Malaysian weeds need mixed modes of action
Malaysian agriculture has had a wake-up call to the threat posed by herbicide resistant weeds. Paraquat has an essential role to play in avoiding this potentially huge problem. A report by the Paraquat Information Center of the discovery of populations the noxious weed goosegrass (Eleusine indica) resistant to the non-selectiveDescription A chemical product used for eliminating all types of weeds (annual and perennial grasses and broadleaved weeds). Authoritative On-line References and Resources http://www.weeds.iastate.edu/ An invaluable source of contemporary information about herbicides and weeds from Iowa State University. herbicide glufosinate has now been confirmed by publication in a scientific journal1.
A vegetable farmer in Malacca state and planters at an oil palm nursery in Pahang state had suspected that glufosinate was failing to control goosegrass. Subsequent investigations have now confirmed that one population shows a two-fold resistance and the other an eight-fold resistance.
These are the first cases of weed resistance to glufosinate to be recorded anywhere in the world after more than 25 years of use. This is reminiscent of the fall of glyphosate to the first resistant weeds in the mid 1990’s. Escalating use of glyphosate over a similar period ultimately resulted in resistance. The second weed species to have confirmed glyphosate resistance was also goosegrass in Malaysia2. Even paraquat has had a few isolated populations become resistant, but overall it has had a very good record with respect to weed resistance.
Malaysia currently has fifteen species recognised as having herbicide resistant biotypes2. The most seriously affected herbicides are ACC-ase inhibitors (‘fops’ and ‘dims’) and ALS inhibitors (eg sulfonylureas). Rice and vegetables are the crops most affected. Fortunately, perennial orchard and plantation crops seem to be have been less affected so far. Perennial crops like rubber, oil palm and cocoa are an important part of the Malaysian economy. However, a closer look at the official records suggests that reporting of weed resistance has been sporadic. Given what is generally known about weed resistance worldwide, a greater problem may be lurking. When surprises such as this case of glufosinate resistance occur, it is a timely reminder that farmers and planters in Malaysia, like elsewhere, cannot afford to be complacent over this serious threat to agricultural productivity3.
The apparent low incidence of weed resistance in plantation crops like rubber and oil palm is undoubtedly due to a number of reasons. The soil is not disturbed so there is less encouragement for annual weedsDefinition Weeds that complete their life cycle within one growing season, or year. From seed to flowering to seed before the year ends. Authoritative On-line References and Resources The International Weed Science Society represents individual associations around the world. to germinate and refresh the population; and a variety of methods of weed control are used. Leguminous cover cropsDescription Cover crops are primarily planted not to be harvested for food but to reduce soil erosion, control weeds and improve soil quality. They are usually plowed or tilled under before the next food crop is planted, in which cases the "cover crop" is used as a soil amendment and is synonymous with "green manure crop." Authoritative On-line References and Resources http://attra.ncat.org/attra-pub/covercrop.html ATTRA is the US National Centre for Appropriate Technology's Sustainable Agriculture Information Centre. are often established between the tree lines which smother-out weeds and integrated weed managementDescription A decision support system for crop protection which focuses on long-term prevention or suppression of pest problems with minimum impact on human health, the environment, and non-target organisms. IPM takes into consideration all available pest control techniques and tactics (cultural, mechanical, biological, chemical). IPM emphasizes the growth of healthy crops for better productivity with the least possible disruption to agroecosystems. Authoritative On-line References and Resources http://www.ipmcenters.org "The USDA's National Site for the Regional IPM Centers' Information System provides information about US commodities, pests and pest management practices, people and issues." practices are widely used.
Weed Resistance Management
- Do not over-rely on any one herbicide
- Use integrated weed management (IWM) techniques to avoid the negative effects of weeds and preserve their environmental benefits
- Rotate herbicide modes of action in IWM systems
Herbicide programs may be based on varying spray rounds between glyphosate and paraquat to achieve a balance between avoiding competition from aggressive, noxious weeds (typically tall perennial grassesDescription The leaves are "narrow" as opposed to the "broad" leaves of broadleaved weeds. Also called 'monocots' having one seed leaf opposed to 'dicots' having two seed leaves. Authoritative On-line References and Resources The International Weed Science Society represents individual associations around the world. and creeping broadleaved weedsDescription The leaves are "broad" as opposed to the "narrow" leaves of grasses. Also called 'dicots' having two seed leaves, while grasses are 'monocots' having one seed leaf. Authoritative On-line References and Resources http://www.iwss.info The International Weed Science Society.) and maintaining a vegetative cover of more benign or ‘soft’ grasses.
Relying on a single herbicide leads to a shift to less susceptible weeds dominating the flora, eg broadleaved weeds soon become the main problem if only glyphosate is used. This phenomenon of weed succession is well known and has led to integrated weed management being practiced. Paraquat was introduced in Malaysia in 1962 and quickly became widely used because of its superior environmental profile to earlier products, its speed of action and rainfastness, in particular. With weed succession issues, spraying paraquat between glyphosate spray rounds helps prevent shifts to more competitive weeds. Now, the distinctive mode of action of paraquat means that using it in a programme of integrated weed management is vital to avoid the threat of resistance to other herbicides such as glufosinate and glyphosate becoming a critical issue for Malaysian agriculture. With no new herbicide modes of action having been introduced since the 1980’s, worldwide, paraquat’s role is more important than ever.
- Adam Jalaludin, Jeremy Ngim, Baki H J Bakar & Zazali Alias (2010). Preliminary findings of potentially resistant goosegrass (Eleusine indica) to glufosinate-ammonium in Malaysia. Weed Biology and Management, 10, 256–260
- International Survey of Herbicide Resistant Weeds: www.weedscience.org
- Zainal Abidin Mior Ahmad (2010). Herbicide resistance awareness in Malaysia. The Planter, 86, 751-752
The brand name of the leading paraquat product sold in Malaysia is Capayam. Worldwide, the leading paraquat brand is Gramoxone.