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C.E. Wieland, J.E. Barrett, C.A. Bartuska, D.G. Clark and T.A. Nell

Salvia (Salvia splendens F.), vinca (Catharanthus roseus L.), and pansy (Viola × wittrockiana Gams.) were examined to determine efficacy of growth retardants for inhibiting stem elongation of seedlings in the plug stage and after transplanting to 10-cm pots. Studies on salvia showed plugs sprayed with single applications of ancymidol at 10 or 20 ppm, paclobutrazol at 30 or 60 ppm, or daminozide/chlormequat tank mix at 2500/1500 ppm inhibited plug elongation by 17% to 22%. Pansy plugs were sprayed either once or twice with ancymidol at 5, 10, or 15 ppm. Number of applications was statistically significant with two applications reducing elongation by an average of 35%, whereas a single application resulted in a 23% average reduction. Ancymidol concentration was significant in reducing stem elongation with increasing rates in pansy; however, the concentration and application time interaction was not significant. In both pansy and salvia, plant size at flowering was similar to controls after transplanting. Vinca plugs were sprayed with ancymidol at 5, 10, or 15 ppm either the 3rd week, 4th week, or both weeks after sowing. As ancymidol concentrations increased, plug height decreased, and the concentration effect was greater week 3 than at week 4. Two applications of ancymidol was most effective in retarding stem elongation (36%) followed by one spray the 3rd week (29%) and one spray during week 4 (20%).

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Richard K. Schoellhorn and A.J. Compton

Plants, which move directly from the wild into commercial propagation, without the benefit of extensive breeding and selection, often pose production-oriented problems for growers. Vigorous plant growth, especially during the propagation phase of production is a common problem. The purpose of this work was to determine the degree of efficacy offered by chemical control of stem elongation in propagation of Porter Weed [Stachytarpheta mutabilis, S. mutabilis var. violacea, and S. urticifolia]. Tip cuttings of three Stachytarpheta species were given a 10-s dip in the following treatment solutions: daminozide (2500 and 5000 mg·L-1), daminozide and chlormequat chloride tank mix (2000 mg·L-1 ea.), paclobutrazol (2 and 4 mg·L-1), uniconazole (2 and 4 mg·L-1), distilled water, and undipped controls. Cuttings were then treated with a 0.1% IBA rooting powder and placed under intermittent mist on the propagation bench. After 2 weeks in propagation, cuttings were harvested and shoot elongation, root development, and dry weights were evaluated. The interaction of chemical and species was significant for stem elongation and dry weight; chemical effect on root development was also significant. Paclobutrazol and uniconazole offered greater control of stem elongation than daminozide, daminozide-chlormequat chloride, water, or control treatments.

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Roberto G. Lopez and Erik S. Runkle

Prohexadione-Ca (ProCa) is a relatively new plant growth regulator (PGR) that inhibits internode length in rice, small grains, and fruit trees. However, little is known about its efficacy and potential phytotoxicity on floriculture crops and how it compares to other commercially available PGR chemicals. The effects of two foliar spray applications (2 weeks apart) of ProCa (500, 1000, or 2000 ppm), paclobutrazol (30 ppm), or a tank mix of daminozide plus chlormequat (2500 and 1000 ppm, respectively) were quantified on Dianthus barbatus L. `Interspecific Dynasty Red', Ageratina altissima R. King & H. Robinson (Eupatorium rugosum) `Chocolate', Lilium longiflorum Thunb. `Fangio', and Buddleia davidii Franch. `Mixed.' All plants were forced in a glass-glazed greenhouse with a constant temperature setpoint of 20 °C under a 16-h photoperiod. Two weeks after the second spray application of ProCa at 500, 1000, or 2000 ppm, plant height of Dianthus and Lilium was shorter than control plants by 56%, 60%, and 65% and by 6%, 26%, and 28%, respectively. However, ProCa bleached and reduced the size of Dianthus flowers. ProCa at 2000 ppm and daminozide plus chlormequat were effective at controlling the height of Eupatorium (64% and 53% reduction, respectively); however, leaves of Eupatorium were discolored and showed symptoms of phytotoxicity 1 week after the first ProCa application. Only daminozide plus chlormequat were effective on Buddleia. ProCa is an effective PGR for most of the crops we tested; however, its discoloration of red flowers and foliage may limit its application for commercial use.

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T.J. Blom

Bract edge burn (BEB) has been observed in different greenhouse operations across North America over the past 10 years. The symptoms develop at anthesis or shortly after shipping. Varieties such as `Supjibi', `V-14 Glory', and `Celebrate 2' are considered susceptible cultivars. A number of trials using endosulfan (Thiodan) have been conducted. In 1993, `Supjibi' branched poinsettias were sprayed with either Thiodan, Decis, Thiodan + Decis, or water or remained unsprayed. The sprays were applied in week 39, 42 or 45. For each treatment period, plants were treated three times at 4-day intervals at label recommendations. At anthesis (week 47), plants sprayed with Thiodan or Thiodan + Decis during week 39 showed necrosis in the margin of the transitional bracts. In 1994, single spray applications in week 39, 40, 41, 42, or 45 of Thiodan, Ca (400 ppm), Thiodan + Ca in a tank mix, unsprayed, or Thiodan followed by four calcium sprays (weekly) in November. At week 48, all treatments except the latter showed necrosis, except this time it was marginal flecking in the transitional or primary bracts. In Spring 1995, single vs. multiple Thiodan applications were compared.

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H.B. Pemberton, G.L. Philley and W.E. Roberson

Plants of Rosa L. `Peace' were field planted in Feb. 1995 in order to test black spot (Diplocarpon rosae Wolf) control efficacy of several compounds. Plants were protected from fungal infection by black spot with weekly sprays of chlorothalonil (Daconil) from 5 Apr. to 8 June 1995 to allow plant establishment. Spray treatments for efficacy testing were started on 23 June and ended on 1 Nov. 1995. All plants were uniformly weeded, fertilized, and irrigated as needed for the duration of the experiment. Plants were rated for defoliation and disease development on 18 July, 1 Sept., and 10 Nov. 1995. A wettable granular formulation of cyproconazole (Sentinel) controlled black spot significantly better when a surfactant, Latron B-1956, was added to the spray solution at 0.5 mL·L–1. Differences between treatments with and without surfactant were greater at lower rates vs. higher rates of cyproconazole. The most effective Sentinel rates with the surfactant were 0.13 g·L–1 applied every 14 days or 0.26 g·L–1 every 21 days. A formulated combination of chlorothalonil and thiophanate methyl (ConSyst) controlled black spot on a 7-day interval at 1.2 g·L–1, but not when applied at 1.8 g·L–1 every 14 days. Control was no better than the standard mancozeb (Dithane) treatment. Neem oil (NeemGard) was not effective on the 14-day schedule tested. Tank mixing neem oil with chlorothalonil or thiophanate methyl (Domain) did not significantly improve control. Neither myclobutanil (Systane) or a formulated combination of mancozeb and myclobutanil (RH 0611) was effective in controlling black spot.

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Royal G. Fader and Martin J. Bukovac

The plant cuticle is the prime barrier to penetration of foliar-applied plant growth regulators (PGR). Spray additives of various chemistries are frequently included in a tank mix to increase performance of PGRs. We have reported that urea and ammonium nitrate (AN) enhance transcuticular penetration of 14C-labeled NAA (pKa 4.2) from aqueous droplets (pH 5.2) and their subsequent deposits through enzymatically isolated tomato fruit cuticular membranes (CM). Studies on effects of Triton × surfactants on AN-enhanced NAA penetration showed an additional 25% increase in NAA penetration and the AN:surfactant interaction was significant. Also, some alkylamine hydrochlorides increased NAA penetration. Studies comparing NAA penetration through tomato and pepper fruit and Citrus leaf CM in the presence of 8 mM AN or 8 mM ethylamine HCl showed that all three species exhibited the same trend for penetration at 120 h: ethylamine HCl > AN > NAA only. Comparative NAA penetration for CM of the three species was pepper > Citrus > tomato, with significant differences (P > 0.006) in NAA penetration, as indexed by initial slope and penetration after 120 h. On addition of AN, NAA penetration was greater (range 3% to 40%) for Citrus and pepper CM than tomato CM. When ethylamine HCl was added, NAA penetration through Citrus and pepper CM was less (–37 and –27%, respectively) than tomato CM as measured by the initial slope, but 6% and 11%, respectively, more than tomato CM for penetration after 120 h. The differences in NAA penetration among the three species cannot be explained by cuticle thickness, since pepper and tomato CM are 2.5- to 3.5-fold thicker than Citrus CM. We have suggested that the enhanced NAA penetration mediated by AN and ethylamine HCl (and other alkylamine HCl examined) may be related to their hygroscopic properties leading to greater deposit hydration. The significance of the differences among the species CM and surfactant-enhanced NAA penetration will be discussed, in relation to diffusion in the non-living, non-metabolic plant cuticle.

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Ross E. Byers and Alson H. Smith Jr.

An analysis of daytime high temperatures for the 10-year period from 1984 to 1993 indicated that, in the 21 days after full bloom (AFB) in 7 of 10 years, there were 3 days or more above 29.5C. In the 15- to 21-day period AFB, when fruit are considered at their optimum diameter (8 to 12 mm) for thinning, only 3 days above 29.5C were recorded. In the 15 to 21 days AFB, the high temperature was only 24C for 7 out of 10 years. Thus, growers would have to spray at temperatures 5.6C degrees lower if they were to choose to spray the warmest 3 days during the 15- to 21-day period when fruit are 8 to 12 mm in diameter. NAA caused thinning of `Golden Delicious' fruit at 8-mm fruit diameter. Tank mixing of one of several pesticides (regulaid or guthion, captan, carzol, imidan, polyram, lorsban, omite, or lannate) had no effect on NAA efficacy. Comparison of identical chemical thinning treatments (carbaryl + Accel + oil) applied to `York' and `Red Delicious' apple trees indicated that more thinning occurred with the PF treatments than at 8 mm. Average 2-day high temperatures at PF were 7.1C higher at PF for the `Red Delicious' experiment and 5.6C higher for the `York' experiment. The higher temperatures at PF could account for the differences in thinning response and not the spray timing. Pollination and fertilization inhibitors caused some fruit thinning at the highest rates and multiple applications. The MYX4801 caused more thinning and more injury to fruit than other materials. Endothall gave good thinning without fruit injury. Wilthin (GWN-6592) did cause some thinning, but fruit injury was a problem in one experiment.

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Debalina Saha, S. Christopher Marble, Brian Pearson, Héctor Pérez, Gregory MacDonald and D. Calvin Odero

. Plastic nursery containers (5.5 inches width × 5.5 inches height with 1.7 L volume) were filled with a PB:peat substrate (Fafard52 growing mix; Sun Gro Horticulture, Agawam, MA) amended with 10 lb/yard 3 15N–3.9P–9.9K controlled-release fertilizer

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Matthew D. Whiting, David Ophardt and James R. McFerson

The commercial adoption of the relatively new rootstock `Gisela 5' (Prunus cerasus L. × P. canescens L.) has been limited in the United States sweet cherry (P. avium L.) industry despite its ability to induce precocity and productivity and reduce scion vigor compared to the standard Mazzard (P. avium). This is due in large part to inadequate crop load management that has led to high yields of small fruit. This paper reports on sweet cherry chemical blossom thinning trials conducted in 2002 and 2003. Two percent ammonium thiosulphate (ATS), 3% to 4% vegetable oil emulsion (VOE), and tank mixes of 2% fish oil + 2.5% lime sulphur (FOLS) were applied to entire 8- and 9-year-old `Bing'/`Gisela 5' sweet cherry canopies at about 10% full bloom (FB) and again at about 90% FB. In both years, ATS and FOLS reduced fruit set by 66% to 33% compared to the control (C). VOE reduced fruit set by 50% compared to C in 2002 but had no effect in 2003. In 2002, fruit yield was 30% to 60% lower from thinned trees. In 2003, fruit yield was unaffected by thinning treatment. In 2002, ATS and FOLS improved fruit soluble solids but had no effect in 2003. VOE did not affect fruit soluble solids in 2002 and reduced fruit soluble solids by 12%, compared to C, in 2003. In 2002, each thinning treatment nearly eliminated the yield of the small fruit (≤21.5-mm diameter) and increased yield of large fruit (≥26.5 mm) by more than 400%, compared to C. In 2003, ATS and FOLS did not affect yield of small fruit but increased the yield of large fruit by 60%. In 2003, VOE-treated trees yielded 4.3 kg of small fruit per tree compared to about 0.15 kg from C, suggesting a phytotoxic response to VOE beyond that which may effect thinning. Compared to C, ATS and FOLS consistently reduced fruit set and improved fruit quality. We conclude that commercially acceptable yields of excellent quality `Bing' sweet cherries can be grown on size-controlling and precocious rootstocks.

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R.E. Byers, D.H. Carbaugh and L.D. Combs

Effectiveness of pollination/fertilization inhibitors for flower thinning depends highly on the precise timing of sprays within 24 to 36 h after flower opening. In 1999, cool weather delayed the application of hormone-type thinners, which were intended for at bloom comparison with pollination/fertilization. Pollination inhibitors applied in bloom and hormone thinners applied at petal fall or 8 mm fruit diameter caused good fruit thinning. Ethephon applied in bloom did not cause thinning of `Empire' fruit, but Sevin + Accel + Oil caused good fruit thinning when applied in bloom. Sevin + Accel + Oil increase fruit diameter and did not affect fruit russet. Ethephon applied at 22 mm fruit diameter at water rates of 935 L/ha or 3741 L/ha and chemical rates of 21.5 L/ha or 42.9 L/ha did not cause significant fruit thinning. In 1998, pollination inhibitors and hormone-type growth regulators caused flower and fruit thinning of `Starkrimson'/MM111/106 trees. Good thinning occurred with both pollination inhibitors and ethephon treatments; but Sevin + Accel + oil was not as effective. Thinex caused the most side russet. Treatments that thinned generally caused increased fruit diameter. In 1999, return bloom was promoted by early thinning, but ethephon did not appear to promote return bloom beyond the thinning effect. In 1998, endothall caused good thinning of `York'/MM.111 with a minimum of foliage injury. Fruit diameter was increased. Thinning with endothall in 1998 greatly increased return bloom in 1999, but trees were slightly over thinned. Fruit injury caused by carbaryl was almost non-existant in 1999 in two tests having over 25 carbaryl treatments that compared different formulations and adjuvants for thinning and injury. Some very slight, non-significant injury, may have occurred with three of nine formulations tested when trees were shaded. Shading trees for 1 day in conjunction with carbaryl sprays also did not promote injury. In a previous year, shading trees promoted carbaryl injury. A tank mix of Oil with either 50WP, 80WP, XLR, or 4L formulations caused 3 to 8% of the fruit to show injury at a very low intensity. However, in an adjoining block, Sevin + Accel + Regulaid caused injury to >50% of the fruit when applied the same day as the other experiments. Further investigations on this problem are in progress.