Fungicides and insecticides applied to pelleted sugar-beet seeds — I. Dose, distribution, stability and release patterns of active ingredients

Cm/’ Promrron Vol. 14, No. 5, pp. 355-362. 199.5 Cowrieht 0 1995 Elsevier Science Ird Printed’ah &a~&itam. All rights reserved 0261.?194/95 $ltl.oo + O.(X)

Fungicides and insecticides applied to pelleted sugar-beet seeds - I. Dose, distribution, stability and release patterns of active ingredients A. W. M. Huijbregts, P. D. Gijssel and W. Heijbroek lnsfitute

of Sugar Beet Research (IRS), Bergen op Zoom, The Netherlands

Loading

of active ingredient

(CV)

for thiram

between

12 and 34%.

and applied Stability

between

individual

ranged from 25 to 77% With

carbofuran

pellets varied significantly.

and for hymexazol,

methiocarb,

the CV ranged from

14 to 62%

The coefficients furathiocarb

depending

of variation

and imidacloprid

on pelleting

process

dose. of applied

combination.

Decrease

pesticide

after storage depended

of thiram

on pellet type and applied

fungicide/insecticide

during storage was related to the pellet type, but hymexazol

decreased

in combination with furathiocarb, benfuracarb and carbosulfan. Carbofuran, methiocarb, tefluthrin and imidacloprid individually were stable during storage. The conversion rate of furathiocarb, benfuracarb and carbosulfan to carbofuran during storage was related to the pellet type and was enhanced by the presence of hymexazol. Analysis of the active ingredients in pellets periodically after sowing showed the percentage of the initial thiram concentrations present 4 weeks after sowing varied O-75%. Hymexazol decreased quickly in the pellets and after 4 weeks no active ingredient could be detected, in most pellet types, even with slow release products. Thirteen to 71% of furathiocarb, benfuracarb, carbosulfan, carbofuran and tefluthrin was still present in the pellets after 8 weeks, depending on pellet type and insecticide/fungicide combination in the pellets. in

all

pellet

types,

especially

Keywords: sugar beet, pelleted

seeds,

Fungicides and insecticides are added to sugar-beet seed during pelleting for the control of seedling diseases and pests. The optimal dosages of the applied pesticides depend on desired efficacy, phytotoxicity and levels of infestation by pests and diseases and required field emergence (Wunderlich, 1986). Efficacy can be affected by type of active ingredients added, pelleting process (composition of the coating material), method of application (inside/outside layer), dose, variation in concentration between individual pellets, release properties and stability of the active ingredients which may be influenced by the formulation (Seaman, 1990). For satisfactory protection a correct average dose has to be applied with a minimal variation in concentration between individual pellets, especially if the difference in the rates which give protective action or cause phytotoxicity is small. The distribution between individual pellets is important too when the active ingredient has a systemic mode of action (Westwood, Bean and Dewar, 1994). The aim of this study was to compare the stability, distribution and release patterns of active ingredients in different pellet types.

insecticides,

Materials

fungicides,

pesticides

in the pellet

and methods

Treatments Fungicides (thiram and hymexazol) and insecticides (methiocarb, carbofuran, furathiocarb, benfuracarb, carbosulfan, tefluthrin and imidacloprid) were applied to pellets at different doses by various pelleting companies according to their own processes (Betakote, Cermer, Germain’s EB, KWS, Maribo, Sarea and SUET). Mean loading of active ingredients sugar-beet seed lots

in pelleted

Two representative samples, usually containing 100 pellets each, were analysed to determine the mean concentration of active ingredients in a sugar-beet seed lot. The analyses are based on extraction of the active ingredients with 100 ml suitable organic solvent and subsequent determination by High Performance Liquid Chromatography (Table 1). Concentrations are expressed as grams active ingredient per 100 000 seeds (g a.i./unit).

Crop

Protection

1995

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14 Number

5

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Pesticides Table

1.

in pelleted

sugar-beet

seeds I: A.W.M. Huijbregts

et al.

Schematic survey of extraction and determination of active ingredients in pelleted sugar-beet seed HPLC

column: I = 250 mm; i.d. = 4.6 mm flow: 1.5 mllmin

Active ingredient

Extraction solvent

stationary phase

mobile phase

thiram methiocarb furathiocarb benfuracarb carbosulfan carbofuran

acetone

Lichrosorb Si 60-5

chloroform/ hexane (35/65)

270

tefluthrin

acetone

Spherisorb 5 ODS-2

acetonitril/ water/l % H7P04 (80/l 515)

270

hymexazol

acetonitrill water/l % H,PO, ( 15/80/5)

Spherisorb 5 ODS-2

acetonitril/ water/l% HXPOI ( 15/80/5)

240

imidacloprid

acetonitril

Spherisorb 5 ODS-2

acetonitril/ water/l % H,PO, (5014515)

240

Distribution of active ingredients individual pellets

between

For the determination of variation of active ingredients between individual pellets of the same lot, at least 20 pellets were analysed individually, using the same method as described (Table 1) with 3 or 5 ml extraction solvent for each pellet. Storage stability

of pesticides

on treated seeds

The stability of applied fungicide and insecticide combinations was determined by analysing mean concentrations of active ingredients before and after storage. For this purpose small seed lots were stored under dry conditions in airtight bags at room temperature. Storage periods varied from 6 months to 2 years.

UV-detection k (nm)

ingredients. If two different extraction procedures had to be used (hymexazol in combination with other active ingredients), 10 pellets were taken for each extraction. In all other cases analytical results were based on four replicates of 20 pellets each. Statistical analysis The F-test (Gore, 1952) was used to determine differences between variations in loading of pesticides in individual pellets. The data of the release experiments were analysed using ANOVA methods (Mead and Curnow, 1983). The means were separated using the least significant difference (LSD) test.

Results and discussion Release patterns of active ingredients

Release characteristics were determined in soil in 1987, 1988 and 1989 with sugar-beet seed pelleted by seven different pellet types (Betakote, Cermer, Germain’s EB, KWS, Maribo, Sarea and SUET), containing one or more of the pesticides thiram, hymexazol, furathiocarbosulfan, carbofuran and carb , benfuracarb, tefluthrin. Two slow-release experimental formulations containing hymexazol were also tested. To determine the release patterns of the active ingredients, pellets were sewn in strips of open woven cloth. Each strip contained 20 pellets with a distance of 5 cm between the pellets. The strips were laid in the soil at normal drilling depth with 50 cm distance between the rows, using a split-plot design with four replicates for each sample at different times. Trial fields were situated at one location in 1987 and 1988 (clay soil, 25% silt) and at two different locations in 1989 (clay soil, 53% silt and loss, 26% silt). Strips were taken out of the soil after different periods between 2 days and 8 weeks. At each sample time, one strip per replicate was analysed to determine the changes in concentration of active

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Accuracy and uniformity different manufacturers

of dosing achieved

by

results of individual pellets showed large variations in loadings of active ingredients on individual pellets. For thiram, hymexazol, methiocarb, furathiocarb and imidacloprid results are summarised in Table Analytical

2.

High CV for thiram, up to 77%, could be explained by the fact this active ingredient is applied directly on the seeds of which surface areas are different. Moreover the mean analysed concentrations of most Betakote samples were low, in some cases below 1 g a.i./unit, which were considerably less than the target rates of 4 g. a.i./unit. For hymexazol, methiocarb and furathiocarb CV for all pellet types were between 12 and 26%. Statistical evaluation for imidacloprid showed a slightly but significantly higher 0, = 0.05) variation for Germain’s EB as compared with SUET. The variation for KWS was significantly higher (p < 0.01) as compared with SUET and Germain’s EB. The mean analysed concentrations for Germain’s EB as well as SUET deviated somewhat from the target rate, which was

Pesticides in pelleted sugar-beet seeds I: A.W.M. Huijbregts et al. Stability of active ingredients

90 g a.i./unit, corresponding with 0.9 mg/pellet. For Germain’s EB the concentration ranged from 0.56 to 1.55 mg/pellet, while for SUET the concentration ranged from 0.50 to 1.21 mg/pellet. However, for KWS the concentration ranged from 0.36 to 1.94 mg/pellet. Recently, Westwood et af. (1994) showed that the loading of imidacloprid in individual pellets was related to the pellet size and that the higher loadings on larger pellets caused significant slowing of emergence in the laboratory. Carbofuran in individual pellets was extensively investigated because the margin between protection and phytotoxicity is rather small (Dewar, 1989). CV between individual pellets were determined in four pelleting types, each using different application rates of carbofuran (Table 3). Statistical evaluation showed a significantly higher (p < 0.05) variation for Germain’s EB pellets compared to Betakote and SUET pellets at all rates. However, at a target rate of 20 and 30 g a.i./unit, the mean analysed concentrations for Betakote were far below target. Concentrations were also too low for Cermer pellets, especially at low target rates. To avoid the problems of insufficient control or phytotoxicity the mean concentration should be close to the optimal target dose and the variation should be as low as possible. Since 1983, when the study on distribution of carbofuran between individual pellets was carried out, pelleting companies have paid more attention to this problem (Hiirner, 1989; Halmer, 1994).

Fungicides. Analyses of pelleted seeds treated with thiram and hymexazol indicated that both fungicides decreased during storage. The stability of thiram depended on the pelleting process (Figure I). A large reduction in thiram concentration was established for Betakote and KWS, while hardly any reduction was found for Sarea. Hymexazol, alone or in combination with insecticides, was degraded quickly. All pelleting processes showed a small reduction of hymexazol after 6 months of storage in pellets with only methiocarb as an insecticide. However hymexazol was considerably reduced in combination with furathiocarb or benfuracarb. The largest reduction was found for Betakote, while Maribo showed the smallest reduction (Figure 2).

Effects of other insecticides on the decrease of thiram and hymexazol was investigated for SUET and Germain’s EB pellets. Apart from thiram (5 g a.i./unit) and hymexazol(14.7 g a.i./unit) carbofuran or tefluthrin or imidacloprid were also added. Thiram and hymexazol were analysed before and after 21 months of storage. The rate of decrease of hymexazol and thiram was not clearly influenced by the presence of these insecticides (Table 4). Insecticides. The decrease of tefluthrin during storage was similar for all pellet types under investigation (Figure 3).

Table 2. Ranges of mean concentrations and coefficients of variation (Cv) for active ingredients in individual pellets from several pelleting processes Number Range of mean of concentrations Range of samples (g a.i./unit) cv (%)

Active ingredient

Pelleting process

thiram

SUET Cermcr Bctakote

hymexazol

Germain’s SUET Betakote

methiocarb

Betakotc

1

4.9

furathiocarb

SUET

2

4248

16-l’)

Betakote

3

41-43

12-19

SUET Germain’s KWS

1 I

85 91 88

19 20 34

EB

2 1 s

4.8-5.9 11.2 0.5-4.0

63-17 32 25-64

1 1 2

11.2 27.3 7.8-9.4

26 19 14-16 14

Proceba imidacloprid

EB

1

Figure 1. Effect of storage on the concentrations of thiram in pellets from various pelleting processes. Analysis before (0) and after (W) 1 year of storage

Table 3. Mean carbofuran concentrations and coefficients of variation (CV) for individual pellets from four different pelleting processes Cermer Target rate g a.i./unit 5 10 20 30

Germain’s EB

Betakote

SUET

mean g/unit

cv %

mean g/unit

cv “A,

mean g/unit

cv %

mean g/unit

cv %

3.6 7.4 17.8 28.0

33 35 22 26

4.7 9.5 19.2 29.4

62 48 so 41

4.9 9.3 16.6 25.3

30 24 17 15

4.6 9.4 19.4 29.2

25 14 15 16

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Protection

1995

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Number 5

357

Pesticides

in pelleted

sugar-beet 12

r

seeds I: A.W.M. Huijbregts

Without

furathiocarb/benfuracarb

et al.

1

With

furathiocarb

With

benfuracarb

I

Process Figure 2. Effect of storage on the hymexazol concentrations in pellets from various pelleting processes, without (left) and with (right) application of furathiocarb or benfuracarb. Analysis before (0) and after (m) % year of storage

Table 4. Mean recovery for thiram (5 g a.i./unit) and hymexazol (14.7 g a.i./unit) with and without addition of insecticides after 21 months of storage

Tefluthrin

Added insecticide active ingredient

Process Germain’s Germain’s Germain’s Germain’s Germain’s Germain’s Germain’s SUET SUET SUET SUET SUET SUET SUET

EB EB EB EB EB EB EB

quantity (g a.i./unit)

Recovery thiram

Recovery hymexazol

W)

W)

carbofuran tefluthrin tefluthrin imidacloprid imidacloprid imidacloprid

30 6 I2 30 60 90

60 48 64 50 70 70 73

34 34 42 40 41 41 45

carbofuran tefluthrin tefluthrin imidacloprid imidacloprid imidacloprid

_ 30 6 12 30 60 90

79 105 75 69 78 78 79

49 45 48 43 49 41 38

Betakote

Analyses of tefluthrin in a number of samples, to which thiram and hyrnexazol had been added too, showed a decrease of 520% per year for tefluthrin. No consistent interactions with the various pellet types could be found. Imidacloprid proved to be stable during storage for all pelleting processes. It is clear from Figure 4 that only a small reduction in imidacloprid was found after 1 year of storage. The lower imidacloprid concentrations for Betakote, compared to the target rate, are due to inaccurate additions. Only small or no reductions in carbofuran and methiocarb concentrations could be established after 1 year of storage. The decrease was less than 20% for all pelleting types under investigation. Analyses within a few months of application showed that the formation of carbofuran from furathiocarb,

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Germain’s

Figure 3. Effect of storage.on the concentrations of tefluthrin in pellets from various pelleting processes. Analysis before (0) and after (m) 1 year of storage. Figures at x-axis indicate target rates of application (g. a.i./unit)

benfuracarb and carbosulfan depended on the pelleting process (Table 5). Considerable amounts of furathiocarb and benfuracarb had been degraded to carbofuran in Betakote pellets. The carbofuran concentration in pellets with carbosulfan was high too in Germain’s EB and SUET pellets. Degradation to carbofuran was enhanced considerably in most pellet types, when hymexazol was applied to the same pellets. Large quantities of carbofuran have been found in combination with hymexazol in all pellet

Pesticides in pelleted sugar-beet seeds I: A.W.M. Huijbregts et al.

types with the exception of Maribo. These results are in agreement with the investigations of Pussemier ef al. (1994) concerning interactions between hymexazol, furathiocarb and some clay minerals used for seed treatments.

Release of active ingredients

in pellets after drilling

Fungicides. Thirum. Initial concentrations for thiram varied from 0.7 to 12.9 g a.i./unit, although the requested target dose for thiram was 4 g a.i./unit.

Table 5. Degradation of furathiocarb, benfuracarb and carbosulfan to carbofuran in various types of pellets, with and without the presence of hymexazol

lmidacloprid

% of active ingredient converted to carbofuran Active ingredient furathiocarb

benfuracarb

Process

without hymexazolwith hymexazol

Betakote Ceres

IS 2

61 _

Germain’s EB KWS Maribo Sarea

2 5 2

7 14 2

1

_

SUET

0

15

Betakote Ceres

15 0

_

Germain’s EB KWS Maribo Sarea

6 10 0

SUET 30 hil YO Betakote

8

I

-

2

Yl

2Y 5 5 14

46 40

30

carbosulfan

Germain’s

Figure 4. Effect of storage on cloprid in pellets from various before (0) and after (m) 1 year indicate target rates of application

the concentrations of imidapelleting processes. Analysis of storage. Figures at x-axis (g a.i./unit)

- =

Not

Germain’s EB Hilleshog Sarea SUET

76

tested

Table 8. Analysed concentrations of thiram directly before and 4 weeks after drilling for various pelleting types in trial fields (Bergen op Zoom, 1987 and 1988; Nieuwdorp, 1989 and Voerendaal, 1989) Thiram concentration (g a.i./unit)

Trial field

Pellet type

I987 Bergen op Zoom

Betakote Ceres Germain’s EB KWS Maribo SUET

1988

Betakote

Bergen op Zoom

Germain’s EB SUET

% of initial concentration after 4 weeks

before sowing

4 weeks after sowing

2.2 0.7 4.4 3.7 12.Y 5.6

0.4 0.1 2.5 0.6 6.7 4.2

16 a* II a 154bc 16 a 52 b 7s c

2.4 3.5 3.2

1.o 2.2 0.6

43 b 63 b 20 a

1989

Betakote

Nieuwdorp

Germain’s EB KWS Maribo Sarea

I.S 3.1 3.8 4.5 2.1 4.2

(1.0 0.8 0.4 0.2 0.1 0.2

0 a 26 c 12 b 5 ab 2a 5 ab

lY8Y Voerendaal

Bctakotc Germain’s EB KWS Maribo Sarea SUET

I.5 3.1 3.8 4.5 2.7 4.2

0.0 0.4 0.3 0.0 0.2 0.0

0 a 13 c 7b 0 a Y bc Oa

‘Figures

in a trial

with

the

same

letter

are

not

significantly

different.

p =

O.OS

Crop Protection 1995 Volume 14 Number 5

359

Pesticides

in pelleted

sugar-beet

seeds I: A.W.M. Huijbregts

et al.

These large variations in initial concentrations made it difficult to compare the decrease of thiram in the various pellet types. The initial thiram concentrations and the remaining quantity 4 weeks after sowing are shown in Table 6. Large differences have been found after 4 weeks for the percentages of initial concentrations (0.75%). The differences between pellet types are not consistent on. each trial field. Statistical evaluation of the results on both trial fields in 1989, where the same pellet lots were used, showed a significant interaction between pellet type and location. So, it can be concluded that soil type and weather conditions also have a considerable influence on the decrease of thiram.

initial concentration, while application of the two slow release formulations did not retard the rapid decrease of hymexazol (Table 7). After 4 weeks the initial concentrations had been reduced to less than 0.2 g. a.i./unit, as in most samples no active ingredient could be detected at all. Insecticides. Furathiocarb, benfuracarb and carbosulfan. In all trials, the release of furathiocarb, benfuracarb and carbosulfan from the pellets was relatively slow for all pellet types. In Table 8, furathiocarb and carbofuran (produced by conversion of furathiocarb) concentrations are given directly before and 8 weeks after drilling. From the results it can be concluded that the decrease of furathiocarb and the conversion to carbofuran depended on pellet type. Carbofuran has been recalculated to furathiocarb to

Hymexazol. Hymexazol decreased very fast. After 1 week the remaining part varied from 20 to 51% of the

Table 7. Analysed concentrations of hymexazol directly before and 1 week after drilling for various pelleting types in trial fields (Bergen op Zoom, 1987 and 1988) Hymcxazol concentration (g a.i./unit)

before sowing

sowing

% of initial concentration after 1 week

Betakote Betakote Germain’s EB KWS Maribo SUET slow rel. 1 slow rel. 2

1.4 9.9 10.5 2.2 2.6 14.7 8.2 8.2

0.7 3.1 3.4 1.1 0.6 2.9 2.1 2.9

51 b* 31 ab 33 ab 49 b 21 a 20 a 26 a 36 ab

SUET SUET SUET

13.6 8.4 13.9

5.2 3.4 5.0

38 a 40 a 36 a

1 week after Trial field

Pellet type

1987 Bergen op Zoom

1988 Bergen op Zoom

*Figures

in a trial

with

the same letter

are not significantly

different,

p = 0.05

Table 8. Furathiocarb and carbofuran concentrations directly before and 8 weeks after drilling for various pellet types in trial fields (Bergen op Zoom, 1987 and 1988; Nieuwdorp, 1989 and Voerendaal, 1989) g. a.i./unit after 8 weeks

g a.i./unit before sowing

% of total initial concentration after 8 weeks

furathiocarb

carbofuran

furathiocarb

carbofuran

Betakote’ Ceres Germain’s EB KWS’ Maribo’ SUET+

25 31 58 36 58 45

23 0.2 1.3 3.5 0.7 3.2

12 16 41 28 40 21

8 0.0 0.4 0.2 0.0 0.3

36 53 70 67 64 43

a* bc d d cd ab

1988 Bergen op Zoom

Betakote Germain’s EB SUET SUET*

53 42 41 36

5.4 0.5 0.0 0.0

33 22 20 16

2.2 0.3 0.8 0.9

60 53 54 49

a a a a

1989 Nieuwdorp

Betakote KWS Maribo

53 68 48

3.2 0.6 1.0

31 33 16

1.1 0.5 0.1

57 b 49 b 32 a

1989 Voerendaal

Betakote KWS Maribo

53 68 48

3.2 0.6 3.2

12 39 I8

2.5 1.8 0.9

29 a 61 b 40 a

Trial field

Pellet type

1987 Bergen op Zoom

*Figures

in a trial

with

‘Addition

of hymexazol

‘Addition

of tefluthrin

360

the same letter

are not significantly

different,

to the pellets to the pellets

Crop Protection

1995 Volume 14 Number 5

p =

0.05

Pesticides in pelleted sugar-beet seeds I: A.W.M. Huijbregts et al. Table 9. Benfuracarb and carbofuran concentrations directly before and 8 weeks after drilling for various pellet types in trial fields (Bergen op Zoom, 1988; Nieuwdorp, 1989 and Voerendaal, 1989) g a.i./unit after 8 weeks

g a.i./unit before sowing carbofuran

benfuracarb

carbofuran

10

3.7 2.3

0.5 22

1.9 7.8 18 1.1

37 42 47

1.4 2.0 0.2

37 42 47

1.4 2.0 0.2

benfuracarb

Trial field

Pellet type

19X8 Bergen op Zoom

Betakote Germain’s EB SUET SUET’

13 39 43 A

Germain’s EB Germain’s EB’ Sarea Germain’s EB Germain’s EB’ Sarea

19x9 Nieuwdorp

1989 Vocrendaal

IFigures Addition

in a trial of

with

the same letter

are not significantly

I .5

different.

2.4

28 b* 29 b 45 c 13 a

3.3 2.8 17

1.3 1.3 0.2

14 a 11 a 40 b

4.0 2.5 21

2.7 2.9 0.8

23 a 17 a 53 b

p = 0.05

directly before and 8 weeks after drilling for various pellet types in trial fields

g a.i./unit before sowing carbosulfan

carbofuran

carbosulfan

carbofuran

Germain’s EB Germain’s EB’ Sarca SUET

40 33 39 55

9.3 16.1 1.2 5.0

9.4 5.2 21 37

2.1 2.4 0.2 1.1

24 b* 16 a 51 c 61 d

Germain’s EB Germain’s EB Sarea SUET

40 33 30 55

Y.3 16.1 1.2 5.0

5.6 6.0 20 32

3.7 8.2 0.6 1.7

22 33 51 54

Pellet type

1989 Nieuwdorp

I Y8Y Vocrendaal

in a trial

with

of hymexazol

g a.i.lunit after 8 weeks

% of total initial concentration after 8 weeks

Trial field

Additmn

0.6

hymexazolto the pellets

Table 10. Carbosulfan and carbofuran concentrations (Nieuwdorp, 1989 and Voerendaal, 1989)

ZFigures

% of total initial concentration after 8 weeks

the same letter

are not significantly

different.

a b c c

p = 0.05

to the pellets

Table 11. Analysed concentrations of tefluthrin directly before and 8 weeks after sowing for various pelleting types in trial fields (Bergen op Zoom, 1987 and 1988; Nieuwdorp, 1989 and Voerendaal, 1989) Tefluthrin concentration (g a.i./unit) Trial field

Pellet type

1988 Bergen op Zoom

% of initial concentration after 8 weeks

before sowing

8 weeks after sowing

Germain’s EB SUET SUET + furathiocarb SUET + hymexazol

10.9 9.2 8.0 11.9

7.7 3.9 3.7 4.9

71 b* 42 47 a 42 a

19x9 Nieuwdorp

Betakote Germain’s EB Germain’s EB + hymexazol SUET SUET + hymexazol Filmcoating (SUET)

13.6 14.2 13.5 18.2 14.7 13.7

7.7 7.0 6.8 9.7 8.3 2.2

57 d 49 b 51 bc 53 bed 56 cd 16 a

1989 Voerendaal

Betakote Germain’s EB Germain’s EB + hymexazol SUET SUET + hymexazol Filmcoating (SUET)

13.6 14.2 13.5 18.2 14.7 13.7

3.2 2.4 4.7 9.9 8.9 1.8

24 b 17 ab 35 c 55 d 61 d 13 a

*Figures

in a trial

with

the same letter

are not sigmficantly

different.

p = 0.05

Crop Protection 1995 Volume 14 Number 5

361

Pesticides in pelleted sugar-beet seeds I: A.W.M. Huijbregts et al. determine the total amount of active ingredient after 8 weeks as percentage of the initial concentration. A significant interaction was found between pellet type and location for the trials in 1989, where the same pellet lots were used on both trial fields. For benfuracarb (Table 9) the release depended also on pellet type. For SUET in 1988 the conversion to carbofuran and the remaining part of active ingredients (benfuracarb + carbofuran) after 8 weeks was significantly influenced by the addition of hymexazol to the pellets. For Germain’s EB pellets the addition of hymexazol did not significantly effect the remaining part of active ingredients after 8 weeks. For carbosulfan (Table IO) the conversion to carbofuran and the decrease of active ingredients (carbosulfan + carbofuran) depended on pellet type and the addition of hymexazol. Soil type and weather have also an effect on the release as can be deduced from the significant interaction which could be established between pellet type and location. Carbofurun. The release of carbofuran was studied for the SUET process in 1988 only. the initial concentration was 28 g a.i./unit, while after 8 weeks 9 g a.i./unit was still present in the pellets. Tefluthrin.

The release of tefluthrin was studied in 1988 and 1989. After 8 weeks considerable quantities of active ingredient were still present in the pellets (Table II).

The remaining quantity depended on pellet type. Field or weather conditions were important too as can be deduced from statistical evaluation which showed a significant interaction between pellet type and location in 1989 (Nieuwdorp and Voerendaal). No clear effects of hymexazol or furathiocarb addition on the release of tefluthrin could be demonstrated. Only for Germain’s EB at the location in Voerendaal the percentage of tefluthrin after 8 weeks differed significantly between the pellets with and without hymexazol. The fastest decrease of tefluthrin was found in the pellets with only a filmcoating.

Conclusions

- The actual loadings of active ingredients may differ considerably from the target doses. Besides inaccurate addition or poor treatment efficiency, this may be caused by decomposition and/or irreversible adsorption (thiram, hymexazol) or by conversion to another active ingredient (furathiocarb, benfuracarb and carbosulfan into carbofuran). - Sometimes considerable variations in concentrations of pesticides were established between individual pellets from the same lot. In particular situations this may lead to insufficient protection of individual seedlings on the one hand and to phytotoxicity of other seedlings on the other hand. - Thiram as well as hymexazol decrease during storage. The decrease of thiram depended on the pellet type. Large decreases for hymexazol were found if furathiocarb or benfuracarb formulations

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Crop Protection 1995 Volume 14 Number 5

had been applied to the same pellets. Applications of insecticide formulations in the pellets, which promote the decrease of hymexazol, should be avoided to prevent insufficient protection by hymexazol. Generally, a reduced protection by thiram and hymexazol should be taken into account if old pellets are sown. - The conversion of furathiocarb, benfuracarb an carbosulfan into carbofuran depended on the pellet rate was increased if type. The conversion hymexazol formulations were applied to the same pellets. - Imidacloprid, carbofuran, methiocarb and tefluthrin were rather stable in all pellets. It may be expected that there is only a small reduction in protective properties if these pellets are stored for 1 year. - Large differences were found in release patterns of various active ingredients after drilling. This may result in differences in the period that a pesticide gives sufficient protection to the plants. Hymexazol decreased quickly compared with other active ingredients studied.

Acknowledgements

We thank Mr L. M. Withagen for the statistical evaluation and Dr A. M. Dewar for critically reading the manuscript. References Dewar, A. M. (1989) Results of the co-operative trials on pesticides in pelleted seeds, 1987-1988. Proceedings 52nd IIRB Winter Congress, pp. 163-178 Gore, W. L. (1952) Statistical Methods for Chemical Experimentation, lnterscience Publishers, Inc., New York, USA, 36 pp Halmer, P. (1994) The commercial practice Monograph No 57, Seed T. Martin) pp. 363-374,

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The effect of to sugar-beet Progress and Council, UK,

Wunderlich, K. H. (1986) Miigliche Wechselwirkung beim Einsatz von Wirkstoffen zum Saatgutschutz in Abhiingigkeit von Dosierung, Wirkungsgrad, Phytotoxizitlt und Befallsdruck. Proceedings 49th IIRB Winter Congress, pp. 53-59 Received Accepted

19 April 1994 21 October 1994