Strawberry Plasticulture

Notebook

A guide to
Strawberry plasticulture production

The North Carolina Strawberry Association
1998

Compiled by Eric Bish and Debby Wechsler,
with help from Barclay Poling, Frank Louws, Gina Fernandez,
Ken Sorensen, and many others.

The Strawberry Plasticulture Notebook is based on
The Chandler Notebook, third edition, 1995, edited by
Dr. E. Barclay Poling
Department of Horticultural Science
North Carolina State University
Raleigh, NC 27695

Additional copies of this book are available for $25 from:
North Carolina Strawberry Association
11 38 Rock Rest Rd.
Pittsboro, NC 27312
919-542-3687
919-542-4037 (fax)
ncstrawbarry@mindspring.com

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply en- dorsement by the North Carolina State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. All recommendations, advice and information herein contained are made without warranties, expressed or implied, of any kind or nature, and without liability on the part of the author. The final decision on the use of the information presented herein rests with the discretion of the grower. Be sure to obtain current information about usage regulations and examine a current prod- uct label before applying any chemical. For assistance, contact your county Agri- cultural Extension Service Agent.

Optimal Growing Regions for Chandler Plasticulture

E. Barclay Poling, Dept. of Horticultural Science, N.C. State University, Raleigh, North Carolina, 27695-7609. Originally presented at the 1995 NASGA Annual Meting in Orlando, Florida.

INTRODUCTION

Today, more than ever before, there is considerable interest in annual production systems for United States and Canada. Northern growers and researchers are aware of the dramatic shifts taking place in production systems in the mid-South, and in the last few years a number of growers in the Mid-Atlantic states have begun to experiment with the North Carolina "recipe" for strawberry plasticulture, using eastern varieties (as a means of producing larger berries that are more easily harvested by consumers). The chief difficulty with strawberry plasticulture in northern regions has proven to be lower yields relative to plasticulture growers further south. It is the author's view that northern growers can achieve higher levels of customer satisfaction and market success by adopting some form of annual production, but a different template of cultivars and growing techniques are needed further north. The mountains of western North Carolina have similar growing conditions to those in northern regions such as New Jersey.

ANNUAL CROPPING IN NORTH CAROLINA

Matted row cultivars and culture are being replaced in North Carolina by an annual production system that utilizes California and Florida cultivars ('Chandler', 'Camarosa', 'Sweet Charlie') at plant densities that are about three times as high as the approximate 5,500 transplants needed to establish an acre of matted row. A survey in February 1995, of all 100 countries in the state, indicated 980 acres of annual production which is expected to reach 1200-1400 acres. Matted row has declined from a high of 2000 acres in 1980 to less than 300 acres in June 1995.

"Strawberry plasticulture" as it is popularly referred to in North Carolina, is technically the annual hill training system in which "green" strawberry transplants (fresh dugs or plugs) are planted in early fall in double rows at densities of approximately 17,400 plants/acre on methyl bromide fumigated, raised beds that are covered with black plastic mulch. In this system, North Carolina growers can harvest berries in just 7 to 8 months after planting compared to approximately 12 months for MR. Other advantages of strawberry plasticulture include an earlier and longer picking season than for matted row strawberries. 'Chandler' is about 7 days earlier than the MR strawberry 'Earliglow', and the harvest period will extend about 1 week past the mid-season cv. Cardinal. By including the early ripening cv. 'Sweet Charlie' with 'Chandler', the total strawberry plasticulture picking season lasts about 6 to 7 weeks in this region. After the strawberry season ends (early to mid-June), the plants are destroyed and the plastic beds may be re-utilized for summer-fall vegetables. North Carolina plasticulture growers do not keep first year planting for a second year of fruiting because of the potential for lower quality fruit as well as high risk of anthracnose infection during the wann and humid summers of southern United States.

IT'S A SYSTEM PACKAGE

As I look back at the applied strawberry research we have been conducting since 1982, there has been an ongoing effort to identify growing techniques that improve the 'goodness of fit" between the growing environments (in North Carolina) and basically just one cultivar, 'Chandler'. It all has to fit together as some sort of package. From the grower's standpoint, it has to be a package where the conversion of strawberries into dollars exceeds the reverse reaction (i.e. dollars going into crop financing, planting, growing, harvesting and marketing).

Background information: Our initial attempts in the early '80's with fall planting in the annual hill system on black plastic mulch involved as collection of three NCSU matted row cultivars, 'Earlibelle', 'Apollo' and 'Atlas', and the California cv. Douglas. Each of the matted row cultivars had relatively concentrated crops on the plastic beds and the picking season lasted 3 weeks at most. With the California cv. Douglas we achieved a longer picking season (approximately 4 1/2 weeks) and the berries were easily picked because of the longer peduncles that placed the fruit on or near the shoulders of the raised beds. The major drawbacks of 'Douglas' were its fair fruit flavor and poor internal flesh color. In addition, any rainy weather caused serious losses in fruit appearance and quality with 'Douglas'. However, the larger berry size, ease of picking and longer season made as great impression on us.

Our research program seemed to "come to life" when we started experimenting with 'Chandler' in the 1984-1985 season. It had all the desirable features of 'Douglas' and an apparent tolerance for wet spring weather. In addition, it had higher yields and was very well liked for its glossy red skin, high internal color and slightly sub-acid flavor. Our 10 year association with 'Chandler' has been highly beneficial for North Carolina growers and consumers alike.

'Chandler' and 'Douglas' are both well adapted to early fall planting and spring season fruiting in both eastern and piedmont North Carolina. These California cultivars are different from northern matted row strawberry cultivars in their ability to grow under short days at relatively low growing temperatures in winter. And, in most winters, the leaves of 'Chandler' remain green in the eastern 2/3rd's of the state. In winters marked by colder temperatures, below 10'F (- 12 degrees C), we can lose this evergreen characteristic. But, this is often as blessing from the standpoint of reducing two-spotted spider mite populations. In late February and early March, growers go through their plantings and mechanically brush each plant to remove the dead and partially desiccated foliage as sanitation control for betroths.

We take advantage of raised beds, full bed black plastic mulches, methyl bromide fumigation and drip irrigation to further enhance plant growth and floral development during our characteristically mild fall and winter months. By late December the new roots have reached a depth of 10- 12 inches and the plants have made an additional branch crown or two, depending on planting date. Additional crowns become visible in late winter, and by the end of the spring fruiting season, a well-balanced plant will have approximately 4-6 fruitful branch crowns. The primary crown is the most productive and has as basal inflorescence; the second, third and fourth crowns are also quite fruitful and the are typically more upper branching in inflorescence structure. Depending on region, the later developing fifth and sixth branch crowns may or may not be that fruitful. It is possible, but highly undesirable, to product more than 8-10 branch crowns in one fall and winter season. There is very little difference between the problems associated with a 10 to 12 branch crown strawberry plant and an unpruned grapevine. Instead of pruning with shears to control bud numbers and fruit load, strawberry growers must rely on later planting dates to control crown numbers. By later, I mean mid-to-late October for the southeastern Coastal Plain, and early October for the upper coastal plan and lower piedmont.

Growers in the upper piedmont, foothills and mountains wrestle with a problem associated with not enough mild weather in late fall and winter. They have adopted various strategies to increase branch crown formation, including earlier planting dates and sometimes spunbound polyester or polypropylene floating row covers are applied in early winter (around mid-December) and removed by mid-to-late February, before new leaf growth is observed in late winter. Flower buds will usually emerge from the crown less than two or three weeks after new leaves are observed, and once flower buds begin to appear, the grower must be prepared to start frost/freeze control. Late winter row covers have the undesirable effect of moving the beginning of the frost/freeze control season up by as much as one week. In early-to-mid March, North Carolina is subject to severe advective freezes which make overhead watering for freeze control quite hazardous.

A "fair weather" production system. I believe that 'Chandler' strawberry plasticulture is best suited to a mild winter weather climate. As we move from the mildest winter areas in North Carolina in the southeast to colder regions in the northern piedmont on the Virginia line, a number of significant horticultural changes occur that influence plant productivity, length of fruiting season, and economic returns. The colder the winter climate, the shorter the fruiting season, and the higher the costs. I have reasons to believe that this technology may be commercially useful in areas as far north as eastern shore Maryland, southern New Jersey, and in areas of the southern Appalachians, but additional management risks and costs are involved.

Darrow (1996) identified zones for late winter strawberry flower initiation and crown crop formation in the South that help to explain the varying levels of success growers are now achieving with strawberry plasticulture in different states and regions:

Figure 1 is taken from Darrow's book, The Strawbegy History, Breeding and Physiology (1996). The map shows the mild winter areas of reliable annual spring flower-bud formation as well as areas of less mild winter weather where only occasional spring flower-bud formation occurs. It is truly remarkable how consistent the flower initiation zones on this map are with the productive potential of 'Chandler' in these different regions. The information that follows is an attempt to provide an economic report card on how strawberry plasticulture growers are faring in each of Darrow's winter flower-bud formation zones.

Darrow's zone for annual spring flower-bud formation. This area includes the eastern coastal plain of North, South Carolina, following the recommendation in "Commercial and Garden Strawberry Plasticulture for North Carolina" (Poling and Monks 1994), it is possible in some seasons for experienced growers on excellent sites and soils to produce marketable crops of Chandler that approach 15 tons/a. Because the growers in this region use a 14 inch in-row spacing (not 12 inch), the plant population for a 5 ft bed center with double rows is about 15,000 plants on a per acre basis. Thus, these growers are achieving marketable yields of about 2.0 lbs per plant. The usage of row covers for winter protection provides no economic benefit in this region (Poling, Fuller and Perry, 1991), and most eastern growers do not use strawberry plugs because of their greater expense relative to bare-root fresh dug transplants brought in from Canada in early-to-mid October. The actual before-picking production costs for an eastern North Carolina strawberry plasticulture producer will usually not exceed $4000/a (Poling 1994), and per unit production costs may be as low as $0.14 per lb in favorable growing seasons. In less favorable seasons with advective freeze conditions during early bloom in March, I have seen yields dive to as low as 1 lb per plant.

Darrow's zone for occasional spring flower-bud formation. This less mild winter area includes portions of the central piedmont region of North Carolina, and is depicted by a diagonal band the continued further south into piedmont South Carolina and Georgia (Fig. 1). Again, following the recommendations given in "Commercial Strawberry Plasticulture for North Carolina" (Poling and Monks 1994), it is possible in "good" seasons like 1994-1995 for experienced piedmont growers to produce marketable crops of Chandler that are more in the range of 9 to 12 tons/a. Because the growers in this region use a 12 inch in-row spacing, the plant population for a 5 ft bed center with double rows is about 17,500 plants per acres. Thus, these growers are achieving "marketable yields" of about 1.0 to 1.4 lbs. The usage of row covers is not common in the piedmont region, but the more expensive strawberry plugs are often used instead of fresh dugs because of less available labor for hand planting of fresh dugs. The intensive watering cycles required for fresh dug plant establishment also cause serious soil erosion problems on most piedmont sites (hilly terrain). In 1995, strawberry plugs are anticipated to cost approximately $140 per thou. or $2,450 per acre as opposed to an eastern North Carolina producer that will spend about $1, 125 per acre for planting 15,000 plants per acre for fresh dugs. The added expense for transplants in the piedmont region increases the breakeven pre-pick cost to about $0.30 per lb, assuming $5325 pre-harvest cost/A and 9 tons per acre of marketable fruit. Off setting the higher unit costs in the piedmont are pick-your-own prices that average $0.10 per lb to $0.15 per lb higher in this more populous region. As a general rule, the 'Chandler' plasticulture season is usually 1 week shorter in the piedmont (picking for 4-5 weeks) than in eastern North Carolina. And, in the most southern and eastern counties in the state I have observed steady picking for a full 7 weeks (New Hanover and Brunswick counties).

In terms of observing the harvest of "crown crops in North Carolina, I would indicate that these are more consistently observed in the southeastern region of the state, especially in milder coastal areas. 'Pajaro', a California cultivar that is no longer produced in North Carolina because of its very high anthracnose susceptibility in the nursery and fruiting field, exhibits a very impressive late spring "crown crop" when berry size in the fifth or sixth week of picking will suddenly jump an average 0.35 oz per berry.

CHANDLER AT ITS NORTHERN AND WESTERN LIMITS

Over the years, as we've refined our cultural management of the plasticulture system, productivity has essentially doubled from 1 lb of marketable fruit per plant to a little over 2 lbs on the best sites and soils in the southeastern coastal plain. In less mild winter regions, such as the central piedmont, we are finding it difficult to increase productivity beyond 1.5 lbs per plant. In the colder winter climates of the foothills and mountains, where there is a good probability of having temperatures below 10 degrees F each winter, there is still a good economic opportunity for annual strawberry plasticulture production. However, exceeding yields of 1 to 1 and 1/2 lbs per plant is more difficult than in the piedmont region to the east.

I have been formulating a mental model of "what to look for" in 'Chander' plants that are being grown in climatic and photoperiodic zones where 'Chandler' cannot seem to get synchronized. I present these indicators in Table 1 with the intention of stimulating more discussion and research. The information is observation-based, and gathered from early, mid and end-of-season visits to plasticulture farms in upper piedmont and mountains of North Carolina, southern and central Virginia, eastern shore Maryland and Cedarville, New Jersey. I believe this information may be particularly useful to northern and mountain growers who are "wrestling mightily" to boost 'Chandler'yields.

In the event of severe winter injury to 'Chandler or 'Douglas', the recovery potential of these cultivars in eastern North Carolina can be quite remarkable. In a record cold freeze of Jan. 1985, when a record low of -8 F was recorded in eastern North Carolina, and crown tissues and flower primordia were extensively damaged, it was still possible for these plants to recover in late Jan., Feb. and.carly March to produce a crop of about 1/2 to 3/4 lbs per plant. Even still, the plants began to runner by the second and third weeks of fruiting. I normally associate this early runnering response with plants that have been planted "too late" for adequate floral development, or crowns that have lost flower buds to cold injury.

In the late 1980s, I observed heavy runnering in the very first trials with 'Chandler' strawberry plasticulture in southern New Jersey (these on-farm demonstrations were conducted by retired Ocean County Agricultural Extension Agent, Norman Smith, in conjunction with Sheppard Brothers, Inc., Cedarville). Adjustments made with earlier planting of plugs in the first week of September plus fall and winter row covers have helped to increase plant productivity and reduce the spring season runnering problem. But, in the event of a severe December or January freeze, the Mid-Atlantic's generally cold temperatures in late winter prevent the development of fruitful replacement crowns.

Other spring phenomena, including sterile fourth and fifth branch crowns and large 'Chandler' leaves on long petioles, occur in higher latitudes, beginning in central Virginia (Fredericksburg) and extending into the Middle Atlantic states.

CONCLUSION

The chief difficulty with annual strawberry plasticulture in northern and mountain regions is proving to be lower yields relative to plasticulture growers in the southern piedmont and coastal plain. In general, I believe that 'Chandler' strawberry plasticulture is best suited to southern mild winter climates. As we move from the mildest winter areas in eastern North Carolina to colder regions, a number of significant changes occur that influence plant productivity, length of fruiting season and economic returns. The colder the winter climate the shorter will be the spring fruiting season. I have reason to believe that modifications (plugs, row covers) this alternative technology may be commercially useful in areas as far north as eastern shore Maryland and southern New Jersey, but additional management risks and costs are involved.

Lower first year yields and higher expenses are compelling Mid-Atlantic growers to keep first year plasticulture beds for a second year of cropping. Second year plasticulture crops have picking characteristics and fruit quality similar to other multiple year cropping systems, and the impact of second and possibly third year plasticulture crops on customer satisfaction and prices needs to be carefully evaluated. It is the author's view that northern and mountain growers can achieve higher levels of customer satisfaction and market success by avoiding carryover crops. The bottom line in North Carolina on annual vs. carryover crops is simple: If your competition is producing only annual crops, you'd better be too. Annual cropping systems, in contrast to multiple year systems, provide the grower with a higher degree of control of strawberry physiological factors that are related to optimum fruit size, appearance, east of picking and overall customer acceptance.

Wherever there is customer impatience with biennial and perennial strawberries, there is an opportunity to grow and market berries in an annual system. I believe that more innovative approaches to true annual cropping for cool climates are needed. Annual 'Elasanta' cropping systems used in the Netherlands and Germany do not rely on plastics or methyl bromide fumigation, and these may prove interesting for U.S. and Canadian growers to pursue, alone, or in combination with different plasticulture techniques.

LITERATURE CITED

Darrow, G. M. 1966. The Strawberry; History, Breeding and Physiology. New York: Holt, Rinehart & Winston.

Poling, E. B. 1993. Strawberry plasticulture in North Carolina: Part II. Preplant, planting, and postplant considerations for growing 'Chandler' strawberry on black plastic. HortTechnology Oct/Dec 3 (4):383-393.

Poling, E. B. and D. W. Monks. 1994. Strawberry plasticulture guide for North Carolina. N.C. Coop. Ext. Ser., Bul. AG-515, 16 pp.

Poling, E. B., H. P. Fuller, and K. B. Perry. 1991. Frost/freeze protection of strawberries grown on black plastic mulch. HortScience 26:(1):15-17.