Pollen-free Sunflower Cultivars That “Make the Cut”

Researchers at the North Mississippi Research and Extension Center evaluated 29 cultivars of Helianthus annuus with general florist use in mind.  Some sunflower blooms and stem diameters are too large for typical florist use.  They limited their research to pollen-free cultivars, which are preferred by florists for longer vase life and cleaner arrangements.  They assessed stem length, stem diameter and bloom diameter of flowers harvested from six summer planting dates.
    
The sunflowers included 13 single-stem cultivars and 16 branching cultivars. The seeds were sown in 1204 cells and transplanted into the field where they were fertigated weekly. Single-stem cultivars were space 6 inches apart, while the branching cultivars were spaced 12 inches apart.  The branching cultivars were pinched at the four- to six-node stage of development to encourage the growth of multiple stems.  Stems were harvested when the blooms were completely open.
    
Based on communication with florists in Tupelo, Mississippi, the florist standard used for comparison was 60-90 cm (23.5-35.5 in) stem length, 0.5-1.5 cm (0.2-0.6 in) stem diameter and 8-15 cm (3-6 in) bloom diameter.
    
Of the single-stem cultivars, the stem diameters of ‘Full Sun Improved’, ‘Superior Gold’, ‘Full Sun’, and ‘Superior Sunset’ were 2.3 cm (0.9 in) or larger, 90 cm (35.5 in) below the bloom.  This size was significantly larger than most of the other cultivars and was considered too large for general florist use.  They observed the flower size generally corresponded to stem diameter.
    
Nine of the single-stem cultivars produced secondary stems after harvest of the terminal stem.  The stem length ranged from 44.4-60.8 cm (17.5-24 in) with no significant difference in bloom size among the cultivars. Most were determined to be satisfactory for florist use.
    
The stem diameters of the branching cultivars ranged from 0.42-0.80 cm (0.17-0.31 in), nearly all acceptable for florist use. The dark-flowered cultivars, including ‘Moulin Rouge’, ‘Claret’, ‘Infrared’, ‘Cappuccino’, ‘Strawberry Blonde’, and ‘The Joker’, produced the most stems with the longest stem length. ‘Though the yellow/gold-flowered cultivars produced few stems and smaller flowers, nearly all of the branching cultivars were determined to produce stems suitable for florist use.

Sloan, R.C. and S.S. Harkness. 2006. Field Evaluation of Pollen-free Sunflower Cultivars for Cut Flower Production. HortTechnology 16(2):324-327.

Fumigation Options Using Drip Irrigation

A variety of weed species can quickly overgrow the sparse canopy of Freesia x hybrida,  reducing crop quality and yield.  Scientists at the USDA’s Agricultural Research Service at the San Joaquin Valley Agricultural Sciences Center in California are looking at improved delivery methods for methyl bromide alternatives.  Using drip irrigation would allow for better distribution of the chemicals and utilize a totally enclosed system for application, which increases worker safety and reduces the environmental impact.
    
Three trials were conducted, one in Encinitas and two in Nipomo.  Soil samples were taken and weed counts were made at each plot.  The data included average plant height, a vigor rating and disease incidence.
    
The first Nipomo trial tested various rates of the methyl bromide alternative 1, 3-dichloropropene (60.8%) + chloropicrin (33.3%), also referred to as DP:CP.  Early season weed control was reasonably good compared to the control plots and at the trial conclusion, all treatments had taller stems, better vigor and significantly less weed cover compared to the control.  The incidence of Pythium spp. populations was also greatly reduced.
    
The Encinitas trial compared four methyl bromide alternatives: 1) DP:CP, 2) iodomethane (50%) + cholopicrin (50%) [IM:CP], 3) Furfural, 4) Furfural + metham sodium (FMS).  All treatments produced lower average weed counts compared to the control.  With the exception of the Furfural treatment, average plant height was greater for all treatments compared to the control, though vigor ratings were not significantly different among the treatments. Pythium spp. populations were again reduced, compared to the control.
    
In the second Nipomo trial, various formulations of IM:CP were tested against MB:CP (methyl bromide + chloropicrin, 50:50) and the untreated control.  All the treatments demonstrated fewer weeds throughout the growing season compared to the control.  The freesia had a higher vigor rating for the treated plots, but there was no significant difference in plant height.  The treatment plots had reduced Pythium spp. populations compared to the control.
    
While this study found the Furfural alone did not perform as well as other treatments for weed control, it concluded that a successful freesia crop can be grown using methyl bromide alternatives applied through drip irrigation.    

Gerik, J.S. 2005. Drip-applied Soil Fumigation for Freesia Production. HortTechnology 15(4):820-823.

Western Flower Thrips’ Flower Color Preference

Previous research has shown that western flower thrips (Frankliniella occidentalis) are attracted to certain flower colors and species.  Those studies used specific colored surfaces, but did not consider the spectral qualities of the colored surfaces.  Researchers at the University of Illinois worked to determine if western flower thrips (WFT) had a flower color preference that could assist in the selection of a trap crop for control of the insect pest.
    
Special observation chambers were used for the experiment.  The test flowers consisted of four different colors of three species (Transvaal daisy, Matsumoto aster and chrysanthemum). Daisy colors were yellow, orange and red.  Aster colors were white, purple, pink and magenta. Chrysanthemum colors were yellow, burgundy, white and lavender.  In an effort to provide a similar surface area for the WFT experiment, it was determined that one Transvaal daisy was equivalent to five Matsumoto aster and three chrysanthemum blooms.
    
Flower color preference was evaluated based on the number of WFT adults collected from each flower after 72 hours.  The spectral reflectance of the flowers and three colored sticky cards were measured to assess any response to specific wavelengths.
    
The most WFT were found on the yellow Transvaal daisy with 54, nearly twice as many as the other flowers.  Yellow chrysanthemum followed with 30 WFT and then white Matsumoto aster and orange Transvaal daisy with 22 each. The most attractive bandwidth to WFT may be between 550- to 600-nm (yellow daisies and yellow sticky cards).  The shorter wavelengths (380- to 450-nm) appear to be less attractive to WFT contradicting the common notion that blue sticky cards are more effective for sampling or trapping WFT.
    
Based on this study, the yellow Transvaal daisy may be used as a trap crop for growers managing WFT; however, the researchers point out that factors other than color likely play a role in WFT attraction.  Further studies of floral volatiles, pollen age, or a combination of these and color will lead to more conclusive information.

Blumthal, M.R., R.A. Cloyd, L.A. Spomer, and D.F. Warnock. 2005. Flower Color Preferences of Western Flower Thrips. HortTechnology 15(4): 846-852.

Megan Bame

Megan Bame is a freelance writer in Salisbury, North Carolina. Contact her at [email protected]