WEEDS FLORA ASSOCIATED WITH CYMBIDIUM CULTIVATION IN SIKKIM

 

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T. K. Bag *

National Research Centre for Orchids (ICAR), Pakyong 737106, Sikkim

*Present address: Indian Institute of Vegetable Research (ICAR), Jakhini (Shahanshapur),

 Varanasi-221 305, UP, India

 

 

 

INTRODUCTION

Association of weeds with cultivated crops is not new. Like other cultivated crops, several weed flora were recorded to be associated with orchids. These weeds are not only siphoning the nutrient from the media but also affect the growth of the plants because of orchid-weed competition for nutrients and free environment for growth. As the Cymbidiums are cultivated in pots with mixtures of coco pit, leaf mould, charcoal, brick pieces and the plants are repotted with a mixture of new growing media in every third years; weeds are automatically eliminated and no special attention is given to weed management by either commercial or amature orchid growers. However, growths of the Cymbidium plants are affected by severely grown/over crowded weed populations in many instances. Besides, there are no reports on the weeds associated with orchids with special reference to Cymbidium cultivation in India. Therefore, during 2000-05, an attempt was made to document the association of weed species with Cymbidium orchid in the pot cultivation system by scientists of National Research Centre for Orchids (ICAR), Pakyong, Sikkim. During our investigation, different Cymbidium growing areas such as Rumtek, Ranipool, Namli, Pakyong, Namchepong and Namchi  in Sikkim and Lava, Kalimpong, Kurseong, Sukia Pokhari, Mirik,  Darjeeling, Takdah orchid sanctuary and Nagri Tea estate in West Bengal were surveyed in different seasons for recording the association of weeds with Cymbidium. Different weeds associated with Cymbidium were given in the Table 1 with brief description.

 

Hairy Bitter cress (Cardamine hirsuta):

It is an annual or a biennial weed. Plant height reaches up to 15 cm. Flowers are yellowish white. Flowers almost throughout the year but the plants which germinate late in the season remain as rosettes through the winter. This weed species mature and produce seed quickly, giving rise to several generations in a year. With the slightest touch the seed capsules explode when they are mature, dispersing their contents widely. This weed is very common with the Cymbidium species and Hybrids. They mainly spread by seed which are carried with the potting media. Sometimes matured capsules explode and seeds disperse widely from one pot to anther pots. The weed is managed by hoe or hand pull before flowering. It will be better to remove the weed by   uprooting plants if seed capsules are present. No herbicides or weedicides are used for controlling the weed in Cymbidium.  

 

Pig Weed (Chenopodium album)

It is a broad leaved annual plant. Height may go up to 1 metre and the stems usually multi-branched. The grey-green leaves are usually oval to diamond shaped, have a powdery coating. They are also used as a leafy vegetable in the tribal areas. Flower spikes emerge at the top leaf axils of the plant in the month of June- October. The weed spread by seeds which usually come with leaf mould or other potting media. This weed is controlled in the Cymbidium cultivation system in pots with the hand pulling before flowering and is easily uprooted.  

 

Broadleaved Plantain (Plantago major)

It is a broad leaved annual plant. Height may go up to 1 metre and the stems usually multi-branched. The grey-green leaves are usually oval to diamond shaped, have a powdery coating. They are also used as a leafy vegetable in the tribal areas. Flower spikes emerge at the top leaf axils of the plant in the month of June- October. The weed spread by seeds which usually come with leaf mould or other potting media. This weed is controlled in the Cymbidium cultivation system in pots with the hand pulling before flowering and is easily uprooted.  

 

Marsh Cudweed (Gnaphalium uliginosum)

This is an annual weed but not a widespread problem for the Cymbidium. The foliage has a grayish appearance. It can reach a height of about 20 cm. Preferring moist conditions, it is found on paths and cultivated ground where there is no competition form vigorous grasses. The flowers which look brownish appear from July to September. The weed spreads by seed. Sometimes another species of Gnaphalium (Gnaphalium sylvaticum) were also recorded in some places. Manual removal by hand pulling before flowering is usually practiced for controlling the weed.

 

 

 

 

Wood Sorrel (Oxalis spp)

 

Creeping red sorrel (O. corniculata) or Yellow wood sorrel (O. stricta)   are very common weed species associated with Cymbidium and its hybrids in the Sikkim Himalayan region as well as Darjeeling Hills.  They may be observed singly or in association with other species of Oxalis. There are so far four species of oxalis were recorded in the Cymbidium house in this region.  These are Oxalis corniculata, Oxalis stricta, Oxalis acetosella and Oxalis latifoliaO. corniculata has purple green foliage and grows in a more prostrate habit. O. stricta has green foliage and grows in a clump shape habit. O. corniculata foliage is more pubescent, particularly along leaf margins. O. stricta foliage is pubescent, but to a lesser extent than O. corniculata. The plant grows as small rounded clump, 10-20 cm tall and wide.  O. corniculata grows low and more prostrate, while O. stricta is taller and more mounded.  Leaves are palmately compound with 3 heart shaped leaflets. First true leaves are typical trifoliate. Flowers are yellow with 5 petals and occur in cluster. Seedpods are long, thin, angular, and pubescent (more so for O. corniculata). The weed species are perennial.  They spread by seed, rhizome, or stolons along with the potting media.  

 

Field milk thistle (Sonchus arvensis):

 

It a deep rooted perennial herbaceous weed plant. Stems are erect, hairy and hollow with milky sap, branching above in inflorescence. Leaves are alternate, sessile, about 30cm long. Inflorescence appears loose corybiform, terminating with branches of flower heads. Peduncles are glabrous or with glandular pubescence. Each division of inflorescence is subtended by small scale like attenuate bract. Flowers are usually fertile. Flowering usually occurs during June October. Its root system allows the plant to quickly establish and to persist under cultivation. Seed production is highly variable, but a typical head produces many seeds, which are generally dispersed by wind. However, the hairs on the end of the seeds have hooked cells that allow them to stick to clothes, fur, vehicles and farm implements.  

 

Black nightshade (Solanum nigrum):

Solanum nigrum is commonly known as black nightshade. It is a fairly common weed plant waste land and found in vegetable field and with potted ornamental plants. Morphologically, it is a brittle stemmed weed that grows up to height of one metre. It has ovate leaves, tiny white star shaped flowers and small round black berries in small hanging clusters. The unripe fruits are green but turned into  black when ripe.  

 

Crassocephalum crepidiodes:

The plant is a strong herbaceous weed with an erect little branched to 1 m tall. Plant stem is glabrous or finely puberulous. Leaves are pinnate, coarsely serrate, petioles 6-32 mm long, blades 3.8 15.9 cm long, 1-7 cm wide, upper leaves more or less sessile. Inflorescences appear terminately with axes of corymbose. Pappus of numerous silky yellowish to white slender hairs, corollas yellow with darker tips; anthers purplish; style-arms purplish. Plumed seeds are distributed by wind. The weeds are removed mechanically by hand picking at the younger stage.  

 

 

 

Ferns:

Different types of ferns are found associated with Cymbidium. Ferns are found to grow very closely with the orchid plants. When the old media are removed from the pots and the plats are replanted in the same pot with new media, the perennial stem bits of the ferns are also come to the new pots and regenerate with the emergence of new branches and leaves.   They are perennial and spread by spores and stem bits along with the growing media.

 

 

 

 

 

 

 

Hydrocotyle sp.:

It is a perennial weed with creeping habit. Leaves are round with kidney like shaped and wavy or slightly lobed margins. Flowers are found in clusters. Flowers are tiny, white or greenish with 5 petals.

 

 

 

 

CONCLUSION

From our over all study, about 15 weed species belonging to 6 families were documented with different Cymbidium species and hybrids in Sikkim and West Bengal. Weed species associated with Cymbidium are- Oxalis corniculata, Oxalis stricta, Oxalis acetosella, Oxalis latifolia, Cardamine hirsuta, Sonchus arvensis, Gnaphalium uliginosum, Gnaphalium sylvaticum, Chenopodium album, Solanum nigrum, Erigeron canadensis, Crassocephalum crepidiodes, Plantago major, Sagina procumbens, Crepis biennis and Hydrocotyle sp. Three to four species of ferns were also recorded associated with Cymbidium.  Four species of Oxalis were found to be associated with Cymbidium. Among them, most common members were- Oxalis corniculata, Oxalis stricta, Cardamine hirsuta, Sonchus arvensis, Gnaphalium sp., Hydrocotyle sp. and ferns. Some of the weeds were recorded as annual or biannual and some were perennial in nature.  The weeds spread through seeds or suckers along with potting media and light air borne seeds carried by wing. Fern (weeds) spread by aerial spores and old stem bits carried by leaf mould. Weeds associated with Cymbidium were usually managed mechanically by hand weeding at 2-3 month interval and application of weedicides /herbicides are not  generally recommended at all in India.


 

Table 1: Weed flora associated with Cymbidiums in the Hills of Sikkim

S No.

Common name

Botanical name

Family

Annual

/perennial

Spread of

the weed

1

Wood Sorrel

 

Oxalis corniculata, O. latifolia and  O.  stricta

Oxalidaceae

Annual

 

By seeds

2

Creeping Wood Sorrel

Oxalis acetosella

Oxalidaceae

Annual

By seeds

3

Bitter Cress

Cardamine hirsuta

Brassicaceae

Annual or biennial

By seeds

4

Marsh cudweed

Gnaphalium uliginosum

Composite

Annual

By seeds

5

Wood cudweed

Gnaphalium sylvaticum

Composite

Annual

By seeds

6

Common Chickweed

Stellaria media

Caryophyllaceae

annual

By seeds

7

Milk Witch

Taraxacum officinale

Asteraceae

perennial

By seeds

8

Broad leaved Plantain

Plantago major

Plantaginaceae

Evergreen perennial

By seeds

9

Pearlwort

Sagina procumbens

Caryophyllaceae

perennial

By seeds

10

Hawksbeard

Crepis biennis

Composite

perennial

seeds

11

Black Nightshade

Solanum nigrum

solanaceae

annual

Seeds

12

Field Milkthistle

Sonchus arvensis

Composite

perennial

Seeds

13

Pig Weed

Chenopodium album

Chenopodiaceae

annual

Seed

14

Pennywort                                                           

 

Hydrocotyle sp.

Apiaceae

perennial

Seeds and Creeping

 Rootstock

15

Fern

 

Pteridaceae

perennial

Spores and  stem bits