(thing) by cami Thu Sep 12 2002 at 5:40:12

Eustoma grandiflorum

A Grower's Guide to Lisianthus Production


Lisianthus has traveled a long way from its origin as a common North American wildflower to its current use as a flowering potted plant, bedding plant and cut flower. Lisianthus are now produced worldwide, and their popularity has grown to the point where they are one of the top 10 cut flowers in the Dutch auction system.

Lisianthus is known botanically as Eustoma grandiflorum, with common names of prairie gentian or Texas Bluebell. Lisianthus is available in a wide range of flower colors, from deep purple-blue, rose, pink and white to various bicolors. Flowers can be a double or single in form.

The Growing Environment

Lisianthus may be produced in open fields, in low-tech greenhouses that simply protect the plants from wind and rain or in climate-controlled greenhouses. For best results, grow Lisianthus with a minimum air temperature above 15 degrees celsius. Air temperatures below this level will inhibit plant development and greatly add to crop time. Crop quality is greatest if the daytime high temperature is less than 25 degrees celsius, although plants will tolerate much higher temperatures. Some cultivars of Lisianthus are extremely susceptible to high temperatures, and may respond by rosetting or premature flowering.

While open-field production is possible, most growers in moderate climates grow Lisianthus in greenhouses equipped with shade cloth systems. These greenhouses provide protection from extremes in the environment that can devastate a crop. Production in full sun can result in 60% shorter stems than the same varieties grown in greenhouses or in outdoor shadehouses.

In regions that require heating, successful Lisianthus production requires both space heating and soil-surface heating. Attempting to produce cut flower Lisianthus with only one of the two methods will mean a delay in harvest due to increased production time, rosetting of plants or an increase in loss due to disease. Space heating increases the air temperature around the crop and can be done with forced air heaters or finned heating pipes suspended above the crop.

Soil-surface heating requires a hot water boiler system. The water should circulate over the surface of the beds in 2-cm tubes. Water temperature does not need to exceed 40 degrees celsius. Use a circulating pump that will provide a complete circuit of water in six minutes. Under Southern California environmental conditions, groundbed-heating systems are recommended from September through May. Soil temperature should not drop below 15 degrees celsius, or root development may slow, followed by a reduction in overall growth.

Bed Preparation and Planting

Bed preparation prior to planting is the most important part of Lisianthus production. First, test the soil. Lisianthus grows best with a pH between 6.4 and 7.0, higher than many other cut flower crops. Lisianthus also grows best with high calcium levels and adequate phosphorous. Adjust the pH and add calcium and phosphorous prior to planting. Generally, optimum pre-plant preparation includes spading and rototilling the groundbeds at least once a year, prior to soil pasteurization. Be sure bed preparation loosens any hardpan that forms below the planting bed.

Lisianthus is very susceptible to soilborne diseases. New groundbeds may not require treatment, but beds known to be infected should be treated to eliminate disease. Growers report success with both steam sterilization and methyl bromide. Biological control is also being tested. Some growers form beds prior to treatment, while others wait until after pasteurization. Disinfect all equipment used in bed preparation or planting to prevent reintroducing diseases. Recent developments indicate repetitive production in groundbeds may increase the potential for disease, even when soil has been treated with Methyl Bromide or steam sterilization. Rotating groundbeds to other cutflower crops is highly recommended after three years of continuous Lisianthus production.

Spacing. Ideal plant density is a function of available light. Outdoor light that averages above 65,000 lux at midday is considered high light; between 32,000 and 65,000 lux is moderate and less than 32,000 lux is low light density. Typical planting density in areas of highlight is 84 plants/m2 or even higher. Growers in regions with less light plant 64 plants/m2. Where light levels vary with the season, growers will utilize higher density plantings in the summer, and lower density in the winter.

Non-pelleted Lisianthus seeds are very small (19,000 seeds per gram), and seedling growth is slow. For these reasons, most Lisianthus growers purchase plug seedlings from a specialist propagator.

Transplant the seedlings before they become root-bound. Any growth restriction in the seedling stage will result in decreased stem quality of the mature plant. Do not damage roots during transplanting. Damaged roots can result in poor growth, delayed maturity or even plants that fail to grow. Seedlings planted more deeply than they were growing in the plug tray are prone to disease.

Crop Culture

Fertility. Lisianthus grows best with high fertility levels in the soil. Some growers broadcast a 3-month slow-release fertilizer over the soil surface immediately after transplant. Other growers begin liquid fertilization immediately following transplant. In general, nitrogen should be predominantly in the nitrate form; potassium should be equal to nitrogen. Feed with liquid fertilizer at 200 ppm N and K at every irrigation or every other irrigation. Use supplemental calcium during production unless the soil has a high calcium content; calcium nitrate may be used as one component of the fertilizer solution to provide calcium.

Irrigation. Lisianthus irrigation requires careful attention. Excessive irrigation increases plant susceptibiliy to soil-borne fungal pathogens. On the other hand, drought stress can cause premature flower initiation resulting in short, weak stems. Generally, the lower the light and temperature, the less water the plants require.

Most growers establish the crop with overhead irrigation, then switch to drip irrigation after roots are established in the beds. Lisianthus also responds positively to overhead irrigation during periods of high heat and light. Increasing humidity in the greenhouse with an early afternoon irrigation can increase stem length in regions with high heat and light. Avoid high humidity and overhead irrigation after buds have formed however, since botrytis can develop.

Lighting. Lisianthus growth, crop time and flower quality are affected by light intensity and daylength; response varies per variety. For example, one would choose the Avila/Ventura series for faster production under low light, short day conditions; Balboa/Malibu series for moderate temperature and light conditions; then Catalina/Laguna series for best stem quality when flowering under high light and long days. Highest plant quality results from plants grown with maximum amount of light, avoidance of extreme temperatures and supplies of sufficient nutrients. In regions with low light intensity, supplemental high-intensity lighting may be necessary to produce a quality crop.

Lisianthus growers debate the effect of daylength modification. Those who have experimented with it feel that under low light conditions, supplemental lighting encourages stem elongation and flower initiation. Growers report that solid set or cyclic lighting, day extension or night interruption have all resulted in high quality Lisianthus. In general, growers have experienced good results with 16-hour daylengths. Dutch growers use HID lighting, while growers in California have had success using one row of 150-watt incandescent lights spaced 3 m apart for each 4.5 m-wide greenhouse section.

Harvest

Cut flower Lisianthus are harvested when one or more flowers are open. The Dutch auction system requires two open flowers. Growers often remove the first and sometimes the second flowers that open before harvesting. This increases the number of flowers open on a stem at one time.

Flowers should be harvested in the mornings, when flower and plant tissues are cool. Remove field heat by transferring harvested bunches to coolers to optimize postharvest life. Always use clean buckets with fresh cool water for harvested Lisianthus. Do not ship flowers that have not had field heat removed.

Lisianthus are not known to be sensitive to ethylene. However, pulsing with 10% sucrose for 24 hours after harvest increases vase life.

In Japan and Holland, cut flower Lisianthus are brought to market in 10-stem bunches. In the United States, the market accepts "grower" bunches that are bunched according to stem caliper; four to 14 stems may comprise a bunch.

Crop Timing

Crop cycle from transplant to harvest is related to variety and environment. In general, Lisianthus production from transplant requires up to 15 to 18 weeks under low light and temperatures, but can be as fast as 11 to 12 weeks from transplant with optimal light and temperatures. While stem quality is highest by producing Lisianthus at lower temperatures, crop time will be extended and may not be economically justified.

Variety Selection

Varietal selections are divided between double and single-flowering Lisianthus. In general the North, Central and South American market prefers only double-flowering varieties while the European and Japanese cut flower markets prefer single-flowering Lisianthus. Recent market trends (1999-2001) in Holland and Japan indicate the preference for double flowering Lisianthus is increasing in these markets as well.

Color preferences also differ between markets. 31% of North American production is concentrated on White, followed by Purple at 22% and Blue Rim at 15%. Dutch and Japanese consumers prefer dark blue flowers, however, Europeans desire these flowers produced from dark blue flower buds, while Japanese consumers accept dark blue flowers only from plants with green flower buds. Other popular colors include blue rim, rose-pink, white, purple, blue blush, pink blush, pink rim, yellow, ivory and various pastel shades.

To date, most Lisianthus breeding has focused on introduction of new colors and flower forms. Breeders now are developing Lisianthus to address some of the production difficulties in existing varieties. As with Antirrhinum, breeding for year-round production is a focus. New varieties have been introduced with better seedling vigor, stem quality (stem length and caliper), crop time, flowering uniformity and resistance to rosetting and disease.

Double-flowered series

--Avila: true winter-flowering double-flowered series, able to flower under lower light and lower greenhouse temperatures than any other currently existing series. Varieties available include Blue Rim, Deep Rose, Ivory, Purple, and Rose Rim.

--Balboa: spring and fall-flowering double-flowered Lisianthus. Varieties available include Blue, Blue-Rim, Blue Blush, Purple, Yellow and White.

--Catalina: summer-flowering double-flowered series, with a high degree of resistance to rosetting. Varieties available include Blue Blush, Yellow and White.

Single-flowered series

--Ventura: ideal for production under short days and low-light intensity, bred for seedling vigor, earliness, uniformity, stem strength and resistance to rosetting. Varieties available include Blue, Blue Rim, Blue Blush, Deep Blue, Purple with dark blue buds, Purple with green buds, Rose, Deep Rose, Peach and White.

--Malibu: best for production under moderate light intensity and daylength, typically used for spring and fall-flowering. Varieties available include Blue Rim, Blue Blush, Deep Blue, Deep Rose, Purple, Lilac, Rose, Rose Rim and White.

--Laguna: first choice under conditions of high light and long days, maintains excellent stem length and strength. Varieties include Deep Blue, Blue Blush, Deep Rose and Rose Rim.

Production Challenges

Rosetting. Rosetted plants have a cluster of leaves with very short internodes on the stem. The most common cause of rosetting is high temperatures sometime during young plant production. Susceptibility to rosetting varies by variety and can be affected by conditions during seed production. Plants that exhibit rosetting have been induced to grow through applications of gibberellic acids. Identify if rosetted plants are present three to four weeks after transplanting, then begin gibberellin applications if necessary. Growers have experimented with rates from 10 to 100 ppm, with one or two spray applications. Growers must verify if such an application conforms to label, local and national laws. Although rosetted plants will usually begin to grow eventually, the steam quality is often reduced, time to flower is unacceptably long and the results are unacceptable for commercial production. New series such as Avila, Balboa and Catalina have demonstrated good resistance to rosetting.

Insects. Lisianthus are not particularly susceptible to insects, but can be attacked by aphids, leaf miner, lepidopterous larvae, thrips and whitefly. Fungus gnat larvae can be a problem in seedling production. A good scouting effort that includes walking all benches can prevent surprises. Initiating a spray program as soon as the problem occurs will usually eliminate the pest quickly; controlling a major outbreak can be quite difficult.

Diseases. Claude Hope, the world-renowned plant breeder, said Lisianthus are susceptible to most common plant diseases, plus a few others. As with insect control, it is imperative that growers scout all their Lisianthus beds regularly to find infections before they become severed.

--Alternaria Leaf Spot: has been observed in Midwest greenhouses during late spring. Numerous minute, tan lesions observed on upper leaf surfaces.

--Botrytis Blight: common with cool temperatures and high humidity, causes flower and leafspots that can cause a tan stem canker that can kill the plant.

--Curvularia Blotch: can cause light tan spots on Lisianthus foliage and flowers. Unfortunately, this fungal disease develops fastest at the moderate temperature best for Lisianthus growth.

--Fusarium Crown, and Stem Rot, and Fusarium Wilt: F. avenaceum causes crown and stem rot typified in late infections by the production of white fungal growth and masses of orange spores. Fusarium crown and stem rot appears to be closely linked to infected transplants, and is favored by cool temperatures. F. oxysporum produces root and crown rot and wilt and salmon to pink spore masses in the steam as the disease progresses (never orange). Fusarium wilt commonly occurs in contaminated soils not properly fumigated or heat-treated, and is favored by high temperatures, a low soil pH, and ammoniacal nitrogen.

--Downy mildew: is typified by light brown or gray-white powdery growth beginning on the undersides of leaves.

--Pythium Root Rot: common in contaminated soil. This fungus causes a root rot that results in the outer root surface separating from the inner section. Slight infections result in decreased plant growth; severe infections result in wilt and plant death.

--Rhizoctonia Stem Rot: Rhizoctonia, a soil-borne fungus that can cause a crown rot, often soon after planting. Under humid conditions and warm to hot temperatures the fungus may also cause aerial blight of stems and leaves.

--Thelaviopsis was reported in January 2000 on Lisianthus produced in Florida. Investigations of the importance of this pathogen to Lisianthus are ongoing.

--Tomato Spotted Wilt Virus/Impatiens Nectotic Wilt Virus (TSWV/INSV): causes stunting, disortion and chlorotic mottling of the foliage and necrotic regions on the stem; spread by thrips.

--Bean Yellow Mosaic Virus (BYMV): results in leaf curl, chlorosis or flower break; spread by aphids.

--Tobacco Mosaic Virus (TMV): causes mottling of the foliage. It is spread by contact with the virus, not insects. Tobacco products, such as cigarettes, can contain the virus, which is easily transmitted on workers' hands.

--Tomato Yellow Leaf Curl Virus (TYLCV): causes distorted growth, cup-shaped leaves, swelling of veins on the undersides of the leaves and lack of flowering; is spread by Bemisia tabaci, the sweet potato or silver leaf whitefly.

Viruses generally produce more severe symptoms when present in combination.

Nutrient toxicity/deficiency. Lisianthus nutrition can be summed up in three important points:

-- maintain high pH (relative to most crops), from 6.3 to 7.0;
-- maintain high calcium levels in the substrate, and
-- keep all nutrients high in the substrate.

The most serious nutritional problem with Lisianthus is a general lack of major nutrients. The only symptom of this deficiency is reduced growth, which is not readily apparent unless well-fertilized plants are grown for comparison. Symptoms such as foliar chlorosis do not appear until growth has already been limited. For this reason, routine substrate analysis and fertilizer applications are necessary.

Calcium deficiency can cause tip burn of young foliage, bud abortion and poor stem strength. Calcium deficiency can occur even with adequate calcium levels in the soil if the air is humid, preventing translocation of calcium in the plant. Foliar applications of calcium fertilizers may be needed. Low pH can result in poor growth and weak stems. Zinc toxicity appears as symptoms of interveinal chlorosis progressing to bleached foliage; it is also more common with low pH.

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