and Integrated Pest Management - part - usaid

USE OF BI TO CONTROL'TROPICAL INSECT PESTS 77
DAT to control a severe whorl maggot infestation. The yields from the Bt
+monocrotophos plots from Farms 6, 4, 1, and 5 were 3.61 t/ha, to 3.73 t/ha,
5.51 I/ha, and 5.62 t/ha, respectively, with an overall average yield of 4.62 t/ha.
Yield of rice from both Bt treatments, applied singly and in combination
with monocrotophos were significantly (P < 0.01) increased relative to both the
IRRI-IPM Working Group (IPMWG) treatments with an average yield of 4.07
t/ha for the IPMWG and 4.26 t/ha for the monitored Farmer's Practice (Litsinger
and Shcpard 1986, unpubl.). The IPM plots failed to give higher yields because
one or two applications of azinphos-ethyl failed to control leaffolder.
The whorl maggot and leaffolder were the only two rice pests to reach
threshold leve!s of I whorl maggot egg/ha and 2 leaffolder larvae/hill,
respectively in our trials. Of the two insects, only leaffolders resulted in
significant yield loss (>40%); fortunately, the larva is highly susceptible to
commercial Bt. IR64, a MV, had sufficient time with ample standing water and
fertilizer (75 kg N/ha) to recover from the early whorl maggot damage.
The leaffolder was able to significantly reduce the rice yield because the adult
population reached levels of 2-3 moths/m 2 by 40 days after transplanting (DT)
and remained nacr this level until 80 DT (Fig. 1). The yield data support the
claim that the control of the leaffolder population was a direct result of the toxic
effects of Bt and not beneficial organisms. Tryon (1986, unpubl.) found three
WP commercial formulation of Bt HD-1 (Dipel®, Bactospeine® and Thuricide®)
100% effective in the laboratory, killing 3rd-instar leaffolder larvae within 96 h
at rates of less than 0.1 kg/ha. A rate of 1.0 kg/ha of Bt is the recommended
application rate.
Average no. leaffolder adults /m 2
5
4
oot,/ /
3 BootFlowering
Panicle
initiation /
16 30 44 58 72
Sampling dates (DAT)
Figure 1. Number of leaffolder Cnaphalocrocismedinalis per m 2 from 5 rice
farms treated with Bacillus thuringiensis, Central Luzon, Philippines, wet
season, 1986.