and Integrated Pest Management - part - usaid

ROLE OF CULTURAL TICNIQUES IN RICE IPM SYSTEMS 89
humid lowlands (Suenaga 1983), and rice fields with standing water have been
found to encourage the multiplication of BPH (Pathak & Dyck 1973). In
Indonesia, BPI- prefers irrigated rice to upland rice. The problcms are more
serious in plots continuously flooded or with standing water. The green
leafhopper Nephotettix virescens also seems to favor fields with stagnant water,
and specially those with intermittent rain as well.
Good water management should therefore be able to help control certain rice
pests. Draining the fields for about two days suppressed BPHl outbreaks in
Malaysia (Miller & Pagdcn 1930). In the Philippiaes, farmers withhold
irrigation in BP-l infested fields when the rice crop is almost mature, and plants
,are spread apart every few rows to help dry out the fields (Dyck 1974). To
effectively control the rice water weevil, fields are drained at the proper time and
irrigation is stopped for a predetermined period (Pimentel et al. 1968). Draining
the water level in rice fields destroys the eggs of BPH laid in the leaf sheaths.
Deep irrigation in the morning followed by the addition of a certain amount of
kerosene (preferably mixed with pyrethrum) to water gives good control of BPH
in Taiwan (Grist 1968, Iso 1954). In Indonesia, it was a common practice to
raise the irrigation water level to control BPH. Sand or sawdust containing 0.25
L kerosene for every 100 m 2 was then broadcast on the raised water level and the
plants were shaken (Tjao 1952).
TIME OF PLANTING
When synchrony and crop rotation are practiced, the planting time of the wet
and dry season rice are December and May or July respectively (Figs. 3 and 4).
In this situation there is no room for manipulating a planting time (early or late)
for controlling certain pest species. In areas where synchrony is difficult to
achieve due to water shortages and labor problems, manipulation of planting
time (early or late) can provide effective control of some rice pests. Late
planting of rice minimi::es infcstation by the white stemborer Scirpophaga
innotata (Walker) (Goot 19., At Cuttack, India, crops planted at the end of
July suffered little from leai,: ,..,,ers and planthoppers, but crops plailted later
were severely damaged (Israel 1969). Gall midge incidence becomes more severe
if rice is planted later than December in West Java.
SPACING
The spacing of rice plants in a field is believed to influence the abundance of
certain rice pests. Close spacing may rapidly increase the BPH population
(Kalode 1974, Kisimoto 1976). Data from IRRI show that a 10 x 10 cm plant
spacing of both tall and short 'Peta' at time of peak insect populations had
significantly more BPH per tiller than a 50 x 50 cm spacing (Dyck 1973, IRRI
1972).
Clic. -,pacing results in a more shaded, cooler, and more humid
microenvironment, which makes it less favorable for the development of the
natural enemies of BPH (Nishida 1975). The thick rice canopy also prevents
foliar insecticidal sprays from reaching the basal portions of the rice plants where