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Joseph P. Albano and William B. Miller

Marigold (Tagetes erecta L.) grown hydroponically in an irradiated nutrient solution containing FeDTPA had root ferric reductase activity 120% greater, foliar Fe level 33% less, and foliar Mn level 90% greater than did plants grown in an identical, nonirradiated solution, indicating that the plants growing in the irradiated solution were responding to Fe-deficiency stress with physiological reactions associated with Fe efficiency. The youngest leaves of plants grown in the irradiated solution had symptoms of Mn toxicity (interveinal chlorosis, shiny-bronze necrotic spots, and leaf deformation). Plants grown in irradiated solution in which the precipitated Fe was replaced with fresh Fechelate were, in general, no different from those grown in the nonirradiated solution. Chemical name used: ferric diethylenetriaminepentaacetic acid (FeDTPA).

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Joseph P. Albano and William B. Miller

We have shown previously that Fe-chelates incorporated into soluble fertilizers are vulnerable to photodegradation, and that such solutions can cause modifications in root reductase activity. The objective of this research was to determine the effects of Fe-chelate photodegradation under commercial production conditions. Marigolds were grown in a greenhouse and transplanted stepwise from #200 plug trays to 804 packs to 11.4-cm (4.5-inch) pots. Plants were harvested at the end of each stage, and treatments consisted of either irradiated (complete loss of soluble Fe) or non-irradiated fertilizer solutions ranging from 100-400 mg/L N (0.5–2 mg/L Fe). In the plug and pack stages, foliar Fe was significantly lower and Mn significantly higher in plants treated with the irradiated than nonirradiated fertilizer solutions, averaging 97 μg·g–1 and 115 μg·g–1 Fe, and 217 μg·g–1 and 176 μg·g–1 Mn, respectively. Fe(III)-DTPA reductase activity of roots of plugs treated with the irradiated fertilizer solution was 1.4-times greater than for roots treated with the non-irradiated fertilizer solution. Leaf dry weight in the plug and pack stages was not affected by treatment, and averaged 0.1 g and 1.2 g per plant, respectively.

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Joseph P. Albano and William B. Miller

Our objective was to determine the effects on plant growth and physiology that a photodegraded Fe-chelate containing lab-prepared nutrient solution would have when used in plant culture. Plants grown hydroponically in the irradiated Fe-DTPA containing nutrient solution had ferric reductase activity 2.2 times greater, foliar Fe level 0.77 times less, and foliar Mn level 1.9 times greater than in plants grown in an identical but non-irradiated solution, indicating that plants growing in the irradiated solution were responding to Fe deficiency stress with physiological reactions associated with Fe efficiency. The youngest leaves of plants that were grown in the irradiated solution had symptoms of Mn toxicity. Restoration of the irradiated solution by removing the precipitated Fe by centrifugation and adding fresh Fe-chelate resulted in plants that were, in general, not different from those grown in the non-irradiated solution (control).

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Joseph P. Albano and William B. Miller

Marigolds under iron deficiency stress exhibited characteristics associated with iron efficiency (e.g. induced reductase and rhizosphere acidification). Ferric reduction rates for roots of the minus Fe-DTPA treatment group was 0.97 μmol·g FW-1·h-1, 14 times greater than the 17.9 μM Fe-DTPA treatment group. Excised primary lateral roots from the minus Fe-DTPA and 17.9 μM Fe-DTPA treatment groups embedded in an Fe reductase activity gel visually confirmed an increased Fe reduction rate for the minus Fe-DTPA treatment group. The pH of the nutrient solution one week after initiation of treatments indicated that the minus Fe-DTPA treatment group was 1 pH unit lower than the 17.9 μM Fe-DTPA treatment group at 4.1 and 5.1, respectively.

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Joseph P. Albano and William B. Miller

Irradiation of, ferric ethylenediaminetetraacetic acid (FeEDTA, iron chelate)-containing commercial fertilizer solutions by fluorescent plus incandescent lamps resulted in the loss of both FeEDTA and soluble iron (Fe), and the formation of a yellow-tan precipitate that was mostly composed of Fe. The ratio of soluble Fe:manganese (Mn) was altered due to FeEDTA photodegradation from 2:1 in the nonirradiated solutions to 1:4 in the irradiated solutions, respectively. Storing fertilizer solutions in containers that were impervious to light prevented FeEDTA photodegradation.

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Cindy L. McKenzie and Joseph P. Albano

Tomato irregular ripening (TIR) disorder is associated with sweetpotato whitefly (Bemisia tabaci) biotype B feeding and is characterized by incomplete ripening of longitudinal sections of fruit. Our objective was to determine the effect of time of sweetpotato whitefly infestation on plant nutrition and the development of TIR disorder. Healthy tomato plants (Solanum lycopersicum ‘Florida Lanai’) were introduced to sweetpotato whitefly infestations at different developmental stages of plant growth: 1) five to seven true leaves, 2) flower, 3) green fruit, and 4) breaking red fruit and were compared with noninfested control plants of the same age. Plants were fertilized every 7 to 14 days. Plant nutrition was monitored over time between the noninfested control and the longest infestation interval (five to seven true leaves) and between all infestation intervals at harvest. Sweetpotato whitefly (egg, nymph, and adult) and plant parameters (height, canopy diameter, number of leaves, flowers, and fruit per plant) were taken every 7 to 14 days after sweetpotato whitefly infestation. Almost all of the fruit (99%) produced by tomato plants infested with sweetpotato whitefly at stages 1 and 2 (78 and 56 days of sweetpotato whitefly exposure, respectively) developed TIR with fruit exhibiting internal and external symptoms. Plants infested at stage 3 (35 days of sweetpotato whitefly exposure) had 79% to 80% of the fruit develop TIR. Surprisingly, 58% of fruit from plants infested at stage 4 (14 days of sweetpotato whitefly exposure) also developed the disorder, indicating that tomatoes may need to be protected from sweetpotato whitefly until harvest to avoid this disorder. Seed germination was unaffected by TIR. Plants infested with sweetpotato whitefly had mean foliar levels of calcium, copper, iron, phosphorous, potassium, magnesium, manganese, and zinc that were greater than in noninfested control plants at final harvest for both studies, regardless of time of infestation.

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Joseph P. Albano and William B. Miller

Our objective was to assess the susceptibility of seven marigold varieties to Fe toxicity. Marigold varieties included were one hedge type, `Orange Jubilee'; five semi-dwarf types, `First Lady', `Gold Lady', `Orange Lady', `Marvel Gold', and `Yellow Galore'; and one dwarf type, `Discovery Orange'. Plants were grown in a greenhouse in a soilless medium and treatments consisted of 0.018 mm (low) and 0.36 mm (high) Fe-DTPA incorporated into a nutrient solution. Plant height was not affected by Fe treatment and ranged from 32 cm in `Orange Jubilee', 13 to 14 cm in the semi-dwarf varieties, and 7.0 cm in `Discovery Orange'. Leaf dry weight per plant was not affected by Fe treatment and ranged from 1.15 g in `Orange Jubilee', 0.68 to 0.95 g in the semi-dwarf varieties, and 0.56 g in `Discovery Orange'. Symptoms of Fe toxicity only developed in the high Fe treatment, and the percent leaf dry weight separated at harvest as symptomatic ranged from 97% in `Orange Jubilee', 55% to 85% in the semidwarf varieties, and 15% in `Discovery Orange'. The Fe concentration in leaves in the high Fe treatment was 5.7-times greater in `Orange Jubilee', 2 to 3-times greater in the semi-dwarf varieties, and 1.6-times greater in `Discovery Orange' than in the low Fe treatment. Based on these findings, `Orange Jubilee' and `Discovery Orange' were the most and least susceptible varieties, respectively, to Fe toxicity of the seven marigold varieties evaluated in this study.

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Joseph P. Albano*, P. Chris Wilson, and Sandra B. Wilson

Sources of irrigation water in South Florida typically contain high levels of dissolved carbonates and bicarbonates. Repeated application of high alkalinity water can cause substrate-solution pH to rise, thereby altering nutrient availability, and possibly leading to the development of nutrient disorders and a reduction in plant growth. The objectives of the current study were to determine the effects of neutralizing alkalinity of irrigation water on the nutritional status and growth of Thryallis (Galphimia glauca Cav.). Plants were grown in 11.4-L containers in a 5 peat: 4 pine bark: 1sand (v:v:v) mix. Treatments were prepared with water collected from a commercial nursery with inherent calcium carbonate levels in excess of 260 mg·L-1 and pH above 7.3. Treatments consisted of 0% (control), 40%, or 80% alkalinity neutralized with sulfuric acid. At harvest, 51 weeks after initiating treatments, foliar levels of Fe were 28% greater, Mn 55% greater, and Zn 27% greater in the 80% than 0% neutralized alkalinity treatment. Growth indices and leaf greenness averaged over the course of the study were significantly greater in the 40% than in the 0% or 80% alkalinity neutralized treatments. Over the course of the study, leachate pH averaged 7.5, 6.8, and 5.3; and electrical conductivity (EC) averaged 1.4, 1.9, and 2.2 dS·m-1 in the 0%, 40%, and 80% alkalinity neutralized treatments, respectively.

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Jeff B. Million, Thomas H. Yeager, and Joseph P. Albano

The capacity for evapotranspiration (ET)-based irrigation scheduling to reduce runoff volume and nutrient leaching was tested in Fall 2004 and Spring 2005. Runoff (container leachate plus unintercepted irrigation and precipitation) was collected continuously for 17 weeks during production of sweet viburnum [Viburnum odoratissimum (L.) Ker Gawl.] in 2.4-L (16-cm top diameter) containers fertilized with an 18N–2.6P–10K polymer-coated, controlled-release fertilizer. Treatments were a factorial arrangement of two irrigation rates (fixed rate of 1 cm·d−1 or a variable, ET-based rate) and two fertilizer rates (15 or 30 g/container in 2004 and 10 or 15 g/container in 2005). Averaged over the two experiments and compared with the 1-cm·d−1 rate, ET-based irrigation reduced the amount of irrigation water applied (L/container) by 39% and runoff volume (L/container) by 42% with greatest reductions observed during the second half of the 2004 experiment and the first half of the 2005 experiment. Compared with 1-cm·d−1 rate, ET-based irrigation reduced runoff nitrogen (N), phosphorus (P), and potassium (K) (mg/container) by 16%, 25%, and 22%, respectively, in 2004 and runoff K 15% in 2005 with irrigation effects varying on a weekly basis. Irrigation treatments did not affect the response of plants to fertilizer rate. Because shoot dry weight was unaffected by irrigation treatments, results indicate that compared with a fixed irrigation rate, ET-based irrigation can reduce irrigation and runoff volumes and to a lesser extent nutrient loss while providing adequate water for plant growth.

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Jeff B. Million*, Thomas H. Yeager, and Joseph P. Albano

The influence of production practices on runoff from container nurseries was investigated in Spring 2003 (March to July) and Fall 2003 (August to January). Viburnum odoratissimum (Ker-Gawl.) liners were planted in 3.8-L containers with a 2 pine bark: 1 sand: 1 Canadian peat substrate and placed on 1.5 m2-platforms at one of two plant spacing densities: 16 or 32 plants/m2 [spaced to 16 plants/m2 after 13 weeks (spring) or 14 weeks (fall)]. Overhead sprinkler irrigation was applied daily (1 cm) and runoff collected weekly. Osmocote 18 N-2.6 P-10 K was surface-applied to each container (15 g) in the spring and surface-applied or incorporated in the fall. Cumulative runoff averaged 1240 L·m-1; in spring (19 weeks) and 1050 L·m-1; in fall (20 weeks), which represented 72% and 66% of applied irrigation plus rainfall, respectively. The lower density spacing resulted in a 19% increase in cumulative runoff in spring (1340 vs. 1130 L·m-1) but had no effect in fall (970 vs. 890 L·m-1). Weighted average ECwa of runoff decreased 10% (0.436 vs. 0.485 dS·m-1) and 12% (0.420 vs. 0.476 dS·m-1) with the lower density spacing in spring and fall, respectively. ECwa in fall was not affected by fertilizer method. Plant size index [(height + width)/2] was reduced 22% in both spring (38.7 vs. 49.7 cm) and fall (26.9 vs. 34.4 cm) when plants were grown at the lower density spacing throughout production. This reduction in plant size was attributed to container heat stress. Plant size was unaffected by fertilizer application method (fall) but fertilizer incorporation resulted in greener plants than surface-applied fertilizer (60 vs. 53 SPAD readings).