Search

Mungbean has potential for expansion as an opportunity crop planted on residual soil water after flood on active floodplains in Cambodia. However, mungbean production is severely affected by insect pests and excessive application of chemical insecticides has led to increased losses from secondary pests such as bean flower thrips (Megalurothrips usitatus Bagnall). In an exploratory study, we evaluated the effectiveness of blue and yellow sticky traps as part of an integrated management strategy to control bean flower thrips in mungbean at three locations in Battambang province in the early dry season 2021. The sites were situated in three different agro-ecological systems: semi-urban (Sala Balat); lowland rice (Os Tuk); and intensive mungbean (Preaek Trab). Blue sticky traps, impregnated with thrip pheromone, were six-times more effective than yellow traps for capturing thrips. Thrip numbers varied between sites but increased in a linear fashion between 15 and 35 days after sowing at Preak Trab which has a history of intensive insecticide use in mungbean. A concern with blue traps was that they were more effective than yellow traps for capturing beneficial ground beetles, rove beetles and hoverflies. Therefore, further study is required to determine potential adverse impacts of deployment of blue sticky traps. This study confirmed the potential value for blue sticky traps to monitor and potentially control bean flower thrips in mungbean in North-West Cambodia. We also put forward a range of Integrated Pest Management (IPM) options to manage bean flower thrips in mungbean and the challenge is to find a way to have them adopted. Transfer of technical information in this community is primarily through the village network, especially for information on fertilisers and pesticides. The key to an effective strategy is to engage the key influencers on insect pest management to facilitate adoption of IPM in mungbean. [ABSTRACT FROM AUTHOR]

Cambodia has experienced a rapid shift from transplanted to hand broadcast seeded rice, with a consequent increase in seeding rates from 25-30 to 100-200 kg ha−1. To reduce costs, farmers keep their own seed for sowing with the risk of greater weed seed contamination of the sowing seed. A survey of weed seed contamination in harvested rice paddy was conducted in two provinces of Cambodia (Battambang and Takeo) at the end of the wet season in 2016. Farmers were interviewed about rice-seeding practices, and a total of 110 farmers' fresh paddy samples were inspected for weed seed contamination from the two provinces. Sowing seed samples collected from 28 seed producer lots and 71 samples of farmer-kept seed were also analysed for weed seed contamination. In both provinces, the majority of farmers kept their own seed or bought seed from a neighbour. Farm-kept seed for sowing accounted for 88% of sown seed in Battambang and 89% in Takeo. Seeds of 41 different weed species from 13 plant families were found in the farmers' freshly harvested paddy samples. Overall, farmers managed to reduce the number of weed propagules by 60% and seed producers by 95%. There was no significant difference between farmer-kept seed and seed producer/seed company seed for the total number of weed seeds present. When shown photos, farmers' rankings of the 10 most common weed species found in freshly harvested paddy did not closely correspond to the actual weed seed frequency in the paddy. When farmers were asked to rank the frequency of weeds in their fields without the option to choose from a list, they ranked the weeds differently. Farmers ranked Ischaemum rugosum, Echinochloa spp. and Fimbristylis miliacea as the three most frequent weed species in their fields. The most frequent weeds in harvested paddy, apart from weedy rice, were I. rugosum and Melochia corchorifolia. Farmers did not rank M. corchorifolia as a frequently occurring weed, and most farmers could not recognise M. corchorifolia from photographs. The priority for improved seed hygiene is to place the emphasis on assisting farmers to further improve their seed purification techniques and to caution them to inspect seed before purchasing from neighbours, seed producers and seed companies in the absence of the implementation of seed certification regulation. [ABSTRACT FROM AUTHOR]

Two-hundred rice farming households from eight lowland rice villages in North-West Cambodia were surveyed in 2020 to determine changes in farmers' knowledge, weed management practices and weed seed contamination in seed kept for sowing. The major yield constraints cited by farmers were lack of water, inability to manage water and competition by weeds. Water shortages result in reduced crop establishment, non-optimal herbicide application timing and poor weed control. Reduced tillage, drill planting and use of pre-emergence herbicides can improve weed management. The adoption of drill planting improves crop establishment and enables the use of pre-emergence herbicides. Possible reasons for changes in weed problems include the change to a two-crop rice system in the wet season and spread of seeds by harvesting machines. The main weed seed contaminants of rice seed kept for sowing were Echinochloa crus-galli, E. colona, Fimbristylis miliacea, Ischaemum rugosum and Melochia corchorifolia. F. miliacea was the only species effectively removed by village cleaning methods. Although prevalent in rice fields, Cyperus. iria with <0.2 seeds per 500 g and Leptochloa chinensis with nil contamination were insignificant contaminants of seed samples. The majority of farmers in the study area are relying on repeated use of a narrow range of post-emergence herbicides, thus leading to increased severity of weed problems in dry direct-seeded rice. Integrated weed management is required to reduce over-reliance on post-emergence herbicides. This will require engagement with the local input supply network to introduce advice on improved weed management and sustainable herbicide use. [ABSTRACT FROM AUTHOR]

The objective of this work was to determine the value of improved establishment methods and herbicide applications as alternatives to high seeding rates to improve weed suppression in rice. Field experiments were carried out in 2010 and 2011 to determine optimal seeding rates and seeding methods with and without weed competition in wet-seeded rice. Under wet seeding conditions, drum seeding at 80 kg ha−1 was the most profitable treatment for both weed-free and unweeded rice. Although pre-emergence herbicides are beginning to be adopted in wet-seeded rice, they are seldom used in dry direct-seeded rice in Cambodia. Experiments were carried out in 2018 and 2019 to test crop tolerance and the efficacy of butachlor, oxadiazon, pendimethalin and pretilachlor applied post-sowing and pre-emergence to dry direct-seeded rice. Oxadiazon and butachlor, with the option for a post-emergence herbicide, provided effective weed control and a high grain yield in dry direct-seeded rice. Pretilachlor did not effectively control weeds under dry seeding conditions. Although pendimethalin exhibited good weed control, crop damage was a risk in poorly prepared seedbeds which typify Cambodian rice systems. With an effective integrated weed management strategy, it might be possible to safely reduce seeding rates below 80 kg ha−1 using drum or drill seeding machines. [ABSTRACT FROM AUTHOR]