green foxtail: seed dormancy, germination and growth

GREEN FOXTAIL: SEED DORMANCY, GERMINATION AND GROWTH W. H. VANDEN BORN

of Plant

Science, University of Alberta, Edmonton, Alberta. Received June 11, 1969, accepted September 22, 1970.

Depart,ment

ABSTR{CT

near- still produce seeds during the same season. ggmplete dormancy when freshly harvested. Impliiations of the findings for green foxtail This dormancy was overcome most readily control are discussed. Severely restricted durirrg moist storage at 6 C for three to sii growth of green foxtail under reduced temweeks. Seed germination occurred over a perature and light intensity is considered to wide range oI temperature, but most rapidly account for at least part of the reported low at or above 25 C. Seedlings emerged readily competitive efficiency of green foxtail infestafrom .planting depths up to 8 im. Plants tions in field crops in western Canada. emerging as late as the end of July could

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Green foxtail seed exhibited complete or

INTRODUCTION Green foxtail, Setaria viridis (L.) Beauv., is a widespread annual weed and is rapidly becoming more prevalent (2, 7, 8). Various taxonomic descriptions of Setqria species have been published (4, 7, 8) but, except for limited information regarding depth of planting provided by King (5) and Dawson and Bruns (1), published data that describe the response of green foxtail to various environmental factors during its development are not available. MATERIALS AND METHODS For dormancy studies, mature seeds were collected frorn greenhouse- or field-grown plants at Edmonton. In addition, seed samples were obtained frorn fleld infestations at 30 locations throughout Alberta and from roadside infestations at two locations in British Columbia (Kamloops and Vernon). Seeds were stored dry at room temperature or on mo,ist filter paper in petri dishes at 6 c. Periodically, triplicate 2O-seed samples or quadruplicate 25-seed samples were taken from the seed lots stored under these conditions and used for germination tests at 22 C. Some samples of dormant seed were placed in open or closed vials and kept at -17 ot 60 C for 24 hours, and some were soaked in 250 or 500 ppm gibberellic acid for 24 hours, prior to germination tests. Seed used to study the response of germination and emergence to temperature was collected in the Edmonton area about six years ago and was stored at room temperature. Seed from this lot germinated nearly 1007o and produced seedlings that appeared normal in all respects. Seeds were placed on moist filter paper in petri dishes or plantod 0.5 cm deep in clay loam soil in 10-cm po s, in quidruplicate 20-seed lots. Both dishes and pots were placed in dark controlledtemperature cabinets, and germination or emergence was recorded daily. Seeds were considered germinated when the radicle had reached a length of 0.5 cm. Seedlings were considered emerged when the coleoptile tip was 0.5 cm above the soil surface. Unless stated otherwise, green foxtail plants were grown in a conventional greenhouse, at approximately 2r c, or in a growth chamber with a 16-hour photoperiod and a 22-10 c day-night te,mperature regime. rn some experiments light intensity at pot level in the growth chamber was varied by placing the plants higher or lower on shelves. Plants were grown in a clay loam-sand-peat mixture (3 : 1 : 1) or in U.C. mixture (sand, peat moss, fertilizer). Can. J. Plant Sci.

5l:

53-59 (Jan, 19?I)

53

cANADTAN JoURNAL

54

oF PLANT scIENcE


Duplicate I.3 X 2 m field plots on Malmo silty clay loam near Edmonton were see-ded with green foxtail by^broadcasting a measured amount of seed on each plot, followed by gently raking each plot, on six different dates spaced about iwo'weeks apart, from May 15 to JuIy 24. Observations regarding emergence, morphological development, and floweiing and seed production, were made and recorded at regular intervals. RESULTS Seed dormancy

Freshly collected mature seed from all sources showed nearly complete dorshowed only partial dormancy, -un"y. Samples from a few Alberta locations exceptions probably resulted These non-dormant. completely was and one ,u-pi" from local conditions pr&ailing during the time prior to seed collection. During dry storage at room t.-p"rutit", the- mean germination percentage in a typical experim"it (seed collect"d in u fi.eld near Edmonton on October 19,1966) gradually rose from 0 to 42Vo in 55 days, and to 56% in 115 days' Exposure of seeds to -17 tr 60 C for 24 hours, or soaking them in Sibbele! lic acid solution, had no noticeable effect on dormancy. Moist storage at 6 C for three to four weeks, on the other hand, resulted in complete loss of dormancy in most instances. Most seeds (79%) lost their dormancy during the second (6Vo) week of cold treatment, but some (I5Vo) required a third week and afew not did few a samples, Columbia Britiih and Atbefia the 32 a fourth week. Of respond readily to the cold treatment, and for most of the samples four weeks was ,roi long .norrgh to completely overcome dormancy (Table -1.) ' After six weeks' howevei, all simples germinated at least to some extent, and in most of them dormancy was almoit cJmpletely overcome. Second-generation seed, collected from plants grown in a growth chamber, showed the same range of dormancy and of iespottt" to cold treatment as did the field-collected seed' Germination temperature Seeds germinated readily at temperatures from 15 to 35 C' though !t togk seven diys longer to reacir maximum germination at 15 C than at 30 C (Table 2). Table ""'"

ccllected from 32 different locations in Alberta i:Lnd Brit-

1. ''t.tGellination of seed samples

Ul;;;

Sample frequencf in different ranges of germination percertage

Treatment Field-collected seed Dr1', room temp. 4 rveeks 6 rveeks Moist, 6 C 4 u'eeks

6 r'eeks

1+ 7+

13 9

2

11

0

U

2l-+0

4F6A

I

2 2

3

n

2

3

61

80

1

1

3

1

2 3

2+

Second.generation seed from plants gro$.n in a grolvth chamber (31 locatior-rs) Drr', room temp. 6 weeks N'{oist, 6 C 4 t'eeks 6 r.veeks

24 3

0

5 2

81-100

2

0

U

2

5

3

1.

1

6

7

0

r.)

2l

))

VANDEN BORN----GREEN FOXTAIL

Table

2. Germination and

emergence of green foxtail seeds

at different remperarures

Germination


Days

to

Temp. C

s0%

10

45

15

7 5 3 2 2

20 25

30 35

l$i:at"?."

Emergence

Days to

Days to

Days

max. o7

Max. 0/ /o

/a

60 1+ 72 11 792 69+

max.

to

Max.

%%

sa%

63 17 25 13 22 71189 5890 3532

62

100 97

90

series (emergence only) was carried out with a difierent seed lot that had a

36* 66 88

muimun of 54le

emergence

At

10 C no visible signs of germination appeared untll26 days had elapsed. The maximum germination at this temperature, 62Vo, was gradually reached after 60 days.

Delays at low temperature were more marked in emergence from clay loam soil than in germination in petri dishes, and total emergence at both high and low temperatures remained well below the maximum germination percentages. At 15 C, for example, it took 17 days longer to reach the maximum percent emergence (66Vo ) than at 30 C (90%). At 10 C, the first seedlings did not emerge until 39 days after planting. Early seedling growth evidently is more sensitive to temperature than are the germination processes. Emerged seedlings were normal in appearance, irrespective of the temperature at which they were produced. Observations of emergence following planting at different dates in the field (Table 3) were in harmony with the conclusions from laboratory experiments. Except for delays in emergence in June plantings due to an extended dry period, temperature appeared to be the major controlling factor. Depth of planting Seedlings emerged readily from depths

of 0.5 to 8 cm in well-drained soil (clay pots in the greenhouse. Emergence from l0 cm took a few days longer, and emergence from 12 cm reached only 7vo. soil moisture, compaction and aeration in these experiments are considered similar to conditions that exist in many cultivated fields in central Alberta. The findings reported are similar to those of Dawson and Bruns (1). waldron, as quoted in King (5), reported that in North Dakota the maximum depth from which seedlings emerged in the field was 7.5 cm. loam-sand-peat mixture)

t"o'"

,'

...*,n

Planting date

May l,Iay

in 15-cm

olf

:?ylt"l; Days to 25/6 emergence

15

28

29

23

June 13

49

June 27

July r0 July 24

2l 16

Days to heading

ot"',"d "" fffd,"t.."- '."0

Total dry wt.

g/plot

65 56 44

1+77 1698 1+96

4+ 38

534 326

JI'

Seed

wt.

g/plot 349 422

401 484 90

/o


56

CANADIAN JOURNAL OF PLANT SCIENCE

1. Green foxtail plants grown in the greenhouse chamber (R), photographed 75 days after planting'

Fig.

(L) and in a controlled-environment

Growth habits

Under poor light conditions during fall and early winter, and with relatively low temperatures 413-15 C) at bench level in the greenhouse used, gfowth-of gle99 foxtail was slow and restricted, and plants reached a maximum height of only 14 cm. Plants in the growth chamber,-by contrast, under a light intensity of a9o-ul 17,000 lux and aZZ_|O C day-night temperature regime, grew to a height of 90 cm (Fig. 1). Single plants in 15-cm pots in the growth chamber produced three times ai many tillirs (32 per plant, mean of six plants) as greenhouse-grown plants, and much.nor"'r".& (5b0 vs. less than 100 seeds per panicle). In the greenhouse and growth chamber, heading occulTed seven and nine weeks after planting, and plants reached maturity in 11 and 17 weeks, respectively' - poitowing planting at different dates in the field (Table 3), final height of plants from the last thiee dates was about half that of plants from the first three dates, and dry weights from late plantings were much reduced. Tiller nurnber per piant was not affected by planting date- Two-week intervals between plantings i"rnlt"d in approximately one-week intervals between maturity dates. Seed production

Panicles ranged in length frorn 1.5 to 12 cm, with the majority 7 Lo 9 cm long. Panicles coniained 50 to 60 seeds per cm panicle length, and most panicles, there-


VANDEN BORN----CREEN FOXTAIL

2. (L-R);

Fig.

57

Green foxtail plants grown under light intensities of 29,500, 17,400 and 12,900 lux photographed 44 days afler planting.

fore, contained 350 to 500 seeds. Under good growing conditions and with limited rowding, a green foxtail plant could produce from 5,000 to 12,000 seeds. This range compares with an average figure of 8,000 reported for yellow foxtail (Setaria Iutescens) by Santelmann et al. (9). In field plots seeded at different dates (Table 3), seed production was variable, and ranged from approximately 100,000 seeds per m'in the first four plantings to 20,000 seeds per m' in the July plantings.

Light intensity and photoperiod Representative green foxtail plants grown at 22 C under iight intensities of I2,9OO, 77,400, and 29,500 lux are shown inFig.2. Dry matter production (means of three plants) was almost directly proportional to light intensity within the range used. At the lowest intensity plants had fewer tillers which grew more slowly, and produced panicles two weeks later than similar plants at the highest intensity. Reproductive growth was influenced more seriously by light intensity than was vegetative growth. Sixty days after planting the number of panicles per plant at the three light intensities was 3i1.5, I4!2, and 22!0, respectively. Plants grown under an S-hour photoperiod showed severe growth inhibition of both roots and shoots as compared with plants under a 16-hour pho operiod or under continuous light (Table 4), probably because of insufficient light energy rather than as a photoperiodic response. Heading was only slightly delayed, but panicle production was reduced to almost nil. A 16-hour photoperiod was optimal for tillering and early heading. Continuous light had no effect on plant height or tiller number, and slightly increased dry matter production, but markedly delayed panicle production. The observations are similar to Schreiber's results (10) with giant foxtail (Setaria faberii), but contrast with findings of Santelmannet al. (9) on yellow foxtail. Thelatter species readily produced panicles in short days, but failed to head under continuous lisht.

)6 Table

CANADIAN JOURNAL OF PLANT SCIENCE

4. Growth

parameters of green foxtail under different photoperiods; data are means of four plants, 61 days after planting Photoperiod, hours

Parameter


Plant height, cm

Dry weight, g/plant Number of tillers/plant Weeks to heading Panicles/plant at harvest

1t+1

0.15+0.04

4.5+0.9 7

1+0

16

24

48+1 5.35+0.17

49+2 6.94+O.76

26.5+0.9 6

18+1

26.2+4.l 8

3.5+1.4

DISCUSSION

The results obtained provide no evidence on which to base an explanation of the dormancy observed in freshly collected mature green foxtail seeds. They do, however, provide a basis for recommending field practices aimed at prompt germination of green foxtail seeds in spring, for most effective subsequent control measures. The observations indicate that, when late surnmer and fall weather is dry, tillage of an infested field immediately after harvest is sound practice, provided that the green foxtail seeds are buried in moist soil and remain relatively close to the surface. In a damp, cool fall, on the other hand, there may be no harm in leaving the seeds on the soil surface, where they can readily lose their dormancy.

In the behavior of the seed samples from different locations in Alberta or British Columbia there was no obvious correlation between location and dormancy, or between initial degree of dormancy and response to cold treatment. The response of second-generation seed to cold treatment indicated that degree of dormancy was not a fixed characteristic of eaoh ecological strain. Degree of seed maturity may have contributed to the variation in dormancy among the samples, but a more acceptable explanation is that the variation was due simply to differences in local weather conditions prior to collection time. The data supplied with the samples unfortunately did not allow a careful examination of this possibility. fn collections at Edmonton, however, a sample of mature seed obtained frorn a small field plot on September 17, 1967, was completely dormant, while a sample collected from the same plot 31 days later germinatedTOVo. This decrease in dormancy almost certainly was brought about as a result of cold treatrnent right on the plant during the damp, cool weather between the first and second sampling.

Green foxtail plants emerging as late as the middle of August are unlikely to affect crop yields by their competitive effects (6). In row crops or in thin stands of cereal grains, however, such plants may still produce a signifioant amount of seed in a short time. Control methods for green foxtail should include among their objectives the prevention of growth to maturity of such late-emerging plants. The sensitivity of green foxtail germination and subsequent growth to temperature and light intensity corresponds generally with findings of Santelmann el al. (9) for yellow foxtail. The requirement of a relatively high temperature for rapid germination and growth, and the severely restricted growth at reduced light intensity, provide supporting evidence for the view that green foxtail plants do not compete strongly with a dense stand of crop plants except in severe infestations (2,

VANDEN BORN---GREEN FOXTAIL

59

3).


It is probable that, at least in moderate infestations, the influence of temperature in spring and early summer is more important than that of light intensity. The latter factor becomes important as soon as shading by crop plants significantly reduces available light. It may be concluded, then, that warrn weather in spring and early summer will result in more competive injury to grain yield by a green foxtail infestation than will cool we,ather. ACKNOWLEDGEMENTS Financial support for this study was provided by the Alberta Agricultural Research Trust. The cooperation of personnel of the Alberta Department of Agriculture in obtaining seed samples from a number of locations is gratefully acknowledged. Mrs. D. Hayley provided capable and careful technical assistance. REFERENCES

1.

2. 3.

4.

DAWSON, J. H. and BRUNS, V. F. 1.962. Emergence of barnyardgrass, green foxtail and yellow foxtail seedlings from various soil depths. Weeds lO: 136-139. DRYDEN, R. D. and WHITEHEAD, C. W. 1963. The effect of TCA on green foxtail in competition with cereals. Can. J. Plant Sci. 43t 451-456. FRIESEN, G. and SHEBESKI, L. H. 1960. Economic losses caused by weed competition in Manitoba grain fields. I. Weed species, their relative abundance and their effect on crop yield. Can J. Plant Sci. 4O: 457-467.

HUBBARD,

F. T. 1915. A

taxonomic study

allies. Amer. J. Bot. 2: 169-198.

of Setaria italica and its

immediate

5. KING, L. J. 1966. Weeds of the world. Biology and control. Interscience Publishers, Inc., New York. 526 p. 6. KNAKE, E. L. and SLIFE, F. W. 1965, Giant foxtail seeded at various times in corn and soybeans. Weeds 13: 331-334.

7. POHL, R. W. 1951. The genus Setaria in Iowa. Iowa State Coll. J. Sci.25: 501-508. 8. ROMINGER, J. W. 1,962. Taxonomy of Setaria (Gramineae) in North America. pp. 78-82. University of Illinois Press, IJrbana. 9. SANTELMANN, P. W., MEADE, J. A. and PETERS, R. A. 1,963. Growth and development of yellow foxtail and giant foxtail. Weeds ll: 139-142. 10. SCHREIBER, M. M. 1965. Development of giant foxtail under several temperatures and photoperiods. Weeds 13: 40-43.