Vietnam is the world’s fifth largest rice producing country. Since methane (CH₄), a potent greenhouse gas (GHG), emission from the rice cultivation accounts for 14.6% of the national anthropogenic GHG emission, developing and disseminating mitigation options are the urgent need. Alternate wetting and drying (AWD) is the irrigation technique, in which a paddy field encompasses several soil-drying phases during the growth period, thereby reducing the CH₄ emission. However, field trials of the AWD’s feasibility in Central Vietnam are limited so far. We therefore carried out a 3-year experiment in a farmer’s field both in winter–spring season and summer–autumn season. CH₄ and nitrous oxide (N₂O) emissions were compared among the three treatments of water management: continuous flooding (CF), AWD, and site-specific AWD (AWDS) that changed the degree of soil drying depending on the growth stage. The total water use including irrigation and rainfall was significantly (p < 0.05) reduced by AWD (by 15%) and AWDS (by 14%) compared to CF, but rice grain yield did not differ among the three treatments. The seasonal cumulative CH₄ emission was significantly reduced by AWD (26%) and AWDS (26%) compared to CF, whereas the seasonal cumulative N₂O emission did not differ among treatments. The resultant global warming potentials (GWPs) of CH₄ and N₂O under AWD and AWDS were 26% and 29% smaller than that under CF, respectively. The GWP of N₂O was only 0.8% of the total GWP of CH₄ + N₂O. The yield-scaled GWP and water productivity (i.e., the ratio of grain yield to water use) were also improved by AWD and AWDS. No significant differences in the measured items between AWD and AWDS were attributed to similar variation patterns in the surface water level. The results confirm the AWD’s performance as a mitigation option for paddy GHG emission in Central Vietnam.

Cassava is a valuable export commodity crop that is often attacked by pests, causing economic losses for this crop. The papaya mealybug Paracoccus marginatus has become a major pest of cassava in Vietnam. The parasitoid wasp Acerophagus papayae has been demonstrated to be the most efficient parasitoid wasp for controlling P. marginatus in many regions. We observed the occurrence of A. papayae in Vietnam, studied the biological characteristics of A. papayae, and investigated its parasitic activity on P. marginatus. The results showed that A. papayae occurred more frequently than Anagyrus loecki, another known parasitoid of P. marginatus. The lifespan of A. papayae was approximately 16 days. In the absence of hosts, a 50% honey solution was an essential diet to increase the longevity of both female and male of A. papayae. The second instar of P. marginatus was a suitable host stage for parasitism by A. papayae. Female A. papayae laid approximately 60.8 eggs within 17 days, mostly during the first 6 to 7 days. These findings suggest that A. papayae has the potential to control P. marginatus, and could inform the development of more effective pest management strategies for cassava crops in Vietnam and other regions affected by this pest.