Ludwigia octovalvis
(primrose willow)

L. octovalvis is found throughout the Tropics, from sea level to 1500 m elevation (see also Notes on Taxonomy).

L. octovalvis is found in wet places, usually associated with agriculture: most commonly in either rainfed or irrigated ricefields (see, for example, Pablico and Moody, 1987).

L. octovalvis is found in wet places, and experimental evidence confirms that it is highly tolerant of fluctuating water levels (Mohankumar and Alexander, 1989). The periderm of the plant tissues swells rapidly when immersed in water: this is probably a defence against waterlogging (Angeles, 1992). Like many rice weeds, the plant responds strongly to application of nitrogenous fertilizer (up to 100 kg/ha) by increased dry matter accumulation, which may increase problems of weed control in heavily fertilized ricefields (Gaffer, 1985; Kim and Moody, 1989).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Herbicides

Rice

Weed species of Ludwigia (primarily L. adscendens, L. hyssopifolia and L. octovalvis) that occur in rice are reported to be susceptible to the following herbicides (results reported as usually at least as good as standard twice-repeated hand-weeded controls).

Standard treatments include MCPA and 2,4-D as post-emergence treatments (Raju and Reddy, 1986). Others are quinclorac + bensulfuron or molinate + 2,4-D. More recently, pretilachlor (often in combination with other active ingredients; see, for example, Llorente and Evangelista, 1990) has emerged as an effective herbicide for use against Ludwigia spp. Good results have been observed in recent years with a range of these and other products and mixes, in varying situations as summarized below.

Post-emergence application of piperophos + propanil was reported to be very effective in direct-seeded and transplanted lowland rice in Nigeria, with oxadiazon + propanil, and fluorodifen [now superseded] + propanil also reasonable. Tank-mixed post-emergence application of thiobencarb + propanil + fenoprop [now superseded] or butachlor + propanil was effective against L. octovalvis. Pre-emergence treatments were less effective because of crop phytotoxicity or poor weed control efficacy (using pretilachlor + dimethametryn, or oxadiazon) (Imeokparia et al., 1992; Imeokparia, 1994).

Pre-emergence thiobencarb plus one hand-weeding was slightly better than butachlor plus one hand weeding in dry and wet-sown rice in Tamil Nadu, India: in these trials, post-emergence treatments were not effective in either crop - using thiobencarb + 2,4-D, butachlor + 2,4-D, fluchloralin + 2,4-D, pendimethalin + 2,4-D or piperophos + 2,4-D (Kandasamy and Palaniappan, 1990).

Other workers have studied herbicide use against other Ludwigia spp. (L. adscendens: Allard and Zoschke,1990; L. hyssopifolia: Azmi and Supaad, 1992).

Pasture

In the South Pacific region, L. octovalvis is reported as one of 14 problem bushy or woody weed species: it is susceptible to control by 2,4-D or glyphosate (Reynolds, 1978).

Biological Control

The chrysomelid beetle Altica foveicollis has been considered as a possible biocontrol agent against L. octovalvis, for example in Bangladesh (Alam and Karim, 1980). Larvae of the lepidopteran Mompha ludwigiae will feed on L. octovalvis, though these larvae primarily provide biocontrol against L. adscendens (Bradley et al., 1973).

Cultural Methods

Soil solarization, using clear polythene sheeting, has been reported to reduce the abundance of broadleaved weeds, including L. octovalvis, in Western Samoa (Ragone and Wilson, 1988).