Henis, Y. and I. Chet. 1968. The effect of nitrogenous amendments on the Monaghan, P. F., G. H. Brinen, and S. R. Kostewicz. 1994. Organic vegetable germinability of sclerotia of Sclerotium rolfsii and on their accompanying production in Florida. Proc. Fla. State Hort. Soc. 107:377-380. microflora. Phytopathol. 58:209-211. Rodriquez-Kabana, R. 1986. Organic and inorganic nitrogen amendments to Jenkinson, D. S. and D. S. Powlson. 1976. The effects of biocidal treatments soil as nematode suppressants. J. Nematol. 18:129-135. on metabolism in soil – V. A method for measuring soil biomass. Soil Biol. Spreen, T. H., J. J. VanSickle, A. E. Moseley, M. S. Deepak, and L. Mathers. Biochem 8:209-213. 1995. Use of methyl bromide and the economic impact of its proposed Lazarovits, G., K. L. Conn, and J. Potter. 1999. Reduction of potato scab, ver- ban on the Florida fresh fruit and vegetable industry. University of Flori- ticillium wilt, and nematodes by soymeal and meat and bone meal in two da, Bulletin 898 (Tech.). Ontario potato fields. Can. J. Plant Pathol. 21:345-353. Tenuta, M. and G. Lazarovits. 2002. Ammonia and nitrous acid from nitrog- Lazarovits, G., M. Tenuta, and K. L. Conn. 2000. Utilization of high nitrogen enous amendments kill the microsclerotia of Verticillium dahliae. Phytopa- and swine manure amendments for control of soilborne diseases: efficacy thology 92:255-264. and mode of action. Acta Hort. 532:59-64. Tsao, P. H. and J. J. Oster. 1981. Relation of ammonia and nitrous acid to sup- Locascio, S. J., J. P. Gilreath, D. W. Dickson, T. A. Kucharek, J. P. Jones, and pression of Phytophthora in soils amended with nitrogenous organic sub- J. W. Noling. 1997. Fumigant alternatives to methyl bromide for polyeth- stances. Phytopathology 71:53-59. ylene mulched tomato. HortScience 32:1208:1211. U.S. EPA. 2002. Methyl bromide phase out web site. http://www.epa.gov.sp- Lumsden, R. D., J. A. Lewis, and G. C. Papavizas. 1983. Effect of organic dpublc/mbr/. amendments on soilborne plant diseases and pathogen antagonists. p. 51- Watkins, G.M. 1961. Physiology of Sclerotium rolfsii with emphasis on parasit- 70. In W. Loceretz (ed). Environmentally Sound Agriculture. Praeger, ism. Phytopathology 51:110-113. New York. World Meteorological Organization. 1998. Scientific Assessment of Ozone Maynard, D. N. and S. M. Olson. 2001. Vegetable production guide for Flor- Depletion: 1998. Executive Summary. Global Ozone Research and Moni- ida. University of Florida Extension, Citrus & Vegetable Magazine. toring Project – Report No. 44.

Proc. Fla. State Hort. Soc. 115:321-329. 2002. COMPARISON OF AND THIAMETHOXAM FOR CONTROL OF THE SILVERLEAF , BEMISIA ARGENTIFOLII, AND THE LEAFMINER, LIRIOMYZA TRIFOLII, ON TOMATO

DAVID J. SCHUSTER spring of 2002 to compare the efficacy of imidacloprid and thi- University of Florida, IFAS amethoxam. When imidacloprid 2F (16 oz/acre) or thiamethox- Gulf Coast Research and Education Center am 2SC (8 oz/acre) were applied to the soil at or within 3 weeks Bradenton, FL 34203 of transplanting, both provided control of whitefly nymphs for eight to 12 weeks at nine sites on sandy soil but only 3 to 5 weeks at one site on gravelly loam soil. Control with imidaclo- ROBERT F. MORRIS II prid appeared to be slightly greater and to persist slightly long- CropScience er at three sites, although differences were not significant Lakeland, FL 33811 when the 2002 data were averaged over all experiments. Foliar applications of imidacloprid 1.6F at 3.75 oz/acre and thia- Additional index words. chemical control, Lycopersicon esculen- methoxam 25WG at 4 oz/acre at a threshold of five nymphs/10 leaflets also provided significant control of nymphs, although tum, insecticidal control, imidacloprid, thiamethoxam control was not as good as with soil applications, and control appeared to be greater with thiamethoxam. The incidences of Abstract. The silverleaf whitefly, Bemisia argentifolii Bellows & plants with symptoms of TYLCV were reduced with soil appli- Perring, also known as strain B of the sweetpotato whitefly [B. cations but not foliar applications. Imidacloprid appeared to tabaci (Genn.)], is the dominant pest of tomatoes, Lycopersi- provide greater and more consistent reductions in the occur- con esculentum Mill, in southern Florida. The insect causes rence of TYLCV infected plants at three sites as well as when damage directly by inducing an irregular ripening disorder of the data were averaged over six sites in 2002, although differ- tomato and indirectly by transmitting plant viruses, particular- ences from thiamethoxam were small and not significant. Soil ly tomato yellow leaf curl virus (TYLCV). The leafminer, Liri- applications of either resulted in significant reduc- omyza trifolii (Burgess), has long been considered a serious tions of L. trifolii leafmines, although control was consistently pest of tomatoes in Florida, causing defoliation through min- better with thiamethoxam. ing of leaves by larvae. Imidacloprid and thiamethoxam are members of a new class of systemic, nicotinoid that can be applied either as soil drenches or as foliar sprays. The silverleaf whitefly, Bemisia argentifolii Bellows & Per- Two experiments were conducted in the fall seasons of 2000 ring, also know as the B strain of the sweetpotato whitefly [B. and 2001 and 10 experiments were conducted during the tabaci (Gennadius)], is the dominant pest of tomatoes, Lycoper- sicon esculentum Mill, in southern Florida (Schuster et al. 1996a). The insect causes direct damage to tomato manifested This research was supported by Bayer Crop Sciences and by the Florida Agricultural Experiment Station, and approved for publication as Journal Se- as spotting of leaves, wilting and death of plants, and irregular ries No. R-08945. ripening of fruit (Schuster et al., 1996b). The insect is even

Proc. Fla. State Hort. Soc. 115: 2002. 321

more damaging as a vector of plant viruses including tomato Materials and Methods mottle virus (ToMoV) and tomato yellow leaf curl virus (TYL- CV). The latter virus is particularly devastating, causing flower Experiments in 2000 and 2001. Two experiments were con- abscission and severe plant stunting (Polston et al., 1999). ducted at the Gulf Coast Research and Education Center The leafminer, Liriomyza trifolii (Burgess), has long been (GCREC), Bradenton. Transplants of the tomato cultivar considered a serious pest of tomatoes in Florida (Schuster et Agriset were set 21 Sept. 2000 and 11 Sept. 2001 18 inches al., 1996a) and recently has become more problematic apart on raised beds of EauGallie fine sand covered with (Schuster, personal observation). The larval feeding within white polyethylene mulch. Plots were three-21 ft long rows on the leaves causes serpentine mines and can result in signifi- 5-ft centers and treatments were replicated four times in ran- cant defoliation of plants, particularly when secondary micro- domized complete block designs. Soil drenches of imidaclo- organisms invade the mines (Musgrave et al., 1975). As is the prid 2F (Admire® 16 oz/acre) and thiamethoxam 2SC case with L. sativae Blanchard, the leafminer is considered a (Platinum®, 8 oz/acre) were applied at transplanting in 4 oz secondary pest; i.e., it generally is kept below economically of water per plant. In 2001 imidacloprid 1.6F (Provado®, 3.75 damaging levels by natural enemies, principally hymenopter- oz/acre) and thiamethoxam 25WG (Actara®, 4 oz/acre) ous parasites, but increases to levels requiring control when were applied foliarly when whitefly densities approached or the densities of natural enemies are reduced, principally by reached the threshold of ≥5 sessile nymphs (2nd or 3rd in- the use of broad spectrum insecticides (Oatman and stars) and/or pupae (4th instars or red eye nymphs) per 10 Kennedy, 1976). terminal leaflets of the seventh or eighth leaf from the top of Nicotinoids are a new class of neurotoxins also referred to one stem from each of the middle 10 plants in the middle row as , nitroguanidines, nitromethylenes and of the respective plots (Schuster, 1998; 2002). Applications chloronicotinyls. The nicotinoids are structured after natural- were made with a self-propelled sprayer operated at 200 psi ly occurring nicotine compounds and act similarly on the cen- and 3.4 mph. It was fitted with eight Albuz orange nozzles per tral nervous system of insects, irreversibly blocking the row and delivered 60 (four nozzles open) or 120 (eight noz- postsynaptic nicotinergic acetylcholine receptors (Bai et al., zles open) gpa, depending upon plant height. In both exper- 1991). The high water solubility of the nicotinoids give them iments Berliner (Mattch at 2 qt/acre, excellent systemic properties and long residual activity, which Javelin at 2 lb/acre, or XenTari at 2 lb/acre) or makes them particularly effective against sucking insects. Nic- (SpinTor at 6 oz/acre) were applied weekly to control lepi- otinoids generally have low mammalian toxicity relative to dopterous larvae, particularly the southern armyworm other neurotoxins and are relatively non-toxic to non-target [Spodoptera eridania (Cramer)]. The number of plants in each species (Wolweber and Tietjen, 1999), which makes them de- plot with definite symptoms of TYLCV were recorded weekly. sirable for integrating into pest management programs. Nic- The numbers of sessile nymphs and pupae of the silverleaf otinoids can be applied as soil drenches or as foliar sprays. whitefly were counted weekly as above. In 2001, the number Imidacloprid (Bayer Corporation, Kansas City, Mo.) and of Liriomyza leafmines was counted by each of two people, one thiamethoxam (Syngenta Crop Protection, Inc., Greensboro, on each side of the middle row of each plot, during a 2-min N.C.) are two nicotinoids that have registrations on vegetable search of each plot on 6 Dec. and the counts by the two peo- crops including tomato. The former was the first nicotinoid ple were combined for each plot. available for use on tomatoes, being registered by the US EPA Experiments in 2002. Ten additional experiments were con- in 1995. Imidacloprid has been used as a drench of tomato ducted in the spring of 2002, one at the GCREC and nine at seedlings in plant production houses at least a week before commercial tomato farms: two in Collier County (Immoka- transplantation. Imidacloprid is applied again as a soil drench lee), one in Dade County (Homestead), two in Hillsborough at transplanting, or by side-dress fertilization injection wheels County (Ruskin), three in Manatee County (Duette, Ft. Ham- or trickle irrigation tubes 1 to 3 weeks after transplanting. Im- mer and Lorraine), and one in Palm Beach County (Boynton idacloprid is formulated as Admire® for soil applications and Beach). Plots at all sites consisted of two rows and treatments as Provado7 for foliar applications and has been effective were replicated three times (four times at Lorraine) in ran- against B. argentifolii, particularly as a soil application (as sum- domized complete block designs. Cultural details for each marized in Palumbo et al., 2001). Thiamethoxam received US site are listed in Table 1. At all locations, imidacloprid 2F (Ad- EPA registrations on tomato in 2001 and is formulated as Plat- mire) was applied at 16 oz/acre and thiamethoxam 2SC (Plat- inum® for soil applications and as Actara® for foliar applica- inum) was applied at 8 oz/acre as a drench to the base of each tions. Foliar applications of thiamethoxam have shown good plant in 1.7 or 3.4 oz per plant. Transplants at all locations efficacy against B. argentifolii in melons (Palumbo, 2001) and were grown commercially and, with the exception of those set tomatoes (Stansly and Conner, 2000; Stansly et al., 2001). A at GCREC and Homestead, were treated with imidacloprid in soil application shortly after transplanting also provided ex- the plant house prior to delivery. Growers applied insecti- cellent control of the whitefly, although the rate evaluated cides for armyworm control but not for . All plants was higher than the maximum rate permitted by the current in each plot were examined weekly for definite symptoms of label (Stansly et al., 2001). There are no published reports on TYLCV (except for Immokalee sites) and 10 plants of one row the efficacy of either nicotinoid against L. trifolii leafminers of each plot were sampled weekly for whitefly sessile nymphs on tomato in the field; however, applications of thiamethox- as above. The numbers of Liriomyza leafmines per plot were am to chrysanthemum resulted in fewer leafmines in the counted, usually weekly, during a 1-min search of one row of greenhouse (Bethke and Redak, 2000; 2002). The purpose of each plot by one person. the present experiments was to compare the efficacy of these Sessile nymph and leafmine counts were transformed for nicotinoids as soil drenches and foliar applications for man- analyses by adding 0.5 to the number and then taking the aging whiteflies and TYLCV and as soil drenches for manag- square root. The percent of plants with TYLCV symptoms was ing leafminers on tomato. calculated for each plot for each date and transformed by arc-

322 Proc. Fla. State Hort. Soc. 115: 2002.

Table 1. Cultural details of experiments comparing the efficacy of soil applications of nicotinoid insecticides for whitefly and leafminer control on tomato, Spring 2002.

Spacing

Irrigation Site Cultivar method Planting date Treatment date Row (ft) Plant (inches) Plant/row Plant/acre Collier County Immokalee1 Florida 47 Seep 23 Dec. 3 Jan. 6 20 15 4356 Immokalee2 Florida 47 Drip 27 Dec. 15 Jan. 6 28 15 3111 Dade County Homestead Florida 47 Drip 12 Mar. 19 Mar. 6 20 15 4356 Hillsborough County Ruskin1 Florida 47 Seep 21 Jan. 21 Jan. 6 30 12 2904 Ruskin2 Florida 47 Seep 18 Feb. 18 Feb. 5 24 15 4356 Manatee County Lorraine Asgrow 91 Drip 1 Mar. 1 Mar. 6 22 15 3960 Duette Florida 47 Drip 7 Mar. 7 Mar. 6 24 15 3630 Bradenton Mt Fresh Seep 12 Mar. 12 Mar. 5 18 15 5808 Ft. Hamer Florida 47 Seep 15 Feb. 15 Feb. 7 28 12 2677 Palm Beach County Boynton Beach Undisclosed Drip 25 Jan. 4 Feb. 6 24 15 3630 grape type sine of the square root of the percent divided by 100. All trans- formed data were analyzed by ANOVA or GLM (SAS Institute, 1989) and means were separated using the Least Significant Difference at the P = 0.05 level. All data are presented in the original scale.

Results

Experiments in 2000 and 2001. The B. argentifolii popula- tion in the 2000 trial was low and no significant differences in the numbers of nymphs per leaflet occurred among the treat- ments (Fig. 1A). Nymphal densities did not reach the thresh- old of 5 nymphs/10 leaflets on check plots until the eighth week after transplanting, the same week that the number of nymphs on leaflets from plots treated with thiamethoxam reached the threshold. The nymphal population on imidaclo- prid-treated plots did not reach the threshold until the tenth week after transplanting. The incidence of plants with symp- toms of TYLCV was high for a fall season, reaching over 12% by the end of the season (Fig. 1B). Nevertheless, treatments with either imidacloprid or thiamethoxam resulted in lower percentages of plants with symptoms by week 7 after treat- ment. Thereafter, only plots treated with imidacloprid had a significantly lower percentage of plants with symptoms rela- tive to the non-treated check. In 2001 the whitefly population was moderate, with the density of nymphs on the check plots equaling or exceeding 5 nymphs per 10 leaflets during nearly the entire sampling pe- riod (Fig. 2). Plants treated at transplanting with either imida- cloprid or thiamethoxam did not exceed the threshold during the sampling period, although the density of nymphs Fig. 1. The density of whitefly nymphs (A) and the incidence of plants with on plots treated with imidacloprid equaled the threshold on symptoms of tomato yellow leaf curl virus (TYLCV)(B) on tomato plants treat- ed at transplanting with soil drenches of two nicotinoid insecticides at Braden- the twelfth week after transplanting (Fig. 2A). Nymphal den- ton, Fall 2000. Means with an asterisk are significantly different from the check. sities on plots treated with imidacloprid or thiamethoxam were significantly less than those on the check on six dates. Foliar applications of either insecticide 5 weeks after trans- imidacloprid and 4 weeks thereafter for thiamethoxam; how- planting resulted in nymphal densities at or below the thresh- ever, this corresponded to a period when the densities on the old 2 weeks after treatment and for three weeks thereafter for non-treated check also generally were declining (Fig. 2B). Re-

Proc. Fla. State Hort. Soc. 115: 2002. 323

Fig. 2. The density of whitefly nymphs on tomato plants following either Fig. 3. The incidence of plants with symptoms of tomato yellow leaf curl soil drenches at transplanting (A) or foliar applications (B) of two nicotinoid virus (TYLCV) on tomato plants following either soil drenches at transplant- insecticides at Bradenton, Fall 2001. Arrows indicate the week of foliar appli- ing (A) or foliar applications (B) of two nicotinoid insecticides at Bradenton, cations. Means with an asterisk are significantly different from the check. Fall 2001. Arrows indicate the week of foliar applications. Means with an as- terisk are significantly different from the check. ductions compared to the check were significant on week 8 nificantly different except on one sampling date at Ruskin2, for thiamethoxam and week 11 for both insecticides. Al- when the density on imidacloprid-treated plots was lower than though an additional foliar application of imidacloprid 11 that on thiamethoxam-treated plots. At Homestead, nymphal weeks after transplanting and applications of both insecti- densities were the highest of any location, with densities on im- cides 12 and13 weeks after transplanting resulted in signifi- idacloprid-treated plots significantly lower from those on the cant reductions in nymphal densities relative to the check by check plots on all five sampling dates and significantly lower week 14, densities remained at or above the 5 nymphs per10 from thiamethoxam-treated plots on three dates. At two addi- leaflets threshold. The percentage of non-treated check tional sites (Boynton Beach and Ruskin2), nymphal densities plants with symptoms of TYLCV were lower in 2001 than in on imidacloprid-treated plots were significantly lower than the 2000 (Fig. 3). Soil applications of either imidacloprid or thia- checks when those on thiamethoxam-treated plots were not methoxam resulted in lower percentages of plants with symp- on at least two sampling dates. However, when the data were toms compared to the check (Fig. 3A) while foliar averaged over all locations except Homestead, control with applications did not (Fig. 3B). Twelve weeks after transplant- imidacloprid and thiamethoxam were not statistically differ- ing, the number of leafmines counted per 2-min search per ent and densities on treated plots were significantly lower than plot did not differ significantly among the plots (80 for the the density on non-treated plots on six dates. check, 80 and 88 for soil applications of imidacloprid and thi- With the exception of Homestead, both insecticides re- amethoxam, respectively, and 69 and 102 for foliar applica- sulted in densities below the threshold of 5 nymphs per 10 tions of imidacloprid and thiamethoxam, respectively: F = leaflets for at least 8 weeks and for as long as 12 weeks. At one 0.72; df = 4, 12; P = 0.59). location (Ruskin1), plots treated with thiamethoxam never Experiments in 2002. With the exception of Homestead, reached the threshold for the 12-week duration of the study; populations of B. argentifolii in the spring 2002 experiments however, the threshold was not reached on the check plots were relatively low for a spring season at all locations, with the until week 11. At Homestead, thiamethoxam-treated plots checks not reaching the threshold of 5 nymphs per 10 leaflets reached the threshold 4 weeks after treatment while those and with significant differences among treatments generally treated with imidacloprid reached the threshold the follow- not occurring until after the sixth week after treatment ing week. (Table 2). Where differences did occur, nymphal densities on The incidence of plants with symptoms of TYLCV never plots treated with imidacloprid or thiamethoxam were not sig- exceeded 10% in the non-treated check plots in four of the

324 Proc. Fla. State Hort. Soc. 115: 2002.

Table 2. The numbers of sessile nymphs of the silverleaf whitefly on tomato foliage at 10 sites following soil drenches of nicotinoid insecticides at transplant- ing, Spring 2002.

No. nymphs/10 leaflets on indicated week after treatment

Amount Treatment per acre (oz) WK1 WK2 WK3 WK4 WK5 WK6 WK7 WK8 WK9 WK10 WK11 WK12 Boynton Beach Thiamethoxam 2SC 8 — — — 2 a — 3 a — 6 ab 11 a 25 ab — — Imidacloprid 2F 16 — — — 3 a — 1 a — 1 a 6 a 16 a — — Control — — — — 4 a — 1 a — 12 b 32 b 58 b — — Bradenton Thiamethoxam 2SC 8 — — 0 a 0 a 0 a 1 a 0 a 1 a 6 a 6 a 13 a 28 a Imidacloprid 2F 16 — — 0 a 0 a 0 a 1 a 0 a 2 a 6 a 9 ab 11 a 31 a Control — — — <1 a <1 a 2 b 2 a 2 b 6 b 8 a 17 b 19 b 33 a Duette Thiamethoxam 2SC 8 — — — 0 a 0 a 0 a 0 a 2 a 4 a 9 a 25 a 18 a Imidacloprid 2F 16 — — — 0 a 0 a 0 a 1 a 2 a 6 a 15 ab 22 a 19 a Control — — — — 0 a 1 a 1 a 3 a 3 a 8 a 16 b 19 a 29 a Ft. Hamer Thiamethoxam 2SC 8 — — — 0 a <1 a 1 a 0 a 1 a 3 ab 5 a 5 ab 10 a Imidacloprid 2F 16 — — — 0 a 0 a <1 a 1 a <1 a 1 a 4 a 4 a 7 a Control —- — — — 0 a <1 a 1 a 2 b 2 a 5 b 7 a 9 b 13 a Homestead Thiamethoxam 2SC 8 — — 2 a 7 ab 44 b 50 b 63 b ————— Imidacloprid 2F 16 — — <1 a <1 a 8 a 7 a 30 a ————— Control — — — 29 b 59 b 91 c 83 c 78 b ————— Immokalee1 Thiamethoxam 2SC 8 — — — 0 a <1 a 0 a 0 a — — 2 a 3 a 9 a Imidacloprid 2F 16 — — — 1 a 0 a 0 a 0 a — — 8 a 5 a 7 a Control — — — — 2 a 8 a 2 a 2 a — — 16 a 9 a 14 a Immokalee2 Thiamethoxam 2SC 8 — 0 a 0 a 0 a 0 a 0 a 3 a 1 a 8 a 6 a 19 a 11 a Imidacloprid 2F 16 — 0 a 0 a 0 a 0 a 0 a 3 a 5 a 6 a 22 a 11 a 6 a Control — — 1 a 13 a 1 b 1 a 2 a 19 a 5 a 10 a 17 a 63 b 19 a Lorraine Thiamethoxam 2SC 8 — — — 0 a 1 a <1 a 2 a 2 a 4 a 8 a 10 a 19 ab Imidacloprid 2F 16 — — — 0 a <1 a 1 a 2 a 3 a 6 ab 7 a 9 a 12 a Control — — — — 0 a <1 a 1 a 3 a 7 b 9 b 12 a 16 a 23 b Ruskin1 Thiamethoxam 2SC 8 — — 0 a 0 a 0 a 0 a 0 a 0 a <1 a <1 a 2 a 4 a Imidacloprid2F 16 — — 0 a 0 a 0 a 0 a 0 a 0 a 0 a 1 a 2 a 5 a Control — — — 1 a 0 a 0 a 0 a 1 a <1 a 2 a 4 b 5 a 7 a Ruskin2 Thiamethoxam 2SC 8 ———— 0 a<1 a2 a1 a1 a8 ab8 b17 a Imidacloprid 2F 16 ———— 0 a2 a2 a2 a2 a2 a3 a17 a Control — ———— 0 a1 a6 b7 b7 b17 b14 c21 a Average over all locations (except Homestead) Thiamethoxam 2SC 8 — 0 a 0 a <1 a <1 a 1 a 1 a 2 a 5 a 8 a 11 a 15 a Imidacloprid 2F 16 — 0 a 0 a 1 a <1 a 1 a 1 a 2 a 4 a 8 a 8 a 14 a Control — — 1 a 5 b 1 a 2 b 1 a 5 a 5 b 10 b 18 b 19 b 19 a

Mean separation in columns within a site by the Least Significant Difference, 5% level, on data transformed by the square root of the number plus 0.5. Data are presented in the original scale. Hyphens indicate no data were taken. eight locations at which TYLCV incidence was monitored (Ta- lower percentages of plants with symptoms on imidacloprid- ble 3). Neither imidacloprid nor thiamethoxam treatments treated plots compared to the check on 10 dates and with thi- resulted in a significantly lower percentage of plants with amethoxam-treated plots on seven dates; however, percentag- symptoms compared to the checks at those four locations ex- es were not significantly different for imidacloprid- and cept week 12 at Lorraine. At the other three locations (Boyn- thiamethoxam-treated plots. At Ruskin1, no plants with symp- ton Beach, Homestead and Ruskin1), there were significantly toms were observed in imidacloprid-treated plots. When the

Proc. Fla. State Hort. Soc. 115: 2002. 325

Table 3. Percent of plants showing symptoms of the silverleaf whitefly vectored tomato yellow leaf curl virus on tomato foliage at eight sites following soil drenches of nicotinoid insecticides at transplanting, Spring 2002.

Percent of plants on indicated week after treatment

Amount per acre Treatment (oz) WK1 WK2 WK3 WK4 WK5 WK6 WK7 WK8 WK9 WK10 WK11 WK12

Boynton Beach Thiamethoxam 2SC 8 0.0 a 0.0 a 0.0 a 0.0 a — 0.0 a — 8.9 a 12.2 ab 12.2a — — Imidacloprid 2F 16 0.0 a 0.0 a 0.0 a 0.0 a — 1.1 ab — 5.6 a 5.6 a 8.9 a — — Control — 0.0 a 0.0 a 0.0 a 0.0 a — 4.4 b — 14.4 a 20.0 b 32.2 a — — Bradenton Thiamethoxam 2SC 8 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 3.3 a 5.5 ab 7.8 a 7.8 a 10.0 a 10.0 a 15.5 a Imidacloprid 2F 16 0.0 a 0.0 a 1.1 a 1.1 a 2.2 a 4.4 a 7.8 b 8.9 a 8.9 a 10.0 a 10.0 a 10.0 a Control — 0.0 a 0.0 a 0.0 a 1.1 a 1.1 a 4.4 a 4.4 a 5.6 a 6.7 a 10.0 a 10.0 a 17.8 a Duette Thiamethoxam 2SC 8 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 4.4 a 4.4 a Imidacloprid 2F 16 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 3.3 a 3.3 a Control — 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 1.1 a 2.2 a 2.2 a 2.2 a 3.3 a 3.3 a Ft. Hamer Thiamethoxam 2SC 8 0.0 a 0.0 a 0.0 a 1.4 a 1.4 a 2.8 a 2.8 a 2.8 a 2.8 a 2.8 a 2.8 a 2.8 a Imidacloprid 2F 16 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 1.4 a 1.4 a 1.4 a 1.4 a 2.8 a 2.8 a 2.8 a Control — 0.0 a 0.0 a 0.0 a 1.4 a 1.4 a 2.8 a 2.8 a 2.8 a 2.8 a 2.8 a 2.8 a 2.8 a Homestead Thiamethoxam 2SC 8 0.0 a 0.0 a 0.0 a 6.7 a 10.0 a 15.6 a 20.0 a 42.2 a ———— Imidacloprid 2F 16 0.0 a 0.0 a 0.0 a 12.2 a 12.2 a 16.6 a 20.0 a 34.4 a ———— Control — 0.0 a 0.0 a 0.0 a 22.2 b 26.7a 32.2 a 52.2 b 72.2 a ———— Lorraine Thiamethoxam 2SC 8 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.8 a 0.8 a 1.7 a 1.7 a 1.7 a 4.2 b Imidacloprid 2F 16 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.8 a 0.8 a 0.8 a 0.8 a 0.8 a 0.8 a Control — 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.8 a 2.5 a 2.5 a 2.5 a 2.5 a 2.5 a 5.0 b Ruskin1 Thiamethoxam 2SC 8 0.0a 0.0 a 0.0 a 0.0 a 0.0 a 1.4 ab 2.8 ab 2.8 a 2.8 a 2.8 a 2.8 a 4.2 ab Imidacloprid 2F 16 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a Control — 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 8.3 b 8.3 b 12.5 b 13.9 b 15.3 b 16.6 b 16.6 b Ruskin2 Thiamethoxam 2SC 8 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 1.1 a 1.1 a 2.2 a 2.2 a 2.2 a Imidacloprid 2F 16 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 1.1 a 1.1 a 1.1 a Control — 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 1.1 a 2.2 a 2.2 a 2.2 a 2.2 a Average over all locations (except Homestead) Thiamethoxam 2SC 8 0.0 a 0.0 a 0.0 a 0.2 a 0.2 a 1.0 a 1.9 a 3.3 ab 3.9 ab 4.4 ab 3.9 a 5.5 ab Imidacloprid 2F 16 0.0 a 0.0 a 0.2 a 0.2 a 0.4 a 0.9 a 1.6 a 2.3 a 2.3 a 3.3 a 2.9 a 2.9 a Control 0.0 a 0.0 a 0.0 a 0.3 a 0.4 a 2.9 b 3.2 a 5.7 b 7.1 b 9.3 b 6.0 a 7.8 b

Mean separation in columns within a site by the Least Significant Difference, 5% level, on data transformed by the arcsine of the square root of the percent divided by 100. Data are presented in the original scale. Hyphens indicate no data were taken.

data were averaged over all locations except Homestead, no leafmines on thiamethoxam-treated plots were significantly significant differences occurred until week 6. Imidacloprid- less than those on non-treated plots on more dates than treated plots had significantly lower percentages of plants were the number of leafmines on imidacloprid-treated with TYLCV symptoms relative to the check on four dates plots. In addition, the density of leafmines on thiamethox- when thiamethoxam-treated plots did not; however, the dif- am-treated plots was often significantly less than the density ferences between imidacloprid- and thiamethoxam-treated on imidacloprid-treated plots. These observations were true plots were small and not significant. at individual locations as well as when the data were aver- The number of Liriomyza leafmines generally were high- aged over all locations (except Homestead). Significant dif- er than densities of whitefly nymphs, although leafmining ferences were observed in as little as 2 weeks after treatment was not especially serious for a spring crop, except at Home- and persisted for as long as 12 weeks; however, most signif- stead (Table 4). The number of leafmines observed on icant differences after about 8 weeks after treatment were plots treated with either imidacloprid or thiamethoxam not large. At Homestead significant differences were ob- were significantly lower than those observed on non-treated served 2 weeks after treatment but were not apparent 1 plots on at least one date at each location. The number of week later.

326 Proc. Fla. State Hort. Soc. 115: 2002.

Table 4. The numbers of leafmines of Liriomyza trifolii in tomato foliage at eight sites following soil drenches of nicotinoid insecticides at transplanting, Spring 2002.

No. leafmines/one min search per plot on indicated week after treatment

Amount Treatment per acre (oz) WK1 WK2 WK3 WK4 WK5 WK6 WK7 WK8 WK9 WK10 WK11 WK12

Boynton Beach Thiamethoxam 2SC 8 ———3 a—3 a—————— Imidacloprid 2F 16 ———5 a—4 a—————— Control — ———8 a—8 b—————— Bradenton Thiamethoxam 2SC 8 0 a 6 a 9 a 13 a 19 a 5 a 3 a 3 a 3 a 4 a 6 a 21 a Imidacloprid 2F 16 3 a 17 ab 20 ab 22 ab 27 b 6 a 7 b 6 ab 6 a 7 a 7 a 18 a Control — 1 a 22 b 30 b 31 b 37 c 8 a 9 b 8 b 7 a 7 a 9 b 16 a Duette Thiamethoxam 2SC 8 0 a 0 a 6 a 3 a 5 a 8 a 12 a 8 a 9 a 14 a 25 a 12 a Imidacloprid 2F 16 0 a <1 a 5 a 9 a 11 ab 12 b 13 a 8 a 10 a 16 a 22 a 12 a Control — 0 a 10 b 8 a 16 a 20 b 15 b 22 b 8 a 11 a 21 a 31 a 18 b Ft. Hamer Thiamethoxam 2SC 8 0 a 0 a 0 a 1 a 5 a 1 a 2 a 3 a 2 a 14 a 9 a 10 a Imidacloprid 2F 16 0 a 0 a 0 a 1 a 2 a 3 b 6 b 11 b 4 a 12 a 9 a 11 a Control — 0 a 0 a 0 a 1 a 4 a 8 c 12 c 18 b 2 a 12 a 9 a 15 b Homestead Thiamethoxam 2SC 8 — 6 a 3 a ————————— Imidacloprid 2F 16 — 30 b 47 a ————————— Control — 61 c 43 a ————————— Lorraine Thiamethoxam 2SC 8 0 a 0 a 1 a 10 a 19 a 5 a 12 a 14 a 18 a 19 a 25 a 27 a Imidacloprid 2F 16 0 a 1 a 7 a 16 b 18 a 4 a 21 a 16 a 26 a 29 b 31 ab 31 a Control — 0 a 3 a 14 a 32 c 19 a 6 a 15 a 19 a 24 a 27 b 32 b 21 a Ruskin1 Thiamethoxam 2SC 8 — — 3 a 3 a 4 a 2 a 14 a 15 a 12 a 29 a 16 a 24 a Imidacloprid 2F 16 — — 46 b 29 b 32 b 20 b 42 b 16 a 21 a 45 b 23 a 24 a Control — — — 79 b 42 b 47 b 38 c 53 b 45 b 49 b 50 b 39 b 36 b Ruskin2 Thiamethoxam 2SC 8 0 a 0 a <1 a 3 a 10 a 26 a 41 a 13 a 10 a 19 a 20 a 18 a Imidacloprid 2F 16 0 a 0 a 2 b 19 ab 35 b 51 c 79 c 15 ab 12 a 21 a 21 a 25 b Control — 0 a 0 a 10 c 21 b 35 b 40 b 61 b 22 b 10 a 28 a 31 a 29 b Average over all locations (except Homestead) Thiamethoxam 2SC 8 0 a 1 a 3 a 5 a 11 a 7 a 14 a 10 a 9 a 17 a 17 a 19 a Imidacloprid 2F 16 1 a 4 ab 13 ab 14 b 21 b 14 ab 28 b 12 a 14 a 22 a 20 a 21 a Control — <1a 7 b 23 b 22b 27 b 17b 28 b 20b 18 a 24 a 25 a 22 a

Mean separation in columns within a site by the Least Significant Difference, 5% level, on data transformed by the square root of the number plus 0.5. Data are presented in the original scale. Hyphens indicate no data were taken.

Discussion and thiamethoxam were not statistically different. Foliar ap- plications of thiamethoxam appeared to provide quicker con- The data demonstrate that both imidacloprid and thia- trol of whitefly nymphs than did imidacloprid. methoxam are effective in controlling nymphal populations Soil applications of either nicotinoid also resulted in re- of B. argentifolii. Soil applications of either insecticide provid- duced incidence of plants with symptoms of TYLCV, although ed control for 8 to 12 weeks, except at Homestead where con- differences were not as consistent as with nymphal control. trol was for 3 to 5 weeks. Soil applications were more effective Again, there was a suggestion that the effects of imidacloprid than foliar applications. Generally, both insecticides provided were slightly greater and longer lasting than thiamethoxam, similar control when applied to the soil, although imidaclo- although differences were not even as large or consistent as prid may have provided slightly greater residual control than they were with nymphal control. Ahmed et al. (2001) and thiamethoxam in 2000 and 2002. However, differences were Stansly et al. (1998) found that soil applications of imidaclo- not large and consistent, except at the Homestead site, and, prid were more effective than foliar applications of conven- to a lesser extent, the Boynton Beach and Ruskin2 sites. When tional insecticides in reducing the percentage of plants with the 2002 data were averaged over all experiments except symptoms of TYLCV. Stansly and Conner (2000) and Stansly Homestead, control of whitefly nymphs with imidacloprid et al. (2001) showed that soil applications of imidacloprid or

Proc. Fla. State Hort. Soc. 115: 2002. 327

thiamethoxam reduced the percentage of tomato plants with However, irrigation management could influence the differ- TYLCV symptoms, although the thiamethoxam rate evaluat- ences in residual efficacy of the two compounds on the flat- ed was higher than the maximum rate permitted by the cur- wood sands because thiamethoxam is more water soluble rent label. Soil applications of imidacloprid also were than imidacloprid. Too much water, whether by irrigation or effective in reducing incidence of ToMoV (Stansly et al., rainfall, could cause thiamethoxam to migrate out of the root 1998). Timing foliar applications based on densities of white- zone more quickly than imidacloprid. The results at Home- fly nymphs in the present study was ineffective in reducing stead and the delay in the increase of whitefly nymph popula- TYLCV incidence. Timing applications based upon densities tions in the non-treated plots at other sites might also suggest of whitefly adults might have more of an impact on virus inci- that treatment of transplants in the greenhouse with imida- dence. The efficacy of foliar applications of thiamethoxam cloprid could provide greater than the2 to 3 weeks of control for managing TYLCV have been inconsistent in other studies that is generally assumed. However, nymphal densities on (Stansly and Conner, 2000; Stansly et al., 2001). non-treated plants at the GCREC were low for 7 weeks after The results of these experiments also demonstrated that transplanting, even though the plants had not been treated soil applications of either imidacloprid or thiamethoxam re- with imidacloprid in the greenhouse. sulted in reduced leafmining by L. trifolii; however, control Because the soil applications were made on a per acre ba- was greater and more consistent with thiamethoxam. The sis, the amount of active ingredient applied per plant varied means by which the nicotinoids reduced leafmining cannot among locations in 2002 (Table 1). Insect control might be be determined from the present studies because only total expected to vary accordingly; however, this was not the case. mines were counted. In a greenhouse study with potted chry- Although densities of whitefly nymphs were low on treated santhemum, (Dendranthema grandiflor, Tzvelev), both soil plots at Ruskin1 (2,904 plants per acre), nymphal densities at drenches and foliar sprays of thiamethoxam resulted in mor- Ft. Hamer (2,677 plants per acre) and Immokalee2 (3,111 tality of L. trifolii larvae that were present in leafmines at the plants per acre) were similar to or greater than those at time of treatment (Bethke and Redak, 2002). Soil drenches Immokalee1 (4,356 plants per acre) or Bradenton (5,808 or foliar sprays applied prior to exposure of the plants to leaf- plants per acre). In addition, the density of leafmines at miner adults resulted in nearly no subsequent leafmining Ruskin1 was greater than the densities at Bradenton and sim- (Bethke and Redak, 2002), which might suggest reduced ovi- ilar to those at Ruskin2 (4,356 plants per acre). Thus, any ef- position; however, in a subsequent observational trial, numer- fects of higher doses per plant at lower plant densities ous leafminer eggs were deposited in leaves previously treated appeared to be overridden by local population pressure. with thiamethoxam, but larvae died immediately upon hatch- Acknowledgments. The authors wish to express their appre- ing before beginning mines (Bethke, unpublished data). ciation to Dr. Jeff Brushwein, Mr. Jim Conner and Ms. Sandra The experiments in 2002 also demonstrated the variation Thompson for their technical assistance and to Alderman in the efficacy of imidacloprid and thiamethoxam at the dif- Farms, Artesian Farms, Deseret Farms, Four Star Tomato Inc., ferent locations. This was particularly evident at Homestead. Lipman & Lipman Inc., Tomatoes of Ruskin, 6Ls Farms, and This experiment was initiated as commercial harvesting in the Taylor & Fulton Farms for their cooperation in establishing area was nearing completion and the transplants used had and maintaining the experiments. not been treated with imidacloprid in the plant house. As a re- sult, whitefly population pressure was great, as evidenced by Literature Cited the large number of nymphs appearing on foliage of non- Ahmed, N. E., H. O. Kanan, Y Sugimoto, Y. Q. Ma, and S. Inanaga. 2001. Ef- treated plants only 3 weeks after transplanting. Furthermore, fect of imidacloprid on incidence of tomato yellow leaf curl virus. Plant control with either nicotinoid did not persist as long as at oth- Dis. 85:84-87. er sites and imidacloprid provided greater and more persis- Bai, D., S. C. R. Lummis, W. Leicht, H. Breer, and D. B. Stelle. 1991. Action tent control of whitefly nymphs than thiamethoxam. These of imidacloprid and a related nitrometheylene on cholinergic receptors results may have been due to the soil type and the physical of an identified insect motor neuron. Pestic. Sci. 33:197-204. Bethke, J. A. and R. A. Redak. 2000. Control of serpentine leafminer on chry- characteristics of the insecticides. The calcareous soil (Enti- santhemum under greenhouse conditions, fall 1999. Arthropod Mgmt. sol) at Homestead is a sandy, gravelly loam of pH 7.5 to 8.5 Tests. 25:G50. underlain with oolithic limestone (Maynard and Locascio, Bethke, J. A. and R. A. Redak. 2002. Control of serpentine leafminer on chry- 1982). The soils (Spodosols) at the other sites are poorly santhemum under greenhouse conditions, 2000. Arthropod Mgmt. Tests 27: G39. drained flatwood sands of pH 3.5 to 4.0 with a spodic horizon Maienfisch, P., L. Gsell, A. Rindlisbacher, and D. Allemann. 1997. CGA (accumulation of organic matter and aluminum in a layer) in 293’343 - A novel broad spectrum insecticide: Chemistry and biological the subsoil (Maynard and Locascio, 1982). Apparently, the laboratory evaluation. in: CGA 293’343 Papers on a Novel Insect Control nicotinoids either did not bind as well to components of the Compound. p. 1-12. Novartis Crop Protection, Inc., Annu. Mtg. Entomol. Entisol soil, were hydrolyzed by the higher pH of the Entisol Soc. Amer., Dec. 16, Nashville, Tenn. Maynard, D. N. and S. J. Locascio. 1982. Nutrition of vegetable crops in Flor- soil or migrated out of the root zone more rapidly in the En- ida, USA. Proc. 21st Intl. Hortic. Congr., Hamburg, Germany. 2:710-725. tisol soil compared to the flatwood sands. The half life of thi- Musgrave, C. A., S. L. Poe, and H. V. Weems, Jr. 1975. The vegetable leafmin- amethoxam at pH 9 at room temperature is a few days er, Liriomyza sativae Blanchard (Diptera: Agromyzidae) in Florida. Cir. (Maienfisch et al., 1997) and that for imidacloprid is much 162, Fla. Dept. Agric. and Consumer Serv., Div. Plant Industry. Oatman, E. R. and G. G. Kennedy. 1976. induced outbreak of Lir- greater than 30 d at pH 5, 7 and 9; therefore, the higher pH iomyza sativae on tomatoes. J. Econ. Entomol. 69:667-668. in the Entisol soil may explain at least partially the shorter re- Palumbo, J. C. 2000. Residual efficacy of foliar chloronicotinyls against silver- sidual efficacy of both compounds as well as the difference in leaf whiteflies on melon, 2000. Arthropod Management Tests 26:E21. nymphal control between the two compounds at Homestead. Palumbo, J. E., A. R. Horowitz, and N. Prabhaker. 2001. Insecticidal control Irrigation method did not appear to be a factor in the differ- and resistance management for Bemisia tabaci. Crop Protection 20:739-765. Polston, J. E., R. J. McGovern, and L. G. Brown. 1999. Introduction of tomato ences in results because the plots at Homestead were drip-ir- yellow leaf curl virus in Florida and implications for the spread of this and rigated, as were those at four flatwood sand sites (Table 1). other geminiviruses of tomato. Plant Dis. 83:984-988.

328 Proc. Fla. State Hort. Soc. 115: 2002.

SAS Institute Inc. 1989. SAS/STAT User’s Guide, version 6, 4th ed., SAS In- Taxonomy, Biology, Damage, Control and Management. pp. 153-165. In- stitute Inc., Cary, N.C. tercept Ltd., Andover, Hants, UK. Schuster, D. J. 1998. Intraplant distribution of immature lifestages of Bemisia Stansly, P. A. and J. M. Conner. 2000. Impact of insecticides on silverleaf argentifolii (Homoptera: Aleyrodidae) on tomato. Environ. Entomol. 27:1- whitefly and tomato yellow leafcurl virus (TYLCV) on staked tomato, 9. 1999. Arthropod Mgmt. Tests 25:173-174. Schuster, D. J. 2002. Action threshold for applying insect growth regulators Stansly, P. A., T.-X. Liu, and C. S. Vavrina. 1998. Response of Bemisia argenti- to tomato for management of irregular ripening caused by Bemisia argen- folii (Homoptera: Aleyrodidae) to imidacloprid under greenhouse, field, tifolii (Homoptera: Aleyrodidae). J. Econ. Entomol. 95:372-376. and laboratory conditions. J. Econ. Entomol. 91:686-692. Schuster, D. J., J. E. Funderburk, and P. A. Stansly 1996a. IPM in tomatoes. Stansly, P. A., J. M. Conner, and D. R. Peach. 2001. Impact of insecticides on in: D. Rosen, J. L. Capinera, and F. D. Bennett (eds), Integrated Pest Man- silverleaf whitefly and tomato yellow leafcurl virus (TYLCV) on staked to- agement - A Florida Perspective. p. 387-411. Intercept. Ltd., Andover, mato, 2000. Arthropod Mgmt. Tests 26: E96. Hants, UK. Wolweber, D. and K. Tietjen. 1999. Chloronicontinyl insecticides: a success Schuster, D. J., P. A. Stansly, and J. E. Polston 1996b. Expressions of plant of the new chemistry. In I. Yamamoto and J. E. Casdia (eds.). Nicotinoid damage by Bemisia. in D. Gerling and R. T. Mayer (eds.). Bemisia: 1995 insecticides and the nicotinic acetylcholine receptor. p. 109-126. Spring- er, Tokyo, Japan.

Proc. Fla. State Hort. Soc. 115:329-336. 2002. VARIATION IN THE SUGAR ACCUMULATION PATTERN OF MUSCADINE GRAPE GENOTYPES

ASHOK K. JAIN1, S. M. BASHA, ALFREDO B. LORENZO, were in the lower leaf sugar group were moved to the upper J. LU AND STEPHEN LEONG group in terms of berry sugar concentration, 12 genotypes Florida A&M University maintained their rank whereas 25 genotypes showed decreas- Center for Viticulture and Small Fruits es in their rank. Further studies are suggested to study the im- pact of leaf sugar concentration on characteristics Tallahassee, FL 32307 contributing to berry sugar such as leaf biomass, number of catkins per vine, number of berry cluster per vine, number of Additional index words. sucrose accumulation, berry sugar con- berries per cluster berry, size and levels of key enzymes in- centration, grape, developmental profile, muscadine, Vitis volved in sucrose synthesis. rotundifolia or Muscadinia rotundifolia The southeastern grape industry is based primarily on Vi- Abstract. The present study was undertaken to determine vari- ation in the accumulation pattern of sugars in leaves and ber- tis species native to the Gulf Plain of the United States, espe- ries at different developmental stages of forty-two muscadine cially muscadine grapes (Vitis rotundifolia Michx). The grape genotypes. In order to compare the sugar accumulation muscadine genotypes are tolerant to most grape diseases, patterns and source sink relationships between bunch and however, muscadine grapes are not desirable as a table grape muscadine grape genotypes, twelve-bunch grape genotypes (fresh fruit) because of sour taste, thick berry skin and seeded were also studied. Leaf and berry sugar concentrations among berries. Muscadine wines are gaining popularity because of the genotypes were significantly different (P ≤ 0.05) at different their unique fruity flavor and full-body (Olien, 1990). Berry developmental stages. Sugar concentrations in the leaves of sugar concentration is an important characteristic that affects muscadine genotypes varied from 1.94% (w/v) to 8.30% at the wine quality (Davies and Robinson, 1996). Sucrose is pro- pre-flowering stage; 0.36% to 4.52% at the flowering stage; 2.19% to 4.10% at the young fruit stage; 2.25% to 6.05% at the duced as a result of photosynthesis in the leaf and transported medium fruit stage; 2.39% to 7.79% at the mature fruit stage; through phloem to the berries (Hawker et al., 1976; Swanson and 1.67% to 7.09% at the ripe fruit stage. Accumulation of and El-Shishiny, 1958). The transported sugar is hydrolyzed sugars in berries varied from 0.61% to 2.25% at the young fruit to glucose and fructose in grape berries. Accumulation of sug- stage; 0.38% to 3.18% at the medium fruit stage; 1.11% to ars in the form of glucose and fructose within the vacuole is 11.37% at the mature fruit stage; and 4.46% to 16.08% at the one of the main features of the ripening process in grape and ripe fruit stage. The mean sugar concentrations over the devel- continues through ripening. Photosynthetic capability, rate opmental stages of the leaf and berry were tested using the of import into individual sink organs, and levels of sucrose RANK procedure that helped to assign the grape genotypes metabolizing enzymes such as invertase or sucrose phosphate into seven distinct groups. Significantly higher leaf sugar con- synthase activity are very important components for sugar ac- tent at fully developed/mature fruit stage (stage 5) and pre- flowering (stage 1), suggests that there are higher leaf sugar cumulation in grape berries (Hawker, 1969; Hubbard et al., requirements after veraison (berry ripening) and during flow- 1991). ering. Change of grouping study shows that 17 genotypes that The sugar level in grape berries varies greatly among dif- ferent genotypes. However, the sugar accumulation patterns in different muscadine genotypes have not been fully studied. 1Corresponding author. The present study was undertaken to determine variation in

Proc. Fla. State Hort. Soc. 115: 2002. 329