Shoot-killing effect of oxyfluorfen on navel orange and its effect on the habitat distribution of citrus psyllid, Diaphorina citri Kuwayama

Citrus psyllid, Diaphorina citri Kuwayama, habitually lays eggs on the new tender shoots. It is an important measure to prevent citrus Huanglongbing by applying pesticides to control citrus psyllids in time after disbudding to let out shoot. In recent years, killing new tender shoots by spraying shoot-killing pesticides as an alternative of artificial disbudding has attracted the attention of fruit farmers, which has become a crucial technique for the control of citrus Huanglongbing. In this study, Newhall navel orange was used as the experimental species. Oxyfluorfen solution of different concentrations were sprayed and evaluated to explore their shoot-killing effect and their effect on the habitat distribution of citrus psyllids. Meanwhile, the grading standard of the wilted tender shoots and the method for studying the habitat distribution of psyllids were established. The results showed that oxyfluorfen had a similar shoot-killing effect on navel orange saplings and planting trees. It has a certain shoot-killing effect at the mass concentration of 10 mg/L, and the optimal mass concentration was 40-55 mg/L. It showed quick-acting properties, and it was harmless to citrus leaves and fruits at maturity. The oxyfluorfen solution at the mass concentrations of 40 and 55 mg/L were sprayed on the saplings. After 3 days, the shoot length inhibition rates were 86.1% and 124.7% respectively, and the shoot diameter inhibition rates were 83.8% and 94.8%, respectively. After 7 days, the corrected mortalities of tender shoots were 93.7% and 84.1% respectively, the corrected mortalities of psyllids were 7.8% and 21.4% respectively and the habitat inhibition rates of psyllids were 81.0% and 84.4%, respectively. When the planting tree was sprayed with the oxyfluorfen solution at the mass concentrations of 40 and 55 mg/L, after 3 days, the length inhibition rates to tender shoots were 85.9% and 118.8% respectively, and the diameter inhibition rates were 83.9% and 104.1%, respectively. After 7 days, the corrected mortalities of tender shoots were 96.6% and 82.4%, respectively. The wilting of tender shoots can cause the death of psyllid eggs and nymphs. However, it has little effect on adult mortality, but the habitat of adult will migrate. Therefore, the application of oxyfluorfen to navel orange can quickly kill tender shoots, reduce food sources of psyllids, and effectively control the population of psyllids.