The influence of climatic conditions around the time of spraying isoproturon on the subsequent injury to barley

Ann. appl. Biol. (1990), 116, 131-142 Printed in Great Britain 131

The influence of climatic conditions around the time of spraying isoproturon on the subsequent injury to barley

By A. M. BLAIR and T. D. MARTIN Institute of Arable Crops Research, Weed Research Unit,

Broom’s Barn Experimental Station, Higham, Bury St Edmunds IP28 6NP

(Accepted 10 January 1990)

Summary Winter barley cv. Igri was grown in pots, either outside under cover, in a

glasshouse or under controlled conditions and treated post-emergence with isoproturon. There was a linear relationship between the subsequent weight of plants treated with 2.5 kg a.i./ha and either evaporation from a water surface between 2-7 days post spraying or cumulative temperature between sowing and spraying. The relationship between subsequent weight of plants treated to the foliage only with 5 kg a.i./ha and cumulative temperature between sowing and spraying varied between years 1984-86. The post spraying environment had the major influence on subsequent activity of isoproturon at 2.5 kg a.i./ha applied overall to barley under controlled conditions. There was a greater reduction in CO, exchange in plants grown after treatment under high compared to low relative humidity. When isoproturon at 5 kg a.i./ha was applied to barley plants with wet foliage, plants were slower to recover their initial rate of photosynthesis when kept wet for 24 h as compared with 11 h or when allowed to dry after treatment. Photosynthesis was decreased to a lesser extent under the same post spray conditions by 2.5 than by 5 kg a.i./ha and reduction was greater and recovery of photosynthesis slower in plants grown inside compared to outside.

Key words: Isoproturon, barley, wet foliage, climate

Introduction Isoproturon and chlorotoluron damaged some crops of wheat and barley in autumn 1983

(Henly, 1988). The damage was a severe scorching of the leaf tips from which plants in many cases recovered. Since the damage was not related to soil type, climatic factors seemed to be implicated. The summer of 1983 was very dry, with only 50% of the average rainfall between June and August recorded in South East England. This dry weather resulted in an early harvest and encouraged the early drilling of succeeding autumn cereal crops. Seed-beds were, in many cases, ‘loose’ but with adequate moisture in September to allow rapid emergence and fast growth of the plants. Enhanced uptake either through wet foliage or by the roots as a result of rapid transpiration were considered possible explanations for the crop damage.

This paper describes experiments with isoproturon on pot-grown barley plants to examine: (a) the interaction between different planting and spray dates in three seasons (1984-86), and (b) the influence of wet foliage before and after spraying. 0 1990 Association of Applied Biologists

132 A. M. BLAIR AND T. D. MARTIN

Materials and Methods

The activity on winter barley of isoproturon applied either to the soil and foliage or the foliage alone on different dates

Experimental details are summarised in Table 1. Plants for the radiolabelled herbicide experiment (Expt 5 ) were grown in controlled environment rooms (16/10"C, day/night) in which the relative humidity was set at two levels (50/75% and 95/98% r.h.) from 24 h prior to treatment.

Influence of foliage wetness around the time of spraying isoproturon on the subsequent injury to barley

In Expts 1 and 2 wet foliage was a result of natural conditions whereas foliage was artificially wetted in Expt 3 by spraying with water and in Expts 6-8 by use of a dew cabinet (Clifford, 1973). This maintains a moisture saturated atmosphere at a given temperature within the chamber which is surrounded by an outer cabinet cooled to a temperature approximately 5°C below that of the chamber. Radiant cooling of the plant surface occurs with the result that free moisture ('dew') condenses on these surfaces. Plants were placed in the dew cabinet (8°C;

Table 1. Experimental details

Expt No

Year

Location

CropNariety

Growing Medium

Growing conditions

Pot size (diam, cm)

Planting depth (crn)

Plant density (m - *)

Approx soil moisture ('70 FC)

Growth stage

Replication

Application to:

1 2 3 4 5

1984 1985 1986 1984 1984

Oxford Broom's Barn Oxford

-______--___- Winter barley cv. Igri------------- WW

Soil" Soilb Soilb Soil" Soil"

outside under cover Table 3 Table 4

21 15 18.6 21 7.5

6 7 8

1987 1988 1988

LARS/Broom's Barn

Winter barley cv. Igri

Peat Peat Peat

10 10 10

300 300 300 300 150 380 380 380

60 100 100 60 100 100 100 100

_______________Table 2 _______________ 13 13 Fig.3 Fig.4 Fig.6

3 5 4 3 4 6 6 6

overall or foliage overall 3rd leaf _____________foliage _____________

a, Yarnton sandy loam; b, Moulton series sandy loam WW - Winter wheat cv. Maris Huntsman

Influence of wet foliage on isoproturon 133

dark) for at least 12 h prior to spraying, removed for spraying and returned within 5-10 min. Plants which were allowed to dry after treatment or exposed to the shorter term dew treatment post-spray were placed in a controlled environment (8°C; dark; Expts 7,s) or in a glasshouse (1525°C) in Expt 6. All plants were placed in a glasshouse (1525°C) 24 h after treatment and then moved outside (10-30°C; Expt 7; 0-20°C, Expt 8) four days after treatment and protected from rain by movable covers as required. In all cases water was applied to the soil surface (avoiding the foliage after the treatment was applied) to keep the soil moisture at the appropriate value (Table 1).

Herbicide treatment Isoproturon formulated at ‘Hytane 500L’ (Expt 1) or ‘Hytane 500FW’ was applied to plants

at a range of growth stages in Expts 1-3 (Table 2) or as detailed for the remaining experiments in the respective Tables and Figures of results. The herbicides were applied in volumes ranging between 215-250 litre water/ha at a pressure of 210 k N/m2. Treatments to the foliage only were made by protecting the soil with alkathene beads which were removed after spraying.

For the labelled studies isoproturon (W labelled in the isopropyl group of the phenyl ring; specific activity 35.5 p Ci a.i./mg) was dissolved in methanol and added to cold isoproturon. Four x 0.5 pl droplets of this solution were applied to the 3rd leaf lamina of wheat (growth

Table 2. Details of Expts 1-3

Cumulative area evap Days day degree under r.h. water (mm) weight # between

sow Spray X ” C between above 2-7 days A B spray & date date GS* sow & spray 90% r.h. post-spray harvest

18 Sept 1984 4 Oct 1984 11 199.7 32 7.2 53.3 - 28 11 Oct 1984 12 284.4 173 6.8 48.4 - 21 18 Oct 1984 13,21 375.7 94 5.4 65.8 68.5 22 24 Oct 1984 13.22 442.4 103.5 3.0 71.2 57.1 22

2 Oct 1984 18 Oct 1984 11 208.1 94 5.4 77.8 87.0 28 24 Oct 1984 12 274.8 103.5 3.0 83.8 78.9 22

11 Sept 1985 1 Oct 1985 12,21 337.5 29 8.6 55.0 74.4 35 7 Oct 1985 13,22 431.5 65 6.2 78.2 71.7 35

14 Oct 1985 13,22 515.9 146.5 3.0 95.7 94.7 35 22 Oct 1985 14,22 599.0 104 2.5 103.7 104.7 35

24 Sept 1985 7 Oct 1985 I 1 230.0 65 6.2 47.0 32.1 35 14 Oct 1985 12.21 314.4 146.5 3.0 59.0 83.9 35 22 Oct 1985 12.21 397.5 104 2.5 - 84.1 35

12 Sept 1986 1 Oct 1986 12 236.4 23.5 8.8 39.0 - 28 7 Oct 1986 13 321.2 36 6.4 53.6 - 30

14 Oct 1986 13 416.3 8 3.5 66.8 - 29

22 Sept 1986 7 Oct 1986 11 218.1 36 6.4 47.0 - 30 14 Oct 1986 12-13 313.2 8 3.5 45.1 - 29 22 Oct 1986 13 388.3 0 3.2 67.1 - 28

# Weight as 070 untreated control after treatment with isoproturon at 2.5 kg a.i./ha overall (A) or 5 kg a.i./ha to foliage (B)

* Growth stage at spraying (Zadoks et al., 1974)


1.6

stage 13,21; Zadoks, Chang & Konzak, 1974) and wash-off and extraction procedures were as described by Okereke, Blair & Caseley (1981).

- I 1 1 1 I I I

Meteorological measurements Data were collected from the local meteorological sites at Begbroke, Oxford (Expt 1) or

Broom's Barn (Expts 2, 3). Measurements of temperature were made at the time of the glasshouse/dew cabinet experiments (Expts 6-8). Areas under the relative humidity chart lines were measured using a computer program (Apple Graphics Tablet).

Assessments Plant growth stages were recorded at the time of treatment in all experiments (Table 2).

Dry weights of plants were measured at the conclusion of each experiment (90°C for 24 h). Intermediate visual observations were made and CO, exchange in the leaf was measured by infra-red gas analysis (IRGA) commencing 24 h after treatment. Leaf tip scorch was assessed (Fig. 5a,b) by dividing leaves into damaged and undamaged portions and the areas measured using a leaf area meter (Lambda Instruments Corporation).

Statistical analysis All experiments were randomised block designs. Where analysis of variance was carried

out standard errors (s.E.) and degrees of freedom (D.F.) are presented in the Tables or Figures. The percentage weight data in Figs 1 and 2 were transformed to log,,% weight for regression analysis.

Results

The effect of isoproturon at 2.5 kg a.i./ha applied overall on different spray dates between 1984-86 (Expts 1-3)

The degree of damage to barley varied with treatment time (Fig. 1). For the combined treatment dates between 1984-86 there was a significant correlation between assessment weight, expressed as a percentage of untreated control weight and either evaporation from a water

2.0 '

1.9 h

E

3

- so 1.8 - 04

I .I


surface between 2-7 days post spraying (Equation 1) or cumulative temperature ("C day > O O C ) between sowing and spraying (Equation 2).

(1) y = 1.56 + 0.00953A (S.E. * 0.00069) (r = 0.639; 16 D.F.; P = 0.01)

y = 1.54 + 0.000759B (S.E. & 0.000045) (r = 0.709; 16 D.F.; P = 0.001) (2)

where y = log,, (weight at assessment as Vo untreated), A = evaporation from a water surface between 2-7 days post-spraying, and B = cumulative day degrees between sowing and spraying. When both factors were included the regression line is:

y = 1.72 + 0.000539B (S.E. f 0.000053) - 0.0205A (S.E. f 0.00284) (r = 0.766; 15 D.F.; P = 0.001) (3)

The regression when both factors are included was not significantly (P = 0.05) better than either alone.

The effect of isoproturon applied on different spray dates to the foliage of barley (soil protected) (Expts 1-3)

The range of damage caused by isoproturon at 5 kg a.i./ha was large and injury was sometimes severe. Scorched plants weighed significantly (P = 0.05) less than unscorched in Expts 1 and 2 (not presented). Symptoms varied with age of plant treated. For example, in Expt 1, the younger plants (2-leaf) showed no symptoms apart from a decreased growth rate after treatment on 18 October 1984. The earlier sown 4-leaf plants treated on the same date showed marked necrosis of the leaf tips which was reflected in a greater weight reduction compared to that on the younger plants. There was a negative correlation (r = - 0.987; sig P = 0.05; Fig. 2a) between cumulative day degrees from sowing to spraying and plant weight at assessment in 1984 (Expt l), whereas in 1985 (Expt 2) the correlation was positive (r = 0.776; sig P = 0.05, Fig. 2b).

The degree of scorching of the foliage could not be correlated with any other of the environmental parameters in Table 2. Damage from 2.5 kg a.i./ha was generally not severe and was not accompanied by scorching of the foliage. Foliage treatments of both 2.5 and 5 kg a.i./ha were less damaging than overall applications at the same doses (not presented).

log,,, wt = 2.10 ~ 0.000754 degree days

I I 1 I I ..

200 250 300 350 400 450 Desi re dab\

Fig. 2u. The relationship between dry weight of barley as Vo untreated and days between sowing and spraying isoproturon at 5 kg a.i./ha onto the foliage in 1984.


r

2.0 -

1.9 - h

E 1.8 - z

P 0" 1.7 -

log,,, wt = 1.44 + 0.00105 degree days

1.4 I I I I I I I I I

200 3 00 400 500 600 Degree days

Fig. 2b. The relationship between dry weight of barley as 070 untreated and degree days between sowing and spraying with isoproturon at 5 kg a.i./ha onto the foliage in 1985.

The effect of pre- and post-spray temperature on the activity of isoproturon applied to barley at the 3-leaf stage (Expt 4)

Isoproturon at 2.5 kg a.i./ha applied only to the foliage was much less active than that applied overall (Table 3). Treatments applied overall caused greater damage where grown throughout in the 16/10°C controlled environment than when grown either pre- or post- treatment outside undercover. Post-spray conditions had the major influence on subsequent activity.

Table 3. The effect of pre- and post-spray environment on the dry weight/barley plant (% untreated) sprayed with isoproturon at 3 leaf (Zadoks 13) stage (Expt 4)

Environment*

A B C D

Dose (kg a.i./ha)

soil & 25.6 38.9 69.1 79.4 2.50 foliage 20.0 27.5 41.9 48.4

foliage 81.1 97.5 73.1 84.0 2.50

1.25 }

S.E. ? 5.02 (35 D.F.)

* Environment A 16/1OoC / 5 5 / 8 5 % rh day/night B Cover before and 16/10"C after treatment C 16/10°C before and cover after treatment D Cover before and after treatment

The influence of high relative humidity on isoproturon entry via the foliage into wheat and barley (Expts 5, 6)

Labelled isoproturon entered wheat foliage more quickly and in greater quantities under high (95/98% dayhight) compared to low (50/75% day/night) relative humidity. This is


Table 4. Uptake of C14-isoproturon in the 3rd leaf of wheat

Sample Time Low r.h. High r.h. (days) (50/75% r.h.) (95/98% r.h.)

aqueous wash 2 82.0 46.8 6 68.3 31.3

S.E. * 11.26 (15 D.F.)

treated area 2 8.9 22.8 6 12.0 20.5

S.E. ? 0.810 (15 D.F.)

reflected by both the leaf wash-off measurements and the amounts recovered from the treated areas 2 and 6 days after treatments (Table 4).

One day after treatment CO, exchange measured with the IRGA, demonstrated that none of the treated plants were photosynthesising. In the subsequent 2-3 day period photosynthesis recovered more quickly in plants kept dry after treatment particularly in those treated at the lower rate of herbicide (2.5 kg a.i./ha) (Fig. 3). Four days after treatment at 5 kg a.i./ha photosynthesis had returned to 80% of its original value in plants allowed to dry in the glasshouse but to only 40% in plants kept in high humidity for 24 h after spraying.

The influence of wet foliage on isoproturon entry via the foliage into barley (Expts 7 and 8)

In Expt 7 plants which had their foliage maintained wet for 24 h after treatment with 5 kg a.i./ha isoproturon were slower to recover their rate of photosynthesis than those kept wet for 11 h after treatment or those allowed to dry. The recovery of photosynthesis in plants grown in the glasshouse prior to treatment was slower and less complete during the 5 days post-treatment than in those raised outside (Fig. 4a,b). Scorch damage to leaves 3 , 4 and 5 was greatest on those plants kept wet for 24 h after treatment (Fig. 5a,b) and the damage visible sooner on those plants raised inside (4 days) than outside (7 days). In Expt 8 photosynthesis was decreased to a lesser extent by 2.5 than by 5 kg a.i./ha but at both doses

looh 80

5.0 kg a.i./ha

Fig. 3. The influence of relative humidity (- dry, -- 11 h at high r.h. or --------- 24 h at high r.h.) after isoproturon application to barley (12/13, 21) on the rate of photosynthesis (70 untreated).


5 E (48 D r )

I I

I I I I I I

I

I I -:y/ I I I #

1 2 3 4 5 0 1 2 3 4 5 Days after treatment

Fig. 4. The influence of foliage wetness (-dry, -- wet for 1 1 h or --------- wet for 24 h after treatment) on the rate of photosynthesis ('70 untreated) of barley plants raised inside ( 4 4 or outside (4b) prior to treatment of the foliage with isoproturon at 5 kg a.i./ha at growth stage 13, 22-14, 23.

I

\ E iinscorch 2 075 (23 D F ) \ L scorch 0.794 ( I I I) F )

, L unscorch 2.429 (23 I) I

\ I 5corch 1.175 ( I I I ) F I

c L unscorch I 466 (23 I) F )

S L worch 0.70 I l l D I 1

A B C D A B C D A B C D leaf 3 leaf 4 leaf 5

Fig. 5a. The area of leaves 3, 4 or 5 of plants raised inside which were scorched (0) or unscorched (R) by foliage treatment of isoproturon at 5 kg a.i./ha to barley kept dry (B), or wet for 11 h (C) or 24 h (D) after treatment compared with untreated plants (A).

reductions were greater and recovery delayed in plants grown inside compared to outside (Fig. 6a-4. Wet foliage exaggerated the effect of 5 kg a.i./ha, more on inside grown plants than outside. Greater scorching of leaf 3 was visible on those plants raised inside than out when treated with 5 kg a.i./ha (not presented).


50 c 30 - Area

(cm2)

20

10

0

5 I nn\corch 1.53 (23 I) I )

\ L worch I .3h ( 1 I 12 I )

- 5 L scorch 1.622 ( I I

A B C D A B C D A B C D leaf 3 leaf 4 leaf 5

Fig. 5b. The area of leaves 3, 4 or 5 of plants raised outside which were scorched (0) or unscorched (a) by foliage treatment of isoproturon at 5 kg a.i./ha to barley kept dry (B), or wet for 11 h (C) or 24 h (D) after treatment compared with untreated plants (A).

2o t Photosynthesis 0 I I I

(070 untreated plant)

- 0 1 2 3 4 0 1 2 3 4 Days after treatment

Fig. 6 . The influence of foliage wetness (-dry, -- wet for 11 h or ---------wet for 24 h after treatment) on the rate of photosynthesis (To untreated) of barley plants raised inside (6a, c) or outside (6b, d) prior t o treatment of the foliage with isoproturon at 2.5 (6a, b) or 5 kg a.i./ha (6c, d) at growth stage 12-12, 21.

Discussion Winter wheat can be damaged by isoproturon (Tottman et al., 1975) particularly where

the recommended rate is exceeded, e.g. due to overlaps, and such damage varied between sites and environmental conditions. The marked scorching of the foliage of many winter cereals in the autumn of 1983 suggested 'that particular environmental conditions could result in damage. Although the symptoms were in many cases transient there is no experimental evidence to show whether there was any effect on subsequent yield. Tottman, Steer & Martin (1988) have reported a lack of correlation between scorching of leaves by broad-leaved weed herbicides and subsequent yield.

140 A. M . BLAIR AND T. D. MARTIN

The barley plants sprayed in 1984 (Expt 1) at a range of growth stages and under different climatic conditions showed that differences could also occur in pot experiments. The leaf tip scorch observed after the application of isoproturon at 5 kg a.i./ha to foliage on 18 October (older plants) and 24 October 1984 (both growth stages) was similar to that observed in the field the previous autumn. It is difficult to measure this type of damage adequately, especially when it is transient. It is only later that retrospective analysis of the meteorological data may help to explain the different effects. These data showed periods of high relative humidity indicating that foliage may have been wet at and following spraying. Since surface wetting has been shown to increase the entry of other herbicides into foliage (Kirkwood, 1987) this might also be the case for isoproturon. Measurements of the areas under the relative humidity curve for the 24 h post-spray period were made for various thresholds (only 90% presented in Table 2) and those for 18 October and 24 October 1984 when damage occurred were among the higher values.

Consequently in 1985 (Expt 2) an effort was made to select at least some dates on which to treat plants when the foliage was naturally wet. In this experiment tip scorch was observed after treatments on 1 October, 7 October and 14 October 1985, but not on 22 October 1985. Not all these dates corresponded with the higher r.h. values (Table 2). In 1986 (Expt 3) an attempt was made to artificially wet leaves and keep them wet for 24 h post-spraying but the system used was unsatisfactory and the results of the foliage treatments are not presented or included in any of the analyses.

Therefore in 1987/88 it was decided to investigate this phenomenon under more controlled conditions. In the first experiment (Expt 6) with the ‘dew cabinet’ the relative humidity was kept high but the barley foliage was not ‘loaded’ with water and the plants probably dried out during the spraying operation. The treatment did not result in the typical leaf scorch symptoms although photosynthesis was reduced immediately post-treatment in the plants kept in high relative humidity. Of the three ‘dew cabinet’ experiments this probably corresponds most closely to the one in which C14 isoproturon was applied to wheat. The much greater entry of isoproturon into wheat under high humidity contrasts with the results of McIntosh, Robertson & Kirkwood (1981) who found the greatest uptake at 30% r.h. Since only uptake into the treated portion of the leaf was measured, any differences in movement from this area under the different r.h. conditions cannot be identified. No published references comparing isoproturon entry into wheat and barley foliage are known to the authors. In the two experiments (Expts 7, 8) where the leaves were very wet and remained wet during the spray operation the typical leaf tip scorch symptoms were observed. The reduction in photosynthesis lasted longer in these two experiments than in the first, perhaps indicating even greater entry when the foliage is wet than under high relative humidity. As the plants raised inside showed a greater reduction in photosynthesis than those outside this may reflect differences in cuticle structure depending upon growing environment, since this effect could not be adequately explained in terms of gross herbicide retention by plants. Kirkwood (1981) comments that glasshouse-grown plants are generally believed to have thinner cuticles than those of field-grown plants although they are not necessarily more permeable. Environmental conditions can affect wax production and hence permeability; changes in response to fluctuation in conditions can be rapid, within 48 h (Kirkwood, 1987). This may explain the scorch visible following the application on 1 October 1985 since this was a warm period both before and after treatment, reflected by the high evaporation data (Table 2). These plants may approximate to those grown under glasshouse conditions. The treatments on 7 October 1985 were made in very light rain which may have redistributed the herbicide into the leaf bases which are potent sites for pesticide entry into plants (Robertson & Kirkwood, 1983). The target presented by the plant’s habit may also influence both retention (Hibbit, 1969) and any redistribution and in this case (7 October 1985), the more erect younger plants showed


a much greater weight reduction than the older plants. Since isoproturon can be washed through the alkathene beads when plants are watered with a spray boom (Martin & Blair, unpublished) this may have occurred in the light rain on 7 October 1985, although it is not thought to be a major factor. The opposing patterns of the relationship between growth stage at treatment and final weight in 1984 and 1985 probably means that environmental factors can override the effects of growth stage on herbicide uptake.

It is concluded therefore that foliage entry is more likely in plants growing rapidly before spraying and consequently in early drilled crops. Periods of wet foliage around the time of spraying could result either in redistribution into leaf bases or in herbicide remaining in solution on the fully hydrated leaves. Thereafter, conditions of high transpiration would increase the movement and concentration of isoproturon in the leaf tips, resulting in scorching, provided there is adequate soil moisture present.

In many cases new leaves will be unaffected since only very small quantities of substituted urea herbicides are reported to be exported from the treated leaf (Muller, Frahm, Sanad & Wilhelm, 1979). It is impossible to relate the weather conditions and plant growth stages where damage occurred in 1983 to those in these experiments, since detailed records from specific sites are not available. However, there were periods of high evapotranspiration which would be conducive to rapid movement and accumulation of isoproturon in the leaf tips once it had entered the plant.

When barley plants were sprayed overall with isoproturon there was a good relationship with cumulative day degrees between sowing and spraying and with conditions conducive to transpiration thereafter (2-7 days evaporation from water). Larger plants will protect more of the soil surface from the herbicide which is a major route of entry into the plant (Blair, 1978). Whether this relationship would hold under field conditions would require further testing since, in pots, both the roots and the herbicide are in the same restricted volume of soil.

These results show that there is a complex relationship between environmental and plant factors around the spray period which determine the subsequent activity of isoproturon on barley. More data is required from this type of experiment if one is to predict isoproturon activity both on the crop and weeds, thereby allowing greater efficacy in its use and explaining any failures which do occur.

Acknowledgements We thank Dr P. Brain for his assistance with the statistical analyses, Dr D. Butler and G.

W. Cussans for their help in the setting up of the dew cabinet experiments at Long Ashton Research Station and Ciba-Geigy (UK) Limited for the gift of both the labelled and unlabelled isoproturon.

References Blair, A. M. (1978). Some studies on the sites of uptake of chlortoluron, isoproturon and metoxuron

Clifford, B. C. (1973). The construction and operation of a dew-simulation chamber. New Phytologist

Henly, S . (1988). It’s now time to watch for weeds. Crops 5 (22), 8-9. Hibbit, C. J. (1969). Growth and spray retention of wild oat and flax in relation to herbicidal selectivity.

by wheat, Avena fatua and Alopecurus myosuroides. Weed Research 18, 381-387.

72, 619-623.

Weed Research 9, 95-107.


Kirkwood, R. C. (1987). Uptake and movement of herbicides from plant surfaces and the effects of formulation and environment upon them. Critical Reports on Applied Chemistry 18, 1-26.

McIntosh, R. M., Robertson, J. & Kirkwood, R. C. (1981): The mode of action and basis of selectivity of isoproturon in wheat, Avena fatua L. (wild oat) and Alopecurus myosuroides Huds. (blackgrass). Proceedings of Grass Weeds in Cereals in the United Kingdom Conference, pp. 247-255.

Miiller, F., Frahm, J., Sanad, A. & Wilhelm, H. (1979). In Herbizide, Abschlussbericht zum Schwerpunktprogram “Verhalten und Nebenwirkungen und Herbiziden im Bodem und in Kulturpflanzen”. Eds M . Borner el al. Dt. Forschungsgemeinschaft, Boppard, Boldt Druck Gmbtl.

Okereke, 0. U., Blair, A. M. & Caseley, J. C. (1981). Some factors affecting the activity of isoproturon against Bromus sterilis and Phalaris minor. Mededlingen van de Fakulteit Landbouwwetenschappen, Rijkuniversitat, Gent 46/1, 83-89.

Robertson, J. & Kirkwood, R. C. (1983). Herbicide uptake and translocation in grasses: effect of site application. Proceedings of 10th International Congress on Plant Protection, p. 575.

Tottman, D. R., Holroyd, J., Lupton, F. G. H., Oliver, R. H., Barnes, T. R. & Tysoe, R. M. (1975). The tolerance of chlortoluron and isoproturon by varieties of winter wheat. Proceedings European Weed Research Society Symposium Status and Control of Grassweeds in Europe, pp. 360-368.

Tottman, D. R., Steer, P. M. & Martin, T. D. (1988). The tolerance of cereals to several foliage-applied broad-leaved weed herbicides at different growth stages. Aspects of Applied Biology 18, 145-156.

Zadoks, J. C., Chang, T. T. & Konzak, C. F. (1974). A decimal code for the growth stages of cereals. Weed Research 14, 415-421.

(Received 16 May 1989)

Documents

The influence of climatic conditions around the time of spraying isoproturon on the subsequent injury to barley