2009 Spring – Research Update

Nitrogen Uptake from Foliar-sprayed Urea on Hydrangeas

Researchers at Mississippi State University understood that perennial plants, including Hydrangea macrophylla, can store nitrogen acquired in the fall, and remobilize the stored nitrogen for new growth the next spring. However, nitrogen applications to the soil late in the season had been shown previously to promote continued growth and cause a delay in dormancy and cold acclimation. This experiment focused on the foliar application of urea. Other studies suggested hydrangea leaves rapidly absorb a majority of the urea from a foliar spray application, even during leaf senescence, translocating the absorbed nitrogen from the leaves into storage tissues. Using ‘Berlin’ hydrangea, this research aimed to determine the duration of nitrogen uptake and translocation from the urea spray, and consider what affect nitrogen status of the plant had on foliar nitrogen uptake.

Hydrangeas were grown under 40% shade in Mississippi. Starting in early July, plants were divided into five treatment groups. The treatments were one of five concentrations of nitrogen (0, 5, 10, 15, or 20 mM from ammonium nitrate) applied twice per week for 10 weeks via drip irrigation. In late October, plants were sprayed with 3% urea to the point of runoff. Plants were sampled before the urea application and 2, 5, 10 and 15 days after the spray treatment.

Analysis of nitrogen content in the hydrangea plants suggests that the hydrangea leaves rapidly absorb nitrogen from urea during the first two days after spray application. At five days after application, there was no significant additional nitrogen uptake. The hydrangea leaves exported between 50% and 77% of the absorbed nitrogen 15 days after the spray depending on the plants’ nitrogen content from previous fertigation treatments. The data indicate that hydrangea with lower nitrogen content can absorb and export more nitrogen, based on unit leaf area, than those plants with higher nitrogen levels from fertigation treatments.

In conclusion, the nitrogen uptake by hydrangea that have been sprayed with urea will not be detrimentally affected by rain or overhead irrigation five days after application.

Guihong, B. and C.F. Seagel. 2008. Nitrogen Uptake and Mobilization by Hydrangea Leaves from Foliar-sprayed Urea in Fall Depend on Plant Nitrogen Status. HortScience 43(7)
pp. 2151-2154.

IPM in High Tunnels

    Pest and disease pressures exist for crops grown in high tunnels, but they can be addressed with an integrated pest management approach. HortTechnology contributors from Colorado and Wyoming addressed similarities and differences of high tunnel IPM compared to IPM for greenhouse and field production.
    Several general guidelines address preventative measures specific to high tunnel production.

• The soil of transplants brought into the high tunnel should be pest and disease free.
• Practice appropriate crop rotation to minimize buildup of soilborne pathogens.
•  Practice soil solarization to eliminate soilborne pathogens that may have infested the soil.
• Use a ground-to-ground mesh screen to keep out many insect  and mite pests.

 While preventative measures are a major aspect of an IPM program, growers must be prepared to address pest and disease issues when they arise. The following are insect and disease-specific approaches suitable for application in a high tunnel setting.

• Fungus gnat and shore fly: These are often introduced from transplants grown in a greenhouse where the media was infested. The predatory mite Hypoaspsis miles is a recommended biological control for management of fungus gnat and shore fly.
• Western flower thrips: Not only do thrips cause aesthetic damage to flowers and foliage, the are also a vector for tomato spotted wilt virus and impatiens necrotic spot virus. Exclusion screening, reflective mulches and the predatory bug, Orius spp. are recommended for thrips management. A natural population of Orius spp. can be attracted by sunflowers.
• Caterpillars: Regular monitoring should catch caterpillar damage early. Screening and use of pesticides or biological controls are the suggested methods for caterpillar management. Insecticidal soaps, Bacillus thuringiensis and parasitic wasps, such as Trichograma spp. and Cotesia spp., are some examples.
• Aphids: Aphids can also vector viruses. The primary approach for pest management is screening, soaps, oils, neem-based insecticides and biologicals, such as ladybird beetles, green lacewing or the predatory midge Aphidoletes.
  Two-spotted spider mite: Spider mites thrive in warm, dry environments (> 80 degrees F, < 50% R.H.). Raising the humidity, which can be accomplished through irrigation management, or the introduction of a predatory mite (Amblyseius californicus does well in a hot, dry environment) are two methods to address spider mites.
• Powdery mildew: This fungal disease requires a dry leaf surface and a high relative humidity. Increased air circulation with horizontal air flow fans is one of the traditional greenhouse management strategies that may be difficult to accomplish in a high tunnel that would not typically have electricity. Plant spacing, roll-up sides, and open ends are energy-alternatives to improving air circulation. Biofungicides including Ampelomyces quisqualis and Bacillus subtilis could be applied as well as neem-based or bicarbonate pesticides for control of powdery mildew.

 IPM involves pest prevention through cultural methods and exclusion methods. Once a pest or disease problem is discovered in a high tunnel proper management must be employed. Biological control organisms can be a first defense followed by the appropriate pesticides for the crop and the market.

Pottorff, L.P., and K.L. Panter. 2009. Integrated Pest Management and Biological Control in High Tunnel Production. HortTechnology 19(1) pp. 61-65.

Producing Cut Flower in High Tunnels   

    High tunnels are generally defined as simple frame structures usually covered by a single layer of clear polyethylene used to produce crops, such as cut flowers, in the ground. There are several advantages to high tunnel cut flower production as well as a few challenges. Chris Wien recently presented an assessment of cut flower production in high tunnels in HortTechnology, including a crop schedule scenario.

Advantages of high tunnel cut flower production:

• Provides protection against low temperatures, allowing for season extension by way of earlier planting and longer harvest period.
• Allows plants to grow taller due to the protected, calm environment.
• Improves flower quality due to protection from rain and subsequent disfiguring diseases.
• May allow for year-round production in southern climates.

Challenges of high tunnel cut flower production:

• Requires acute awareness of flower triggers such as temperature and daylength.
• Must manually operate ventilation in a way that avoids supercooling or overheating.
• May need to install a windbreak to allow sufficient air exchange without excessive air movement in the tunnel that can result in shorter stems.
• Requires more strategic management of crop space relative to crop value, i.e., a  willingness to remove one crop before it has been completely harvested to make room for a more valuable crop.

Considering the season extension high tunnels offer, Wien suggested a possible cropping scenario including commonly grown cut flowers. The first crops of the season might include tulip, ranunculus and anemone followed by snapdragons, stock, sunflowers and godetia. Lisianthus, trachelium, celosia and amaranth could be grown during the main, warm season, and for the fall, sunflowers, small-fruited varieties of pepper and grass species should suit the market well.
    Wien concludes that the advantages seem to outweigh the disadvantages especially considering the wide range of flower species that can be grown in high tunnels. But he does warn that it will be an important task to observe the affects of tunnel-modified temperatures and daylengths on plant performance to optimize production.

Wien, H.C., 2009. Floral Crop Production in High Tunnels. HortTechnology 19(1) pp. 56-60.

New Introduction: ‘Mimi’ Sweet Pea    

    Sweet pea is a popular forced cut flower in Japan, marketed from November to April. In fact, in 2004, the value of sweet pea cut flower production in Japan was $27 million (USD). The introduction of the new cultivar, ‘Mimi’, represents a 145% increase in marketable flowers compared to                         the pink cultivar currently favored (‘Super Rose’).
    Lathyrus odoratus L.‘Mimi’ was developed at the Miyazaki Agricultural Research Institute by first crossing ‘Stella’ and ‘Early Salmon Pink’ in 1998. Pedigree selection occurred over six generations. Forcing sweet peas requires vernalizing the germinated seeds in cold storage for 4 weeks at 2C (35.6F). Seeds were transplanted in early September at intrarow spacing of 12 cm (4.7 in) and between row spacing of 100 cm (39.3 in). A minimum temperature of 5C (41F) was maintained through the growing season until the end of March.
    The average flower diameter of ‘Mimi’ is 5.8 cm (2.3 in), with 3.8 flowers per inflorescence. According to the Royal Horticultural Color Chart, the flower color is strong pink, and this sweet pea has a moderate fragrance.
    Flower budding of the vernalized plants occurred in mid-October while the first fully opened bloom wasn’t observed until mid-November. The budding of non-vernalized plants occurred in late March, making the natural flowering type, spring. Forced plants produced 35.7 flowers per plant of which 29.9 were marketable.

Akashi, R., 2008. ‘Mimi’ Sweet Pea for Forcing Culture. HortScience 43(7)
pp. 2238-2239.