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. However, due to the phase out of methyl bromide mandated by the U.S. EPA, growers are looking for alternative soil fumigants. Therefore, in 1999 through 2000, ‘Chandler’ strawberries receiving selected soil fumigation treatments were evaluated at the University of Tennessee Plateau Experiment Station located near Crossville, TN.

The Tri-Form 35 treated plots produced yields comparable to or greater than the standard MC 67:33 fumigated plots. However, the Tri-Form 35 treatment tended to delay maturity 2 to 3 days, as compared to all other treatments. Lack of weed control was expected to be a major concern with the Tri-Form 35 treatment; however, weed control was not an issue in this test. Hendrix and Dail has conducted some research that has shown very acceptable weed control from Tri-Form 35 if injected at least 12 inches below the top of the bed. Basamid treated plots overcame the delay and produced quite well. Had they not been later, they might have produced yields greater than the MB 67:33 and Tri-Form 35 plots. However, it appears that Basamid will never be labeled for use in food crops. This data suggests that for the time being, Tri-Form 35 will provide an alternative to methyl bromide for soil fumigation in plasticulture strawberries.

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 before the crop will be harvested. Total production costs will range in the neighborhood of $10,000 to $12,000/A.

However, at the same time producers are considering growing annual plasticulture strawberries, growers are faced with the loss of methyl bromide as a soil fumigant. According to the timetable of the Montreal Protocol, which has been adopted by the U.S. EPA, the use methyl bromide as a soil fumigant is to be phased out by 2005. Due to the phase out and mandated reductions in use, methyl bromide prices have almost doubled in the last two years. The combination of methyl bromide and chloropicrin (67:33) has provided excellent broad spectrum control of weeds, insects, and diseases. However, the broad spectrum efficaciousness of the proposed replacements are questionable. Therefore, in 1999 through 2000, yield, berry size, and maturity date of ‘Chandler’ strawberries receiving selected soil fumigation treatments were evaluated 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. Fumigation treatments were applied immediately before or during bedding and the laying of the plastic mulch film. Fumigation treatments included: methyl bromide / chloropicrin 67:33 (MB 67:33) at 400 lb/A, 1,3 dichloropropene / chloropicrin (Tri-Form 35, also known as Telone C-35) at 40 gallons/A, dazomet (Basamid) at 400 lb/A, and metam sodium (Vapam) at 100 gal/A, along with and untreated check. The MB 67:33 and Tri-Form 35 treatments were injected 7 inches deep during bed formation. The Basamid and Vapam treatments were applied to the soil surface and incorporated at a depth of 4 to 6 inches with a rototiller immediately before bed formation. 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 ‘Chandler’ transplants were set on September 24. Due to the dry weather experienced during the late summer and fall, soil moisture was not sufficient to activate the Basamid, which is manufactured in a granular form. Therefore, when the trickle irrigation was applied, the Basamid began to "gas off’. This resulted in significant injury and subsequent death of plants set in the Basamid treatment. The number of dead plants were counted and dead plants were replaced on October 2. An additional inch of water was applied on October 3, and 0.5 inches was applied on each of October 27 and 28.

During the middle of January, plant development and weed control were evaluated. The diameter of plant canopies were measured and used to calculate plant area; the diameter of plant crowns were measured; and the number of holes with emerging weeds were counted. Covertran® crop covers (0.5 oz/yard²), to promote plant development and aid in freeze protection, were applied on January 16, 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 28 and continued every 2 to 3 days until May 30, for a total of 15 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. Even the replacement plants that were set in early October developed and produced quite well. As mentioned above, the Basamid treatment caused significant injury, and 88% of the plants had to be replanted (Table 1). By January, those plants were still smaller than the rest of the treatments, but they were healthy and growing. The plants from plots receiving MB 67:33 and Fri-Form 35 were large and more vigorous than plants from the Vapam treatment or the untreated check. All of the plots receiving fumigation were weed free in January, and remained so throughout the growing season. Light infestations of winter annuals (henbit and hairy bittercress) were observed in the untreated check plots. Concern over the amount of plant development, prompted the application of the row covers, which were applied on January 16 and left in place until the last week in April.

‘Chandler’ strawberries plants fumigated with MB 67:33, Tri-Form 35, or Basamid produced significantly higher yields than the non-fumigated strawberry plants (Table 2). This yield increase was not due to weed control since relatively little weed pressure was observed. Therefore it is surmised that the yield increase was a result of disease control. This is very interesting considering that this plot area had never been in strawberry production. As has been reported in many trials, plots treated with Vapam produced in the range between the MB 67:33 and the untreated check plots. Berries from the Basamid fumigated plots were larger than berries from the other fumigated plots. The main explanation for this response is that Basamid contains significant amounts of nitrogen, and a rate of 400 lb/A adds about 60 lb of N/A. There have also been reports that later planted strawberry plants produce earlier and larger fruit. The non-fumigated plots produced berries that were significantly larger than the plots that were fumigated with Tri-Form 35. This appears to be related to the fact that the Tri-Form 35 treated plots produced a significantly larger number of berries, and there was not enough N available to maintain berry size.

Yields of ‘Chandler’ strawberry plants treated with various soil fumigation treatments responded similarly (Figure 1). However, no fruit was harvested from the plants treated with Tri-Form 35 until the second harvest date, indicating a to 2 to 3 day delay in maturity. Berry size of plants from all treatments tended to decrease in size as the harvest season progressed (Figure 2).

The Tri-Form 35 treated plots produced yields comparable to or greater than the standard MB 67:33 fumigated plots. Lack of weed control was expected to be a major concern with this treatment; however, weed control was not an issue in this test. Hendrix and Dail has conducted some research that has shown very acceptable weed control from Tri-Form 35 if injected at least 12 inches below the top of the bed. Basamid treated plots overcame the delay and produced quite well. Had they not been later, they might have produced yields greater than the MB 67:33 and Tri-Form 35 plots. However, it appears that Basamid will never be labeled for use in food crops. This data suggests that for the time being, Tri-Form 35 will provide an alternative to methyl bromide for soil fumigation in plasticulture strawberries.

Table 1. Crop injury and plant growth of ‘Chandler’ strawberries, along with weed control ratings of plots receiving selected fumigation treatments 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.