• Pests and diseases in food crops have developed significant resistance to most commonly used pesticides in China

• Comparing with assessment on dietary/residue, health and environmental risks, the assessment approach, criteria, testing method and technical guidelines for pest resistance is comparatively underdeveloped

Last month, China NATESC (National Agricultural Technology Extension Service Center) reported the pest resistance monitoring results of 2017. 60 sites in 19 provincial areas were investigated, covering 21 patent or off-patent pesticides including chlorantraniliprole, penoxsulam, quinclorac, dinotefuran, bensulfuron, bispyribac and clodinafop-propargyl etc. The center pointed out that the main pests and diseases in food crops have developed significant resistance to the most commonly used pesticides and there is an urgent need of integrated and rotational measures and development of better system to monitor risk and assessment of pest resistance.

Rice
Planthopper has developed high level resistance to imidacloprid and thiamethoxam( over 200 fold) and extremely high resistance to buprofezin (over 1000 fold) and  high or moderate resistance to dinotefuran, mitenpyram and chlorpyrifos. NATESC suggested that uses of these insecticides should be limited to 1 time per growing season and rotational use of triflumezopyrim, sulfoxaflor, nitenpyram and dinotefuran is preferable. Planthopper often occurs with white back planthopper and the resistance to buprofezin and chlorpyrifos is moderate or high. Thus the uses of buprofezin and chlorpyrifos should be discontinued.
Stem borer demonstrates varying resistance from region to region. Some pests in places in Zhejiang, Jiangxi and Hubei have shown moderate or high resistance to chlorantraniliprole and moderate resistance to chlorpyrifos. Even though the resistance to abamectin is relatively low, NATESC discouraged the excessive use of abamectin due to its contact effect on predatory and parasitic natural enemies. Bakanae disease has developed high resistance to carbendazim and prochloraz while blast disease has become highly resistant to thiophosphate fungicides such as isoprothiolane and iprobenfos. The efficacy of tricyclazole fungicide is also decreasing. Alternates with different mechanisms are suggested, including phenamacril, fludioxonil and azoxystrobin, etc.
Most weeds have become resistance to commonly used herbicide in varying degrees. In some double-cropping area along Yangtze River, barnyard grass demonstrated high resistance to penoxsulam, quinclorac and bispyribac. Despite that rice growers have doubled the registered dosage. Sulfonylurea group has been widely used in China for over 20 years and become ineffective against cyperus rotundus and broad-leaf weeds including Monochoria vaginalis and Eleocharis yokoscensis, etc.

Wheat
Rhopalosiphum padi has varying susceptibility to different insecticides. The insect has generated low or moderate resistance to imidacloprid in Jiangsu, Anhui and Hubei but is still susceptible to other insecticides such as acetamiprid, sulfoxaflor, omethoate, pirimicarb and beta-cypermethrin, etc. 86.4% of Alopecurus japonicas have become resistant to clodinafop-propargyl, of which 68% are highly resistant and 66% of Beckmannia syzigachnehave developed resistance to the herbicide, of which 51% are highly resistant.
Fusarium Head Blight (FHB) is one of the most frequent disease in wheat. The disease developed evident resistance to carbendazim in Jiangsu and Anhui. NETESC also detected tebuconazole-resistant pathogens in Hebei, Jiangsu, Anhui, Shandong, Henan and Hubei. Growers should be judicious in their use of fungicides and alternates such as phenamacril and prochloraz are encouraged.

Risk Assessment on Pest resistance and Pesticide Registration
In China's new regulation for pesticide registration, risk assessment has been ascribed unprecedented importance and pest resistance is required for new pesticide and/or other registration categories involved with new pest targets:

• In-door Experimental Data: method for sensitivity determination on the target pest, criteria for resistance identification (sensitivity baseline), information on cross-resistance, assessment result and possible risk mitigation measures；

• In-field Monitoring: sampling method, number of sampling, storage and transport of samples, as well as testing method of pest resistance；

The assessment approach, criteria, testing method and technical guidelines are relatively less available for resistance assessment when comparing with other assessments that require a final and formal risk assessment report: dietary risk assessment of crop-use pesticide, health risk assessment on resident or professional applicators and the environmental risk of field use pesticide.