By Milonjyoti Konwar

1.   Introduction
Panicum repens, commonly known as ‘torpedo’ grass, is one of the most serious perennial weeds. It grows in or near shallow waters where it can quickly displace native vegetation. It is reproduced by both seeds and rhizomes. It produces lots of rhizomes, which support long dry periods and can easily adapt to the flooding condition. Because of its rapid vegetative growth, plants can occupy the reservoirs margins quickly. Torpedo grass occurs in both aquatic and terrestrial plant communities, including coastal sand, wetland, and forested plant communities.

P. repens belongs to the family Poaceae. It is called as ‘torpedo’ grass because of its sharply pointed or torpedo-like growing tips. It can grow up to 3 feet tall, with hairy leaf sheaths and hair on the upper margins of the leaves and has a panicle-type inflorescence, 3-9 inches long. The spread of torpedo grass is limited to rhizomes either by rhizome expansion or fragmentation.

P. repens increases the incidence of insect vectors of diseases, as they provide a favourable environment for the proliferation of these agents. The control of such weeds can be part of a control strategy of such vectors by reducing used of it by the insects. It is difficult to control. Plants possess numerous dormant buds associated with extensive rhizomes and can sprout from deep in the soil. Several years of treatment may be needed to control torpedo grass .Torpedo grass exhibits some characteristics that enable it to survive fire. Torpedo grass has been observed sprouting following fire, herbicide application, grazing, cutting, and plowing or disking. 

2.Control Measures
The following control measures to be used for controlling P.repens in different situations.

2.1  Preventative
Preventive control can be accomplished by preventing the spread and fragmentation of rhizomes. It is a very difficult practice as if even a tiny fragment of rhizome is left in an area, it will re-establish itself. Control of infestations near waterways will prevent long-range spread via water and this should be a priority. If mowing or tillage is used, care must be taken to prevent transport of rhizome or stolon fragments. Population spread may also be limited by preventing the fragmentation and spread of torpedo grass rhizomes, controlling established populations near waterways, not accepting contaminated materials such as fill dirt and hay, and cleaning vegetation off of machinery.

2.2 Cultural
P. repens generally invade open or disturbed areas – following a burn, clearing mowing, etc., so these areas are particularly vulnerable to invasion. Therefore, a healthy ecosystem with good species diversity will help to control infestation. The presence of other vegetation may limit the establishment or it’s spread.

2.3 Mechanical
Mechanical control is only moderately effective for torpedo grass control. Continuous tillage will provide good control, but it is often impractical in many natural areas. A single tillage operation may help to enhance herbicidal effectiveness, but disking alone may increase infestation levels through rhizome fragmentation. Mowing is marginally effective. Repeated mowing through a growing season limited the development of new rhizomes, but did not ultimately prevent regeneration. Flooding or maintaining deep water could limit torpedo grass establishment and growth.

2.4 Biological
There are limited agents being studied for biological control of torpedo grass. Torpedo grass is very palatable for cows and goats, and grazing may be integrated in an overall management scheme. There is no biological agent has been identified to control torpedo grass. Laboratory experiments suggest that fungal pathogens may be useful in controlling torpedo grass.

2.5 Chemical
Herbicides are effective in gaining initial control of a newly invasion or a severely infestation weed, but they are rarely a complete or long-term solution to weed management. Currently, the most widely used herbicide in the world are the following: 2,4-D, glyphosate, diquat, endothal, compounds based on copper, and imazapyr, fluridone.

Glyphosate has been the most effective herbicide used to control torpedo grass. A 2 to 3% solution of glyphosate (Roundup, etc.) is very effective. Imazapyr (Arsenal, Chopper, Habitat) is also very effective at 0.5 to 1% solution. Be sure to include a non-ionic surfactant at 0.25% .These herbicides are systemic so care must be exercised to minimize off-target damage. Regardless of habitat conditions, multiple re-sprays may be required for complete control.

Application of oxadiargyl 70 g/ha under normal method of planting resulted in lowest weed density at 30 DAT while lowest dry weight at 30 DAT was recorded with normal planting +oxadiargyl 70g/ha.

2.6 Integrated Weed Management
Herbicide treatment following fire may reduce torpedo grass populations. Herbicide application is the most widely-used method for controlling torpedo grass. Repeated applications may be needed to achieve control. Greenhouse studies suggested that young torpedo grass plants or plants in the reproductive stage may be most susceptible to herbicides. Integration with other methods may increase the effectiveness of herbicide treatments.

There is a great variation in weed flora under different agro-climatic conditions. However, P. repens was found to a great extent between non-cropped and cropped ecosystem. Weed management methods showed that application of glyphosate along with various management practices helps in effective control of torpedo grass. In aquatic ecosystem with transplanted rice, application of oxadiargyl 70g/ha or almix (chlorimuronmethyl + metsulfuron methyl) 4 g/ha was very effective. By careful prevention as well as appropriate management practices control of P. repens is possible.

About the author: Mr. Milon Jyoti Konwar, did his B. Sc, in Agriculture from Assam Agricultural University (AAU), Jorhat, Assam (India) with first class. At present, he has been pursuing M.Sc. Agriculture with specialization in Agronomy in the Department of Agronomy, AAU, Jorhat. His master degree’s dissertation programme is related to Crop and Fertility management. Linking to his specialized subject, Mr. Konwar has published a number of articles in various magazines. [Read More]


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