Variable Salt Tolerance of Statice

Scientists with the United States Department of Agriculture’s (USDA) research arm, the Agricultural Research Service (ARS), along with faculty from the University of California-Davis, have evaluated various cut flower crops for their productivity when irrigated with saline wastewater. The studies were initiated in response to the increased competition between urban and agricultural use of high quality water. This study focused on two species of statice: Limonium perezii ‘Blue Seas’ and Limonium sinuatum ‘American Beauty’.                

Three-week-old seedlings were planted in greenhouse sand beds and irrigated with prepared water solutions that simulated the saline drainage waters of the San Joaquin Valley in California. The treatments consisted of seven EC levels (Electrical Conductivity measures amount of soluble salts).  The control water had an EC of 2.5, while the other treatment ECs were: 7, 11, 15, 20, 25 and 30 dS/m.                         

Though all treatments resulted in flower production, stem length declined significantly as salinity increased. Overall, L. sinuatum performed better than L. perezii. Since both species completed their lifecycle at salt concentrations exceeding 30 dS/m, they can be considered halophytic plants.                 
From a production perspective, L. sinuatum ‘American Beauty’ was shown to produce commercially acceptable cut flowers with moderately saline water.  It was rated moderately tolerant, compared to L. perezii’s rating as salt sensitive.  

Grieve, C.M., J.A. Poss, S.R. Grattan, P.J. Shouse, J.H. Lieth, L. Zeng. 2005. Productivity and mineral nutrition of Limonium species irrigated with saline wastewaters. HortScience. 40(3):654-658.

Midas: A Methyl Bromide Alternative for Celosia Production

With the continued elimination of methyl bromide use for soil fumigation, alternatives are continually being tested in field trials for acceptable weed, nematode and pathogen control. Midas is a commercial product consisting of a 50:50 mixture of methyl iodide and chloropicrin. ARS scientists conducted a study on the effectiveness of Midas by evaluating the production of Celosia argentea in Martin County, Florida.

The three treatments consisted of 200 lbs/ac of Midas, 200 lbs/ac of methyl bromide:chloropicrin (98:2), and control plots that were untreated. The treatments were covered with metalized film for 15 days. Five days after removing the film, seeds of Celosia argentea ‘Chief Rose’ were planted. Data collected at mid-season and harvest included weed density, fungal colony formation, disease incidence, gall ratings and nematode counts.

In every data category, the incidence of weeds, pests and pathogens was greater in the untreated control plots. The plots treated with Midas had comparable control to the methyl bromide treatment. The stem diameter and height was lowest in the untreated control, with no difference between the two fumigants. The number of marketable stems was significantly higher in the fumigated treatments than the control group.

The use of Midas provided weed, pest and pathogen control in Celosia production comparable to what is achieved using methyl bromide.

Rosskopf, E., N. Burelle, R. Driggers, R. Kreger, J. Holzinger. 2006. Evaluation of Midas for production of ornamental cockscomb (Celosia argentea) in Florida. http:// www.ars.usda.gov/research/publications Acquired 2/27/2007.

Another Closer Look at Temperature and Humidity for Botrytis Control in Freesia

It is widely recognized that temperature is a principal environmental factor affecting initial infection by Botrytis cinerea, and relative humidity (R.H.) affects conidial germination and lesion development. The specific temperature and relative humidity as it affects B. cinerea in freesia flowers was the focus of research conducted in the United Kingdom. The study mimicked the cold chain from harvest to wholesaler monitoring the development of B. cinerea.

Flowers of Freesia cv. ‘Cote d’Azur’ were harvested at a commercially mature stage, with the oldest bud fully developed but still closed. At harvest, no symptoms of Botrytis specking were evident. Flowers were artificially inoculated with B. cinerea. The humidity treatments were 100% R.H. or 80-90% R.H. Inoculated flowers were held for 24 hours at 5, 12 and 20C (41, 54, and 68F). On the second and third incubation days, the flowers were moved from 12 and 20C to 5C simulating the wholesalers storage room temperature.

Data were collected 24, 48 and 72 hours after inoculation. Disease severity was measured according to an arbitrary scale from 0=no lesions on the petals to 4=50-100% of petal surface area affected by lesions. The number of lesions and diameter of lesions were also measured. The lesions are brown or white volcano-shaped specks that decrease flower quality.

The study suggests that R.H. is a critical factor for infection of B. cinerea in freesia flowers. At 100% R.H., at 5, 12 and 20C, disease establishment occurred within the first 24 hours of inoculation. R.H. below 90% suppressed disease incidence at all treatment temperatures. In fact, only at 12C were lesions produced at 80-90% R.H. Previous studies suggested that 20C was the optimum temperature for Botrytis infection; however, this experiment did not generate visible lesions at 20C and 80- 90% R.H., even after 72 hours.

After the initial 24 hours, disease severity, lesion numbers and lesion diameters showed a marked increase when held at 5C compared to 20C. Flowers held at 20C did produce lesions, but they did not expand over the 72 hours of data collection.
While temperature is a factor in Botrytis infection, this study suggests relative humidity should be the greater consideration for reducing disease incidence in freesia.

Darrau, A.I., D.C. Joyce, L.A. Terry and I. Vloutoglou. 2006. Postharvest infection of Freesia hybrida flowers by Botrytis cinerea. Australasian Plant Pathology. 35:55-63.