CHLORMEQUAT         JMPR 1976


         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.



         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

         Lindley (1973) has reviewed published and unpublished data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

         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.


         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 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
                                  6/75      0.41                                                      11.4      3.7,
                                  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
                                  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
    (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

    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

                                  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,
                                  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,
                                  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,

    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.


    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.


         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).


         Information available to the Joint Meeting indicated that the
    following national tolerances have been established for chlormequat

    TABLE 2. National tolerances for chlormequat reported to the Meeting

    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



         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

         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

         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


         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.

             Commodity                          mg/kg

             Straw, of barley, oats,
             rye and wheat                      50

             Oats                               10

             Wheat                              5


    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

    3.   Information on the fate of residues in meat following the feeding
         of straw from treated crops.


    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

    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)