Growing Day-neutral Strawberries Using the Sunbelt/Polyacrylamide Gel System

PROJECT BACKGROUND
Compton Family Farm is a beautiful 30 acre section of land situated about 12 miles north of Buffalo, Missouri and 10 miles west of Bennett Springs State Park. Currently, most of the acreage is pasture, and we have plans to develop it into fruit and vegetable gardens. We have owned the farm for nearly two years. The first year we had about ½ acres in production, mostly sweet corn, pumpkins, and tomatoes. This year we added 1/5 acre of strawberries, ½ acre of melons (watermelon and muskmelon). Each year will see additional expansions. We had good success with an on farm market this year, and we will continue to use that as the main outlet for our produce sales.

The use of sustainable farm practices has been an aim in all of our endeavors. In 1996, our establishment year, we used synthetic mulch to control weeds and retain soil moisture in tomatoes and pumpkins. We also avoided the use of pesticides to get a feel for exactly what diseases and pests were going to be a problem in our area. Because we have yet to acquire a tractor, we have been using my brother’s draft horses to prepare the garden area. It’s been a good experience.

PROJECT DESCRIPTION AND RESULTS
The project’s goal is to reduce soil erosion, soil salinity problems resulting from irrigation, the need for chemical pesticides, and production cost of strawberries by experimenting with strawberries grown with the sunbelt/polyacrylamide gel system. Also, to determine the feasibility of growing day-neutral strawberries in this area. The Sunbelt (a woven synthetic mulch) theoretically will reduce soil erosion, control weeds, and reduce physical contact with soil borne fungal pathogens, while allowing infiltration of rain water. Controlling weeds and reducing contact with fungal pathogens will reduce the need for chemical inputs. The polyacrylamide gel will theoretically help to retain soil moisture and nutrients, eliminating the need for a irrigation system and associated costs, and promoting a reduction in the amount of salts deposited in the root zone with irrigation water.

Process:
Half of the strawberry study was planted in an old garden plot, while the other half was planted in an area which had been in pasture until fall of 1996. Originally, we had plans to plant all the strawberries in the old pasture. However, the literature warned that, because of the danger of white grubs to strawberries, planting directly into an area that had recently been pasture might be unwise. Thus half the strawberries were planted in the garden plot. However, in the end there was no significant differences between the plots. A cover crop of annual ryegrass was planted in the garden plot in September of 1996 and tilled under in early March 1997.

The high profit potential of day neutral strawberries together with the fact that they had not been grown extensively in Missouri made them a perfect candidate for this study. We used two cultivars, Tribute and Tristar, which have been reported to be the strongest day neutral cultivars for cold winter areas. We wanted to see how they compared with each other in our area.

Good drainage is essential in strawberry production, thus the strawberries were planted on raised beds of approximately nine inches in height, and two feet in width. Originally we planned on having six feet between row centers, but it ended up being closer to four feet. That was probably too close; six feet would have been better. The Sunbelt we used was 15 feet wide, thus each raised bed as well s the furrows in between were covered with Sunbelt.

Weed control is one of the most difficult things to manage in strawberry production, and this is one of the main functions of the Sunbelt. Small holes were burned with a propane torch in the Sunbelt to allow a space to plant the strawberries. This left very little room for weeds. As the holes were cut, the torch cauterized the edges of the holes, preventing the woven plastic from unraveling. The plants were planted in a staggered double row, with eight inches between plants, and one foot between row centers. We made a template out of PVC to facilitate burning the holes at the proper spacing. Day neutral strawberry production requires removing the runners so they do not produce daughter plants. If allowed to produce daughter plants, much of the energy is lost that would have been used to produce berries. Therefore, the Sunbelt did not interfere with traditional management of day neutral strawberries. The Sunbelt is also water permeable, allowing infiltration of rain water. At the same time it works great to help retain soil moisture by preventing soil water loss through evaporation.

The two strawberry cultivars were tested under five different treatments, making a total of ten plots per rep. The treatments tested the efficiency of polyacrylamide gel as a tool for irrigation by comparing it with a traditional drip irrigation system. Polyacrylamide gel has the consistency of rock salt when dry, but swells several times its original size when hydrated, with a resulting consistency similar to finger jello. When plant roots grow into the gel, it is like tapping into a water source. To find out how much get it would take to replace an irrigation system and if it would be cost effective, the following treatments were studied.

Table 1 – Strawberry cultivars and treatments
1A – Tristar with drip irrigation
1B – Tribute with drip irrigation
2A – Tristar with no gel or drip irrigation
2B – Tribute with no gel or drip irrigation
3A – Tristar with 10 pounds of gel/1000 ft2
3B – Tribute with 10 pounds of gel/1000 ft2
4A – Tristar with 25 pounds of gel/1000 ft2
4B – Tribute with 25 pounds of gel/1000 ft2
5A – Tristar with 50 pounds of gel/1000 ft2
5B – Tribute with 50 pounds of gel/1000 ft2

Each treatment was replicated six times in a randomized complete block design. Each plot contained 32 strawberry plants and was 11 feet in length, separated from a neighboring plot by strawberries in border areas which were about 5.5 feet. Before the plastic was rolled out the gel was applied by hand and worked into the top inch of the soil with a garden rake.

Soil samples were taken previous to planting to find the amount of fertilizer required. The plots with drip irrigation were fertilized with water soluble fertilizer injected through the drip system. The other plots were fertilized with a slow release fertilizer which was put down before the plastic was rolled out. The objective in both cases was to give the strawberries 20 pounds of nitrogen per acre on a monthly basis. Subsequent soil and plant tissue tests were taken in July to determine the cause of nutrient deficiency symptoms.

The strawberries arrived April 18 and were planted April 19-25. The blossoms were removed the first six weeks to allow the plant to establish itself before it started bearing fruit. Runners started developing approximately two weeds after planting and were removed throughout the season.

The berries were harvested from the weed of 21 June to mid October. However, data was only recorded up to the week of 20 September. Harvesting was done as needed; sometimes this required picking three times a week, and at other times only weekly. All the berries were picked and weighed, whether they were good or cull. The berries from the different plots were harvested into separate containers which allowed us to record the exact yield from the different plots. The berries sold almost entirely at our on farm market. Customers responded to signs put on the highway as well as newspaper advertisements and word of mouth.

Results:
The results were measured by recording the yield from each individual plot. We found that the Tristar treatments yielded more than the Tribute in every instance except one (Fig. 1). The drip irrigated plot had the highest yield, followed by the gel rates of 25, 0, 50, and 10. The same pattern was seen in both Tristar and Tribute. Statistical analysis (analysis of variance) was performed on the different treatments to determine if there were any statistical significant differences, which there were. The Duncans Multiple Range test was used to determine exactly which treatments were different.

[Editor’s note: There are tables, charts and graphs that could not be posted on the website. If you would like to see these please email us at ncrsare@umn.edu or call us at 800-529-1342. Thanks]

It was found that the three highest yielding treatments were not significantly different (Fig. 1). These were 1A, 4A and 2A (table 1). Among the Tristar treatments none of the gel rates were significantly different from each other (see attachments under marked with “b”). Each Tristar treatment was significantly better than the corresponding Tribute treatment. Among Tribute treatments, none of the gel rates were different, but 1B was significantly better than all treatments except 4B.

The timeline in Figure 2 also shows that Tristar produces more than Tribute nearly the entire summer. This timeline also shows the production pattern of day neutral strawberries. The reduction in yield experienced in August was a result of the hot July weather (2 weeks of 95-105 degrees), which reduced flowering, resulting in lower August yields. As he weather cooled off in August the result was higher yields in September.

Due to mechanical problems we conducted very little pest control. While this resulted in more cull berries than we wanted, we observed some interesting differences between Tribute and Tristar in disease resistance. While we recorded the amount of cull berries, we did not subtract their weight from the total yield reported. The yield from all of the Tribute treatments had a higher percent cull than the Tristar treatments, with the lowest percent cull being 4A (Fig. 3). The timeline in Figure 4 shows how the relationship of good and cull berries changed as the season progressed. Initially there were very few diseased berries, but in July leather rot and grey mold increased dramatically. As the yield dropped in August, the proportion of the yield that was cull increased dramatically. Nearly half of the yield in August was cull berries. In September as the yield began to increase again, the amount of cull increased slightly, but the amount of good berries was many times greater than the cull berries.

To determine the economic viability of this system, we looked at the variable costs associated with the gel versus the variable costs associated with the drip irrigation (Table 2). It can be seen that the treatment with the greatest return over variable costs is the irrigated treatment.

While table 2 shows the treatment with the greatest return over variable costs was irrigated, there are many factors to consider. To determine the profitability of the proposed system, we adapted a enterprise budget from the “Day Neutral Strawberry Production Guide”, published by Cornell Cooperative Extension (Table 3, 4, 5). We used most of the numbers they had, but used our number for the information we had available. The end result is the highest net return of $6,368 was found in the drip irrigation plots (Table 6). For comparison, average June bearing strawberries will yield about 10,000 lbs/acre with a net return from $3,000 to $4,000/acre.

Discussion:
While the numbers indicate that drip irrigation will give us the greatest return, this could vary depending on available labor and resources. The labor to put in drip irrigation can vary greatly. A bed maker that lays drip line as it forms a raised bed can install drip line very efficiently. However, if the farmer is laying it all out by hand, the labor could be quite a bit more. Also, the labor to apply the gel and slow release fertilizer will vary depending on available equipment.

There are other factors to consider. The gel requires no maintenance, while irrigation systems do. With the gel, no weekly watering or fertilization is required. On the other hand, with an irrigation system the grower can apply or with hold water and fertilizer when they want to. Using the gel one is left to whatever water the rainfall provides.

The Sunbelt synthetic mulch completely eliminated erosion and was excellent as a weed barrier. The only labor spent on weeds was done while picking strawberries and was minimal. With the Sunbelt there is no need for chemical herbicides to control weeds. While there were no plots without the Sunbelt to compare against, the fact that the plot with no irrigation was no significantly less than the drip irrigated plot tells us that the Sunbelt was very helpful in retaining soil moisture. There was a period of about a month from mid-May to mid-June where we received very little moisture, and the temperatures were in the upper 80’s and lower 90’s. Yet even the strawberries that had no gel or irrigation showed no signs of water stress. None of the strawberries throughout the summer showed visible signs of water stress. We received about three inches of ran/month through the growing season, except August when we received over six inches of rain (Fig. 4).

The Sunbelt may have reduced production in mid-summer due to the fact it is black and traps heat. Day neutral strawberry production drops dramatically when the temperature is greater than 85 degrees, and the black plastic certainly added to the heat.

The Sunbelt did not meet our expectations in relation to disease control. Leather rot is a soil borne disease, and was a significant problem in our strawberries. It is actually possible that once the disease is on the plastic, that the plastic might enhance infection due to the increase in splashing on the plastic versus the soil.

We also had problems with Grey mold, Leaf spot, tarnish plant bugs, and wasps. Our only hypothesis as to the different percentages of cull berries (Fig. 3) is that some of the treatments produced healthier plants which were more disease resistant. It is apparent that Tristar has greater disease resistance than Tribute. It is felt that a regular spray program would readily pay for itself. There is a challenge with day neutral strawberries and spraying because many pesticides require a certain number of days before harvesting is allowed, and day neutral strawberries are being harvested all summer long. Thus, the pesticide needs to be labeled to allow picking within a day or two.

The gel did not work as well as anticipated. We expected to see a strong positive relationship between gel rate and yield, but we did not (Fig. 5). In both Tristar and Tribute a surprising pattern is seen where the treatments of both 10 and 50 lbs of gel have lower yields than no gel at all, while the treatment with 25 lbs of gel did better than the others. Technically, however, there were no significant differences between gel treatments (Fig 1). The gel itself created some problems in planting. After a quarter of the strawberries were planted, it rained, which hydrated the gel. This made it challenging to plant strawberries into the plots with 50 pounds of gel because there was so much gel it was difficult to pack soil around the plant roots. Thus it was actually more difficult for the plants in that treatment to become established, and could be at least part of the reason the high gel treatment did not perform as well as anticipated. Another possible problem with the 50 pounds treatment is that strawberries require good drainage, and it may be that the higher rate of gel retained too much moisture. This has been only one summer of data, and perhaps further examination would give us more information.

We strongly recommend Tristar as it performed better than Tribute in total yield and had fewer bull berries (Fig. 1, 2, 4, 5). We fell that there is potential for growing day neutral strawberries in this area. Many customers were surprised and pleased to find strawberries in the heat of summer as well as in the fall. As the people in our area become more accustomed to this we feel there will be more demand than we will want to supply and we will be able to raise our prices a bit.

The main liability of day neutral strawberries is they are very labor intensive. After planting them there is about a week before the buds and blossoms need to be removed, and shortly after that the runners start and need to be pinched throughout the growing season. Once the strawberry plants start bearing fruit, the work doesn’t end until there is a hard frost. Unless a farmer has access to long term, inexpensive labor, he will find it hard to have other projects in addition to the strawberries. While average June bearing strawberries have less net return per acre, they also have a much shorter harvest season. This is definitely a factor to consider if one is deciding between June bearing and day neutral strawberries.

One other liability of day neutral strawberries is berry size. They tend to be small, and in the heat of the summer the majority of the berries are almost marble sized. The flavor of the berries is very good, we had many repeat customers who reported to us they were the best strawberries they had ever eaten.

OUTREACH
We had several articles in two local newspapers, The Buffalo Reflex and the Lebanon Daily Record, as well as one in the Joplin Globe. Our on farm market provided an ongoing opportunity for outreach. We were able to explain about the SARE program to a large proportion of our customers. Many of them were given a tour of the berry patch and SARE brochures.

We advertised our field day in the above mentioned papers and three others, as well as through the local Extension office. Patrick Byers, Small Fruit Grower Advisor at the SMSU Experiment Station, and Andrew Thomas of MU Southwest Research Center also advertised the field day in their newsletters. About 40 people attended the field day, most of them came from within an hour drive. Daniel Wofford Jr. of Western Polyacrylamide Inc. assisted in the field day by having a display and giving a presentation on Sunbelt and polyacrylamide gel. Patrick Byers also gave a short presentation on day neutral strawberries. Andrew Thomas also spoke. The remainder of the time was spent touring the plots and answering questions. SARE brochures and pamphlets were distributed to all of our guests. The field day lasted nearly four hours and overall went very well.

A short summary of the project will be printed in the local papers, and people can contact us for more information. The results of this project will also be published in the proceedings of the Missouri Small Fruit Conference, and we will give a presentation reporting our finding at that conference. The conference will be held in Springfield, MO on February 16, 17, and 18.