The Real Risks Behind Herbicide-Tolerant Rice (and How to Manage Them)

Herbicide-tolerant rice varieties represent a transformative technology for weed management in direct-seeded rice, offering real efficiency and yield benefits. They give farmers greater flexibility in weed control, reduce the risk of crop phytotoxicity, and enable effective management of problematic weeds, including weedy rice. HT varieties also let farmers replace older, less efficient herbicides with newer formulations that have better environmental profiles, while lowering the labour costs associated with manual weeding and herbicide application. CR Dhan 807, grown under direct-seeded conditions, can reduce the cost of cultivation by 30% in normal rainfall years — a substantial enough gain that the technology's risks deserve serious, rather than dismissive, attention.

It is worth being precise about what 'non-GM' does and doesn't guarantee here, since it is easy to conflate the two. Being non-GM — bred through induced mutation and conventional backcrossing rather than genetic engineering — is what let India's HT rice varieties clear regulatory and political hurdles that a transgenic crop would face. It has no bearing on the ecological risks covered below: gene flow, volunteer rice and herbicide resistance arise from the herbicide-tolerance trait itself and how the herbicide is used in the field, regardless of whether that trait was introduced by mutagenesis or by inserting a foreign gene. A non-GM HT variety is not, on that basis alone, a lower-risk one.

One of the most significant concerns is the risk of gene flow from HT rice to wild or weedy rice populations, which can create herbicide-resistant weedy rice and worsen weed management challenges rather than solve them. This risk is not uniform across geographies — in tropical regions where multiple rice crops are grown annually, such as Malaysia, the risk of gene flow and introgression of resistance traits is particularly high, since more cropping cycles mean more opportunities for cross-pollination between cultivated HT rice and nearby weedy relatives.

Malaysia's own experience is instructive here. The Malaysian Agricultural Research and Development Institute (MARDI), working with BASF, released two IMI-tolerant rice varieties — MR220CL1 and MR220CL2 — in 2010, showing 98.5% and 92.5% genetic similarity to their local parent variety MR220 respectively, and yield potential up to 9,700 kg/ha. Widely adopted specifically because weedy rice threatened production sustainability there, these varieties are also the clearest real-world illustration of how gene flow risk and continuous cropping intersect.

HT rice varieties can also give rise to volunteer plants in subsequent cropping seasons — seeds or plant material from an HT crop that persist and re-emerge, complicating crop rotation and weed management strategies in the following season. Separately, and more seriously, continuous reliance on a single herbicide mode of action has already led to the evolution of resistance in several weed species — the same resistance dynamic that made older herbicides less useful in the first place, now repeating itself with newer ones. The continuous and inappropriate use of Imidazolinone (IMI) herbicides such as OnDuty™ has led to the emergence of IMI-resistant weedy rice in Malaysia — a clear, already-observed warning sign for any HT system relying on one class of herbicide. It is a genuinely double-edged outcome: HT varieties give farmers new options for managing weeds that conventional herbicides can no longer control, while simultaneously creating the conditions for the next generation of resistant weeds if used carelessly.

Herbicide drift to neighbouring fields, and carryover effects on rotational crops, pose additional challenges — particularly for herbicides with high residual activity, which can damage sensitive crops planted afterward in the same field. Addressing all three risk categories points to the same set of solutions. Integrated weed management — combining HT varieties with cultural, mechanical, and chemical weed control methods — reduces reliance on any single herbicide and delays resistance. Continuous monitoring of weed populations helps detect emerging resistance early, before it spreads across a region the way IMI-resistant weedy rice has. Regulatory frameworks need to be established specifically to ensure responsible use of HT technologies, rather than leaving application rates and timing entirely to individual farmer discretion. And farmer education and training on the proper use of HT varieties and herbicides is essential to minimizing drift, carryover and misuse in the field.

Ongoing research into new HT varieties carrying multiple herbicide-tolerance traits, alongside continued exploration of alternative weed-management solutions, is also recommended — so that no single mode of action ever again carries the entire weed-control burden for a system as widely planted as Indian rice.

One reasonable read on India's own exposure: because most of India's rice area still grows a single crop per year rather than the multiple annual cycles common in Malaysia, the baseline risk of gene flow between HT rice and weedy relatives is likely lower nationally than in the geographies where IMI-resistant weedy rice has already emerged. That said, the risk is not uniform within India either — states and belts that support two or even three rice crops a year, and that also carry meaningful DSR area, are the ones where continuous cropping and HT rice adoption could realistically overlap. That is precisely why the monitoring and regulatory safeguards described above matter most in exactly the states already leading on DSR and HT variety adoption, rather than being treated as a generic, uniform national policy applied identically everywhere.