HortTechnology, January - March 2001:69-71
Performance of Strawberry Cultivars on Fumigated and Nonfumigated Soil in Florida
C.K. Chandler1, D.E. Legard1, and J.W. Noling2
1Gulf Coast Research and Education Center, University of Florida, 13138 Lewis Gallagher Road, Dover, FL 33527
2Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850
Florida Agricultural Experiment Station Journal Series no. R- . We are grateful to James C. Sumler, Jr. for his technical assistance on this trial.
Additional index words. Chloropicrin, methyl bromide, Fragaria Hananassa
Summary. Five strawberry (Fragaria Hananassa Duch.) cultivars in the 1995-96 season and four cultivars in the 1996-97 season were grown in the annual hill plasticulture system, with and without pre-plant soil fumigation (98% methyl bromide / 2%chloropicrin at a rate of 240 lbs per treated acre [269 kg/ha]). These trials were established on land that had been cropped with strawberries for 20 years. Significant cultivar x fumigation interactions were not detected for either yield or average fruit weight. Plants grown in nonfumigated soil produced 54% and 68% of the yield obtained from the plants grown in fumigated soil in 1995-96 and 1996-97 respectively, and the average fruit weight from plants grown in nonfumigated soil was also reduced, compared to that of plants grown in fumigated soil. Plant mortality was # 3% in the nonfumigated plots. These results indicate that strawberry productivity in Florida can be substantially reduced by growing plants in soil that has not been fumigated prior to planting, even in the absence of lethal pathogens.
For over 20 years, preplant soil fumigation with methyl bromide-chloropicrin (MBC) has been the standard method used by Florida strawberry growers to prevent soil-borne pest and disease problems. MBC has been an extremely effective biocide on the sandy soils of Florida, and is undoubtably a major reason why west central Florida is currently one of the most productive winter strawberry production areas in the world (Hancock and Scott, 1988). No other single, labeled pesticide has been shown to control the full range of soil-borne strawberry pests and pathogens as consistently and effectively as MBC (Himelrick and Dozier, 1991). Nematodes and weeds can be significant pests in Florida strawberry fields (Overman, 1963; Albregts and Howard, 1983), but lethal soil-borne pathogens, such as Phytophthora and Verticillium spp., have only caused sporadic problems (Howard et al., 1985; Legard et al., 1997). In studies conducted in California where nematodes and lethal pathogens were not a problem and weeds were removed regularly, plants grown in MBC fumigated soil produced significantly higher fruit yields than did plants grown in nonfumigated soil (Larson and Shaw, 1995; Shaw and Larson, 1996; Fort et al., 1996). The California researchers attribute this beneficial effect to a reduction in a highly variable complex of sublethal or competitive soil microorganisms.
Because of the impending ban on the use of methyl bromide in the U.S., beginning January 1, 2005, there is an urgent need to develop alternatives that are safe, effective, and economically viable. One potential alternative to MB fumigation is to use cultivars that are productive despite attack by soil-borne pests and pathogens. Galletta and Bringhurst (1990), in their chapter on strawberry management, list a number of cultivars that are resistant to the potentially lethal pathogens Phytophthora fragariae C.J. Hickman var. fragariae and Verticillium albo-atrum Reinke & Berthier, but they make no mention of any cultivars being resistant to sublethal soil organisms. In fact, the results of several recent studies in California (Larson and Shaw, 1995; Shaw and Larson, 1996; Fort et al., 1996) suggest that there may be little promise for developing cultivars specifically adapted to the sublethal effects of nonfumigated soils. The purpose of our study was to 1) determine the importance of sublethal soil effects on strawberries in Florida, and 2) determine if there is significant variation in tolerance to a nonfumigated soil environment (free of identifiable lethal pathogens) among the standard or new cultivars currently being grown in west central Florida.
Materials and Methods
Field trials were conducted at the University of Florida=s Gulf Coast Research and Education Center at Dover (15 miles [24 km] east of Tampa) during the 1995-96 and 1996-97 fruiting seasons. The trials were established in an area that had been annually fumigated (with MBC) and cropped with strawberries for the past 20 years. They consisted of split plot experiments where the main plots were single 75 ft (23 m) or 32 ft (10 m) long x 2 ft (0.6 m) wide raised beds that were fumigated or not fumigated with methyl bromide (98%)/chloropicrin (2%) at a rate of 240 lbs per treated acre (269 kg/ha). Each treatment was replicated four times in a completely random design. Within the main plots there was one subplot of 12 plants for each of eight entries in 1995-96 and 14 plants for each of four entries in 1996-97 (Table 1). The eight entries in 1995-96 included five cultivars, two of which came from both northern and southern latitude nurseries, and one of which was planted as both a bareroot and a plug plant. Propagation site and plant type were included as factors in this trial because they are know to affect plant vigor and therefore may influence a cultivar=s ability to tolerate nonfumigated soils (Bish et al., 1997; Chandler et al., 1989). The 1995-96 and 1996-97 trials were planted on October 18 and October 15 respectively, and were treated according to the commercial recommendations described by Chandler et al. (1994). Fruit from each plot was harvested twice weekly during the fruiting season, which ran from December through the end of March. Fruit was graded, counted, and weighed. Marketable yield and average fruit weight data were analyzed by analysis of variance. Plant mortality was recorded at the end of March.
Results and Discussion
During the 1995-96 season, there was greater mortality among plants grown in the fumigated plots than in the nonfumigated plots. A total of 25 plants (7%) died in fumigated plots by the end of the season compared to only 11 plants (3%) in the nonfumigated plots. (Mortality was <1% in 1996-97.) The plants grown in fumigated soil were generally more vigorous than the plants grown in nonfumigated soil, a characteristic that may have actually made them more vulnerable to Colletotrichum crown rot (caused by Colletoctrichum gloeosporioides Penz.). High levels of crown rot have been observed when strawberry plants are growing vigorously due to excessive nitrogen fertilization or warm weather (C.M. Howard, personal communication). We suspect that the plants that died were already infected (but asymptomatic) at the time of transplanting. That would mean that the plants, not the soil, were the source of the problem.
Fumigation and genotype treatment effects were highly significant for yield and fruit size in both seasons (Table 2). However, significant genotype x fumigation interactions were not detected. This indicates that all of the genotypes were similarly affected by the nonfumigated soil environment. The total marketable fruit yield obtained from the plants grown in the nonfumigated soil was only 54% and 68% of the yield obtained from the plants grown in the fumigated soil in 1995-96 and 1996-97 respectively, and the average fruit weight from plants grown on nonfumigated soil was 10% and 6% less than the average fruit weight from plants grown on fumigated soil in 1995-96 and 1996-97 respectively (Table 3). These results are very similar to those that have been obtained in California (Larson and Shaw, 1995, and Shaw and Larson, 1996), and are indicative of important sublethal soil effects. The effects were greatest in 1995-96, despite the fact that more plants died in the fumigated plots than in the nonfumigated plots.
Propagation site (Florida vs Canada for >Sweet Charlie= and >Rosa Linda=) and plant type (plug vs bareroot for >Sweet Charlie=) did not have a significant influence on ability to tolerate nonfumigated soils. >Sweet Charlie= plug plants grown in nonfumigated soil had the lowest fruit yield of any entry in the 1995-96 trial, but their yield was not statistically different (P=.05) than the >Sweet Charlie= plants set as bareroot transplants.
From a breeding perspective, the results obtained from this two-year study are discouraging, yet not unexpected. We feel that the conclusion Larson and Shaw made in their 1995 paper C that little opportunity exists within the Univ. of California germplasm for developing cultivars specifically adapted to sublethal effects of nonfumigated soil C is also applicable to the University of Florida germplasm collection. The results of our study show clearly that total marketable yield and average fruit weight can be reduced significantly when strawberry plants are grown in nonfumigated soil in west central Florida. Current fumigation research on strawberries in Florida is focused on the use of combinations of chloropicrin and dichloropropene to control nematodes and other sublethal microorganisms.
Albregts, E.E. and C.M. Howard. 1983. Weed control in the strawberry fruit production field. Proc. Fla. State Hort. Soc. 96:75-76.
Bish, E.B., D.J. Cantliffe, G.J. Hochmuth, and C.K. Chandler. 1997. Development of containerized transplants for Florida’s winter production system. Acta Hort. 439:461-468.
Chandler, C.K., E.E. Albregts, C.M. Howard, and A. Dale. 1989. Influence of propagation site on the fruiting of 3 strawberry clones grown in a Florida winter production system. Proc. Fla. State Hort. Soc. 102:310-312.
Chandler, C.K., E.E. Albregts, J.F. Price, and T.E. Crocker. 1994. Growing strawberries in Florida: guidelines for the 1994-95 season. Citrus and Vegetable Magazine, August:10-14.
Fort, S.B., D.V. Shaw, and K.D. Larson. 1996. Performance responses of strawberry seedlings to the sublethal effects of nonfumigated soils. J. Amer. Soc. Hort. Sci. 121:367-370.
Galletta, G.J. and R.S. Bringhurst. 1990. Strawberry management, p.83-156. In: G.J. Galletta and D.G. Himelrick (eds.) Small fruit crop management. Prentice Hall, Englewood Cliffs, N.J.
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Table 1. Entries in field trials at GCREC-Dover, Florida
z Plug plants
Table 2. Analysis of variance for trials at Dover, FL involving four or five strawberry cultivars and two preplant soil fumigation treatments.
|F x G||0.57||0.81||1.59||0.49|
**, *** Significant at P=0.05 or 0.01 respectively; mean squares fro yield have been multiplied by 10-6 for ease of presentation.
Table 3. Total season marketable yield and average fruit weight of strawberry cultivars grown at Dover, FL in fumigated and nonfumigated soil.
|Fumigation||Yield (g/plant)||Fruit Weight (g)|
|+||417 Ay||530 A||17.4 A||17.9 A|
|-||227 B||363 B||15.6 B||16.8 B|
z (-) and (+) indicate no soil fumigation and preplant soil fumigatin with 240 lbs per treated acre (269 kg.ha) of 98 methyl bromide : 2 chloropicrin (wt/wt) respectively.
y Mean separation within columns by Fisher's protected LSD at P< 0.01