Harvest Time
Careful with herbicides
By Sosimo Ma. Pablico
RICE FARMERS should now be careful with the use of herbicides or chemical weed killers, as two weed species in Nueva Ecija and Iloilo can no longer be controlled with the recommended application rates of three groups of herbicides.
Dr. Madonna C. Casimero and Leylani M. Juliano of PhilRice (Philippine Rice Research Institute) said the herbicides butachlor, propanil and their combination can no longer control the baranyardgrass Echinochloa crusgalli and Echinochloa glabrescens with the recommended application rates.
The two weed species are known in the dialects as marapagay (Ilocano), telebisyon (Nueva Ecija), paray paray (Cebuano and Ilonggo) and bayakibok (Tagalog).
Both are almost similar in their physical appearance, except that the spikelets of Echinochloa crusgalli are red to purple, while those of Echinochloa glabrescents are green to brown. These are the most dominant weeds in Nueva Ecija and the second in Iloilo, but these are also abundant in the Ilocos region.
In their interviews with farmers in Nueva Ecija and Iloilo, where large areas are planted to direct seeded rice at least twice a year, Juliano and Casimero found that many of the farmers have been using herbicides for as long as 15 and 20 years, respectively.
On the average, Iloilo and Nueva Ecija farmers have used butachlor for 8.3 and 8.7 years, respectively. Over the years they observed that the formulation was no longer strong to effectively control the weeds and so they shifted to other herbicides.
Thus, most of them (80 percent in Iloilo and 86.7 percent in Nueva Ecija) shifted to butachlor +propaniland have been using it for an average 9 and 7.1 years, respectively.
Amazingly, 10 percent of the Nueva Ecija farmers have been using butachlor +propanil for 15 to 20 years. Some farmers have even been applying another brand of butachlor + propanil or a mixture of two brands 15 days after seeding.
In the screen house, Juliano and Casimero found that 89.5 percent of the total weed populations collected and screened are resistant to butachlor and propanil and one population is developing resistance.
Moreover, seven populations survived the application of four times the recommended rate of butachlor +propanil. Ten populations survived butachlor application up to four times the recommended rate. The populations resistant to butachlor +propanil were also resistant to butachlor. Six out of seven populations also survived the application of four times the recommended rate of propanil.
The farmers used higher doses of butachlor + propanil and increased the frequency of applications because they perceived that the herbicide formulation was no longer as effective as when it was still relatively new.
Juliano and Casimero said the continuous use of a single herbicide for several years provided selection pressure, resulting in resistant populations. Thus, the farmers have been using higher rates at more frequent application per season.
“What was perceived as a result of reduced herbicide efficacy is actually resistance of the weeds to butachlor and then to butachlor + propanil,” hey added.
The herbicides containing butachlor as their active ingredient are Macho 60 EC, Weeder 60 EC, Butataf 60 E, Sonic 60EC, Ancom Butachlor 60 EC, Samurai 60 EC, bLADE 60 EC, Machete 5 G, Machete EC, Machete Express, and Butachlor 600 EC.
Those containing butachlor +propanil as their active ingredients are Cleanfild 5 EC, Tornado 60 EC, Twister EC, Toro, Klik 70 EC, and Advance EC.
What happened to the Nueva Ecija and Iloilo farmers could also happen in the Ilocos if the farmers repeat the mistakes of counterparts.
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