Henis, Y. and I. Chet. 1968. The effect of nitrogenous amendments on the

germinability of sclerotia of Sckrotium rolfsii and on their accompanying

microflora. Phytopathol. 58:209-211.

Jenkinson, D. S. and D. S. Powlson. 1976. The effects of biocidal treatments

on metabolism in soil - V. A method for measuring soil biomass. Soil Biol.

Biochem 8:209-213.

Lazarovits, G., K. L. Conn, andj. Potter. 1999. Reduction of potato scab, ver-

ticillium wilt, and nematodes by soymeal and meat and bone meal in two

Ontario potato fields. Can. J. Plant Pathol. 21:345-353.

Lazarovits, G., M. Tenuta, and K. L. Conn. 2000. Utilization of high nitrogen

and swine manure amendments for control ofsoilborne diseases: efficacy

and mode of action. Acta Hort. 532:59-64.

Locascio, S.J.,J. P. Gilreath, D. W. Dickson, T. A. Kucharek,J. P.Jones, and

J. W. Noling. 1997. Fumigant alternatives to methyl bromide for polyeth

ylene mulched tomato. HortScience 32:1208:1211.

Lumsden, R. D., J. A. Lewis, and G. C. Papavizas. 1983. Effect of organic

amendments on soilborne plant diseases and pathogen antagonists, p. 51-

70. In W. Loceretz (ed). Environmentally Sound Agriculture. Praeger,

New York.

Maynard, D. N. and S. M. Olson. 2001. Vegetable production guide for Flor

ida. University of Florida Extension, Citrus & Vegetable Magazine.

Monaghan, P. F., G. H. Brinen, and S. R. Kostewicz. 1994. Organic vegetable

production in Florida. Proc. Fla. State Hort. Soc. 107:377-380.

Rodriquez-Kabana, R. 1986. Organic and inorganic nitrogen amendments to

soil as nematode suppressants. J. Nematol. 18:129-135.

Spreen, T. H., J. J. VanSickle, A. E. Moseley, M. S. Deepak, and L. Mathers.

1995. Use of methyl bromide and the economic impact of its proposed

ban on the Florida fresh fruit and vegetable industry. University of Flori

da, Bulletin 898 (Tech.).

Tenuta, M. and G. Lazarovits. 2002. Ammonia and nitrous acid from nitrog

enous amendments kill the microsclerotia of Verticillium dahliae. Phytopa

thology 92:255-264.

Tsao, P. H. andJ.J. Oster. 1981. Relation ofammonia and nitrous acid to sup

pression of Phytophthora in soils amended with nitrogenous organic sub

stances. Phytopathology 71:53-59.

U.S. EPA. 2002. Methyl bromide phase out web site, http://www.epa.gov.sp-

dpublc/mbr/.

Watkins, G.M. 1961. Physiology of Sclerotium rolfsii with emphasis on parasit

ism. Phytopathology 51:110-113.

World Meteorological Organization. 1998. Scientific Assessment of Ozone

Depletion: 1998. Executive Summary. Global Ozone Research and Moni

toring Project - Report No. 44.

Proc. Fla. State Hort. Soc. 115:321-329. 2002.

COMPARISON OF IMIDACLOPRID AND

THIAMETHOXAM FOR CONTROL OF THE SILVERLEAF WHITEFLY,

BEMISIA ARGENTIFOLII, AND THE LEAFMINER, LIRIOMYZA TRIFOLII, ON TOMATO

David J. Schuster

University ofFlorida, IFAS

Gulf Coast Research and Education Center

Bradenton, FL 34203

Robert F. Morris II

Bayer CropScience

Lakeland, FL 33811

Additional index words, chemical control, Lycopersicon esculen

tum, insecticidal control, imidacloprid, thiamethoxam

Abstract. The silverleaf whitefly, Bemisia argentifolii Bellows &

Perring, also known as strain B of the sweetpotato whitefly [B.

tabaci (Germ.)], is the dominant pest of tomatoes, Lycopersi

con esculentum Mill, in southern Florida. The insect causes

damage directly by inducing an irregular ripening disorder of

tomato and indirectly by transmitting plant viruses, particular

ly tomato yellow leaf curl virus (TYLCV). The leafminer, Liri-

omyza trifolii (Burgess), has long been considered a serious

pest of tomatoes in Florida, causing defoliation through min

ing of leaves by larvae. Imidacloprid and thiamethoxam are

members of a new class of systemic, nicotinoid insecticides

that can be applied either as soil drenches or as foliar sprays.

Two experiments were conducted in the fall seasons of 2000

and 2001 and 10 experiments were conducted during the

This research was supported by Bayer Crop Sciences and by the Florida

Agricultural Experiment Station, and approved for publication asJournal Se

ries No. R-08945.

spring of 2002 to compare the efficacy of imidacloprid and thi

amethoxam. When imidacloprid 2F (16 oz/acre) or thiamethox

am 2SC (8 oz/acre) were applied to the soil at or within 3 weeks

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

prid appeared to be slightly greater and to persist slightly long

er at three sites, although differences were not significant

when the 2002 data were averaged over all experiments. Foliar

applications of imidacloprid 1.6F at 3.75 oz/acre and thia

methoxam 25WG at 4 oz/acre at a threshold of five nymphs/10

leaflets also provided significant control of nymphs, although

control was not as good as with soil applications, and control

appeared to be greater with thiamethoxam. The incidences of

plants with symptoms of TYLCV were reduced with soil appli

cations but not foliar applications. Imidacloprid appeared to

provide greater and more consistent reductions in the occur

rence of TYLCV infected plants at three sites as well as when

the data were averaged over six sites in 2002, although differ

ences from thiamethoxam were small and not significant. Soil

applications of either insecticide resulted in significant reduc

tions of L. trifolii leafmines, although control was consistently

better with thiamethoxam.

The silverleaf whitefly, Bemisia argentifolii Bellows & Per

ring, also know as the B strain of the sweetpotato whitefly [B.

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

as spotting of leaves, wilting and death of plants, and irregular

ripening of fruit (Schuster et al., 1996b). The insect is even

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

more damaging as a vector of plant viruses including tomato

mottle virus (ToMoV) and tomato yellow leaf curl virus (TYL-

CV). The latter virus is particularly devastating, causing flower

abscission and severe plant stunting (Polston et al., 1999).

The leafminer, Liriomyza trifolii (Burgess), has long been

considered a serious pest of tomatoes in Florida (Schuster et

al., 1996a) and recently has become more problematic

(Schuster, personal observation). The larval feeding within

the leaves causes serpentine mines and can result in signifi

cant defoliation of plants, particularly when secondary micro

organisms invade the mines (Musgrave et al., 1975). As is the

case with L. sativae Blanchard, the leafminer is considered a

secondary pest; i.e., it generally is kept below economically

damaging levels by natural enemies, principally hymenopter-

ous parasites, but increases to levels requiring control when

the densities of natural enemies are reduced, principally by

the use of broad spectrum insecticides (Oatman and

Kennedy, 1976).

Nicotinoids are a new class of neurotoxins also referred to

as neonicotinoids, nitroguanidines, nitromethylenes and

chloronicotinyls. The nicotinoids are structured after natural

ly occurring nicotine compounds and act similarly on the cen

tral nervous system of insects, irreversibly blocking the

postsynaptic nicotinergic acetylcholine receptors (Bai et al.,

1991). The high water solubility of the nicotinoids give them

excellent systemic properties and long residual activity, which

makes them particularly effective against sucking insects. Nic

otinoids generally have low mammalian toxicity relative to

other neurotoxins and are relatively non-toxic to non-target

species (Wolweber and Tietjen, 1999), which makes them de

sirable for integrating into pest management programs. Nic

otinoids can be applied as soil drenches or as foliar sprays.

Imidacloprid (Bayer Corporation, Kansas City, Mo.) and

thiamethoxam (Syngenta Crop Protection, Inc., Greensboro,

N.C.) are two nicotinoids that have registrations on vegetable

crops including tomato. The former was the first nicotinoid

available for use on tomatoes, being registered by the US EPA

in 1995. Imidacloprid has been used as a drench of tomato

seedlings in plant production houses at least a week before

transplantation. Imidacloprid is applied again as a soil drench

at transplanting, or by side-dress fertilization injection wheels

or trickle irrigation tubes 1 to 3 weeks after transplanting. Im

idacloprid is formulated as Admire® for soil applications and

as Provado7 for foliar applications and has been effective

against B. argentifolii, particularly as a soil application (as sum

marized in Palumbo et al., 2001). Thiamethoxam received US

EPA registrations on tomato in 2001 and is formulated as Plat

inum® for soil applications and as Actara® for foliar applica

tions. Foliar applications of thiamethoxam have shown good

efficacy against B. argentifolii in melons (Palumbo, 2001) and

tomatoes (Stansly and Conner, 2000; Stansly et al., 2001). A

soil application shortly after transplanting also provided ex

cellent control of the whitefly, although the rate evaluated

was higher than the maximum rate permitted by the current

label (Stansly et al., 2001). There are no published reports on

the efficacy of either nicotinoid against L. trifolii leafminers

on tomato in the field; however, applications of thiamethox

am to chrysanthemum resulted in fewer leafmines in the

greenhouse (Bethke and Redak, 2000; 2002). The purpose of

the present experiments was to compare the efficacy of these

nicotinoids as soil drenches and foliar applications for man

aging whiteflies and TYLCV and as soil drenches for manag

ing leafminers on tomato.

Materials and Methods

Experiments in 2000 and 2001. Two experiments were con

ducted at the Gulf Coast Research and Education Center

(GCREC), Bradenton. Transplants of the tomato cultivar

Agriset were set 21 Sept. 2000 and 11 Sept. 2001 18 inches

apart on raised beds of EauGallie fine sand covered with

white polyethylene mulch. Plots were three-21 ft long rows on

5-ft centers and treatments were replicated four times in ran

domized complete block designs. Soil drenches of imidaclo

prid 2F (Admire® 16 oz/acre) and thiamethoxam 2SC

(Platinum®, 8 oz/acre) were applied at transplanting in 4 oz

ofwater per plant. In 2001 imidacloprid 1.6F (Provado®, 3.75

oz/acre) and thiamethoxam 25WG (Actara®, 4 oz/acre)

were applied foliarly when whitefly densities approached or

reached the threshold of >5 sessile nymphs (2nd or 3rd in-

stars) and/or pupae (4th instars or red eye nymphs) per 10

terminal leaflets of the seventh or eighth leaf from the top of

one stem from each of the middle 10 plants in the middle row

of the respective plots (Schuster, 1998; 2002). Applications

were made with a self-propelled sprayer operated at 200 psi

and 3.4 mph. It was fitted with eight Albuz orange nozzles per

row and delivered 60 (four nozzles open) or 120 (eight noz

zles open) gpa, depending upon plant height. In both exper

iments Bacillus thuringiensis Berliner (Mattch at 2 qt/acre,

Javelin at 2 lb/acre, or XenTari at 2 lb/acre) or spinosad

(SpinTor at 6 oz/acre) were applied weekly to control lepi-

dopterous larvae, particularly the southern armyworm

[Spodoptera eridania (Cramer) ]. The number of plants in each

plot with definite symptoms of TYLCV were recorded weekly.

The numbers of sessile nymphs and pupae of the silverleaf

whitefly were counted weekly as above. In 2001, the number

of Liriomyza leafmines was counted by each of two people, one

on each side of the middle row of each plot, during a 2-min

search of each plot on 6 Dec. and the counts by the two peo

ple were combined for each plot.

Experiments in 2002. Ten additional experiments were con

ducted in the spring of 2002, one at the GCREC and nine at

commercial tomato farms: two in Collier County (Immoka-

lee), one in Dade County (Homestead), two in Hillsborough

County (Ruskin), three in Manatee County (Duette, Ft. Ham

mer and Lorraine), and one in Palm Beach County (Boynton

Beach). Plots at all sites consisted of two rows and treatments

were replicated three times (four times at Lorraine) in ran

domized complete block designs. Cultural details for each

site are listed in Table 1. At all locations, imidacloprid 2F (Ad

mire) was applied at 16 oz/acre and thiamethoxam 2SC (Plat

inum) was applied at 8 oz/acre as a drench to the base of each

plant in 1.7 or 3.4 oz per plant. Transplants at all locations

were grown commercially and, with the exception of those set

at GCREC and Homestead, were treated with imidacloprid in

the plant house prior to delivery. Growers applied insecti

cides for armyworm control but not for whiteflies. All plants

in each plot were examined weekly for definite symptoms of

TYLCV (except for Immokalee sites) and 10 plants ofone row

of each plot were sampled weekly for whitefly sessile nymphs

as above. The numbers of Liriomyza leafmines per plot were

counted, usually weekly, during a 1-min search of one row of

each plot by one person.

Sessile nymph and leafmine counts were transformed for

analyses by adding 0.5 to the number and then taking the

square root. The percent of plants with TYLCV symptoms was

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.

Site

Spacing

Cultivar

Irrigation

method Planting date Treatment date Row (ft) Plant (inches) Plant/row Plant/acre

Immokaleel

Immokalee2

Homestead

Ruskinl

Ruskin2

Lorraine

Duette

Bradenton

Ft. Hamer

Boynton Beach

Florida 47

Florida 47

Florida 47

Florida 47

Florida 47

Asgrow 91

Florida 47

Mt Fresh

Florida 47

Undisclosed

grape type

Seep

Drip

Drip

Seep

Seep

Drip

Drip

Seep

Seep

Drip

23 Dec.

27 Dec.

12 Mar.

21 Jan.

18 Feb.

1 Mar.

7 Mar.

12 Mar.

15 Feb.

25Jan.

Collier County

3Jan.

15Jan.

Dade County

19 Mar.

Hillsborough County

21 Jan.

18 Feb.

Manatee County

IMar.

7 Mar.

12 Mar.

15 Feb.

Palm Beach County

4 Feb.

6

6

6

6

5

6

6

5

7

6

20

28

20

30

24

22

24

18

28

24

15

15

15

12

15

15

15

15

12

15

4356

3111

4356

2904

4356

3960

3630

5808

2677

3630

sine of the square root of the percent divided by 100. All trans

formed data were analyzed byANOVA 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. IB). 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

on plots treated with imidacloprid equaled the threshold on

the twelfth week after transplanting (Fig. 2A). Nymphal den

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

planting resulted in nymphal densities at or below the thresh

old 2 weeks after treatment and for three weeks thereafter for

- Imidacloprid 2F

--■—Thiamethoxam 2SC /

a Check /

14-

B

-•— Imidacloprid 2F

--•-- Thiamethoxam 2SC

-■•▲•■■ Check

WK6 WK6 WK7 WK8 WK9 WK10 WK11 WK12

Week after transplanting

Fig. 1. The density of whitefly nymphs (A) and the incidence of plants with

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

ton, Fall 2000. Means with an asterisk are significantly different from the check.

imidacloprid and 4 weeks thereafter for thiamethoxam; how

ever, this corresponded to a period when the densities on the

non-treated check also generally were declining (Fig. 2B). Re-

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

25-

20

15

10

0-

A

..A

A*"

—•— liridactoprid 2F

—■—Thiamethoxam 2SC

a Check ^

/ \-..

A

A

\ / /^

A

....£

* *

* *

26

20

15

10

-•—Imidacloprid 1.6F

-■— Thlamathoxam 26WG

a Chock

WK6 WK6 WK7 WK8 WK9 WK10 WK11 WK12 WK13 WK14

Week after transplanting

Fig. 2. The density of whitefly nymphs on tomato plants following either

soil drenches at transplanting (A) or foliar applications (B) of two nicotinoid

insecticides at Bradenton, Fall 2001. Arrows indicate the week of foliar appli

cations. Means with an asterisk are significantly different from the check.

5

3-

2

-•— lrrtdacloprfd2F

-■— Thianrethoxam 2SC

a Check

>•*

- Imidacloprid 1.6F

- Thiamethoxam 26WG S

Check /

WK3 WK4 WK5 WK6 WK7 WK8 WK9 WK10 WK11

Week after transplanting

Fig. 3. The incidence of plants with symptoms of tomato yellow leaf curl

virus (TYLCV) on tomato plants following either soil drenches at transplant

ing (A) or foliar applications (B) of two nicotinoid insecticides at Bradenton,

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

for thiamethoxam and week 11 for both insecticides. Al

though an additional foliar application of imidacloprid 11

weeks after transplanting and applications of both insecti

cides 12 and13 weeks after transplanting resulted in signifi

cant reductions in nymphal densities relative to the check by

week 14, densities remained at or above the 5 nymphs perlO

leaflets threshold. The percentage of non-treated check

plants with symptoms of TYLCV were lower in 2001 than in

2000 (Fig. 3). Soil applications of either imidacloprid or thia

methoxam resulted in lower percentages of plants with symp

toms compared to the check (Fig. 3A) while foliar

applications did not (Fig. 3B). Twelve weeks after transplant

ing, the number of leafmines counted per 2-min search per

plot did not differ significantly among the plots (80 for the

check, 80 and 88 for soil applications of imidacloprid and thi

amethoxam, respectively, and 69 and 102 for foliar applica

tions of imidacloprid and thiamethoxam, respectively: F =

0.72; df= 4, 12; P= 0.59).

Experiments in 2002. With the exception of Homestead,

populations of B. argentifolii in the spring 2002 experiments

were relatively low for a spring season at all locations, with the

checks not reaching the threshold of 5 nymphs per 10 leaflets

and with significant differences among treatments generally

not occurring until after the sixth week after treatment

(Table 2). Where differences did occur, nymphal densities on

plots treated with imidacloprid or thiamethoxam were not sig

nificantly different except on one sampling date at Ruskin2,

when the density on imidacloprid-treated plots was lower than

that on thiamethoxam-treated plots. At Homestead, nymphal

densities were the highest ofany location, with densities on im

idacloprid-treated plots significantly lower from those on the

check plots on all five sampling dates and significantly lower

from thiamethoxam-treated plots on three dates. At two addi

tional sites (Boynton Beach and Ruskin2), nymphal densities

on imidacloprid-treated plots were significantly lower than the

checks when those on thiamethoxam-treated plots were not

on at least two sampling dates. However, when the data were

averaged over all locations except Homestead, control with

imidacloprid and thiamethoxam were not statistically differ

ent and densities on treated plots were significantly lower than

the density on non-treated plots on six dates.

With the exception of Homestead, both insecticides re

sulted in densities below the threshold of 5 nymphs per 10

leaflets for at least 8 weeks and for as long as 12 weeks. At one

location (Ruskinl), plots treated with thiamethoxam never

reached the threshold for the 12-week duration of the study;

however, the threshold was not reached on the check plots

until week 11. At Homestead, thiamethoxam-treated plots

reached the threshold 4 weeks after treatment while those

treated with imidacloprid reached the threshold the follow

ing week.

The incidence of plants with symptoms of TYLCV never

exceeded 10% in the non-treated check plots in four of the

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

thiamethoxam reduced the percentage of tomato plants with

TYLCV symptoms, although the thiamethoxam rate evaluat

ed was higher than the maximum rate permitted by the cur

rent label. Soil applications of imidacloprid also were

effective in reducing incidence of ToMoV (Stansly et al.,

1998). Timing foliar applications based on densities of white-

fly nymphs in the present study was ineffective in reducing

TYLCV incidence. Timing applications based upon densities

of whitefly adults might have more of an impact on virus inci

dence. The efficacy of foliar applications of thiamethoxam

for managing TYLCV have been inconsistent in other studies

(Stansly and Conner, 2000; Stansly et al., 2001).

The results of these experiments also demonstrated that

soil applications of either imidacloprid or thiamethoxam re

sulted in reduced leafmining by L. trifolii; however, control

was greater and more consistent with thiamethoxam. The

means by which the nicotinoids reduced leafmining cannot

be determined from the present studies because only total

mines were counted. In a greenhouse study with potted chry

santhemum, (Dendranthema grandiflor, Tzvelev), both soil

drenches and foliar sprays of thiamethoxam resulted in mor

tality of L. trifolii larvae that were present in leafmines at the

time of treatment (Bethke and Redak, 2002). Soil drenches

or foliar sprays applied prior to exposure of the plants to leaf-

miner adults resulted in nearly no subsequent leafmining

(Bethke and Redak, 2002), which might suggest reduced ovi-

position; however, in a subsequent observational trial, numer

ous leafminer eggs were deposited in leaves previously treated

with thiamethoxam, but larvae died immediately upon hatch

ing before beginning mines (Bethke, unpublished data).

The experiments in 2002 also demonstrated the variation

in the efficacy of imidacloprid and thiamethoxam at the dif

ferent locations. This was particularly evident at Homestead.

This experiment was initiated as commercial harvesting in the

area was nearing completion and the transplants used had

not been treated with imidacloprid in the plant house. As a re

sult, whitefly population pressure was great, as evidenced by

the large number of nymphs appearing on foliage of non-

treated plants only 3 weeks after transplanting. Furthermore,

control with either nicotinoid did not persist as long as at oth

er sites and imidacloprid provided greater and more persis

tent control of whitefly nymphs than thiamethoxam. These

results may have been due to the soil type and the physical

characteristics of the insecticides. The calcareous soil (Enti-

sol) at Homestead is a sandy, gravelly loam of pH 7.5 to 8.5

underlain with oolithic limestone (Maynard and Locascio,

1982). The soils (Spodosols) at the other sites are poorly

drained flatwood sands ofpH 3.5 to 4.0 with a spodic horizon

(accumulation of organic matter and aluminum in a layer) in

the subsoil (Maynard and Locascio, 1982). Apparently, the

nicotinoids either did not bind as well to components of the

Entisol soil, were hydrolyzed by the higher pH of the Entisol

soil or migrated out of the root zone more rapidly in the En-

tisol soil compared to the flatwood sands. The half life of thi

amethoxam at pH 9 at room temperature is a few days

(Maienfisch et al., 1997) and that for imidacloprid is much

greater than 30 d at pH 5, 7 and 9; therefore, the higher pH

in the Entisol soil may explain at least partially the shorter re

sidual efficacy of both compounds as well as the difference in

nymphal control between the two compounds at Homestead.

Irrigation method did not appear to be a factor in the differ

ences in results because the plots at Homestead were drip-ir

rigated, as were those at four flatwood sand sites (Table 1).

However, irrigation management could influence the differ

ences in residual efficacy of the two compounds on the flat-

wood sands because thiamethoxam is more water soluble

than imidacloprid. Too much water, whether by irrigation or

rainfall, could cause thiamethoxam to migrate out of the root

zone more quickly than imidacloprid. The results at Home

stead and the delay in the increase of whitefly nymph popula

tions in the non-treated plots at other sites might also suggest

that treatment of transplants in the greenhouse with imida

cloprid could provide greater than the2 to 3 weeks of control

that is generally assumed. However, nymphal densities on

non-treated plants at the GCREC were low for 7 weeks after

transplanting, even though the plants had not been treated

with imidacloprid in the greenhouse.

Because the soil applications were made on a per acre ba

sis, the amount of active ingredient applied per plant varied

among locations in 2002 (Table 1). Insect control might be

expected to vary accordingly; however, this was not the case.

Although densities of whitefly nymphs were low on treated

plots at Ruskinl (2,904 plants per acre), nymphal densities at

Ft. Hamer (2,677 plants per acre) and Immokalee2 (3,111

plants per acre) were similar to or greater than those at

Immokaleel (4,356 plants per acre) or Bradenton (5,808

plants per acre). In addition, the density of leafmines at

Ruskinl was greater than the densities at Bradenton and sim

ilar to those at Ruskin2 (4,356 plants per acre). Thus, any ef

fects of higher doses per plant at lower plant densities

appeared to be overridden by local population pressure.

Acknowledgments. The authors wish to express their appre

ciation to Dr. Jeff Brushwein, Mr.Jim Conner and Ms. Sandra

Thompson for their technical assistance and to Alderman

Farms, Artesian Farms, Deseret Farms, Four Star Tomato Inc.,

Lipman & Lipman Inc., Tomatoes of Ruskin, 6Ls Farms, and

Taylor & Fulton Farms for their cooperation in establishing

and maintaining the experiments.

Literature Cited

Ahmed, N. E., H. O. Kanan, Y Sugimoto, Y. Q. Ma, and S. Inanaga. 2001. Ef

fect of imidacloprid on incidence of tomato yellow leaf curl virus. Plant

Dis. 85:84-87.

Bai, D., S. C. R. Lummis, W. Leicht, H. Breer, and D. B. Stelle. 1991. Action

of imidacloprid and a related nitrometheylene on cholinergic receptors

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

santhemum under greenhouse conditions, fall 1999. Arthropod Mgmt.

Tests. 25:G50.

Bethke,J. A. and R. A. Redak. 2002. Control of serpentine leafminer on chry

santhemum under greenhouse conditions, 2000. Arthropod Mgmt. Tests

27: G39.

Maienfisch, P., L. Gsell, A. Rindlisbacher, and D. Allemann. 1997. CGA

293'343 - A novel broad spectrum insecticide: Chemistry and biological

laboratory evaluation, in: CGA 293'343 Papers on a Novel Insect Control

Compound, p. 1-12. Novartis Crop Protection, Inc., Annu. Mtg. Entomol.

Soc. Amer., Dec. 16, Nashville, Tenn.

Maynard, D. N. and S. J. Locascio. 1982. Nutrition of vegetable crops in Flor

ida, USA. Proc. 21st Intl. Hortic. Congr., Hamburg, Germany. 2:710-725.

Musgrave, C. A., S. L. Poe, and H. V. Weemsjr. 1975. The vegetable leafmin

er, Liriomyza sativae Blanchard (Diptera: Agromyzidae) in Florida. Cir.

162, Fla. Dept. Agric. and Consumer Serv., Div. Plant Industry.

Oatman, E. R. and G. G. Kennedy. 1976. Methomyl induced outbreak of Lir

iomyza sativae on tomatoes. J. Econ. Entomol. 69:667-668.

Palumbo, J. C. 2000. Residual efficacy of foliar chloronicotinyls against silver-

leaf whiteflies on melon, 2000. Arthropod Management Tests 26:E21.

Palumbo, J. E., A. R. Horowitz, and N. Prabhaker. 2001. Insecticidal control

and resistance management for Bemisia tabaci. Crop Protection 20:739-765.

PolstonJ. E., R.J. McGovern, and L. G. Brown. 1999. Introduction of tomato

yellow leaf curl virus in Florida and implications for the spread of this and

other geminiviruses of tomato. Plant Dis. 83:984-988.

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

SAS Institute Inc. 1989. SAS/STAT User's Guide, version 6, 4th ed., SAS In

stitute Inc., Cary, N.C.

Schuster, D. J. 1998. Intraplant distribution of immature lifestages of Bemisia

argentifolii (Homoptera: Aleyrodidae) on tomato. Environ. Entomol. 27:1-

9.

Schuster, D. J. 2002. Action threshold for applying insect growth regulators

to tomato for management of irregular ripening caused by Bemisia argen

tifolii (Homoptera: Aleyrodidae). J. Econ. Entomol. 95:372-376.

Schuster, D. J., J. E. Funderburk, and P. A. Stansly 1996a. IPM in tomatoes,

in: D. Rosen,J. L. Capinera, and F. D. Bennett (eds), Integrated Pest Man

agement - A Florida Perspective, p. 387-411. Intercept. Ltd., Andover,

Hants, UK.

Schuster, D. J., P. A. Stansly, andj. E. Polston 1996b. Expressions of plant

damage by Bemisia. in D. Gerling and R. T. Mayer (eds.). Bemisia: 1995

Taxonomy, Biology, Damage, Control and Management, pp. 153-165. In

tercept Ltd., Andover, Hants, UK.

Stansly, P. A. and J. M. Conner. 2000. Impact of insecticides on silverleaf

whitefly and tomato yellow leafcurl virus (TYLCV) on staked tomato,

1999. Arthropod Mgmt. Tests 25:173-174.

Stansly, P. A., T.-X. Liu, and C. S. Vavrina. 1998. Response of Bemisia argenti

folii (Homoptera: Aleyrodidae) to imidacloprid under greenhouse, field,

and laboratory conditions. J. Econ. Entomol. 91:686-692.

Stansly, P. A., J. M. Conner, and D. R. Peach. 2001. Impact of insecticides on

silverleaf whitefly and tomato yellow leafcurl virus (TYLCV) on staked to

mato, 2000. Arthropod Mgmt. Tests 26: E96.

Wolweber, D. and K. Tietjen. 1999. Chloronicontinyl insecticides: a success

of the new chemistry. In I. Yamamoto andj. E. Casdia (eds.). Nicotinoid

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,

J. Lu and Stephen Leong

Florida A&M University

Centerfor Viticulture and Small Fruits

Tallahassee, FL 32307

Additional index words, sucrose accumulation, berry sugar con

centration, grape, developmental profile, muscadine, Vitis

rotundifolia or Muscadinia rotundifolia

Abstract. The present study was undertaken to determine vari

ation in the accumulation pattern of sugars in leaves and ber

ries at different developmental stages of forty-two muscadine

grape genotypes. In order to compare the sugar accumulation

patterns and source sink relationships between bunch and

muscadine grape genotypes, twelve-bunch grape genotypes

were also studied. Leaf and berry sugar concentrations among

the genotypes were significantly different (P < 0.05) at different

developmental stages. Sugar concentrations in the leaves of

muscadine genotypes varied from 1.94% (w/v) to 8.30% at the

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

medium fruit stage; 2.39% to 7.79% at the mature fruit stage;

and 1.67% to 7.09% at the ripe fruit stage. Accumulation of

sugars in berries varied from 0.61% to 2.25% at the young fruit

stage; 0.38% to 3.18% at the medium fruit stage; 1.11% to

11.37% at the mature fruit stage; and 4.46% to 16.08% at the

ripe fruit stage. The mean sugar concentrations over the devel

opmental stages of the leaf and berry were tested using the

RANK procedure that helped to assign the grape genotypes

into seven distinct groups. Significantly higher leaf sugar con

tent at fully developed/mature fruit stage (stage 5) and pre-

flowering (stage 1), suggests that there are higher leaf sugar

requirements after veraison (berry ripening) and during flow

ering. Change of grouping study shows that 17 genotypes that

'Corresponding author.

were in the lower leaf sugar group were moved to the upper

group in terms of berry sugar concentration, 12 genotypes

maintained their rank whereas 25 genotypes showed decreas

es in their rank. Further studies are suggested to study the im

pact of leaf sugar concentration on characteristics

contributing to berry sugar such as leaf biomass, number of

catkins per vine, number of berry cluster per vine, number of

berries per cluster berry, size and levels of key enzymes in

volved in sucrose synthesis.

The southeastern grape industry is based primarily on Vi

tis species native to the Gulf Plain of the United States, espe

cially muscadine grapes (Vitis rotundifolia Michx). The

muscadine genotypes are tolerant to most grape diseases,

however, muscadine grapes are not desirable as a table grape

(fresh fruit) because of sour taste, thick berry skin and seeded

berries. Muscadine wines are gaining popularity because of

their unique fruity flavor and full-body (Olien, 1990). Berry

sugar concentration is an important characteristic that affects

wine quality (Davies and Robinson, 1996). Sucrose is pro

duced as a result of photosynthesis in the leaf and transported

through phloem to the berries (Hawker et al., 1976; Swanson

and El-Shishiny, 1958). The transported sugar is hydrolyzed

to glucose and fructose in grape berries. Accumulation of sug

ars in the form of glucose and fructose within the vacuole is

one of the main features of the ripening process in grape and

continues through ripening. Photosynthetic capability, rate

of import into individual sink organs, and levels of sucrose

metabolizing enzymes such as invertase or sucrose phosphate

synthase activity are very important components for sugar ac

cumulation in grape berries (Hawker, 1969; Hubbard et al.,

1991).

The sugar level in grape berries varies gready among dif

ferent genotypes. However, the sugar accumulation patterns

in different muscadine genotypes have not been fully studied.

The present study was undertaken to determine variation in

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