Strawberry Plasticulture in North Carolina: II....

Strawberry Plasticulture in NorthCarolina: II. Preplant, Planting,and Postplant Considerations forGrowing ‘Chandler’ Strawberryon Black Plastic Mulch

HortTechnology ● Oct./Dec. 1

E.B. Poling!

Addit ional index words. Fragaria × ananassa, fresh-dugs, plugs, fertility, frost/freeze protec-tion, rowcovers

Summary. North Carolina is experiencing a revitalization of the strawberry industry due tothe adoption of plasticulture technologies and the California cultivar Chandler, which pro-duces excellent yields and fruit quality on black plastic mulch. With this system, berries can beharvested in just 7 to 8 months after planting. The spring harvest season can last up to 6 weeksin most years. Strawberry plasticulture growers in North Carolina typically experience yields of17,000 to 18,000 lb/acre (19,054 to 20,174 kg·ha-1). Cash expenses for the system are about$4345/acre ($l0,736/ha). The system requires both an overhead sprinkler system for blos-som and bud frost/freeze protection, and drip irrigation for supplying water and fertilizer inthe prebloom, bloom, and fruiting periods. Sandy loam and clay loam soils are ideal forforming the lo-inch-high (25.4-cm) beds with bedding machines. Usually, 33% of the N, 50%of the K, and all of the P is applied preplant, with the remaining N and K applied through thedrip-irrigation system. Problems associated with the plasticulture system include higher initialinvestment relative to matted-row production, and only one fruiting season is possible withthe anthracnose-susceptible ‘Chandler’ in the southeastern United States.

“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 atdensities of ≈ 17,400 plants/acre (43,000 plants/ha) on fumigated, raisedbeds that are covered with black plastic mulch. In this system, growers inNorth Carolina plan to harvest berries just 7 to 8 months after planting,compared to ≈ 12 months for strawberries grown in matted row (MR)production. The picking season is normally 6 weeks, but, in cooler-than-average spring temperatures, the harvest can last 2 months. ‘Chandler’ isabout 7 to 10 days earlier than the MR strawberry ‘Earliglow’, and theharvest period will extend 1 to 2 weeks past the late-midseason cultivarCardinal. After the strawberry season ends (early to mid- June), ‘Chandler’plants are destroyed and the plastic beds sometimes are re-used for sum-mer/fall vegetable crops.

Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-76091Professor.

993 3(4) 383

Fig. 1. With ‘Chandler’, theCalifornia breeding pro-gram scored a phenomenalsuccess-not only does it shipwell, but it also has a good fla-vor, glossy skin, and brightred flesh. The flesh and proc-essed quality of ‘Chandler’,its yield potential, and resis-tance to frost and rain dam-age are some of the key attri-butes that have led to this cul-tivar’s widespread adoptionin North Carolina.

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General informationThe ‘Chandler s t rawberry . ‘ C h a n -

dler’ (Univ. of California, Plant Patent 4487)was named in 1982 for the late William Hen-ry Chandler, prominent author and horti-culturist of the Univ. of California (Bringhurstand Voth, 1983) (Fig. 1). ‘Chandler’ is one ofthe most-important strawberry cultivars inthe world; it occupies a large percentage ofthe southern California strawberry acreageand is a major cultivar in Louisiana, Mexico,Central America, Italy, France, and Spain. Itssuperior yield performance relative to othercultivars evaluated on black plastic (Poling etal., 1988) and resistance to rain and frostdamage are key attributes that led to itswidespread adoption by plasticulture grow-ers in North Carolina and other states in themid-south. ‘Chandler’ is popular with con-sumers in North Carolina because of its excel-lent fresh and processed quality (Fig. 1).

Many people have questioned the wis-dom of North Carolina’s 100% dependencyon a plasticulture strawberry cultivar that wasbred for growth in California-not the hu-mid southeastern United States. In fact, theNorth Carolina plasticulture industry wasnearly ruined in Spring 1990, as field afterfield of ‘Chandler’ became severely infectedwith anthracnose fruit rot (Col le totr ichumacutatum). With the loss of the emergencySection 18-C registration for Difolatan (capta-fol) in 1987, it became nearly impossible togrow anthracnose-free ‘Chandler’ nurseryplants in North Carolina.

There are still no effective fungicidesavailable for anthracnose control. and grow-ing disease-free ‘Chandler’ crops basicallydepends upon raising the plants in very north-ern areas in the United States and Canada,where the summers are cool, and then fall-

transplantingin North Car-olina. After thespring straw-berry seasonends , ‘Chan-dler’ plants aredestroyed be-cause of thiscultivar’s ex-treme suscep-tibility to an-t h r a c n o s esummer infec-tion. Further-more, growersa r e e n c o u r -aged to rotateplanting fieldsand minimizeoverhead wa-tering during

plant establishment. Thus, growing anthrac-nose-susceptible ‘Chandler’ in North Caro-lina depends on sanitation and manipulationof the plant environment to avoid the diseaseor reduce losses.

Economics and market ing . O p e r a t -ing expenses for this system ofproduction areabout $4345/acre ($l0,736/ha) (Tables 1and 2). North Carolina growers typicallyachieve marketable yields of 17,000 to 18,000lb/acre (19,054 to 20,174 kg·ha -1), but totalyields of ‘Chandler’ on black plastic mulchcan be less than the total yields reported forh ighly product ive MR cul t ivars , such as‘Apollo’ and ‘Atlas’ (Galletta and Scott, 1970).Pick-your-own (PYO) prices generally fallb e t w e e n $ 0 . 6 5 a n d $ 0 . 7 5 / b ( $ 1 . 4 3 t o$1.65/kg), and “ready-pick” fruit is priced$0.25 to $0.35 ($0.44 to $0.55/kg) higherthan PYO berries. Direct marketing (PYO,ready-pick, farmers’ market) is generally moreprofitable for local growers of ‘Chandler’than trying to sell to North Carolina super-markets, which import large volumes of inex-pensive strawberries in April and May fromthe southern and central coast areas of Cali-fornia. Atypical ‘Chandler’ plasticulture plant-ing in North Carolina of 3 to 4 acres ( 1.2 to1.6 ha) is not very large by comparison tothose in California or Louisiana, but just a fewacres can provide a good supplemental in-come for small and part-time growers.

Equipment needs for plasticulture.Specially equipped and trained custom appli-cators should be considered for fumigation.They can form beds, inject fumigant, applyplastic, and lay trickle tubes in one operation.Where custom services are unavailable forbed-shaping/fumigation/plastic-laying, thegrower must purchase equipment costingabout $5500 and become certified to applymethyl bromide.

Strawberry plasticulture also requiresoverhead irrigation for plant establishment(fresh-dugs) and sprinkling for frost/freezeprotection. The expense for solid-set irriga-t ion can run f rom $1200 to $2500/acre($2965 to $6177/ha) depending on whethermore expensive aluminum or cheaper PVCpipe is used. This does not include the ex-pense for the diesel or electric pump, or a newpond. At least 60 to 70 gal/min (227 to 265liters/min) of pumping capacity is necessaryfor each acre (0.405 ha) that is frost-pro-tected.

More than 75% of the ≈ 700 acres (280ha) of the strawberry plasticulture industry inNorth Carolina uses drip irrigation. The higherlo-inch (25-cm) beds require drip irrigationbecause of poor capillary water movement.The proper use of plastic mulches and dripirrigation can provide maximum control ofthe environment, and the most-efficient use

HortTechnology ● Oct./Dec. 1993 3(4)

of water and fertilizer. Drip irrigation systemscan be designed by a specialist to irrigate anysize strawberry production unit. A line-sourceemitter with pre-punched holes is used tomaintain a continuous moist strip along therow. Because strawberries grown on plasticmulch are considered annuals and are grownfor only one season, a thin disposable tubing(4 to 8 mil thick) is commonly used. Watermay come from wells, ponds, lakes, municipallines, or pits. Well water sources generally arefairly clean and require only a screen filter toremove particles. However, precipitates orother contaminants in the water should bedetermined by a water quality test prior toconsidering a drip system. Any surface water,such as streams, ponds, pits, or rivers, willcontain bacteria, algae, or other aquatic life,and sand filters are an absolute necessity(Lamont, 1989).

Because the ‘Chandler’ berry is the most-important marketing tool for attracting cus-tomers to the farm, the balance of this articlediscusses important preplant, planting, andpostplant considerations for growing thiscultivar in North Carolina and, potentially,other regions as well.

Replant considerationsSite selection. The plasticulture system

has been examined under a variety of site andsoil conditions in North Carolina. Strawberryplasticulture is most ideally suited to themilder coastal plain (USDA hardiness zone8a) and lower Piedmont (zone 7b), but grow-ers in the upper Piedmont and mountains ofNorth Carolina (USDA zones 7a and 6b,respectively) are beginning to experience suc-cess with the system as well. Some of the beststrawberry plasticulture sites are those with awooded area or a windbreak on the north ornorthwest side of the field. This helps toreduce losses associated with wind-bornefreezes in late winter and early spring. Toomuch wind protection and restricted-air-flowlocations often lead to increased fungal pres-sures. Sufficient air movement is needed sothat plants can dry quickly after dews andrainfall.

A north-south orientation of strawberrybeds is recommended to encourage more-uniform plant development and ripening onboth sides of the double-row bed. If rows areoriented east-west, plants on the north sideof the bed will become partly shaded by theplants on the south side of the row during thewinter season.

Soil. Soil type has a decided influence onhow well the planting beds are formed. Sandyloam and clay loam soils are ideal for buildingand shaping the 8- to lo-inch raised beds.However, soils with a high clay content, orthose that are rocky or very stony, are more


difficult to prepare. As a general rule, thephysical conditions of the soil in relation to itsbed-making characteristics and internal drain-age are more-important considerations than

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Fig. 2. Freshly “pressed”strawberry bed before fumi-gation and plastic mulchapplication. Prior to bed-pressing and fumigation,this Norfolk sandy loam soilwas well-worked, free fromplant debris, and bad ade-quate moisture for weed seedtermination. The top of thebed is smooth (no pockets)and the bed shoulders arewell-formed.

soil fertility. High clay content, stones orrocks, and underlying hardpan are more-difficult conditions to manage than low pHor a lack of minerals, which can be balancedthrough the applications of lime and appro-priate fertilizers.

Growers are encouraged to rotate straw-berry field sites as often as possible, but thegeneral practice in North Carolina is to cropstrawberries continuously on the same landbecause of existing irrigation lines and marketlocation considerations. The elimination ofmethyl bromide soil preplant fumigant willlikely change this practice, and growers maybe forced to evaluate the benefits of fieldrotation, especially with regard to controllingsoil-borne strawberry diseases, nematodes,and insect pests that can build up in continu-ously cropped (untreated) fields.

Water drainage. The raised beds en-hance internal soil water drainage, but plasti-culture growers frequently encounter prob-lems with getting rid of excess “surface wa-ter.” This problem occurs because 50% of astrawberry field has been covered with animpermeable plastic film. For this reason, it isdesirable to have a field with enough slope sothat surface water is removed uniformly andgently from the field after periods of heavyprecipitation, without causing erosion or leav-ing puddles. On fields with more than 2%slope, continuous overhead sprinkling forfresh-dug plant establishment may cause se-vere soil erosion. Unlike highly perishablefresh-dug transplants, plug plants do notrequi re in tense overhead spr inkl ing forpostplant care and survival (see the section onplanting).

Soi l preolant fer t i l i ty . A soil test ismade several months in advance of plantingto provide an indication of how much dolo-mitic lime is needed to raise the soil pH to

6.0. About 33% of the N, 50% of the K, andall of the recommended P (based on soiltesting) is applied preplant, with the remain-ing N and K being applied in a 1:1 ratiothrough the drip irrigation system. For sandysoils that do not retain K or N well, the usualrecommendation for a preplant fertilizer pro-gram is to broadcast 120 lb K/acre (135 kg·h a-1), in addition to the 60 lb N/acre (67kg ·ha-1). The recommended fertilizer sourcefor Kis potassium sulfate. Ammonium nitrateis the usual preplant N fertilizer, and it iseither broadcast or banded 4 inches (10 cm)deep in the bed center. Essentially, these pre-plant fertilizer applications of N and K supplyearly nutrition to ‘Chandler’ in fall and earlywinter, when North Carolina growers typi-cally do not run their drip irrigation systems.Soil tests for boron are generally not veryaccurate and, as a rule, growers make a pre-plant soil surface spray of ≈ l lb B/acre usingsolubor (20% B) in 100 gal of water/acre.

F u m i g a t i o n . M e t h y l b r o m i d e / c h l o -ropicrin fumigation has been a standard prac-tice in California and Florida, where annualhill plastic mulch culture has been practicedsince the 1960s. Beds are fumigated withmethyl bromide for weed, nematode, disease,and insect control. Annual hill production onthe same site year after year is not advisablewithout pre-plant fumigation. The amountof material actually applied per acre will de-pend on row width and will be a percentageof the broadcast rate. The air temperatureshould be at least 50F (10C). The soil shouldbe well-worked, free from plant debris, andhave adequate moisture (for weed seed ger-mina t ion) (F igs . 24) . To have good so i lmoisture for forming the beds, it is frequentlynecessary to wet up the sprinkler irrigationsystem and apply ≈ 0.5 inch (1.3 cm) of water1 to 2 days in advance of bed-making andfumigation. If both weather and soil arewarm, most fumigants escape from the bed inabout 7 days. An additional precaution toreduce the likelihood of methyl bromideinjury to the strawberry transplant would beto cu t o r punch p lan t ho les th rough theplastic mulch a day or two prior to planting(Pig. 5 top).

S t r a w b e r r y b e d . M o s t g r o w e r s i nsoutheastern North Carolina have 10-inch(25-cm) -high “super-beds” to promote thedevelopment of larger root systems and morebranched crowns. The super-beds provide anearly ideal air-soil-water environment forvigorous strawberry root development. Thebeneficial effect of these beds on root growthis observed easily by excavating the soil be-neath the plastic mulch film at the end of theseason (see Fig. 12). A few roots may befound as deep as 24 inches (0.61 m), but thelargest concentration is in the upper 10 to 12


Fig. 3. This basic unit is de-signed for forming the bedand applying the fumigantand plastic mulch in onefield pass. The unit can bemodified easily for applyingdrip tape as well.

Fig. 4. The black plastic filmmust be in direct contactwith the soil beneath toachieve the desired soil-warming effect needed forgood plant establishment,growth, and fruiting daringNorth Carolina’s “cool”seasons (fall, winter, andearly spring).

inches (25 to 30 cm) of soil. Grower yields of‘Chandler’ on fertile sandy loam soils withlo-inch (25-cm) -high beds have exceeded36,000 lb/acre per year (40 t·ha-1) for 3 yearsin a row on several sites in southeastern NorthCarolina.

The lo-inch (25-cm) -high plastic mulchbeds are typically 32 inches (0.81 m) wide atthe base and 30 inches (0.76 m) wide on thetop. The beds are slightly crowned so thatwater will run off and not rest on the plastic[a bed with a 30-inch (0.76-m) top shouldslope from the center to the edge with a dropof 1.25 inches (3.2 cm)]. With lower bedheight, the long fruit trusses of ‘Chandler’come in direct contact with the soil in the rowaisles. Thus, it becomes necessary to applystraw mulch to the aisles to keep the berriesclean-this is not necessary with 10-inch (25 -cm) -high beds. Bed centers are 4.5 to 5 ft(1.37 to 1.52 m).

Drip tubing ins ta l la t ion . D r i p t u b -ing is installed with the orifices facing up-wards. The tubing is typically buried 1 to 2inches deep in the bed center. During instal-lation, several workers should be watching toensure that the tubing maintains its orifice-upwards orientation, to assist in case tubingbecomes tangled in the injector, and to signalwhen the drip tape reel is empty. Tubing endsshould be closed off by kinking-or knotting,until the tubes are hooked up to the system.Generally, growers do not use the drip systemuntil late winter/early spring; fall irrigation isapplied by overhead sprinklers.

Cover crops on sloping terrain. A ssoon as the land is fumigated and mulched, itis often a good idea to broadcast ≈ 50 lb ofannual ryegrass/acre (56 kg·ha -1) over theentire field. The ryegrass can be spread thesame day fumigation is completed. The rye-grass will reduce soil washing in the aislesafter heavy rains or irrigation for plant estab-lishment (fresh-dugs) on sloping terrain. It isvital to dress the land immediately after fumi-gating so that surface water can flow easilyout of the rows. It is much more difficult todeal with surface drainage problems after theryegrass is established. Obviously, it is bestnot to apply any pre-emergent herbicide tothe aisles if a “living mulch” is grown for thefall and winter season. In fact, very few herbi-cides are labeled for strawberry plasticulture,and growers should check with the Coopera-tive Extension Service or their crop consult-ant if there are questions about availableherbicides, rates, and timing of application.

Planting considerationsPlant quality. The success of a straw-

berry plasticulture planting, in large part,depends on the health and vigor of the plant-ing stock. Plants should be purchased from a


reputable nursery. ‘Chandler’ plants shouldbe true-to-variety, and not a tissue-culturemutation of the cultivar. The plants should befree of insects, diseases, nematodes, and vi-ruses. The North Carolina Strawberry Assn.,Inc. (Association Management, Box 52276,Rale igh , NC 27612) main ta ins a cur rentlisting of ‘Chandler’ nursery plant sources inthe United States and Canada for interestedgrowers.

Plant type. Plug plants are generallymore expensive to purchase than fresh-dugstrawberry plants, but they do have the ad-vantage of being suitable for mechanical trans-planting with a water-wheel or pot mulchplanter, whereas fresh-dug plants most oftenare transplanted by hand. The establishmentprocedure for highly perishable fresh-dugtransplants depends on intense overhead sprin-kling for 1 to 2 weeks, depending on weather.Commercial grower experiences in North

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Carolina with plug plants indicate that thesedo not require intensive overhead sprinklingfor post-planting care. Plugs are definitelyrecommended over fresh-dugs for part-timegrowers who do not have the time to overseethe continuous overhead watering of fresh-dug plants during the first week followingfield transplanting. Also, less-experiencedgrowers are encouraged to consider plantingplugs because they are more “mistake-proofthan highly perishable fresh-dug plants. Trans-planting dates for plugs can also be slightlylater than for fresh-dugs without as great ayield reduction. This is because plugs estab-lish more quickly than fresh-dugs after trans-planting. Plug plants have been found to becomparable to fresh-dug plants in both mar-ketable yield and fruit size (Poling, 1992).

Planting period. Until recently, plasti-culture growers could not obtain fresh-dug(green) plants until sometime in very lateSeptember or early October from northernU.S. and Canadian nurseries. This happens tobe the best time of year for transplanting inthe lower piedmont and southeastern NorthCarolina, but earlier transplanting dates areneeded to achieve full crops in colder climaticareas, such as the upper piedmont and moun-tains of North Carolina (USDA zones 7a and6b, respectively), Virginia, Delaware, Mary-land, and New Jersey. Growers in westernNorth Carolina can achieve target plantingdates in mid-September by using fresh “con-tainer-grown” strawberry plug plants.

P l a n t s p a c i n g . There are two plantrows per bed (“double row hill”). Plantsbetween rows are generally offset for im-proved light and air circulation (Fig. 5 middle).There is usually 12 to 14 inches (30 to 36 cm)between the plant rows, and 12 to 16 inches(30 to 41 cm) between plants in the row.With 5 ft (1.52 m) between bed centers,17,400 plants/acre (43,000 plants/ha) willbe required at the 12 × 12-inch (30.5 × 30.5cm) spacing; 14 ,900 plants /acre (36,800plants/ha) at the 14 × 12-inch (35.6 × 30.5-cm) spacing; and 13,000 plants/acre (32,120plants/ha) at the 16 × 12-inch (40.6 × 30.5-cm) spacing.

S t o r a g e , h a n d l i n g , a n dt r a n s p l a n t i n g p r o c e d u r e s

Fresh-dugs. Freshly dug plants may bestored in a cold room at 40F (4.4C) for 1 to2 days before setting. Storage for a longerperiod can make the plants more difficult toestablish. Plants in a nursery box or crate arepacked tightly enough (typically packed 500to 1000 plants per crate) to make them proneto what is called a “heat’‘-rendering themunfit for subsequent planting in the grower’sfield. It is very important to cool the plants prior


Fig. 6. Fresh-dug transplantsshould have three or morehealthy original leaves re-maining at the end of theestablishment period. Notethe development of two newleaves from the crown ≈ ≈ 3weeks after transplanting.

Fig. 7. The appearance offresh-dug ‘Chandler’ plantsin late December (plantstransplanted in the 3rd weekof September). Actually, theseplants may be considered “tooadvanced,” as the leaves fromplants in the row should nottouch until late winter.

to transit. During hot weather, it may benecessary to run water through the crates tokeep plants cool.

The fresh-dug strawberry plant is hand-transplanted through the plastic mulch in2.5-inch (6.4-cm) slits cut by specially con-structed spacing wheels that also open a nar-row hole for planting (Fig. 5 bottom). Thisequipment can reduce substantially the timerequired to set fresh-dug strawberries ( ≈ 4 0h/acre, or ≈ 100 h/ha). Some root pruningmay be needed to shorten roots to 5 to 6inches (12.7 to 15.2 cm) prior to transplant-ing. The plants need to be set so that themidpoint of the crown is level with the soilsurface. If plants are set too deep, the plantsare unthrifty and crowns may rot and plantsmay die. If planted too shallow, the root sys-tem is exposed, which can result in poor root-ing and shifting of the plants. Often plantsmay be set at the right depth, but either be ina small depression or have soil ridged aroundthe crown. When irrigation is initiated toestablish plants, the depression can fill andbury the crown, or the ridge may erode andexpose the roots. A firm plant bed assists inpreventing the bed from settling or eroding.

Overhead irrigation should begin as soonas plants are set-no more than 1 h shouldelapse. These plants will require irrigationvarying from 5 to 7 days after transplanting.Each morning, irrigation should be startedwhen plants show moderate wilt, and shouldcontinue until the hot part of the day haspassed. After a few days, irrigation can beinitiated a little later in the morning, and canbe discontinued earlier in the afternoon. Theprimary purpose of these irrigations is toprevent foliage loss until the root system candevelop and absorb sufficient moisture tosustain the plant. Plants should have three ormore filly green leaves remaining at the endof the establishment period (Fig. 6). Only arelatively small volume of water is requiredfor mist cooling-we have been successfulusing 1/10 inch (0.25 cm)/h. Figure 7 showsthe appearance of ‘Chandler’ fresh-dug plantsin late December.

Plugs. Extended storage of the plantletsor tips generally is not needed. Northerncommercial nurseries can harvest fresh tipsweekly from early July through mid-Octo-ber. The tips are shipped by refrigerated truckto the grower’s farm for delivery ≈ 35 daysprior to field-transplanting. Tips can be storedup to 2 weeks at 34 to 40F (1.1 to 4.4C)without deterioration in quality. The boxes(containing ≈ 1000 plantlets) must be stackedloosely so that the cool air can circulate freelyaround the boxes. The strawberry tips areliving, respiring plants and must be kept cooluntil the grower is ready to root them undermist. The relative humidity in the cooler


should be maintained around 75% to 80%.Prior to rooting, additional plantlet prep-

aration is needed to trim away excess runner-cords . An approximate 3 /8- to 1 /2- inch(1.0- to 1.3cm) runner “stub” serves to an-chor the plantlet until new roots develop(Fig. 8). Fresh strawberry tips are best rootedunder a fine mist, which will wet the foliage yetput very little excess water on the soil. The goalis to keep moisture on the leaves until the plantis well-rooted-about 7 to 10 days. As theroots form, the plants can be weaned from themist and allowed to get their moisture fromthe soil. This is a gradual reduction over 2 to5 days. Two weeks after sticking, most plantsshould be able to be pulled from the cell withthe root ball remaining intact (Fig. 9). Whenthat occurs, misting can be terminated.

Strawberry plants raised in containersare grown in specially prepared growing me-dia. Many different media are available, but a

Fig. 8. (A) Fresh plantletused for rooting has one totwo epanded leaves with thefirst root nodules visible. (B)Three-eighths- to 0.5-inch (1to 1.3-cm) of the runner at-tached so that it can be in-serted in the media to boldthe plantlet secure. (C) Side-view of the plantlet insertedin a 2-3/8-inch (6-cm) plug.

Fig. 9. Two weeks aftersticking, most plan& shouldbe able to be pulled from thecell with the root ballremaining intact.

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soilless media based on peat, sand, grit, ver-miculite, perlite, polystyrene, or other mate-rials is recommended. This requires ≈ 4 ft3

(0.11 m3) of media for ≈ 1000 tips in 60-cellrigid plastic trays measuring 2-3/8 × 12 × 20inches (6 × 30.5 × 50.8 cm). The 60-cell trayis suggested for small and medium-size straw-berry tips. If the tips are quite variable inplantlet length, it is well worth the extra stepto grade the tips into large-, medium-, andsmall lots. The large tips should be rooted in50-cell trays, the medium tips in 60-cell trays,and the smaller tips rooted in 72-cell trays.Sticking large tips [>5 inches (12.7 cm)] inthe same tray with small tips [2 to 3 inches(5.1 to 7.6 cm)] will result in light competi-tion and irregular root growth of the smaller,shaded tip plants. During misting, shadedtips are susceptible to botrytis infection.

After the misting cycle is complete, traysare moved to a fully exposed gravel pad foranother 2 to 3 weeks of growth and acclima-tion before field transplanting. During thisfinal field-conditioning phase, a single dailywatering is suggested, along with a weeklysupplemental drench of a complete fertilizermaterial. A root-bound plug is desirable formechanical transplanting; plugs for trans-lanting by hand can be set before this stages reached. In transplanting plugs, the plantrown (bud) should be just above the soiline, and not buried.

Plug plants pose less-serious problemshan fresh-dugs for field transplanting. Potulch planters or vegetable water wheels can

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b e u s e d t o t r a n s p l a n t s t r a w b e r r y p l u g smechanically. Careful size-grading of tip plantswill produce more-uniform plugs for efficientmachine transplanting. A few hours of over-head sprinkler irrigation after transplantingplugs is also recommended.

Postplant carePostplant fer t i l i ty . I n s o u t h e a s t e r n

North Carolina, drip irrigation applicationsbegin at first bloom (late February) and con-tinue through harvest (ending in late May orearly June). In conjunction with a plant analysisprogram, drip fertigation has the potential toimprove N and K efficiency and, possibly,berry firmness and quality. Over about a 100-day period from late February through lateMay or early June, N and K maintenance dripapplications are made daily, or weekly, at theequivalent of 1 lb/acre per day (1.12 kg·ha-1)of N, along with 1 lb/acre per day (1.12 kg.h a-1) of K 2O. We have not been able toobserve yield or fruit quality benefits in ‘Chan-dler’ by injecting higher amounts of K 2Orelative to N in this maintenance program.(unpublished data).

Biweekly plant analysis is used in the latewinter and early spring to make more-precisedeterminations ofnutrients that may becomelimiting for optimum plant growth and fruitproduction. Most recent, fully expanded leavesare selected and analyzed for identification ofnutritional problems. The following suffi-ciency ranges are used for “Chandler” straw-berry in North Carolina: N, 3.0% to 4.0%; P,0.2% to 0.4%; K, 1.1% to 2.5%; Ca, 0.5% to1.5%; Mg 0.25% to 0.45%; Fe, 50 to 150ppm; Mn, 30 to 100 ppm; Zn, 15 to 50 ppm;Cu, 4 to 15 ppm; and B, 25 to 50 ppm.Petioles are detached and analyzed for nitratenitrogen concentration. Experience to dateindicates that highest yields are obtainedwhenpetiole nitrate nitrogen ranges from 5500 to6000 ppm early in the season, to 800 to 1200ppm at the end of the season (R. Campbell,personal communication).

Water management and opera t ion .As the strawberry plant grows, larger quanti-ties of water are needed because root systemsbecome more extensive and more foliage ispresent . In the fa l l , o ther than for p lantestablishment in the first 2 weeks after plant-ing, relatively little water is needed. In the latewinter, as the drip fertigation program begins(late February/early March), water is fur-nished to the plants through drip fertigation,

s foliage and blossoms begin to developapidly in March and early April, more waters needed. Peak water use occurs in May,uring harvest; obviously, more water iseeded under hot, dry conditions to replacevaporative loss.

Measuring water loss. (Adapted from


Fig. 10. In coastal-plainNorth Carolina, floatingrowcovers can provide pro-tection for strawberry crownsand flower buds during ad-vective freezes in late winter,but the rowcovers are not usedfor sprint radiation frosts,when strawberry blossoms areprotected more reliably withoverhead sprinkler irriga-tion.

Lamont, 1991.) Water loss by evaporationcan be measured by an open pan and is usuallyquoted by agricultural weather reports as panevaporation. Afar easier method of determin-ing daily water need for crops on drip irriga-tion system is the use of tensiometers. Atensiometer consists of a porous, porcelain-tipped tube containing water with a vacuumgauge at the top. The tensiometer is placed atroot-zone depth with the porous tip buried inthe soil. As water attempts to move from theporous tip, a vacuum reading (in centibars ofsoil suction) indicates the moisture status ofsoils. Tensiometers work well for the sandysoils commonly found in many vegetable andstrawberry growing areas in North Carolina.A value of 0 means the soil is completelysaturated with water. A reading of 10 repre-sents a normal field capacity soil water status.The system should be turned on when areading of 20 to 30 appears on the gauge.

Tensiometers usually are installed in pairs,called a “station,” one at a 6-inch (15.2-cm)depth and one at a 12-inch (30.5-cm) depth.The system is turned on when the 12-inch(30.5-cm) tensiometer reads 20 to 30, and isturned off when the shallow [6-inch (15.2-cm)] tensiometer drops to 10 or below. Ten-siometers can be purchased with solenoidswitches to completely automate the pro-cesses.

Rowcovers . It should be realized thatrowcovers should not be regarded as frostprotection systems. For total frost protec-tion, bonafide sprinkler irrigation systems arethe answer. Rowcovers do provide tempera-ture modification, and crops may be slightlyearly if covers are applied in winter, but thepractical value of having a winter rowcoverwould depend on obtaining a very substantialprice for the early crop (Poling et al., 1991).Overwintering covers (strips or floating) maybe justified in western North Carolina andmore northern climates.

We have observed that floating coversdo provide economic benefits in late winterand early spring during advective or windbornefreezes (Fig. 10). During such freezes, sprin-kler irrigation cannot be used to protect thecrop because of high winds. The floatingcovers can be deployed for short durations.The covers can be returned to storage oncefield conditions have moderated. This willhelp to extend the life of the covers-2 or 3years is typical.

Spring frost/freeze control. Overheadsprinkler irrigation is still the best and most-reliable means for protecting strawberry blos-soms from cold injury in March and April. InNorth Carolina, it is not uncommon to pump10 or more nights each spring for as many as8 to 10 h each night. If, for example, thepump is used four consecutive nights, for an


average of 10 h each night at the rate of l/8inch/h (0.32cm/h), ≈ 136,000gal (514,800liters) of water will be needed for protectingjust 1 acre (0.405 ha). The irrigation waterprovides heat to the plant as the temperatureof the water drops to 32F (0C), and especiallyas it freezes. As long as the temperature of theflower or fruit stays above 30F, no damageusually results. The lower the air temperaturethe greater the amount of water needed tomaintain the temperature of the flowers andfruit above the damaging level. Open straw-berry flowers are more prone to freeze dam-age than green fruit, which, in turn, are moresensitive than ripe fruit. If wind speed is 10 to15 mph (16 to 24 km·h -1) or greater, waterapplication with this technique is erratic, andplants as well as flowers and fruit can bedamaged severely. With little or no wind,≈ 0.15 inch/h (0.38 cm·h -1) of irrigation isrequired for frost protection down to a tem-perature of 22F (-5.6C), and ≈ 0.25 inch/h( 0 . 6 4 c m · h- 1) f r o m 2 2 t o 1 8 F ( - 5 . 6 t o-7.8C). Sprinklers should be turned on at34F (1.1C), and left on until the ice begins tomelt and continues to melt when no addi-tional irrigation is applied. Thermometersshould be calibrated in an ice bath and placedin the lowest spot(s) in the field, fully exposedto the sky, and just above the mulch (notprotected by nearby plants).

Plant s i ze management . These f ina lcomments are intended to highlight a few ofthe more-important practices to help manage‘Chandler’ plant size to create a more-opencanopy for easier picking and higher-qualityfruit (Fig. 11 top). Possibly, the most criticalfactor influencing plant size is planting date.In each new region where ‘Chandler’ plasti-culture is attempted, it is important to estab-lish the optimum planting date with fieldtrials. Time of planting trials at the Central

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Fig. 11. (Top) In research studies at the Central Crops Research Station, Clayton, N.C.,the best planting date for Chandler is in the first week of October. (Middle) Berries onthis compact plant are picked easily (canopy not excessive); fruit weight will average ≈ ≈ 20g; and total marketable yield should exceed 1 lb (454g) (photo taken in late April).(Bottom) Following the final harvest in early June, the shoot portion of the plant can besevered to reveal branch formation (five branch crowns is optimum).

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Crops Research Sta t ion , Clayton , N.C.(lat.35°40’N, long.78°30’W, elev. 106 m)have consistently demonstrated that the op-timum planting window is during the firstweek in October (Fig. 11 middle). Earlierplanting dates can result in larger plants withas many as eight to 10 branch crowns. Thickcanopies hinder picking and will result ingreater disease pressure from reduced aircirculation; air movement is also needed toenhance pollination and fruit set. ‘Chandler’plant size management also entails decisionsregarding plant spacing, irrigation, and fertil-izer practices. In North Carolina, the influ-ence of ‘Chandler’ in-row plant spacing onmarketable yield and fruit quality has notbeen investigated adequately. The 12 × 12-inch (30.5 × 30.5-cm) plant spacing usually isrecommended, bu t a number of growersrecently have adopted a wider in-row spacingbecause of problems with excess ‘Chandler’plant vigor. The 14-inch (35.6-cm) in-rowspacing allows easier picking, improved spraypenetration, and less botrytis fruit rot thancloser plant spacing. However, many growersinadvertently are creating a plant “spacingproblem” by planting too early, applying ex-cessive amounts of N and K preplant fertilizer,and by overwatering with their drip irrigationsystems. An interdisciplinary team is currentlyinvestigating thevarious relationships betweenplant spacing and different fertilization prac-tices on the fresh fruit quality, size, and shelf-life of ‘Chandler’ strawberry grown in plasti-culture. As a convenient means of assessing‘Chandler’ plant size, the grower can simplyremove the above-ground portion of the plantat the end of the harvest and count the numberof branch crowns. Optimum plant size charac-teristics and fruit size and quality are associatedwith the production of five to six branchcrowns (Fig. 11 bottom).

Conclus ionStrawberry plasticulture has replaced

bare-ground matted-row culture in much ofNorth Carolina. The major advantages of thissystem are:

● uniform plant stands every year-unaffectedby summer disease, drought, or weed com-petition;

● earlier picking-about 2 weeks;● larger berry size;● easier picking; and● shorter turnaround time from planting to

harvest (7 months).

Against these advantages, one must con-sider higher initial plant costs, higher costs forhand-transplanting, and the fact that thissystem does not lend itself to renovation fora 2nd year of fruiting. Also, total yields with


Fig. 12. In a soil with goodinternal drainage, straw-berry roots will penetrate to adepth of 12 to 14 inches (30 to35 cm).

the plastic mulch system may be no betterthan yields from matted rows, yet establish-ment costs can be higher. There is consider-ably less margin for error with this productionsystem. It is suggested that even seasonedstrawberry growers consider only a 0.5 - to 1-acre (0.2 to 0.4 ha) initial planting to “learnthe ropes” of strawberry plasticulture beforemaking a large financial commitment.

Literature CitedBallington, J.R. and R.D. Milholland. 1993. Screening strawberries for resistance to Colletotrichumacutatum in North Carolina. Acta Hort. (In press.)

Galletta, G.J. and D.H. Scott. 1970. The ‘Apollo’and ‘Atlas’ strawberries. North Carolina StateUniv. Agr. Expt. Sta. Bul. 438.

Hochmuth, G.J. 1992. Concepts and practices forimproving nitrogen management for vegetables.HortTechnology 2(1):121-125.

Lamont, W.T. 1989. Use of a portable pumping andfiltering’& for on-farm plastic mulch-drip irriga-tion demonstrations. HortScience 24(5):848-849.

Lamont, W.J. 1991. Drip irrigation for plasticulturestrawberry production. Proc. 21st Annu. Conf.,N.C. Strawberry Assn., Inc. 21-22 Nov. 1991. p.2 - 6 .

Poling, E.B. 1992. A two-year field comparison of


strawberry fresh-dug and plug transplants on plas-tic mulch. 2nd Intl. Strawberry Symp., Baltimore,Md., 13-20 Sept. 1992 (In press.)

Poling, E.B., K.B. Perry, W.J. Lamont, and J.B.Earp. 1988. Annual hill system strawberry re-search. Hort. Sci. Res. Ser. 76, N.C. Agr. Res. Ser.

Poling, E.B., H.T. Fuller, and K.B. Perry. 1991.Frost/freeze protection of strawberries grown onblack plastic mulch. HortScience 26:15-17.

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