the treatments that had not been tilled the strawberry rows seemed to exhibit increased stand over their tilled comparison treatments. The higher stand in the non-tilled plots did not result in greater production in 2000 (Table 2). In fact, the lowest yield was produced in the burn only treatment that had no-tilling or Devrinol applied (11,248 lb/a). When tilling was done and Devrinol applied, burn treatments were better than the traditional mow/till/devrinol treatment (15,249 lb/a compared to 14,035 lb/a } Table Fruits and Vegetables Wildung 113 Table 2. Strawberry Burn Renovation, 2000 Yield and Growth Effects )=064F0;41 Burn/Mow/Till/Devrinol d Burn/Till/Devrinol e Mow/Till/Devrinol f Burn/Mow b Burn/Till c Burn/Mow/Till g Burn a S>03: '"h + 14.1 14.0 12.9 12.4 12.0 10.3 15,365 15,249 14,035 13,854 13,509 13,072 11,248 ^=6F1L 12.3 11.5 13.9 13.2 10.8 10.0 1.8 31 30 26 17 31 30 30 9 71 79 72 81 65 68 74 #L'&L"" Early Season 6/30-7/6/2000 (3 Harvests), Total Season 6/30-7/20/2000 (7 Harvests) Treatments: a Burned 7/30/99 b Burned 7/30/99; mowed after burning 8/3/99 c Burned 7/30/99; tilled 8/5/99 d Burned 7/30/99; mowed after burning 8/3/99; tilled 8/5/99; Devrinol 8/26/99 e Burned 7/30/99; tilled 8/5/99; Devrinol 8/26/99 f Mowed 8/3/99; tilled 8/5/99; Devrinol 8/26/99 g Burned 7/30/99; mowed after burning 8/3/99; tilled 8/5/99 Table 3. Strawberry Burn/Till Renovation, 1999-2000 )=064F0;41 Burn/Till/No Devrinol a Burn/Till/Devrinol b Burn/No-till/No Devrinol c Burn/No-till/Devrinol d No-till S>03: '"h + 9.8 9.6 8.1 10,645 10,409 8,829 7,901 ^=6F1L 12.3 11.5 11.2 Early Season 6/30-7/6/00 (3 Harvests), Total Season 6/30-7/20/00 (7 Harvests) Treatments: a Burned 7/30/99; tilled 8/5/99; b Burned 7/30/99; tilled 8/5/99; Devrinol 8/26/99; c Burned 7/30/99; d Burned 7/30/99; Devrinol 8/26/99 20 27 11 24 6 71 69 57 #L'&L"" 2). In a second study conducted in 1999 in which burning was done with and without tilling and with and without the application of Devrinol herbicide the tilled plots were both better than the no-till plots (Table 3). Both burn and till plots produced over 10,000 lb/a while the no-till plots produced 8,829 and 7,901 lb/a. In this study use of Devrinol herbicide had no effect on final yield. In both of these studies burning had no negative effect on the growing plants or yield. No-till plots while exhibiting a slightly greater plant stand did not result in an increase in final yield. Use of Devrinol herbicide showed a positive effect in one study but not in the other. Because of promising results at NCROC, on-farm studies were initiated at two grower cooperator locations in the
114 Fruits and Vegetables Wildung summer of 1998. At each location burning replaced one of the traditional cultural practices the grower used at renovation. By fall, significant reduction in leaf spot was observed in the burn treatments at both locations. At one farm, GlooscapJ did not show any vigor or stand differences, while at the other farm bentj was significantly more vigorous in the burn treatments compared to traditional renovation. Table 4. Strawberry Burn Renovation, Lavalier Farm 2000 )=064F0;41. K'---N Burn Burn/Devrinol Mow/Devrinol!""".S>03: '"h + 7.2 6.6 7,953 7,890 7,165 D>T0.^FL 7.7 8.2 6.9 0.8 Q6=P014 37 41 37 7.1 6.9 6.7 Cultivar - Glooscap - 3 Replications Treatments: 2, 4-D - 7/13/99, Mowed - 7/21/99, Burned - 7/21/99 Picking Season 7/5-7/14/00, 3 Harvests; Early Season 7/5/00 70 70 (L![,06O DG74 7.8 7.7 7.8 Table 5. Strawberry Burn Renovation, Lunemann Farm 1999-2000 )=064F0;41!""".S>03: '"h + D>T0 ^FL Q6=P014 '"L!- '--- 7.8 8.1 8.2 8.1 (L![!""",06O. DG74 '"L!- (L![ '---!""" '"L!- '--- (L![!"""!""". U00: H7;4=73 ^=61101 B=76:306O 2, 4-D/Mow/Sinbar Mow 2, 4-D/Burn Burn 2, 4-D/Mow Burn/Sinbar 2, 4-D/Burn/Sinbar Mow/Sinbar 23.1 22.2 21.7 20.8 20.4 20.4 20.2 19.7 25,174 24,177 23,587 22,614 22,246 22,198 21,999 21,421 14.9 15.4 15.2 15.2 16.1 13.9 14.2 14.9 13 15 22 17 14 16 22 15 9.0 9.0 9.2 9.1 9.1 9.1 9.2 9.0 6.3 6.0 7.0 6.3 7.0 6.0 0.7 7.7 76 73 77 73 74 73 72 82 86 84 80 84 82 84 Cultivar Glooscap 3 Replications Picking Season 7/03 7/21/00, 9 Harvests; Early Season 7/03 7/07/00, 3 Harvests Treatments: 2, 4-D - 7/19/00, Mowed - 7/28/99, Burned - 7/28/99 Tilled - 7/28/99, Fertilized - 7/29/99, Sinbar - 7/29/99 Weed control was good at both farms on all treatments. During harvest, vigor and stand ratings were equal for all treatments at both farms. 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. At the Lavalier farm, traditional renovation resulted in the best production while at the Lunemann farm, production was the least for the traditional renovation treatment. At both farms the differences were not significantly different and burn renovation did not harm the plantings in any way. Plant growth and production at the Lunemann farm was much greater due to a vigorous spring fertility program. In 1999, burn renovation treatments were repeated at both grower locations on a larger scale using the tractor mounted unit on.16 acre and.33 acre, respectively. By fall, no growth differences were noted except for reduced leaf spot infection where burning was used. iield, berry size, plant vigor, stand and leaf spot are presented for the 2000 fruiting season at the Lavalier Farm (Table 4) and the Lunemann Farm (Table 5). At the Lavalier Farm, burning with or without an application of Devrinol herbicide produced a larger crop than the traditional mow/devrinol treatment. Berry size and plant vigor were also slightly better on the burn treatments (Table 4). At LunemannJs, treatment combinations included mowed and burned plots with and without 2, 4-D herbicide applied before mowing or burning, and mowed and burned plots with and without Sinbar herbicide applied after renovation (Table 5). Fruit production and fruit size at the Lunemann farm were very heavy for the season, but no single component of renovation seemed to result in better production than another. Again burning resulted in yields equal to traditional mowing renovation. Plants in the burn treatments also showed slightly greater vigor and significantly less leaf spot than mowed treatments in the fall after renovation (10/29/99 } Table 5). However, by the beginning of the fruiting season (6/27/00) vigor and leaf spot ratings were the same. Weed control in all renovation treatments was similar. The same situation that makes burning difficult in new strawberry plantings appears to aid burning for strawberry renovation. Strawberry foliage and weed growth is especially vulnerable to flaming. Burn renovation is fast to not destroy organic matter or injure strawberry plant
Fruits and Vegetables Wildung 115 crowns. Initially there was concern about starting straw mulch fires. However, these fires were relatively minor especially with the burner as modified in 2000. Flames are confined to the plant canopy and few mulch fires occur. 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. In all instances, burning at renovation has not been harmful with fruit production being equal to or greater than conventional methods of 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 and leaf scorch development. The results of 1999-2000 renovation studies at NCROC would indicate that tilling at renovation is still critical to obtaining optimum production (Tables 2 and 3). Tilling may provide some soil aeration or throw some soil around the remaining crowns at renovation. In these studies there did not seem to be any significant advantage to using herbicides such as Devrinol, 2, 4-D or Sinbar at renovation particularly if the fields had been maintained in good weed free conditions. While use of herbicides is an individual growers management choice, in some situations, burning at renovation could certainly replace the traditional renovation practices of mowing and herbicide application.!24"45.2,'4;'f+$"."%< The first tractor mounted liquid propane unit used in these studies was built in 1999 at a cost of o500. Modifications to the unit in 2000 added a heat shield to protect the tractor operator and propane tanks, larger burner heads, a heat blanket to confine flame around the strawberry plant canopy, and two optional fuel tanks for more operating range and portability. The cost of these modifications was about o600. This unit, as set up, will do an excellent job of burn renovation and could be built for less than the o1,100 we spent. In 2000 studies, when burn renovating larger areas we were able to travel between.63 to. mph including turning time. On three renovation burns of over.2 acre fuel consumption averaged about 150 lb of propane per acre. Propane is sold on a sliding scale based on the number of pounds purchased. The current cost is rapidly increasing and varies depending upon where you live. In our area, the cost for up to 30 lb was o.73/lbd while at 90 lb the cost was o.44/lb. Because of the sliding propane costs and the tendency of smaller tanks (30 lb or less) to heat up excessively, the machine should utilize the largest tank practical. With the modifications made in the 2000 unit, we were able to eliminate tank heating and wind blowing the torches out, to confine the heat to the plant canopy allowing for the entire row to be burned in one trip, and practically eliminate undesirable straw mulch fires } all problems encountered with the first unit. While we had our best success when burning on clear, hot, windless days with this unit, we were able to successfully burn renovate when conditions were cloudy with a heavy dew on the plant canopy. Management Tips 1. Flame cultivation is a very different approach for most producers so each producer needs to evaluate it on their own farm. 2. Small hand burners can be purchased at most hardware stores and offer farmers an opportunity to try burning on a small scale. 3. 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. With careful direction of the flame and proper shielding, it can be done effectively. 4. Periodic burning for weed control in new plantings does not give as good weed control as hand weeding and cultivation. Dave at a field day
116 Fruits and Vegetables Wildung 5. Strawberry burn renovation had resulted in no reduction in fruit production compared to traditional methods of renovation (mowing). In most instances, burn renovation has resulted in greater strawberry plant vigor and less leaf diseases than mowing. 6. Burn renovation provides good weed control and could replace or reduce herbicide use in a traditional renovation system. 7. Burning at renovation will not replace rototilling. Rototilling at renovation appears necessary to obtain optimum production. 8. Propane use of about 150 lb/a with tractor field speed of between.6 to.8 mph was obtained. The economics of burn renovation improve with each use. 9. The burning unit as modified in 2000 will do an excellent job of strawberry burn renovation. Cooperators 82"2%Q7C7.-$5B Grower, New Hope, MN P-V$%7#/%)*.%Q"#$+7##%b%=7+-.1B%Growers, Cohasset, MN _$-23%P7##B Research Plot Coordinator, University of Minnesota } NCROC, Grand Rapids, MN :#6$.7%A-#$32B Junior Laboratory Technician, University of Minnesota } NCROC, Grand Rapids, MN Project Location Contact David Wildung for directions to field plots. Other Resources \.7+$%4#6-#$$5-#6B%>#;E West Hwy 4, P.O. Box 577, La Crosse, bs 648, 800-255-2469. <$2$59*#B%!$7#B%7#/%:.%82$5#$5E 8910 Hwy 12, Delano, MN 55328, 612-972-2052. Jean and Al have been using flame weeding for several years and are always very helpful in providing their ideas and encouragement. P-##$9*27%\5"-2%7#/%c$6$270.$%`5*?$59%:99*;-72-*#E Ham Lake, MN.