As many tobacco and traditional row crop growers are looking for ways to supplement farm income, vegetables and small fruits are receiving much attention. Due to the potential returns/A, annual plasticulture strawberries have received significant attention. Since this production technique was developed on the West Coast, and is still considered marginal for use in the Mid-South, variety selection, as well as other production practices need to be evaluated. In 1999 and 2000, yield, berry size, and maturity date of ‘Camarosa’, ‘Chandler’, and ‘Sweet Charlie’ strawberries were compared on black and white plastic at the University of Tennessee Plateau Experiment Station located near Crossville, TN.

‘Chandler’ was the most productive variety in this trial, and appears to adapt to a wide range of environmental conditions. Although, ‘Camarosa’ and ‘Sweet Charlie’ produced significantly less fruit than ‘Chandler’ in this trial, there are some production tricks to improve the yield of these two varieties. Planting ‘Sweet Charlie’ 2 to 3 weeks earlier in the fall has been found to aid in plant development, which translates into higher yields in the spring. This is beneficial, since ‘Sweet Charlie’ matures earlier than ‘Camarosa’ and ‘Chandler’, which enable a producer to start harvesting sooner. Also, ‘Sweet Charlie’ offers the possibility of producing fruit in the fall utilizing the annual plasticulture production system. Daytime temperatures in the 70's and nighttime temperatures in the 50's enhance bud and flower development in ‘Camarosa’. Therefore, if row covers can be used to maintain these optimum temperatures for 2 to 3 more weeks longer in the fall, yields of ‘Camarosa’ can be improved next spring. ‘Camarosa’ offers producers a variety that is firm fruited enough to ship.

Plants on the black plastic mulch produced significantly higher yields than plants on white plastic mulch, except for ‘Chandler’, which produced acceptable yields on either color plastic mulch. The white plastic mulch also delayed maturity by up to 8 days. The use of white plastic would have delayed the need to begin frost production, but it also delayed and compressed the production season.

With the present state and uncertain future of the tobacco industry, many growers are looking to vegetable and small fruit enterprises to augment farm incomes. Even traditional row crop farmers are looking to these enterprises to generate some profit. Among the most lucrative of these enterprises is annual plasticulture strawberries, which can produce potential gross returns of over $20,000/A. However, this production system requires significant investments of capital, labor, and management. Establishment of the crop requires an investment of $4,000 to $6,000/A in the fall. Total production costs will range in the neighborhood of $10,000 to $12,000/A.

Much of the information and technology for this production system has originated in other areas of the country. Therefore there has been concerns about the applicability to Tennessee growing conditions. For example, the industry began about 30 years ago in California. Florida producers were able to make some modifications and utilize the technology. North Carolina Researchers began working with the system in the early 1980's, and have developed a significant industry in the coastal plains and Piedmont. Charlie O’Dell has worked over the last 10 years adapting the system to the higher elevations of Virginia. However, the system is still considered marginal for use in the Mid-South (Kentucky, Tennessee, and higher elevations of Virginia). One of the concerns about this production system has been related to variety selection. The varieties used in this production system were bred in California and Florida, and little is known about there performance in Tennessee. Another issue has been concern of flower development during the warm spells in late winter and early spring resulting in the necessity to begin frost protection earlier than desired. Therefore, in 1999 and 2000, yield, berry size and maturity date of three varieties for use in the plasticulture production system were compared on black and white plastic at the University of Tennessee Plateau Experiment Station located near Crossville, TN.

The plot area had been used for snap bean tillage research earlier in the season. Due to poor stands, the test had been abandoned; therefore the entire area was mowed in preparation for use. To conserve moisture, the plot area was not plowed until the day before fumigation of the plots. The entire area was moldboard plowed at a depth of 6 to 8 inches on September 2, 1999. The soil was disked early on the morning of September 3. Two hundred lb/A of 15-15-15 and 300 lb/A of 0-46-0 were broadcast and incorporated with a rototiller the same day. All beds were fumigated with methyl bromide / chloropicrin 67:33 (MB 67:33) at 400 lb/A. The MB 67:33 was injected 7 inches deep during bed formation, and covered immediately with plastic mulch film. Half of the field was covered with black plastic mulch and the other half was covered with white plastic mulch. Holes were punched in the plastic mulch on September 20, 1999, 1 inch of water was applied through the trickle irrigation system on September 22, and strawberry transplants were set on September 25. Varieties evaluated included ‘Camarosa’, ‘Chandler’, and Sweet Charlie’. An additional inch of water was applied on October 3, and 0.5 inches was applied on each of October 27 and 28.

Covertran® crop covers (0.5 oz/yard²), to promote plant development and aid in freeze protection, were applied on March 11, 2000. Overhead irrigation was utilized for frost / freeze protection during March and April. Ten lb/A of both calcium nitrate and potassium nitrate were applied through the trickle irrigation system on April 7, 20, and 27 in 0.25 inches of water, and on May 5 and 15 in 0.5 inches of water. A total of 50 lb/A N was applied in the spring. Elevate at 0.75 lb ai/A was applied for Botrytis control and Danitol at 0.2 lb ai/A was applied for spittle bug control on April 29. Harvest began on April 25 and continued every 2 to 3 days until May 30, for a total of 16 harvests. Berries from each harvest were counted and weighed. Experimental design was a randomized complete block with 4 replications. All data were analyzed using ANOVA procedures, and means of dependent variables found to be significant at the 0.05 level of probability were separated using Student Newman Keuls mean separation technique.

Overall the season was mild, therefore the plants that were transplanted a week to 10 days later than recommended, developed and yielded quite well. However, when averaged across varieties, plants on the black plastic mulch produced significantly greater yields than plants on the white plastic mulch (Table 1). Some preliminary temperature data suggests that the temperatures were warmer under the black plastic mulch than under the white plastic mulch (data not shown). These warmer temperatures may have been beneficial, especially since the plants were set later than generally recommended. Plants on white plastic mulch produced larger berries than plants on black plastic mulch. Plants on the black plastic mulch produced more berries, so those plants might have benefitted from additional N in order to maintain fruit size. Spring N applications started later than desired, and less total N was applied than would normally be recommended (80 lb/A N vs. 120 lb/A N).

When averaged across plastic mulch colors, ‘Chandler’ produced significantly higher yields than both of the other varieties, and ‘Camarosa’ produced more than double the yields produced by ‘Sweet Charlie’ (Table 1). Although no hard evidence or actual yield data had been generated in Tennessee, these results were suspected from previous observations. ‘Chandler’ appears to be much more adaptable to a wider range of environmental conditions than the other two varieties. Average berry weight was not significantly different among varieties.

‘Chandler’ on black and white plastic mulch produced significantly greater yields than any other variety and plastic mulch combination (Table 2). ‘Camarosa’ on black plastic mulch produced significantly greater yields than ‘Camarosa’ on white plastic mulch and ‘Sweet Charlie’ on either color plastic mulch. ‘Sweet Charlie’ on white plastic produced the lowest yields. Plants of ‘Camarosa’ and ‘Chandler’ on black plastic mulch produced smaller berries that all other variety and plastic mulch combinations. These two treatments would likely have benefitted from earlier spring applications of N, as well as more N fertilization.

Figure 1 illustrates the maturity of the different variety and mulch combinations. ‘Sweet Charlie’ on black plastic mulch, followed by ‘Sweet Charlie’ on white plastic mulch, were the first treatments to produce fruit. ‘Camarosa’ and ‘Chandler’ on black plastic mulch were the next treatments to begin production, while these two varieties on white plastic mulch were 8 days later than the earliest treatment.

Figure 2 illustrates average berry weights of each variety and mulch combination. Berry weight tended to decrease as the season progressed. Fruit of all treatment combinations except fruit of ‘Sweet Charlie’ on black plastic mulch increased in weight for the first 2 to 3 weeks, then started to decrease in fruit weight.

‘Chandler’ was the most productive variety in this trial, and appears to adapt to a wide range of environmental conditions. Planting ‘Sweet Charlie’ 2 to 3 weeks earlier in the fall has been found to aid in plant development, which translates into higher yields in the spring. Maintaining optimum temperatures for 2 to 3 more weeks longer in the fall can improve yields of ‘Camarosa’ next spring.

Table 1. Yield and average berry weight of strawberry varieties (averaged across variety or mulch color) grown on black and white plastic mulch at The University of Tennessee, Plateau Experiment Station, Crossville, 1999-2000.

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Copyright © 1999 by The University of Tennessee. All rights reserved.

This research represents one season's data and does not constitute recommendations.  After sufficient data is collected over the appropriate number of seasons, final recommendations will be made through research and extension publications.