Perla Bangit, integrated pest management coordinator of the provincial agriculture office, told The STAR that farmers in San Miguel and San Ildefonso towns in northeastern Bulacan first noticed the infestation late last month.
Had it not been contained promptly, Bangit said the infestation could have affected 500 hectares.
Hardest hit were farmlands in 20 San Miguel barangays. In San Ildefonso, only five hectares of ricefields were affected in Barangay Nabaong Garlang.
The tungro virus carried by green leafhoppers earlier ravaged some 1,000 hectares of farmlands in Isabela.
When the infestation was confirmed, Bangit said farmers and local officials joined hands in containing it by cutting and burning infested palay stalks.
Lito Capule, hybrid rice coordinator of the provincial agriculture office, said three factors contribute to tungro infestation — the host plant, the vector or insect, and favorable conditions.
He said the host plants refer to in-bred or hybrid rice varieties, especially those prone to tungro infestation, while the vectors are insects like the green leafhoppers that serve as the carriers of the virus that infects the host plants. Improper sanitation and land preparations also contribute to the infestation.
Capule said tungro was last detected in Bulacan in 1995, but it ceased after tungro-resistant rice varieties were introduced.
He said local farmers shifted back to aromatic rice varieties — which are prone to tungro especially during the cold season - because they fetched high prices in the market.
The tungro virus, according to Capule, may be airborne or water-borne but is inefficient without the green leafhopper or berdeng ngusong kabayo that serves as its vector.
Green leafhoppers usually attack palay during the booting to the heading stage or the first 30 to 40 days from transplanting.
The insects bore holes into the stalks and suck their juice. In the process, they suck in the tungro virus, which multiplies in their stomach.
Thus, when the green leafhoppers hop from one stalk to another, they spread the virus which eventually stunts the palay’s growth.
To prevent infestations, farmers are reminded to be careful in preparing their farmlands for planting.
If ricefields are allowed to "rest" for at least three weeks before planting, Capule said this dramatically reduces the possibility of viral infestations.
He said tungro infestations will not take place in the absence of one of the three factors which, however, can be addressed by utilizing tungro-resistant rice varieties, and proper sanitation and land preparation.
He said spraying insecticides kills not only bad insects like the green leafhoppers but also friendly insects like the tutubing karayom that eats up to 15 ngusong kabayo per day.