CHLORMEQUAT JMPR 1976
Explanation
The data relative to the identity of chlormequat and of
residues in food and their evaluation were reviewed at the 1970
Joint Meeting (FAO/WHO, 1971b). In 1972 the biochemical and
toxicological studies were evaluated to ether with additional data
on the nature and level of residues and their fate in grain, fruit
and vegetables. Recommendations were made for an acceptable daily
intake and maximum residue limits (FAO/WHO, 1973b).
Since that time the principal manufacturers of chlormequat
plant growth regulators have advised of modifications to their
formulations to include choline chloride. The reason for this is
that choline chloride may reduce the mammalian toxicity of
chlormequat. The recommended application rate for chlormequat is
the same in both formulations.
Data on residues resulting from the application of chlormequat
with and without choline chloride, and on the fate of chlormequat
residues, are discussed in this monograph addendum.
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
Since the original publications of Tolbert (1960a, b), Wittwer
and Tolbert (1960) and Lindstrom and Tolbert (1960) on the
properties and use of chlormequat, several hundred papers have been
published. Many of these relate to its use in wheat, thousands of
hectares of which have been treated annually in Europe since 1964.
In recent years emphasis on field research with chlormequat has
been on vines, cotton, vegetables and certain fruit crops and
several of these uses have been commercialised in Mediterranean
countries.
Lindley (1973) has reviewed published and unpublished data
from Egypt, Italy, Spain, France, Greece, Turkey, India and
elsewhere covering the use of chlormequat on wheat, grape vine,
peach, apricot, almond, plum, strawberry, mango. cotton, tomato,
potato, sweet potato, olive and pepper.
By far the most important outlet for chlormequat remains the
use on small grains, particularly oats, rye and wheat, where it
functions mainly to reduce lodging.
For the reduction of lodging in oats and rye, foliar sprays
are used to apply 1.5-2.0 kg of chlormequat chloride per hectare
alone or in combination with choline chloride. The time if spraying
is critical: if too early or too late, the effect on lodging is
severely reduced. The optimum time for application to oats is at
crop growth stage 7 to 8 (Feeks-Large) which is normally in
mid-summer. A wetting agent is added. The optimum time for treating
rye is when the plants are 25-30 cm in height, corresponding to
growth stage 3 to 4 (Feeks-Large). This is normally in early summer.
It is estimated that of the total amount of chlormequat used
world-wide, 80% is applied to small grain crops.
In addition to the dwarfing effect on the growth of cereal
plants, chlormequat greatly increases the diameter of the stem of
the plant, with an increase in the thickness of the cortex and a
large increase in the number of vascular bundles. This leads to
considerably greater structural strength and stability and enables
increased amounts of nitrogenous fertilizer to be applied without
risk of lodging. Even without additional nitrogen there is often a
pronounced increase in yield. Part of the incentive to use
chlormequat is its capacity to increase significantly the yield
potential of cereal crops.
Supervised field trials and practical experience have not
demonstrated any difference between the effectiveness of
chlormequat alone and in its mixture with choline chloride.
Osborne (1974) reported a study to compare the efficacy and
crop safety of chlormequat with and without the addition of choline
chloride, in a spring oat crop. No signs of phytotoxicity were
observed, even with double rates, and both formulations appeared
similar in efficacy, reducing stem length from approximately 800 mm
to 600-650 mm. All plots eventually lodged during adverse weather
conditions. None of the treatments tested affected the yield
significantly.
Taylor (1974) reported a trial designed to compare chlormequat
chloride alone with the chlormequat formulation containing choline
chloride on wheat heavily infected with eyespot (Cercosporella).
Both formulations gave equally good reduction in infection
severity, lodging and crop height. Double rates (3.36 kg/ha) of
each formulation reduced lodging and crop height further increasing
the yields from 6% response to 9% response, both yield responses
being significant at the 1% level. Lodging was drastically reduced
in the treated plots, with little difference between the two rates
and no differences between the two formulations. Crop height was
reduced by 80 mm with the recommended rate and by 100 mm with the
double rate. Again there was no difference between formulations.
Caldicott (1974) reported grower trials aimed at comparing the
efficacy of chlormequat with and without Choline chloride on height
reduction and lodging in wheat and oats. The two formulations were
applied at the same recommended level of active ingredient to 10
separate crop situations. Each caused a mean crop height reduction
for the series of 10%. Insufficient early lodging occurred for
satisfactory comparison of the two formulations.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Extensive data are provided in the monographs of the 1970 and
1972 Meetings (FAO/WHO 1971b and 1973b). Additional data on
formulations with and without choline chloride are summarized in
Table 1 and discussed below. The residues found in these studies
were variable, but the variation was not apparently related to the
presence or absence of choline chloride.
Two laboratories in Finland, using the method of Mooney and
Pasarella (1967), determined the residues of chlormequat in rye
grains following different rates and dates of application of
chlormequat or chlormequat plus choline chloride. The residues were
extremely variable, ranging from a maximum of 8.4 mg/kg to a
minimum of less than 0.1 mg/kg. The residues are not directly
related to the rate of application of chlormequat or the date of
treatment. In view of the statement in the 1970 monograph (FAO/WHO
1971b) that Residues are highest in grain grown under particularly
dry conditions. High rainfall apparently, almost entirely eliminate
the detectable residue in grain at harvest", it is possible that
some explanation might be forthcoming if the meteorological
conditions were known. As chlormequat is used to counteract the
effect of wet conditions on the growth of cereal crops, it is not
surprising that rainfall, temperature and the nutritional status of
the soil should have a bearing on the level of chlormequat
residues.
Residues in oats also vary widely. The data from Finland
indicate that a difference of 10 days in the date of treatment can
increase the residue level in grain by a factor between 4 and 10.
Following treatments made over a period of 20 days from June 9 to
June 29 the residue in the grain harvested at the end of August
increased from less than 0.5 mg/kg to more than 20 mg/kg for the
same formulation and rate of application on the same site.
Residue data from trials in the Federal Republic of Germany
and England in 1973, 74 and 75 indicate the extreme variability of
the residue levels found at harvest following the application of
similar rates of chlormequat plus choline chloride to oats. The
differences are greatest in these samples examined shortly after
application. Residues in grain harvested 50 to 70 days after
treatment were found, in the 8 separate trials, to be invariably
below 5 mg/kg.
Samples of many varieties of wheat treated with chlormequat or
chlormequat plus choline chloride in Poland over the years 1967, 68
and 1971 were not found to contain detectable amounts of
chlormequat. The interval between application and harvest was not
indicated. The data provided previously (FAO/WHO 1971b, 1973b)
suggest that although use on wheat appears to give rise to lower
residues than in oats and rye, the residue levels can fluctuate
TABLE 1. Chlormequat residues in oat and rye grain and oat straw
Residue (mg/kg) at interval (days) after application*
Grain Country Date Rate 0 20-30 31-40 41-50 51-60 61-70 71-80 81-95 >95
(Variety) kg/ha
Oats Finland 6/74 0.41 2.9, <0.5
2.9
6/75 0.41 11.4 3.7,
<0.5
6/74 0.82 5.0, 0.8,
4.3 1.1
6/75 0.82 20.7 6.1 0.7
6/75 1.0 3.3 3.3
6/75 1.0 4.2 3.5
6/75 1.0 4.2,3.4
6-7/72 1.125 5.0 3.1
6/74 1.125 0.5 4.6, <0.5
4.0
6/75 1.125 17.6 5.8 <0.5 <0.5
(Tiger) Germany -/74 1.125 116 15.0 9.17 4.83 2.36
(Tiger) -/74 1.125 100 17.3 1.81 1.52
Finland 6/75 1.29 32.5 9.4 3.6
Finland 6/74 1.38 3.2 2.5
(Flämings- Germany -/73 1.38 84 8.07 6.76 3.66
krone)
(Arnold) -/73 1.38 15.1 3.93 3.91 0.33
(Arnold) Germany -/75 1.38 17 3.7 2.5 0.14
(Tiger) -/75 1.38 17 7.6 3.3 1.6
(Marino) Germany -/75 1.38 17 6.4 5.1 1.9
England -/74 1.68 3.8
Finland 6/74 2.0 4.3 3.2
Oats 6/75 2.0 7.6, 7.6,
7.5, 6.9
8.1
TABLE 1. (Cont'd.)
Residue (mg/kg) at interval (days) after application*
Grain Country Date Rate 0 20-30 31-40 41-50 51-60 61-70 71-80 81-95 >95
(Variety) kg/ha
Oats 6/71 2.25 9-12
6-7/72 2.25 9.1 4.7
6/73 2.25 11.6
6/74 2.25 6.7, 1.0,
8.8 0.6
6/75 2.25 20.3 9.2 0.5
6/75 3.0 8.6 8.5
6/75 3.0 9.2 8.5
6/75 3.0 9.8
6/75 3.0 10.6
Rye Finland 5/74 0.41 1.6 1.0
6/74 0.69 0.8
5/75 0.82 4.9 2.4, 1.0
1.5
6/74 1.0 1.0
5/74 1.125 4.1 2.2 3.0 1.2
5/75 1.29 5.5 2.8,
2.2
5-6/71 1.5 3.5, 0.55, 3.0
0.95 0.6
5/71 1.875 8.4
6/74 2.0 1.3
6/72 2.25 4.1 2.2 0.3 3.5
5/75 0.41 2.7 1.5,
0.9
5/74 0.82 2.4 1.5,
5-6/72 1.5 1.4 <0.1 <0.1
5/71 2.25 6.5
5/73 2.25 0.7
TABLE 1. (Cont'd.)
Residue (mg/kg) at interval (days) after application*
Grain Country Date Rate 0 20-30 31-40 41-50 51-60 61-70 71-80 81-95 >95
(Variety) kg/ha
Rye 5/74 2.25 2.9 1.8
5/75 2.25 5.0 3.5,
1.9
Oat
Straw Germany -/74 1.15 3.95 8.16
Germany -/73 1.38 5.18 1.15
Germany -/75 1.38 2.0 0.9
England -/74 1.68 9.8
* Where two or more values are given for a single time interval, they are from separate trials
over a considerable range. The limit of determination decreased
from 0.7 mg/kg in 1967 through 0.25 mg/kg in intervening years to
0.03 mg/kg in 1971.
FATE OF RESIDUES
In plants
Dekhuijzen and Bodlaender (1973) studied the distribution and
persistence of chlormequat in potato plants and in the progeny from
their tubers. Considerable amounts of chlormequat were present in the
leaves (40 mg/kg) and the tubers (28 mg/kg) and underground parts (248
mg/kg) 14 weeks after spraying a solution, containing 3 g/l
chlormequat, on the leaves. After storage for 9 months, it was found
that seed potato tubers had lost none of their chlormequat residues
and 2 months after planting virtually all of the chlormequat was
recovered in the whole potato plant, most of it being found in the
underground parts. Potato tubers harvested from chlormequat-treated
plants produced temporarily dwarfed plants with reduced tuber yield.
The authors concluded that the relative stability of chlormequat in
potato plants and its harmful after-effects on the progeny did not
favour a possible use of the compound on potatoes.
As indicated in the 1970 and 1972 monographs, numerous studies
have failed to show any significant metabolism of chlormequat in
plants or the conversion of chlormequat to choline.
Choline is a natural constituent of virtually every food and
occurs at levels of about 1000 mg/kg in many food items. The use of
chlormequat/choline chloride mixtures will not significantly affect
the level of choline in food commodities.
METHODS OF RESIDUE ANALYSIS
No new information was presented on methods of residue analysis.
The subject is adequately reviewed in the monographs of the 1970 and
1972 meetings (FAO/WHO, 1971b and 1973b).
NATIONAL TOLERANCES REPORTED TO THE MEETING
Information available to the Joint Meeting indicated that the
following national tolerances have been established for chlormequat
residues.
TABLE 2. National tolerances for chlormequat reported to the Meeting
Tolerance,
Country Commodity mg/kg
Belgium Fruit and vegetables 0
(not potatoes)
Crude cereals 0.5
Czechoslovakia Wheat and rye 0.3
Netherlands Fruit and vegetables 0
(not potatoes)
Spices 0
Netherlands Apples and pears 2
Grain 0.5
Switzerland Summer and winter wheat 2
Oats 5
APPRAISAL
Chlormequat was evaluated by the Joint Meeting in 1970 and 1972
(FAO/WHO, 1971b, 1973b). Since then, some formulations of chlormequat
which include choline chloride have been in use, and the present
Meeting evaluated new data on residues resulting from the use of
chlormequat alone or in combination with choline chloride. The
recommended application rate for chlormequat is the same with both
formulations.
Data from supervised field trials and practical experience were
submitted which demonstrated that choline chloride has no effect on
the growth of the plant or on the growth-regulating function of
chlormequat.
Extensive information is available from supervised residue
studies carried out, mostly in Finland with a smaller number in
Germany and England. Most of the data are for oats but there was sonic
information on residues in rye. Only a few reports are available to
indicate the level and range of residues in wheat.
Whilst the data clearly indicate that the level of residues is
generally inversely related to the interval between application and
harvest of the grain, the maximum residues found vary over a very wide
range. In a total of thirty trials, residues in oat grain after 50-70
days varied from 0.14 to 32.5 mg/kg.
Fewer data were available for rye than for oats but there was a
considerably smaller range of residue levels. A maximum range of
eight-fold was found however in trials from crops treated at the same
rate with the same pre-harvest interval.
In some studies there was noticeable variation in residue levels
found in samples of grain from plants grown on the same site and
treated at the same rate but at intervals of 10 days. The rate of
application or formulation used did not influence the residue level to
the same extent.
The data provided indicate that the variation in residue levels
from one year to the next may be very great, possibly owing to the
influence of prevailing meteorological conditions.
A number of studies indicate that control of lodging is
critically depending upon the timing of application in relation to the
age of the plant at the time of treatment. This will vary greatly from
one country to another, one cereal variety to the next and probably
from season to season. It does not appear possible to regulate the
residue level by controlling the pre-harvest interval without, at the
same time, greatly interfering with the critical performance of the
growth regulator.
In addition to new data and information published in previous
monographs the Meeting considered a study of the distribution and
persistence of chlormequat in potato plants, from which it appears
that chlormequat would not be suitable for use on potatoes. These
studies clearly indicate that there is very little metabolism in the
plant so that physiologically potent concentrations may be carried
through to the progeny of tubers from treated plants.
Since choline occurs in most foods, often at levels of about
1000 mg/kg, the use of chlormequat/choline chloride mixtures will not
significantly affect the level of choline in food commodities.
No new information was available on methods of analysis. The
meeting noted that maximum residue limits have been established in
some countries and that these limits appear to be inadequate to cover
residues resulting from uses of chlormequat approved in other
countries.
RECOMMENDATIONS
On the basis of new data examined at this meeting and data
considered previously the following maximum residue limits for
chlormequat are recommended. The limits for oats and wheat replace,
and that for straw is additional to, previous recommendations.
Limit,
Commodity mg/kg
Straw, of barley, oats,
rye and wheat 50
Oats 10
Wheat 5
FURTHER WORK OR INFORMATION
REQUIRED (before further maximum residue limits can be recommended)
1. An explanation for the variability of residue levels on grain.
2. An indication of the pre-harvest interval for each type of small
grain crop in the various regions where the use of chlormequat is
important.
3. Information on the fate of residues in meat following the feeding
of straw from treated crops.
REFERENCES
Anon. - 1971 Report of State Institute for Agricultural Chemistry,
1971 Helsinki, No. 7.
Anon. - 1972 Report of State Institute for Agricultural Chemistry,
1972 Helsinki, No. 9.
Anon. - 1974 Report of State Institute for Agricultural, Chemistry,
1974 Helsinki, 4349-4360/74
Anon. - 1975 Report of State Institute for Agricultural Chemistry,
1975 Helsinki, 4098-4114/75
Caldicott, J.J.B., Comparative effect of CYCOCEL and CYCOCEL
1974 5C in grower trials on height reduction and
lodging in wheat and oats - Cyanamid International
Report 208/UK/22/74
Dekhuijzen, H.M., and Bodlaender, K.B.A. Distribution and
1973 Persistence of Chlormequat in potato plants.
Pestic. Sci. 4, 619-627
FAO/WHO - 1970 Evaluations of some pesticide residues in food.
1971b FAO/AGP/1972/M/12/1: WHO Pesticide Food
Add./71.42.
FAO/WHO - 1972 Evaluations of some pesticide residues in food.
1973b FAO/AGP/1972/M/9/1 - WHO Pesticide Residues Series
No. 2.
Lindley, C. D. A review of some practical uses of CYCOCEL plant
1973 growth regulant. PANS. 19 (1) March 1973 87-92
Lindstrom, R.S., and Tolbert, N. E. - (2-chlorethyl) trimethyl
1960 ammonium chloride and related compounds as plant
growth substances IV. Effect on chrysanthemums and
poinsettias. Q. Bull. Mich. Agric. Exp. Stn. 42
(4) 917-928
Mooney, R.P. and Pasarella, N. R. Determination of chlorcholine
1967 chloride residues in wheat grain, straw and green
wheat foliage. J. agr. Fd Chem., 15, 989
Osborne, R. To evaluate CCC + CC and compare with CC on spring
1974 oats. BASF United Kingdom Ltd. TB Report No. 270
Taylor, J. S. To compare chlormequat with Chlormequat + Choline
1974 Chloride for approval purposes. BASF United
Kingdom Ltd. TB Report No. 243
Tolbert, N. E. - (2-chlorethyl) trimethylammonium chloride and
1960a related compounds as plant growth substances, I.
Chemical structure and bioassay. J. Biol. Chem.
235 (2): 475-579.
Tolbert, N. E. -(2-chlorethyl) trimethylammonium chloride and
1960b related compounds as plant growth substances, II.
Effect on growth of wheat. Pl. Physiol.,
Lancaster, 35 (3): 380-385.
Wittwer, S. H. and Tolbert, N. E. - (2-chlorethyl) trimethylammonium
1960 chloride and related compounds as plant growth
substances, III. Effect on growth and flowering of
the tomato. Am J. Bot. 47(7), 560-565.
See Also:
Toxicological Abbreviations
Chlormequat (AGP:1970/M/12/1)
Chlormequat (WHO Pesticide Residues Series 2)
Chlormequat (Pesticide residues in food: 1994 evaluations Part II Toxicology)
Chlormequat (Pesticide residues in food: 1997 evaluations Part II Toxicological & Environmental)
Chlormequat (JMPR Evaluations 1999 Part II Toxicological)