The acreage of arable land assigned to rice cultivation in China now exceeds 33 million hectare. Almost 50% of the total volume is subject to serious threats from weeds. The most significant threats in China are represented by: gramineous weeds (18 varieties), cyperaceae weeds (21), broadleaved weeds (81) and algae weeds (3). Expressed in total volume, the damage these weeds caused amounted to more than 10 million tons of rice, accounting for 15% of total rice harvests. Hypothetically speaking if the crops were not treated with herbicides,harvest yield would decrease between 5-15% and 15-30% in severe cases. Herbicides are widely used in China and are now used in 45% of all rice cultivation.

In the 1990’s chemical control of weeds relied primarily on butachlor, acetochlor, and benthiocarb. After this bensulfuron-methyl metsulfuron-methyl and amide combinations came into widespread use. As Barnyard grass became the most significant threat to the rice crop and now accounts for more than two third of all damage, the majority of herbicides target this weed. The product, consumption and application area are summarized in the table below:

As seen from above table, paddy herbicides in China do not necessarily conform to international market trends.

Some herbicides have varying efficacy dependent on the stage of development of their target weed. For example butachlor, acetochlor, pretilacholr and thiobencarb are suitable for 2-leaf age of barnyard grass. The best solutions for 3-leaf age are mefenacet, anilofos and oxadiazon. Molinate is more applicable to 4 and 5-leaf stages while quinclorac is best for the 5-leaf stage weeds. With the development of more efficient and technologically based advanced planting techniques in China and a move away from traditional methods rice has become increasingly susceptible to weeds. There is currently no effective solution for Barnyard grass resulting in farmers usually increasing the dosage of herbicides applied to crops, often at levels in excess of regulated levels resulting in MRL violations and often crop damage. To increase the treatment efficacy and save on labor costs many herbicides are usually applied in combinations which results in multi-herbicide resistant strains of weeds.

To cope with the weed problems in “no-till” and “direct-sowing paddy field”, Chinese agronomists have suggested that broader-spectrum herbicides should be thoroughly applied before crops are planted and suggest using combinations of herbicides designed to work synergistically through a number of different mechanisms of action. However these methods are not going to solve the long-term problems of barnyard grass. Chinese growers are searching for new and effective herbicide products. In response to these needs, Chinese pesticide producers have developed several new formulation types and combinations, which tend to be based on out of patent or generic active ingredients. The presence of the MNCs has made novel herbicides introduced by overseas companies popular amongst Chinese growers, which included Dow’s cyhalofop-butyl, penoxsulam, FMC’s metamifop and halosulfuron-methyl and Kumiai’s pyriminobac-methyl. The demand for these herbicides often exceeds supply in some paddy growing provinces and has negatively impacted sales of domestically produced herbicides.

Reference Link

www.pesticide.com.cn