Want to know why citrus scale insects are so rampant in Youxi County? Click to view the prevention and control technology
Zhan Shengwei
Funds: Fundamental Research Project of Fujian Provincial Public Welfare Research Institutes (2020R1024004)
The planting area and yield of citrus in Youxi County, Sanming City, Fujian Province are about 5 224.8 hm 2 and 94,000 t, accounting for 85.5% and 89.2% of the total number of fruit trees in the county, respectively. However, in recent years, the occurrence of scale insects has become more and more serious, which not only causes the leaf loss, flower drop, fruit drop and plant growth weakening of citrus trees, but also secretes honeydew to induce soot disease and aggravate the harm, which directly or indirectly affects the quality, yield and economic value of citrus. Citrus scale insects like shade and dampness, and often cluster in the leaves, shoots, shoots and fruits of citrus trees, and are not easy to be identified and controlled because the back of the insect body is covered with thick wax powder or wax shell. To this end, this study took the planting bases of five townships and towns, including Guanqian Town, the main citrus producing area in Youxi County, as observation points to investigate the occurrence dynamics and types of scale insects, and introduced the comprehensive control technology of scale insects, so as to help the green and sustainable development of the local citrus industry.
1 Survey location and methodology
1.1 Survey Locations
The experimental survey site was the citrus planting base of five townships and towns, including Guanqian Town, Baziqiao Township, Yangzhong Town, Banmian Town and Union Town, the main citrus producing areas of Youxi County, and the local main cultivars were selected as the survey objects, among which Guanqian Town and Baziqiao Township were kumquat, Yangzhong Town was Ou Mandarin, Banmian Town was Lu Mandarin, and United Town was Navel Orange, and the area of each citrus planting base was more than 6.67 hm 2, the age of the trees was 6~10 years, and the fertilizer and water and diseases and insects were managed normally.
1.2 Survey Methodology
From March 2021 ~ February 2022, 10 citrus plants were randomly selected from each base by checkerboard sampling method, each plant was taken in 5 directions of east, west, south, north and middle, and 1 branch tip of 30~40 cm was randomly selected in each direction, and the total number of scale insects on the branches was recorded, and the field dynamics of scale insects were counted once on the 1st of each month. During the investigation, the relevant citrus scale insects were collected and sent to the Institute of Plant Protection of Fujian Academy of Agricultural Sciences for classification and identification, and the female adults with the most significant morphological characteristics were mainly classified as specimens, and their species were identified under stereo microscope with reference to "Fujian Entomology" and "Citrus Diseases and Insect Pests Quick Diagnosis and Treatment".
2 Findings and analysis
2.1 Field dynamics of citrus scale insects
The dynamic change of citrus scale insects in the field in the main citrus producing areas of Youxi County was relatively large. In March 2021, the number of scale insects remained at a low level, then began to rise gradually, and remained low in April, after April, the number of scale insects at 50 shoots per base began to rise sharply, peaking at 330 in May, in early June, the number of scale insects decreased but remained high, in June and July, the number of scale insects decreased sharply, reached a trough in August, and gradually recovered, and after September, the number of scale insects increased rapidly, reaching a peak of 174 in October Since then, it has continued to decline and remained at a low level until January and February 2022 (Figure 1).
Figure 1 Field dynamics of citrus scale insects
2.2 Citrus scale insect species
通过对尤溪县柑橘主产区的介壳虫调查，结合体视显微镜下观察和文献比对，初步鉴定为矢尖蚧 Unaspis yanonensis、褐圆蚧 Chrysomphalusaonidum、橘臀纹粉蚧 Planococcus citri、长尾粉蚧 Pseudococcus adonidum、日本龟蜡蚧 Ceroplastesjaponica、 角 蜡 蚧 Ceroplastes ceriferus 和 吹 绵 蚧Icerya purchasi。 7 种柑橘介壳虫形态特征如下：
Sagittal scale, female adult body length 2.8~3.5 mm, width 1.4~1.9 mm, anterior point, posterior end wide, with a significant longitudinal ridge line in the middle, the whole flattened, resembling the tail of an arrow, the body is brownish-red or orange-yellow, the length of the thorax accounts for about 1/3 of the body length, and is clearly divided into 3 segments.
Brown round scale, female adult diameter 1.0~2.0 mm, the shell is round, flat, the middle is raised, thick and hard, brown, the molting shell point is located in the center, it is umbilicus, orange or reddish-brown, the body is pear-shaped, the cephalothorax is the widest, there is a spiny protrusion on each side of the thorax, and there are 3 pairs of hip angles on the edge of the hip plate.
Adult orange rump mealybug, female adult body length 3.0~4.0 mm, width 2.0~2.5 mm, oblong or broadly ovate, pink or yellow-green, covered by white powdery wax on the outside of the body, segmentation is obvious, body margin has 18 pairs of white wax filaments, the last pair is the largest.
The adult female is 2.5~3.5 mm long and 1.5~2.0 mm wide, oblong in shape, yellowish-brown in body, covered with white wax powder, with 17 pairs of white wax filaments, and 2 wax filaments at the tail end almost the same length as the worm body.
The adult female shell is 3.0~4.0 mm long and 2.0~4.0 mm wide, the wet wax shell is very thick, white or gray in vitro, the wax shell is round or oval, the back of the shell is up, the helmet-shaped bulge is up, and the surface is concave to divide the back into tortoiseshell-like plates.
Ceratoceleus wax scale, female adult body length 4.0~5.0 mm, width 3.0~4.0 mm, oblong or oval, the outside of the body is covered with a white wax shell, the middle dorsal is almost hemispherical, and the tail end protrudes a short horn process.
The adult female has a body length of 4.0~7.0 mm and a width of 3.5~4.6 mm, which is broadly oval or oblong-oval; the body is orange-red or dark red, with short black hairs on the surface, and white wax powder and flocculent on the back and bulging upward.
3 Summary and discussion
Citrus scale insect species in Youxi County include Sagittal Scale, Brown Round Scale, Orange Hip Mealybug, Long-tailed Mealybug, Japanese Turtle Wax Scale, Horned Wax Scale, and Blowing Cotton Scale. The overall number of this kind of pest in March and April 2021 is not high, and it is in the rising development stage, mainly because the temperature has just risen in this period, the insect has just recovered from the overwintering state, and has not yet begun to carry out a large number of activities and lay eggs; the number of scale insects in April and June reaches the highest level of the year, which is the first peak period of the insect, mainly because the environmental temperature and humidity are suitable in this period, and the population of the insect is harmful to new shoots, young leaves and young fruits, and the population surges; after June, the number of scale insects begins to decline, and in July and August The month remained at a low level, mainly because the weather was gradually hot during this period, the growth and reproduction of the insect were inhibited, coupled with the control of natural enemies, the number of scale insects decreased rapidly, which was the decline period of the insect population; the temperature dropped from August to September, and the number of scale insects gradually rebounded, and entered the development stage again; from September to November, the number of scale insects began to rise to a higher level, which was the second peak period of the insects, mainly because the temperature in this period dropped to a suitable range, and the citrus autumn shoot extraction was also conducive to the reproduction of the insects, but the peak was lower than the first After November, the number of scale insects began to decline again, and remained at a low level in January and February 2022, mainly because the temperature dropped significantly during this period, which was not conducive to the expansion of scale insects, and the insects gradually entered the overwintering state. Therefore, strengthening monitoring, grasping the insect situation, and strengthening the prevention and control of citrus scale insect populations in the rising and developing stages are the keys to effectively suppress their field populations.
4. Comprehensive prevention and control technology
The prevention and control of citrus scale insects should be based on the principle of "prevention first, comprehensive control", and comprehensive use of agricultural, physical, biological and chemical prevention and control measures to achieve green and sustainable control of such pests and improve the quality, yield and economic value of citrus.
4.1 Agricultural control
Agricultural control is the basis of citrus scale insect control, through agricultural measures to improve the quality of citrus growth environment, enhance the plant's own insect resistance, increase the number of natural enemies in citrus orchards, can fundamentally curb the occurrence and damage of scale insects. First of all, reasonable dense planting, 50~60 plants per 667 m 2 is appropriate, combined with pruning to remove insect branches in time, improve the permeability of citrus orchards and canopy, not only conducive to the growth of citrus plants, but also reduce the source of insects; In addition, timely clearing of the garden in winter can effectively reduce the source of overwintering insects and reduce the occurrence base of scale insects in the following year.
4.2 Physical control
Physical control is a direct and effective means of pest control, which can not only monitor the occurrence dynamics of scale insects, but also effectively reduce the number of insect populations, so as to achieve simultaneous monitoring and prevention and control. Before the scale insects recover from overwintering in spring, wrap the yellow sticky worm tape around the base of the citrus trunk and change the tape regularly, which can not only stick to the young nymphs of the scale insects, understand the dynamics of this type of pests, but also treat other pests and play a good blocking role.
4.3 Biological control
Biological control is a safe, effective and long-lasting pest control method, which can significantly reduce the application of chemical pesticides, maintain the ecological balance of citrus orchards, and help to achieve a virtuous cycle of ecological regulation of scale insects, which plays a vital role in the green and sustainable control process of crop diseases and pests. When the number of scale insects in citrus orchards is still low, the population of scale insects can be effectively controlled by releasing natural enemy insects such as Ladybug seven-star Ladybug, Ladybug heterochromia and Sagittal Aphid wasp and applying biological pesticides such as Beauveria bassiana, Metarhizium aeruginosa and mineral oil.
4.4 Chemical control
Chemical control is still an important and effective means of controlling pests and diseases, green and sustainable pest control measures are not the use of chemical pesticides, the key is how to use them scientifically and rationally, strictly control the prohibition and restriction of chemical pesticides, pay attention to the application of high-efficiency and low-risk chemical pesticides, strictly control the interval between safe use of pesticides, and pay attention to the rotation and alternating use with biological pesticides to delay the emergence of scale insect resistance. When the use of agricultural, physical and biological measures still cannot control the citrus scale insect below the economic threshold, it is recommended to use 100 g/L pyridyl ether EC 1 250~1 750 times and 22.4% spirofen ethyl ester suspension 3 500~4 500 times spray for 1~2 times, which can quickly reduce the population of scale insects.