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Robert H. Stamps

Six shadehouses were used in tests of irrigation rates and crop covers for cold-protecting leatherleaf fern [Rumohra adiantiformis (Forst) Ching]. Each shadehouse was equipped with two irrigation systems—one over-the-crop to supply heat and one over-the-shadehouse to supply water for sealing the openings in the shade fabric with ice. The over-the-crop irrigation system consisted of frost protection wedge-drive impact sprinklers providing water application rates of 0.30, 0.56, and 0.76 cm/h. Six-m × 9-m spunbonded polypropylene crop covers weighing 20 and 51 g·m–2 were tested. During radiation freezes, all water application rates protected immature fronds from damage. Damage during advective freezes decreased with increasing water application rate, but, even when crop covers were used in conjunction with irrigation, some damage still occurred. Temperatures under the lighter-weight cover were higher than under the heavier-weight one, probably because more water passed through the lighter cover to the crop. Water application rates had no effect on frond yield.

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Robert H. Stamps

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Robert H. Stamps

Six preemergence herbicides were applied twice a year at 1x and 2x rates for 2 years to leatherleaf fern [Rumohra adiantiformis (Forst.) Ching] starting from the time of rhizome planting. Predominant weeds present were Cardimine hirsuta, Erechrites hieracifolia, Oxalis stricta, and Phyllanthus tenellus. All herbicides, except pendimethalin and oxadiazon at the 1x rates, reduced weed biomass by 60% to 99% compared to the unweeded control during the fern bed establishment phase (year 1). During that period, hand-weeding times were reduced (51% to 95%) by prodiamine and dithiopyr at both rates, and oxadiazon and pendimethalin at 2x rates. During year 2, herbicides were of greatly reduced benefit due to reduced weed growth caused by the increasingly competitive fern. After 2 years, only 2x dithiopyr-treated plots had reduced yields compared to the hand-weeded controls. Herbicide treatments had no detrimental effects on frond postharvest longevity. In fact, fronds harvested from the 1x isoxaben-treated plots exhibited increased vase life compared to the controls.

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Robert H. Stamps

As the area devoted to cut foliage production has increased and residential development has encroached upon these agricultural areas, conflicts between growers and homeowners have increased. Withdrawals of water for cold protection produce severe reductions of local artesian levels which render domestic wells inoperative and lowered lake levels have made some boat docks useless. Overhead sprinkler irrigation has been used for irrigation and cold protection of cut foliage crops since the 1960's. Using water application rates of about 0.84 cm·hr-1 growers were able to reliably supply product on a year-round basis. Water management district developed regulations mandate that certain water saving methods be implemented prior to the issuance or renewal of consumptive use permits and limit water application rates for cold protection to 0.56 cm·hr-1 under certain circumstances. Research on irrigation scheduling and various cold protection strategies have and are being conducted to allow further reductions in water use during the production of cut foliage crops.

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Robert H. Stamps

Established leatherleaf fern was grown for one year in a glasshouse in intact soil columns (Astatula fine sand, 21 × 61 cm) contained in drainage lysimeters. Columns were fertilized at rates of 224, 448, or 672 kg N ha-1 yr-1 using controlled-release (CR) fertilizer, either 360-day (360CR) or 180-day (180CR) term, or weekly applications of liquid (L) fertilizer. Water use, yield (number of harvestable fronds) and average frond weight increased linearly with increasing fertilization rate and more fronds were produced using L than CR fertilizers. Frond color measurements paralleled yield results. During cool weather when vase life is greatest, fronds from L fertilizer lysimeters lasted longer than fronds from CR treated plots. During warmer weather, treatments had no effect on vase life. Nitrate nitrogen (NO3-N) leaching increased with fertilization rate and exceeded 10 ppm in leachate from the L and 180CR treatments at all application rates. NO3-N in leachate from 360CR lysimeters never exceeded 8 ppm at any application rate.

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Robert H. Stamps

Four spunbonded crop covers were evaluated for use with and without irrigation for cold protection of leatherleaf fern [Rumohra adiantiformis (Forst.) Ching]. Heavier and less porous covers provided the most protection when used without over-the-crop irrigation. However, differences in cover weight and porosity did not affect temperatures under covers when over-the-crop irrigation was applied. Damage to immature fronds was decreased by 75% to 99% when the covers were used alone and by 98% to 99% when the covers were used with over-the-crop irrigation. Covers had no effect on frond vase life.

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Robert H. Stamps

Impatiens `Dazzler Violet', Petunia × hybrida `Carpet Blue', and Spathiphyllum `Ty's Pride' plugs were planted in 10-cm pots containing a commercial peat-based soilless growing medium composed of Canadian 60 peat: 20 vermiculite: 20 perlite (by vol) not treated with surfactant. Growing medium was treated, or not treated, 1) at planting, 2) during production, and/or 3) preshipment with experimental surfactants. The production phase consisted of growing plants on raised benches in a greenhouse until they reached marketable size. Phytotoxicity, plant water use and growth were determined. At the beginning of the postproduction phase, growing medium in all pots was brought to container capacity. Plants were then dried to wilting three times. Water loss and water retained on rewatering and times to wilt and recovery were recorded. Surfactant treatments caused no foliar phytotoxicity and did not delay flowering for petunia or spathiphyllum. However, surfactant treatments delayed flowering for impatiens by ≈4 days. Surfactant treatments increased top growth of petunia but not of the other crops. Postproduction, water retention at rewatering, and times to wilt were increased for petunia and spathiphyllum when they were in surfactant-treated medium. For impatiens, treatments had no effects on water retention or wilting, probably due to the small root systems and limited attendant medium dewatering for this crop. Generally, all three experimental surfactants performed similarly and weekly and preshipment surfactant applications were of no additional benefit compared to a single initial application at planting.

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Robert H. Stamps

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Robert H. Stamps

Water is an economical source of heat to prevent cold damage to certain crops; however, ways to reduce the quantity of this limited resource required for cold protection need to be developed. Rapidly rotating (6 rpm) wedge-drive impact sprinklers (conventional practice) were compared with a rotary action spray head and patented slow-rotating stream sprinklers for cold-protecting a subtropical crop {leatherleaf fern [Rumohra adiantiformis (Forst.) Ching]} growing in shadehouses. Treatments were applied in a 3 × 3 latin square design to nine 29 × 29-m post- and-cable shadehouses covered with woven polypropylene shade fabric designed to provide 73% shade. Temperatures in each shadehouse were monitored 45 cm above the soil surface using four constantan–copper thermocouples. Ambient temperatures and wind speeds were monitored using additional thermocouples and an anemometer at a nearby weather station. All sprinklers had 2.8-mm orifices, were operated at 0.25 Pa, and applied 0.5 (rotating stream, rotary) or 0.54 (wedge-drive) cm·hr–1 of water. During an advective freeze with windspeeds up to 19 m·s–1 and temperatures to –2°C, there were no temperature differences due to treatments. During a radiational freeze with readings below –2°C for over 12 hr and a low of –5°C, all three irrigation systems maintained thermocouples at about –1°C. No significant damage to mature fronds were detected. Percentage of immature fronds damaged was not affected by treatments and ranged from 11% for rotary to 43% for the wedge-drive sprinkler treatments. The two newer sprinkler designs (rotary action spray head and patented slow-rotating stream) provided satisfactory protection equivalent to the industry standard (wedge-drive) while using about 10% less water.