Effective monitoring strategies against rice planthopper

Rice planthoppers (RPH), including the brown planthopper (BPH), small brown planthopper, and white-backed planthopper (WBPH), are constraints to rice production because of their direct damages. They can transmit viruses that can be devastating to rice plants.

A study made by the Philippine Rice Research Institute (PhilRice) showed that continuous crop monoculture of high-yielding varieties with high fertilizer rate, unnecessary usage of pesticides, and the changing cultural practices, could possibly implicate the development of BPH population leading to breakdown of major genetic resistant varieties.

In keeping an environmentally-sound and a partnership-based research on rice research, Genaro Rillon of PhilRice and co-researchers have worked on project, “Construction of Epidemiology Information Interchange System for Migratory Disease and Insect Pests in Asia Region: Assessment of Rice Planthoppers Populations and Viruses in the Philippines”. The project was funded by the Asian Food and Agriculture Cooperation Initiative (AFACI), which is being coordinated by the Bureau of Agricultural Research. It was established to monitor RPH and other viruses causing significant rice production losses in Asian countries. The goal is to reduce the vulnerability of rice crops losses caused by RPH outbreaks in the Philippines and to participate in the establishment of collaborative network.   

 Results can be accessed through the internet platform of the AFACI-Asian Migratory Insects and Viruses Surveillance (AMIVS), web-based portal system, designed as a depository for valuable information and a monitoring system.  

Project assessment and monitoring results

The monitoring of RPH populations, using light traps, was conducted at the PhilRice Central Experiment Station (CES) in Munoz, Nueva Ecija.  And in two sites using stick traps in PhilRice CES and in Mabini, Sto. Domingo, Nueva Ecija.  

The light trap was set up weekly and used to approximate numbers of planthoppers (BPH and WBPH) density, while the sticky traps started at ten days after transplanting until maturity of rice crop. In each sampling per week, sticky trapping was conducted at ten hills randomly selected per field. At each trapping spot, the sticky trap was placed between two plants. The traps were brought to the laboratory for counting and recording the number of collected BPH and WBPH including spiders.

According to Rillon, observed high populations of RPH monitored using sticky trap coincided with the reproductive to ripening phases of rice plants in the field. Planthoppers prefer these phases of rice growth as they can get better nutrition around these stages.  It was further observed that planthopper adults invaded rice at reproductive phase and seems that they invade rice earlier during wet season.

For both dry and wet seasons, monitoring showed that WBPH was usually recorded earlier to colonize rice plants than BPH. During field samplings, spiders, coccinellids, mirids, and tiger beetles were commonly observed in the field.

The population patterns observed would indicate that RPH develops in the field and peaked towards the end or as the crop neared maturity during the dry or wet seasons. Comparing these two population peaks recorded, higher peak of population occurred in wet season as compared with dry season.  However, Rillon pointed out there was an increasing trend in the number of planthopper populations recorded and its associated hopperburn damage in some areas in the Nueva Ecija.

Initial planthopper population was usually observed during the reproductive stages and continuously increases as the crop matures. Population peaks were recorded from March to April, and from August to September. Similar patterns of populations of RPH were recorded during the dry (June - June) and wet (July - December) seasons. Consistently more BPH were recorded than WBPH. Only few patches of hopperburn injury were observed in farmers’ fields during the year. Incidence of injury ranged from 5 to 20 percent.  Incidence of rice virus disease was not recorded.

In the latter rice growth stages, populations decreased because planthoppers usually emigrate when rice is maturing due to poor food conditions of host plants. It was commonly observed that planthopper adults attacked rice at reproductive phase and seems that they invade rice earlier during wet season. For both dry and wet seasons, monitoring showed that WBPH was usually recorded earlier to colonize rice plants than BPH.

The project proponent was also able to input the data obtained from the monitoring conducted in the AMIVS system.

Recommendations and other researchable areas

Although the damage was not in serious outbreak proportions, there is also a need to continuously monitor RPH populations to prevent pest outbreak in the future.

To prevent RPH outbreak in the field, different management strategies were presented such as planting of varieties that are resistant to planthoppers, synchronous planting to avoid overlapping populations, conservation of beneficial organism to maximize natural biological control and proper use of chemical control when needed.

It is also necessary to study the changes in the practices of farmers like insecticide spray, nutrient application, variety usage and intensity of planting that favors the development of planthopper populations in the field.

PhilRice plans to continue monitoring RPH to establish population patterns of the insect pests. This is also to sustain the strong regional collaboration that is essential for the generation of information to improve management of RPH in the country.

AFACI is an international cooperation body committed to improving food production, promoting the adoption of sustainable agriculture practices, and enhancing the extension services of Asian countries.  The Philippines is one of the member-nations of AFACI since it was inaugurated in 2009. ### (Patrick Raymund A. Lesaca)

 

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