Joenje, W.

Kropff, M.J.

Wageningen Yield 

1987 BRITISH CROP PROTECTION CONFERENCE-WEEDS 9A-5 
RELATIVE TIME OF EMERGENCE, LEAF AREA DEVELOPMENT ~~D PLANT HEIGHT AS MAJOR 
FACTORS IN CROP-WEED COHPETITION 
W. JOENJE and M. J .{ KROPFF 
Agricultural University, Wageningen, The Netherlands 
ABSTRACT 
Growth analysis data (dry weight, LAI and height) are presented of com-
petition experiments with sugar beet (Beta vulgaris cv. monohill and cv. 
salohill) , Fat hen (Chenopodium album) and Chickweed (Stellaria media) , 
as well as with beet and early and later sown Chenopodium. Yield losses 
are not related to leaf area, the worst weed Chenopodium having the 
lower LAI. The paradox is explained by different height growth of the 
weed species in view of the competition for light. 
A time lag of 21 days between the emergence of crop and Chenopodium 
still leads to yield losses; weeds emerging 30 days later than the crop 
no longer develop a canopy on top of the crop's and no longer lower 
yields. 
INTRODUCTION 
In open and early sown crops such as sugar beet, a group of late summer 
annuals tends to escape the current mechanical operations and even soil 
herbicides; mechanical control measures during early crop growth may only be 
effective between the rows. Remaining weeds in the row, even at low density, 
often cause substantial damage (Solanum niorum, Chenopodium album, Echinochloa 
crus-oalli) (Zimdahl 1980). In these circumstances the need is felt for re-
liable prediction of yield losses and advice for herbicide application 
(Cousens in prep.) 
In the search for practical warning systems and thus in the development 
of empirical models (Spitters et al. 1983), the following characters (para-
meters) are put forward as useful descriptors of weed infestation: 
- the time of emergence of the weed with respect to the crop emergence date 
(Cousens 1985, Lapointe 1985, O'donovan et al. 1985, Spitters et al. 1983), 
- the weed species (provided that we have data on specific biological and 
physiological characters such as growth form, height and other morphological 
responses to competition, a.o.), 
- the weed density. This parameter on its own has only a limited value, as 
demonstrated in many experiments on damage thresholds: large differences 
in yield loss - weed density relations between experiments are often found 
(Koch 1974, Kropff et al 1984, Poole et al. 1987, Schweizer 1981, Wahmhoff 
et al. 1985, Zimdahl 1980). 
Plant responses to environmental factors can be quantified. For many 
crop species these relations are used in growth models, but data on physio-
logical characteristics of weeds are still lacking. Present versions of the 
crop-weed competition models, equally based on physiological growth para-
meters, suqgest a predominant influence of differences in the times of 
emergence of crop and weed, and of two biological characters, the leaf area 
development and plant height (Kropff et al. in prep.). However, there appear 
to be few complete sets of field data on growth and performance of both weed 
and crop in monocultures and mixtures, in well monitored environmental con-
ditions, in different years and with different time lag between crop and 
weed emergence. This labourious type of field experiment is rewarding, since, 
apart from datasets for validation of simulation models and the testing of 
971 
9A-5 
hypotheses generated with the models, it offers a discriminating view on 
competition-related processes in the course of a growing season. 
In this contribution we present the analysis of two field experiments in 
subsequent years, in order to evaluate the influence of the relative time of 
emergence, and of plant height and leaf area development, given the crop and 
weed species and their responses to different weather conditions. 
EXPERIMENTAL DESIGN 
The field experiments, in split plot design with four replicates, were 
carried out in Wageningen on a loamy sand (4% soil organic matter) with ade-
quate supply of water and nutrients. 
2 In 1985 suqar beet was grown at 30 em equidistant spacing (11 plants per 
m ); the weeds were gro~n equally distributed between tqe crop plants, Fat 
hen at 5.5 plants perm in mixture and ~1 plants per m in monoculture, 
Chickweed at 11 (clumps of) plants per m , both in mixture and monoculture. 
The plot size was 6 x 1.5 m, allowing harvest of 15 plants. The dates of 50% 
emergence for sugar beet, Fat hen and Chickweed were 9 May, 21 May and 20 May, 
respectively. 
In 1986 sugar beet was2grown in rows 50 em apart, at distances of 18 em in the row (11 plants perm); Fat hen was equally grown in rows at plant 
distances of 18 em in monoculture or in the rows of the crop, alternating 
with the sugar beet plants. Plot size was 6 x 1.25 m. Fat hen was sown at 
crop emergence and 15 days later and had final densities of 11 ~lants per m2 
in monoculture, but in the mixtures of 9.1 and 9.7 plants perm , respectivel~ 
The dates of 50% emergence for sugar beet, Fat hen (early) and Fat hen (late) 
were 4 ~1ay, 25 May and 3 June, respectively. 
RESULTS 
The 1985 experiment produced growth curves of the type expected for the 
monocultures of ~' Chenopodium and Stellaria (Fig. 1A) and illustrates the 
shorter life cycles of the weeds, especially Stellaria. The time lag between 
sugar beet and weed emergence of about 10 days leads to substantial crop 
losses at final harvest, but even at the beginning of July there is an in-
fluence of~ (by then over 2 t ha-l) on the weed.especially Stellaria, and , 
vice versa. Table 1 shows that total crop biomass was reduced with 21% by 
Stellaria and with 37% hy Chenopodium. The time course of the height develop-
ment and the leaf area index of ~-weedfree (B) , ~ with Chenopodium (Be) 
and li· with Stellaria (Bs) is summarized in Table 2, as well as height and 
LAI for Chenopodium and Stellaria monocultures (Chm and Stm) and their mix-
tures with.~ (Chb and Stb). Marked differences were the height development 
of Chenopodium (more than twice as high as the crop) and the much higher LAI 
of Stellaria (LAI 2.68, against 0.96 in Chenopodium). 
The 1986 experiment offers comparable results, with respect to mono-
cultures of ~ and Chenopodium 1 (early). Apparently weather conditions 
(August and September being drier, colder and more clouded than 1985) were 
less favourable for ~ and its final production stayed well behind 1985. 
The weather did not affect final biomass of Chenopodium 1, emerging on May 25 
(four days later than previous year), due to its shorter life cycle. Even the 
Chenopodium 2 (late) emeraing on June 3, produced almost the same final bio-
mass, well over 13 t ha-1. 
In the mixtures only the early Chenopodium with a time lag of 21 days, 
972 
9A-5 
ton. ha-1 
22 
18 
14 
10 
6 
5 
4 Ce 
2 
0 
50 100 150 d. a. e. 
Fig. l.A. Development of dry weight (t. ha-1) in 1985 of Beta in 
monoculture (B) 1 in mixture with Stellaria (Bs) and with Chenopodium (Be). 
Dry weight of the weeds comprise Stellaria in monoculture (S) 1 in Sugar 
beet (SB) and Chenopodium in monoculture (C) and in Sugar beet (CB); dae: 
days after emergence of the sugar beet crop. 
973 
9A-5 
ton. ha-1 
22 ® 
18 
14 
10 
6 
4 
2 
so 100 
Bcz 
8 
C1 
C2 
Fig. l.B. Development of dry weight in 1986 of Beta and Chenopodium (early: 
Cl, and late: C2) in monocultures and mixtures. (Explanation of symbols lA). 
974 
TABLE 2 
Height development in Beta (B: mono, B : with Chenopodium, B : with Stellaria), Chenopodium \C: mono, 
c 8 : with Beta) and Stellaria (S: mono,cS : with Beta), and d~velopment of leaf area index LAI in 1985. For 1986 heiqht and LAI data relate to B~ta and Chenopodium only, the latter sown early (Cl) and late 
(C2). Dae: days after emergence of the crop. 
Height em ( 1985) LAI ( 1985) 
dae B Be Bs c CB s SB B Be Bs c c B s SB 
39 18 17 17 13 13 10 9 .77 .79 .85 .09 .04 .54 .21 
53 34 33 32 53 53 21 22 2.35 1.98 1.94 .81 .24 3.30 1.15 
74 50 51 51 142 127 35 50 5.65 3.97 4.03 4.63 .96 10.61 2.68 
95 62 57 60 159 145 29 56 5.10 4.17 3.87 4.73 .80 9.33 2.68 
118 59 58 60 166 142 - - 5.10 4.19 4.13 4.24 .59 1.26 .67 
140 61 59 56 159 142 11 53 4.66 3.27 3.08 1.15 .12 .58 .17 
Height em (1986)* LAI (1986) 
---dae dae Cl C1 C2 C2 B Bet BC2 Cl C1B C2 C2B Cl C2 B B 
28 38 28 28 12 13 2.29 2.22 2.56 .81a .18b .23b .02c 
48 58 136 72 101 31 3.36 2.73 2.40 3.43a .27a 2.98b .07c 
69 79 158 74 158 43 3.77 2.89 3.34 3.75a .29a 3.78b .07c 
90 100 159 92 156 43 3.18 2.50 3.15 3.33a .26a 3.78b .05c 
104 114 156 81 149 45 2.85 2.79 3.11 2.64a .05a 2.67b .03c 
CD 
* Height of Beta compare data 1985 :1> 
co I 
-.::J Ul Ol 
9A-5 
reduced Beta production with 11% at final harvest (Table1B); already on July 
1st a lo~ng of ~biomass and of Chenopodium biomass is shown (Fig. 2). 
TABLE 
The 1985 and 1986_yugar beet production at final harvest in mono- and mixed 
cultures, in t ha and in (%) of weed-free. 
Different letters indicate significant difference between treatments 
(P <0.05, capitals P (0.01). 
1985 weed-free with with 
Stellaria Chenopodium 
Total dry weight (t ha-l) 23.1 ( 100) a(A) 18.2 (79) b(AB) 14.6 (63) b(B) 
Shoot dry weight (t ha-l) 8.6 (100) a(A) 6.8 (80) b(AB) 6.4 (74) b(B) 
Root dry weight (t ha -1) 14.5 (100) a 11.3 (78) ab 8.2 (57) b 
Total fresh weight (t ha-l) 61.9 (100) A 48.9 (79) B 33.1 (53) c 
Sugar content (%) 15.04 a 15.43 b 15.43 b 
Suqar production (t ha-l) 9.3 ( 100) A 7.5 (81) B 5.1 (55) c 
1986 weed-free with early with late 
Chenopodium Chenopodium 
Total dry weight (t ha-l) 20.3 a 18.1 b 20.5 a 
Shoot dry weight (t ha-l) 7.4 - 6.9 - 7.0-
Root dry weight -1 (t ha ) 12.9 a 11.2 b 13.5 a 
Total fresh weight (t ha-l) 53.5 a 45.4 b 56.3 a 
Sugar content (%) 17.7- 17.9 - 18.0 -
Sugar production -1 (t ha ) 8.5 a 7.3 b 9.0 a 
CONCLUSIONS 
LAI and height 
The results of the 1985 experiment show marked differences between the 
two weedspecies, Chenopodium causing by far the highest yield loss. Supply 
of water and nutrients taken as sufficient, the competition will have been 
for light exclusively. This result stands in marked contrast to the lower 
yield loss by Stellaria, which had a strong leaf area development (LAI 2.7 
and in its monoculture even 10) compared to Chenopodium (LAI 0.96 and in 
monoculture 4.6). This is explained by the data on heicrht development (Table 
2) • In monoculture Chenopodium plants grew up to a height of 160 em and up 
to 150 em between the sugar beets, which topped at 60 em, and was able to 
use its lower LAI more effectively in the light interception. Stellaria in 
monoculture remained of low statue (35 em), but part of it used the beet 
plants to climb up to the same height as the crop. 
976 
9A-5 
Relative time of emergence 
The results of the 1986 experiment clearly show the strong effect of a 
difference of 10 days in the period between sugar beet and weed emergence. 
The latest sown weed did not gain a high statue, reached only modest LAI and 
finished its growth together with the early sown weed, at the end of a 
shorter life span and without seriously hampering crop production. 
DISCUSSION 
Height- and leaf area development, together with emergence date and two 
differinq years, they once more revealed their serious influence on the out-
come of crop-weed competition (viz. also Elberse et al. 1979, Lapointe 1985). 
On the one hand the relative date of emergence proves to be an indis-
pensible datum in any discussion of competition and it is amazing that in 
many publications this aspect is neglected. 
The results draw attention to the germination and to developmental 
characteristics of the weeds and above all to the rate of leaf areadevelop-
ment and height growth of the weeds relative to the crop canopy. Although 
Chenopodium is known for its capacity to increase height in a shadowy envi-
ronment, the plants of the later generation in the 1986 experiment did not 
develop a canopy on top of the crop's. Shorteninq daylength urged the onset 
of flowering and although the weed had a substantialproduction including a 
seed crop, it did not interfere with the sugar beet. 
The results of the present experiments, although permitting clear con-
clusions, cannot lead to causal understanding or generalization. This is 
only to be expected from simulation studies based upon knowledge of the 
underlyino physiological processes, governing photosynthesis and morpholo-
gical development (height growth, lateral spread, leaf development). The 
hypotheses generated may lead to relatively simple and less casuistic field 
experiments. 
REFERENCES 
Cousens, R. (1985) An empirical model relating crop yield to weed and crop 
density and a statistical comparison with other models. Journal of 
Agricultural Science, Cambridge 105, 513-521. 
Cousens, R; Brain, P.; O'donovan, J.T.; O'Sullivan, P.A. (in prep.) The use 
of biologically realistic equations to describe the effects of weed 
density and relative time of emergence on yield. 
Elberse, W.Th.; Kruyf, H.N. de (1979) Competition between Hordeum vulgare L. 
and Chenopodium album L. with different dates of emergence of Chenopo-
dium album. Netherlands Journal of Agricultural Science 27, 13-26. 
Koch, W. (1974) A comparison of various methods for competition studies 
between crop plants and weeds. Eppo Bulletin 4, 339-346. 
Kropff, M.J.; Vossen, F.J.H.; Spitters, C.J.T. (19S4) Competition between a 
maize crop and a natural population of Echinochloa crus-galli (L.) P.B. 
Netherlands Journal of Agricultural Science 32, 324-327. 
Kropff, M.J.; Spitters, C.J.T.; Joenje, W.; Groot~W. de (in prep.) Simu-
lation of crop-weed competition III. Evaluation of model performance. 
Lapointe, A.-M. (1985) Effet de la duree de l'interference du Chenopode 
blanc (Chenopodium album) sur le rendement de l'avoine et de la luzern~ 
Phvtoprotection 66, 37-45. 
O'donovan, John T.; St Remy, E. Ann de; O'Sullivan, P. Ashely; Dew, Dan A.; 
Sharma, Arvind K. (1985) Influence of the relative time of emergence 
977 
~-5 
of wild Oat (Avena fatua) on yield loss of Barley (Hordeum vulgare) and 
Wheat (Triticum aestivum). Weed Science 33, 498-503. 
Poole, M.L.; Gill, G.S. (1987) Competition between crops and weeds in 
southern Australia. Plant Protection Quarterly 2, 86-96. 
Schweizer, E.E. (1981) Broadleaf weed interference i~ sugarbeets (Beta 
vulgaris). Weed Science 29, 128-133. 
Spitters, C.J.T.; Aerts, R. (1983) Simulation of competition for light and 
water in crop-weed ·associations. Asp~cts of Applied Biology 4, 467-483. 
Wahmhoff, W.; Heitefuss, R. (1985) Untersuchungen zur Anwendung von Schaden-
schwellen fur Unkrauter in Wintergerste. I Einflussfaktoren und 
Prognosemoglichkeiten der Entwicklung von Unkrautbestanden. Zeitschrift 
fur Pflanzenkrankheiten und Pflanzenschutz 92, 1-16. 
Zimdahl, R.L. (1980) Weed crop competition: a review. International Plant 
Protection Centre, Oregon State University Corvalis, Oregon, USA. 195pp 
978 \ 


Relative time of emergence, leaf area development and plant height as major factors in crop-weed competition.

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