Two weed species in Nueva Ecija and Iloilo now resist herbicides
Two species of the weed barnyardgrass in Nueva Ecija and Iloilo rice farms are now resistant to the recommended application rate of the chemical weed killers butachlor, propanil, and butachlor + propanil due to continued application over the years.
As a result, farmers practicing direct wet seeding of rice have been applying much more than the recommended rate to be able to control the weeds. In some instances, farmers apply four times the recommended rate and, hence, their cost of chemical weed control has increased tremendously.
In a nutshell, this is the gist of a paper by Leylani M. Juliano and Dr. Madonna C. Casimero of PhilRice [Philippine Rice Research Institute], which won the best paper award from the Weed Science Society of the Philippines during the recent scientific meeting of the Pest Management Council of the Philippines.
The two weed species are known in science as Echinochloa crusgalli and Echinochloa glabrescens. In Philippine dialects, both are called marapagay [Ilocano], telebisyon [Nueva Ecija], paray paray [Cebuano and Ilonggo], and bayakibok [Tagalog].
These weed species have almost identical physical appearance, except the color of their spikelets. Echinochloa crusgalli has red to purple spikelets, while Echinochloa glabrescens has green to brown spikelets. These are the most dominant weeds in Nueva Ecija and the second in Iloilo.
In their study, Juliano and Casimero interviewed farmers from the top 10 municipalities in Nueva Ecija and Iloilo with the largest areas planted to direct seeded rice. They gathered data on herbicide use history, cropping intensity, major weeds, and cultural management practices.
They also collected mature seeds of the two Echinochloa species, which they used later for screenhouse studies on resistance screening and response dose assays (or the determination of the weeds reaction to different rates of application).
Mature seeds were collected in the towns of Aliaga, Rizal, Quezon, Bongabon, Sta. Rosa, and Talavera, and in the Science City of Munoz, Nueva Ecija, as well as in Barotac Nuevo, Pototan, and Dingle, Iloilo..
Results of the survey show that, on the average, farmers have been using the direct-seeded rice technology for 14.5 years in Iloilo and 16.4 years in Nueva Ecija. Iloilo farmers practice intensive rice monocropping – an average of 2.5 and a maximum of 3.0 crops a year by 80 percent, while Nueva Ecija farmers usually have two crops a year.
Most of them started to use herbicides when they began to practice direct seeding. Some have used herbicides for at least two years. However, many Iloilo and Nueva Ecija farmers have been using herbicides for as long as 15 and 20 years, respectively.
Butachlor was the first herbicide used on direct-seeded rice by two-thirds of Iloilo farmers and three-fifths of Nueva Ecija farmers. They have used it for an average of 8.3 and 8.7 years, respectively. Over the years the farmers observed that the formulation of butachlor was no longer strong to effectively control the weeds and so they shifted to other herbicides.
From butachlor, most of the farmers [80 percent in Iloilo and 86.7 percent in Nueva Ecija] shifted to butachlor + propanil. These Iloilo and Nueve Ecija farmers have been using this herbicide for an average of 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.
Juliano and Casimero pointed out: “The continuous use of a single herbicide for several years provided selection pressure, resulting in resistant populations. This … explains why farmers in these areas have been using higher doses of herbicides and increasing the number of applications per season. What was perceived as a result of reduced herbicide efficacy is actually herbicide resistance of the weeds to butachlor and then to butachlor + propanil.”
AGRI-INFO/AUGUST 15, 2006
TITLE: TWO WEED SPECIES IN NUEVA ECIJA AND ILOILO NOW RESISTS HERBICIDES
ALAM BA NINYO NA DALAWANG URI NG MGA DAMO SA MGA PALAYAN SA LALAWIGAN NG NUEVA ECIJA AT ILOILO ANG RESISTANT SA REKUMENDADONG APPLICATION RATE NG CHEMICAL WEED KILLER, BUTACHLOR, PROPANIL AT BUTACHLORS+PROPANIL.
DAHIL SA KATIBAYAN NG MGA DAMONG ITO, AY NAPILITAN ANG MGA MAGSASAKA NA GUMAMIT NG MGA KEMIKAL NA ITO NG HIGIT PA SA REKUMENDASYON.
ANG DALAWANG WEED SPECIES NA ITO AY KILALA SA PANGALANG ECHINOCHLOA CRUSGALLI AT ECHINOCHLOA GALBRESCENS, KUNG SAAN ANG MGA ITO AY KAPWA TINATAWAG SA PANGALANG MARAPAGAY SA MGA ILOKANO, TELEBISYON SA NUEVA ECIJA, PARAY PARAY SA CEBUANO AT ILONGGO AT BAYAKIBOK SA TAGALOG.
KUNG BAKIT NAGING RESISTANT ANG MGA DAMONG ITO DAHIL SA TULUY TULOY NA PAGGAMIT NG SINGLE HERBICIDE SA MARAMING TAON KUNG KAYAT ANG INAKALANG PAGHINA NG HERBICIDE AY SA KATUNAYAN, LUMAKAS LANG ANG RESISTANSIYA NG MGA PESTENG DAMO SA PALAYAN.