OFA Bulletin March/April 2011 : Page 3

March/April 2011 • N u m b e r 9 2 6 Grower These rates are based on North Carolina growing conditions, so make adjustments for other growing areas. For instance, more northern growers will want to experiment with half rates. The use of plant growth regulators (PGRs) greatly improved plant quality, produced more compact plants, and increased the water use efficiency of Snow Princess®. The incidence of drought stress was significantly reduced when PGRs were used. This avoided the need to constantly irrigate the plants and eliminated the lower leaf yellowing which can occur at the base of the plant (Figure 6, page 6). Plants with optimal rates of PGRs applied performed very well in the landscape. They reached a plant diameter of around 3 feet. Recommendations Substrate drenches were more effective than foliar sprays with Snow Princess®. Plants were more compact. Liner preplant soaks have the advantage of being applied to the plugs before transplanting. We found that the second pinch was not needed when preplant liner soaks were used and the plants bloomed 7 to 10 days earlier. A second pinch may be used as a method of delaying the crop. Figure 3. Plant growth for Snow Princess ® Lobularia grown with 50, 75, 100, 200, 300, or 400 ppm N. Photograph taken after six weeks of growth. differences among greenhouses, a narrower target fertilization rate between 150 and 200 ppm N should be used. The corresponding target E.C. levels are listed in Table 1. 3. What Causes the Lower Leaf Yellowing of Snow Princess® Lobularia? On occasion, growers have noticed that the oldest leaves at the base of the plant turn yellow and then brown (Figure 6, page 6). The two top reasons proposed were insufficient fertility or drought stress. Table 1. Target E.C. Range. Measurement Method 1:2 Method SME PourThru Target Range (mS/cm) 0.5 to 1.2 1.2 to 2.5 1.8 to 3.75 What We Found The answer to this question was provided by both the fertilization rate study and the plant growth regulator study. The primary cause of this problem is drought stress. The vigorous growth of Snow Princess® can make it challenging to always provide timely irrigations, and if the plants dry down, the lower leaves yellow and then die. 2. What Rate of PGRs Control Growth of Snow Princess® Lobularia? Snow Princess® is a vigorous plant, so growth management is required to control excessive stem elongation and decrease irrigation requirements. Therefore, a series of experiments were conducted to determine the optimal foliar spray and substrate drench rates of Piccolo® (Paclobutrazol) and Concise® (Uniconazole). In addition, we decided to investigate the effectiveness of both Piccolo® and Concise® preplant liner soaks. Recommendations Overcoming this problem requires providing adequate fertility of 150 to 200 ppm N and controlling excessive stretch with plant growth regulators. The combination of cultural practices prevents this problem from occurring. What We Found Snow Princess® was very responsive to the PGR applications (Figure on page 4 and Figure on page 5). Preplant liner soaks of 4 to 8 ppm Piccolo® (paclobutrazol) or 0.5 to 1 ppm Concise® (uniconazole) produced compact plants (Figure 4, page 4). Once growth reaches the side of the pot, foliar sprays of 75 to 100 ppm Piccolo® or 20 to 25 ppm Concise® or substrate drenches of 2 to 4 ppm Piccolo® or 1 to 2 ppm Concise® can be used (Figure 5, page 5). 4. What Causes Tip Death and Distorted Growth of Snow Princess® Lobularia? We gained first-hand experience of a total meltdown of Snow Princess® after a tank mix of insecticides was applied. Symptoms occurred two days after the application during the heat and humidity of the summer (Figure 7A, page 6). The plants stalled and once the new growth began it was distorted (Figure 7B, page 6). Continued on page 4 3 OFA Bulletin

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