List of noxious farm weeds: 1. Cyperus Rotundus L. 2. Cynodon Dactylon (L.) Pers. 3. Sorghum Halepense (L.) Pers. 4. Saccharum Spontaneum (L.) 5. Pluchea Lanceolata (DC), C.B. Clarke 6. Alhaghipseudalhagi (M. Bieb) Desv. 7. Partheniumhysterophorus L. 8. Striga Spp. 9. Orobanche Spp. 10. Cuscuta Spp. 11. Solanum Elaegnifolium 12. Avena Fatua L. 13. Chromolaena Odorata R.M.K. 14. Lantana Camara L. and a Few Others.
Farm Weed # 1. Cyperus Rotundus L. (Purple Nutsedge, Motha):
(Family: Cyperaceae):
C. rotundus is a perennial herb with linear leaves apparently- looking like a grass. This has led it to be, sometimes, wrongly called as nutgrass instead of nutsedge. It reproduces extensively through its underground bulbs which form chains and ramify into the soil up to 60 cm deep although majority of these tubers are located in the top 12 cm of soil. The viability of purple nutsedge seeds is hardly 2%.
Purple nutsedge is one of the most difficult weeds of the world, particularly on heavy soils. Vegetable crops are worst affected by it though it infests almost all summer and rainy season crops. Sometimes under mild winter conditions it also infests rabi crops in the country.
Hot weather cultivation is the first step in the management of purple nutsedge. In the crop season EPTC, 2,4-D, amitrole-T, liquid atrazine, bentazon, MAA, paraquat, propanil, and linuron are found effective herbicides against this weed. The choice among these shall depend upon the crop grown. Two to three years’ integrated efforts can results in freeing the land from purple nutsedge.
Farm Weed # 2. Cynodon Dactylon (L.) Pers. (Bermudagrass, Doob):
(Family: Poaceae):
Bermudagrass is a perennial weed which has spread on agricultural lands throughout the country. It propagates and disperses rapidly through its shallow rootstocks and stolons. Its seeds are not important in its dispersal.
Summer tillage, suggested for the purple nutsedge control, is also an important component in the integrated management of bermudagrass. Paraquat, glyphosate, and Amitrole-T are very effective herbicides to complement summer tillage against this grass. The uprooted bermudagrass should to be collected and burnt time to time.
In the bermudagrass infested fields one should try to sow some wide-row crops to permit easy intercultivations for the destruction of this grass. Of recent, fluazifop, haloxyfop, and clomazone have proved very good herbicides for the selective control of bermudagrass in certain broadleaf crops. Therefore, attempt should be made to grow such crops and use one of these selective herbicides to control this weedy grass.
Farm Weed # 3. Sorghum Halepense (L.) Pers. (Jhonsongrass, Baru):
(Family: Poaceae):
Johnsongrass is a perennial, robust plant with up to 2 m high clumps, resembling a sorghum plant. The weed is usually first seen in undisturbed areas of the farm. From here it moves to the agricultural fields through its wind-borne seeds and stout, deep rhizomes. Once johnsongrass enters the fields, it is extremely difficult to get rid of its rhizomes.
Therefore, attempts to destroy johnsongrass should be initiated right when it is first seen in the non-crop areas of the farm. The early clumps should be dug deep and its rhizomes burnt at the spot. The foliage of large patches of johnsongrass can be treated with potent herbicides like dalapon, diuron, and glyphosate (0.5-1.0%) at its pre-arrowing stage.
In crop fields, the scattered clumps of johnsongrass can be spot- treated with dalapon, glyphosate. MSMA, DSMA or sethoxydim spray, depending up on the crop.
Summer tillage is a must in any johnsongrass control programme.
Farm Weed # 4. Saccharum Spontaneum (L.) (Tigergrass, Kans):
(Family: Poaceae):
The growth behaviour and control measures of this perennial grass are similar to those described for johnsongrass.
Farm Weed # 5. Pluchea Lanceolata (DC), C.B. Clarke (Arrowood, Baisuri):
(Family: Fabiaceae):
It is a semi-woody, perennial herb with very deep tap roots; reaching up to 6 m deep in soil. Upon cutting its shoots, the weed regrows from its crown buds. It spreads to new areas rapidly through its seeds and roots. Arrowood is largely a weed of the light soils. It grows luxuriantly during the summer months but remains dormant during the rainy season. It depletes the soil of its deep seated moisture which is of serious concern, particularly in the dry farming areas.
During the off season, and on non-crop lands, arrowood provides a built-in safeguard against wind erosion and recycles the nutrients from deep layers to the plow layer of the soil. Because of this advantage many farm owners decline to control this weed during the summer fallow period.
But when required, foliar application of 0.1% spray of glyphosate is found very effective in controlling P. lanceolata during the summer follow period. When needed, a summer tillage may be combined with it. Two to three years’ efforts can almost recover the land from this weed.
Farm Weed # 6. Alhaghipseudalhagi (M. Bieb) Desv. (Camelthorn, Jawasa):
(Family: Fabiaceae):
Camelthorn is a thorny plant.
Farm Weed # 7. Partheniumhysterophorus L. (Carrotgrass):
(Family: Compositae):
P. hysterophorus is an annual weed with wide amplitude of ecological adaptability. It reproduces freely from its seeds. The cut plants put forth new shoots from their crown buds. Starting as a weed of non-crop situations and neglected areas throughout the country, carrot grass is now a weed also of crop lands, particularly in Madhya Pradesh where it has invaded both rabi and kharif crops, displacing some local weeds in the process.
In the dry summer months Patrhenium tends to remain in its rosette form, with its growth suspended. But during the rainy and winter seasons it grows to a thick stand, up to 90 cm high, with profuse flowering and seed setting.
In non-crop areas, 2,4-D, diquat, glyphosate, and metribuzin have been found potent herbicides against carrotgrass.
In crop fields carrotgrass is susceptible to several premergence and preplant herbicides. Their choice will depend upon the crop grown.
Mexican beetle, Zygogramma bicolorata, has been demonstrated as highly successful insect bioagetn against carrotgrass in Madhya Pradesh and some other states of India.
Farm Weed # 8. Striga Spp. (Striga, Witchweed):
(Family: Scrophulariaceae):
Striga is an annual, parasitic herb with a wide range of host crop plants. In India it is most problematic in pearlmillet and sorghum. Of the several species of Striga in India, S. asiatica (= S. lutea) is most common. Sorghum and pearlmillet are parasitised by two different strains of this striga species.
Striga produces millions of dust like seeds with high degree of viability. The seeds germinate in response to stimulus from the root exudates of the host plants and form haustoria on the host roots to establish contact with their vascular bundles for tapping food material and water from the plant.
After staying underground as a total parasite for 3-4 weeks, striga emerges through the soil as a green plant; now depending upon its host only for water and mineral nutrients. At this stage it grows as a semi-parasite. The affected host crops develop symptoms of drought and stunted growth. Application of extra irrigation and nitrogen may tend to revive the crop, temporarily.
Cotton, sunflower, cowpea, groundnut, certain beans, and castor form good trap crops for striga. They induce striga seeds to germinate in soil but do not permit infection of their roots. Such crops should form part of crop rotations in the striga-sick plots.
Now some chemicals have been synthesized which can induce germination of striga seeds in the soil, independent of any host plant. Of these, ethylene (C2H5) is most commonly used in USA where it is applied to the sick fields before sowing of the crop with help of mechanical soil injectors.
It is observed that many new hybrids of pearlmillet in India are not infected with striga. Also, some farmers have evaded the striga problem in pearlmillet by switching over to sorghum, and vice versa, since the strains of striga in the two crops, are different. Besides, the young growth of striga in pearlmillet and sorghum can be treated with directed spray of 2,4- D at 2.0 kg ha-1, mainly to prevent the parasite from forming seeds for future.
Farm Weed # 9. Orobanche Spp. (Broomrape, Lidda):
(Family: Orobanchaceae):
Orobanche is a parasitic weed, much similar to striga in its behaviour but with two major differences. First, its shoot has no underground life cycle; they emerge from the soil soon after infecting the host roots. Second, it lacks green tissue and so it is a total parasite. The orobanche shoots, called clones, are fleshy and cream coloured. At about 3-4 weeks’ age, each shoot produces numerous tiny flowers and viable seeds which are easily dispersed.
There are three major parasitic species of broomrape in India. These are – O. cernua on tobacco and sunflower; O. ramosa and O. aegyptica on tomato and brinjal and O. ramosa in rapeseed and mustard.
Pepper, linseed, sunnhemp, sorghum, seasame, and rice are considered good trap crops for broomrape. Where possible, these should be included in crop rotations in the tobacco areas.
Postemergent allylalcohol (0.1-0.2% spray) provides sufficiently selective control of Orobanche in tobacco. In tine western countries where herbicide resistant tobacco varieties have been developed, glyphosate forms a very effective postemergence herbicide to control orobanche.
The challenge of controlling this parasite in rape seed and mustard continues. Orobanche is also found susceptible to preplant soil incorporation of pebulate, dalapon, linuron, and metobromuron in the relevant tolerant crops. Orobanche growing outside the crop fields should be destroyed by frequent tillage before it had chance to set seeds.
Farm Weed # 10. Cuscuta Spp. (Dodder, Akashbel):
(Family: Convolvulaceae):
Cuscuta is a wiry plant. It is rich in carotenoid pigment which imparts it a golden yellow color. The leaves, flowers, and seeds in cuscuta are inconspicuous. The wiry stems of cuscuta go around the host plant and slowly cover it completely. In India, cuscuta is problematic in lucerne, lemon, and several ornamental trees and hedges. Of recent, it has been reported to infest also Niger (Guizotia abyssinica), cowpea, greengram, blackgram, and chilli.
Contrary to striga and broomrape, the cuscuta seeds do not require any stimulus from its host plant for their germination. Adequate soil moisture and right temperature alone are good enough to germinate these. The cuscuta seedlings emerge from the soil and look for the host plants. If present, these form haustoria on their shoots to share their food and water.
To some extent dodder also conducts its own photosynthesis, making it thus a semi-shoot parasite. The affected host plants die slowly due to chiefly water stress. But when the cuscuta seedlings fail to find a suitable host plant in viscinity they themselves die of starvation.
Therefore, adoption of crop rotations with non-host crops, like small grains, chickpea and mustard, is the easiest way to control this weed, Cuscuta is one of the very few weeds that can be controlled completely by rotating the host crop with a non-host crop.
Prevention of striga in lucerne starts with cleaning of its seeds by dipping the admixture in 5-10% solution of common salt for five minutes. The light seeds of cuscuta will float on the surface of water from where these can be skimmed out. The lucerne seeds that settle at the bottom should be washed with plenty of fresh water to remove the salt.
In the standing Cuscuta infested crop of lucerne, application of a spray of 0.05 to 0.1% paraquat shall destroy the cuscuta shoots. This should be preferred over grazing the infested crop to the animals which will disseminate the weed. Lucerne may show temporary paraquat scorching but it will soon put forth new growth after an irrigation. The left-over patches of cuscuta must be retreated with paraquat by spot treatment.
Ornamental trees and perennial hedges infested with cuscuta can also be sprayed with paraquat. However, this treatment should not be attempted in fruit trees.
Farm Weed # 11. Solanum Elaegnifolium (Wild Brinjal):
(Family: Solanaceae):
It is a perennial, broadleaf weed with 2-3 m deep roots. It infests gardenlands and neglected drylands during rainy season. A noxious weed of Southern India, it bears blue flowers. Its root pieces can give rise to new plants.
The weed has been found susceptible to 2,4-D, but it regrows after about 15 days of the treatment. Further research on its control is under way.
Farm Weed # 12. Avena Fatua L. (Wildoat, Junglijai):
(Family: Poaceae):
Avena fatua is a problem, annual grass weed of chiefly wheat fields. Besides wheat, however, it may also infest other winter crops. Avena fatua is the most prevalent species of this weed in the country although A. ludoviciana Dur also occurs in many fields.
During its vegetative phase it is difficult for the farmers to differentiate it from wheat plants because of which it escapes manual weeding. When possible, adoption of crop rotation with broadleaf crops can help its easy identification and consequent physical removal at its early growth stages.
Certain postemergence herbicides have proved very effective in the control of wildoat in wheat. These are- diclofop (1 kg/ha), flamprop (1-2 kg/ ha), tralkoxydim (0.25 – 0.4 kg/ ha) and terbutryn (0.6-1.0 kg/ha), besides herbicides mentioned under Phalaris minor, ahead.
Farm Weed # 13. Chromolaena Odorata R.M.K. (Siamweed, Croftonweed, Kali Basuti):
Siamweed is a noxious weed largely of plantations in Kerala and Tamilnadu. It has also invaded heavily citrus orchards in the north-eastern states. It is a fast growing, much branched shrub, growing up to 5 m high. It is disseminated with its air-borne seeds. Its cut plants regrow fast from its crown buds.
Siamweed is susceptible to 2,4-D, atrazine, diuron, glyphosate, paraquat, diquat, and picloram.
Farm Weed # 14. Lantana Camara L. (Lantana, Putus, Phul-Kakri):
(Family: Verbenaceae):
Lantana is a perennial, evergreen shrub which spreads mainly with its abundant, bird-disseminated seeds, although it multiplies also with its shallow crown buds. It is an alien invasive weed from Mexico brought to India for use as a hedge plant bearing small, colourful flowers. Now it has infested thousands of hectares of land on hill slopes and in forests, depleting our valuable pasture reserves. Also it has invaded many seasonal river beds and other non-crop areas.
It is a very difficult semi-woody noxious weed. Its physical cutting is very labour-intensive and expensive method. Also, the cut stumps of lantana put forth new shoots, rather rapidly.
Biological control of lantana with certain insect bioagents has been highly successful in Australia and Hawaii but it has not yielded any encouraging field results in India, thus far.
Lantana is found very susceptible to glyphosate (0.1 – 0.2% spray).
Farm Weed # 15. Mikania Micrantha H.B.K. (Mile-A-Minute Weed):
(Family: Asteraceae):
Mikania is an alien invasive weed which has spread heavily in the north-eastern states and Kerala. It is a voracious climber. It climbs even medium-sized trees, besides grasses and other vegetation on the ground. It grows extremely fast which gives its name, ‘mile-a- minute’ weed. The weed is unpalatable to animals. It disseminates with its air-bone seeds. Major damage inflicted by this weed is to our grasslands which lose enormously their grazing values. The weed may also infest some agricultural systems.
Mikania is found susceptible to glyphosate, paraquat, and 2,4-D. Its workable control methods, however, require further attention from the weed scientists.
Farm Weed # 16. Mimosa Spp. (Sensitive Plant):
(Family: Leguminosae):
There are two major weedy species of Mimosa which have recently spread in the North-Eastern states of India. These are M. prainiana Gamble and M. invisa Mart. These two alien weed species seriously threaten our native pasture grasses. Also, Mimosa spp. have now entered rice and sugarcane fields. Being thorny and woody, these are not subjected to any biotic stress by the grazing animals.
Physical removal of M. spp. is almost impossible. Minosa is found susceptible to glyphosate, 2,4-D, paraquat, atrazine, diuron, heaxzinone and sodium arsenite. Selectivity to the non-target plants should be considered before choosing a herbicide for destroying this weed.
Farm Weed # 17. Phalaris Minor Retz. (Littleseed Canarygrass, Gullidanda, Varni):
(Family: Poaceae):
P. minor is an annual, noxious grass which has infested wheat crops in almost entire north-west region of the country. It mimics wheat plant in its early vegetative phase, making it difficult for the farmer to identify and remove it from his field by physical methods. The weed shows itself distinctly only at its spike formation stage standing amongst the wheat plants.
But then it is too late to remove it for curbing the weed-crop competition for obvious reasons. Nevertheless, its late stage removal is helpful in reducing its seed production which otherwise would add enormously to the soil seed bank. It may be noted that each plant of P. minor is capable of bearing 300-400 shiny black, flat, minute seeds. The uprooted littleseed canarygrass plants form good forage for milch animals.
For the last almost 15 years, the farmers in India have kept P. minor in wheat under acceptable control with isoproturon. This herbicide is applied at 0.75-1.0 kg ha-1, 30-35 days after sowing wheat.
But, unfortunately, now new races of P. minor, which are resistant to isoproturon, have developed and infested the wheat fields in large areas. To deal with these resistant races, alternative herbicides had to be discovered for use by the farmers. These herbicides include clodinafop, fenoxaprop, mesosulfuron, sulfosulfuron, and metribuzin. All these compounds are very low dose herbicides, effective at only few g/ha.
Cultural control of P. minor is also found possible where wheat can be rotated with some broadleaf crop for its easy identification and consequent physical removal. Forage crops like lucerne and berseem are additionally useful in this respect since these are cut repeatedly during the season.