Foliar Applications of Benomyl and Mancozeb Do Not Affect Leatherleaf Fern Carbon Assimilation, Transpiration, Light Compensation Point or Vase Life

Carbon assimilation (A) and transpiration (E) at 400 fxmol • s-1 • m~2 light intensity, as well as light compensation points (LCP), were determined for selected, mature leatherleaf fern (Rumohra adiantiformis [Forst.] Ching) fronds on plants growing in controlled-environment chambers. Two foliar ap plications spaced one week apart with either benomyl (300 ppm) or mancozeb (1438 ppm) solutions had no effect on A, E, or LCP compared to deionized water treatments. Sub sequent vase life of treated fronds averaged 13.2 days and was not affected by fungicide treatments. Fungal leaf spot diseases are a serious problem encoun tered in leatherleaf fern production in Florida (5). Be nomyl and mancozeb are commonly used to control leath erleaf fern diseases and are often applied at 7 day intervals during humid, rainy weather (13). While this procedure can control disease development, the effects of these sprays on leatherleaf fern are unknown. In fact, neither fungicide has commercial labeling specifically for leatherleaf fern; benomyl products have general ornamental labeling and mancozeb products are applied under a generic fern spec ial local need label. In work on pecan seedlings, three of eight fungicides tested reduced carbon assimilation (A) by about 35% one Florida Agricultural Experiment Station Journal Series No. 8531. 362 day after application (16). Six of the fungicides (benomyl included) decreased A when it was measured 9 days after one application. In later studies, eight of nine insecticides tested suppressed A of mature pecan leaves within 1 day after a single treatment (17). On apples, single applications of benomyl, alone or in combination with oil, had no effect on A (3). Multiple applications of the fungicide dodine to 'Delicious' and 'Golden Delicious' apple trees had no effect on A in another study (10). Reductions in A could result in decreased yields if the effects were of great enough du ration and/or magnitude. The effects of production practices on postharvest longevity are of great concern with a cut foliage crop like leatherleaf fern. The ability of a plant or plant part to maintain homeostatic carbon exchange under low intensity light (light compensation point, LCP) may be a factor in its durability under home/office conditions (1). Additionally, the inability to maintain water balance after harvest can cause vase life termination of floral crops (2, 4) and has been shown to be a serious problem for leatherleaf fern (8, 14, 15). Interestingly, research has shown that the problem of reduced vase life of leatherleaf fern is associated with fronds produced during those months when the fungicides benomyl and mancozeb are most heavily used (7, 9). The following experiment was conducted to determine the effects of spray applications of benomyl and mancozeb on carbon assimilation, transpiration (E), light compensa tion point, and vase life of leatherleaf fern. Materials and Methods Tissue culture derived leatherleaf fern plants in 6-inch clay pots were placed, three pots per chamber, in each of four controlled-environment chambers (Model E30B, Percival, Boone, IA) in this randomized complete block design Proc. Fla. State Hort. Soc. 100: 1987. experiment with four replications. The day/night (12 hrs each) temperatures in the chambers were 24°C and light ing during the day period consisted of 335 jxmol • s~l • nr2 from fluorescent and 40 |xmol • s"1 • n~r2 from incandescent lamps. Plants were watered daily and after a week acclimatization period each of the three plants in each chamber received one of the following treatments: deionized water (DIW), benomyl (300 ppm, equivalent to 0.5 lb. of Benlate 50WP/100 gal), or mancozeb (1438 ppm, equivalent to 1.5 lb. of Manzate 200 80WP/100 gal) sprays to the point of runoff. Treatments were applied at 25 psi using a flat fan spray nozzle (Teejet 8006, Spraying Sys tems, Bellwood, IL). The two spray treatments were applied 7 days apart. Carbon assimilation and E of individual recently ma tured, non-sporulating leatherleaf fern fronds was mea sured at 400 \Linol • s-1 • nr2 using an open flow infrared gas analyzing (IRGA) system described previously (11). In addition, LCPs were determined for each leaf. Leaf tem peratures were maintained at 24° ±1.5° during the mea surements which were made 1 and 6 days after the initial spray application and 1 day after the second spray applica tion. After the final readings were made using the IRGA, the test fronds were harvested and held in deionized water for vase life determinations under simulated home/office conditions as previously described (15). Fronds were termi nated when they started to show symptoms of desiccation or yellowing (7). Results and Discussion The fungicide sprays had no effect on A of attached leatherleaf fern fronds when measured 1 and 6 days after the first application and 1 day after the second application (Fig. 1A). Carbon assimilation averaged 4.5, 4.0, and 3.8 juimol • nr2 • s"1 for the deionized water (DIW), benomyl, and mancozeb sprayed fronds, respectively. Similarly, there were no treatment differences for E at the three measurement dates (Fig. IB); E averaged 0.98, 0.97, and 0.86 mmol • mr2 • s~l for the deionized water (DIW), be nomyl, and mancozeb sprayed fronds, respectively. These A and E values are similar to those published for leather leaf fern in other studies (6, 11). Treatments had no effect on LCPs on days 1, 6 or 8 after the first spray was applied (Fig. 1C). Average LCPs were 2.7, 3.5, and 4.0 |xmol • s"1 • nr2 for the DIW, benomyl, and mancozeb treatments, re spectively. Vase life of harvested fronds were not affected by treat ments and averaged 11.25, 15.75, and 12.5 days, respec tively, for DIW control, benomyl, and mancozeb. These vase life values are similar to those reported in a study that showed that postharvest benomyl dips are not detrimental and are sometimes beneficial to leatherleaf fern frond vase life (12). There were no treatment differences in the symptoms that caused frond termination in the postharvest evaluation reported here; three-quarters of the fronds in each treatment were discarded due to yellowing and the rest were terminated due to desiccation of the foliage. Under the conditions of this test, two spray applications of benomyl or mancozeb appeared to have no effect on A, E, LCP, or vase life of leatherleaf fern fronds. However, benomyl and mancozeb are only two of the many chemicals Proc. Fla. State Hort. Soc. 100: 1987. applied repeatedly during the summer to leatherleaf fern. There may be other commonly used chemicals or combina tions of chemicals that do have effects on A, E, LCP, or vase life of leatherleaf fern.