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To clarify the effect of aerial spray on hilly citrus orchards when applying unmanned aerial vehicles (UAV) under the precision fruit tree operation mode, three types of spray adjuvants (vegetable oil adjuvant Beidatong, non-ionic surfactant adjuvant Y-20079 and silicone adjuvant 806) were studied. The results showed that comparing with the control check (CK), different types of adjuvants and different concentration of the same adjuvant have different effects on droplet density, coverage and deposition under the same operation parameter. Among them, the result of adding Beidationg with a 1.0% volume fraction was significantly superior to that of 0.5% volume fraction, which could increase the maximum droplet density, coverage and deposition amount by 42.0%, 92.3% and 33.6%, respectively; the result of adding Y-20079 with a 1.0% volume fraction was significantly superior to that of 0.5% volume fraction, which could increase the maximum droplet density, coverage and deposition amount by 101.0%, 86.5% and 36.0%, respectively; the result of adding 806 with a 0.5% volume fraction was significantly superior to that of 0.25% volume fraction, which could increase the maximum droplet density, coverage and deposition amount by 43.9%, 76.0% and 35.0%. respectively. After adding adjuvants, the penetration rate of the test solution to the upper and lower parts of the citrus canopy can be increased by 10.2%-41.5% and 4.0%-42.0% (Beidatong), 101.0% and 7.3%-78.7% (Y-20079), 10.2%-43.9% and 41.3% (806). Compared with the control check, the deposition of pesticides in the canopy projection area was reduced by 38.2%-48.5% (Beidatong), 10.1%-46.3% (Y-20079) and 42.1%-56.2% (806). Comparing with the control check, the amount of pesticide deposition in the blank area between adjacent plants incresed by the addition of Beidatong (3.7%-39.3%), Y-20079 (7.0%-50.9%), and 806 (22.3%-41.4%). The results of the research showed that when applying precise aerial spraying to mountain and citrus orchards, adding a volume fraction of 1.0% Beidatong, 1.0% Y-20079, or 0.5% 806 in the spray solution can effectively improve the application on the canopy of the hilly citrus. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]