How to prevent and control arrowhead scale damage to young fruit when growing citrus

The citrus arrowhead scale is currently one of the main pests in citrus orchards in eastern Guangdong and northern Guangdong, with more than 50% of the orchard area in these regions affected to varying degrees, impacting production. The author conducted systematic fixed-point, regular observations of the occurrence of the citrus arrowhead scale, and carried out large-scale control trials and demonstrations, achieving good results, for the reference of farmer friends.

Occurrence patterns

1. The citrus arrowhead scale shows a central distribution in citrus orchards, often beginning on one or more vigorous and shaded citrus trees. It then spreads and expands to the surrounding area until it covers the entire orchard; on hillsides it shows an extension from central points to patches, and generally large-scale disasters are relatively rare; when the tree canopy is completely closed, the pest population density is high and damage is severe; trees with weak vigor and poor management also suffer severe damage. For a given orchard, the pest population density is high on the central trees and damage is severe, while the pest population density is low at the surrounding edges and damage is light; young trees have low pest population density and light damage. Short-distance spread of the citrus arrowhead scale occurs mainly through adjacent contact of branches and leaves, carrying by people entering and leaving, and wind dispersal; long-distance spread occurs mainly through the introduction of seedlings and branches and the transport of fruit.

2. The citrus arrowhead scale can produce three generations per year in eastern Guangdong and northern Guangdong. The first-generation young scales appear in early May, with the peak occurrence period in mid-to-late May; the second-generation young scales appear in mid-July, with the peak occurrence period in late July; the third-generation young scales appear in mid-September, with the peak occurrence period in early October. Because the arrowhead scale generations overlap, in this region the first sighting date of the first-generation embryonic eye spot is around April 21, and the first sighting date of young scales on leaves is in early May, 13-14 days apart. The beginning of the peak period is May 12-16, the peak period is May 18-21, and the final period is May 25-26; the interval between the first sighting date of young scales and the peak period is 14-17 days. The first-generation young scales mainly parasitize old leaves, and in severe cases a small number damage new leaves and young fruit; the second-generation young scales move to new leaves or some young fruit to cause damage; the third generation mainly damages fruit, with a small number remaining on new leaves.

Control strategies

Based on the occurrence patterns of the arrowhead scale and combined with local conditions, a scientific control strategy was formulated, namely taking agricultural control as the foundation, chemical control as the focus, generally treating the overwintering generation, vigorously treating the first generation, and selectively treating the second and third generations; at the same time, attention should be paid to grasping the three key technical aspects of the appropriate control timing, correct application methods, and suitable chemical pesticides, so as to achieve the ideal control effect.

1. Appropriate control timing: during the young scale stage, because the waxy covering has not yet formed and resistance is weak, the pesticide solution can easily penetrate the insect body, making this the appropriate control period for each generation. This is especially true for the relatively concentrated and uniform first-generation young scales; application during the peak occurrence period in mid-to-late May can achieve twice the result with half the effort.

2. Application methods: first, before applying pesticides, agricultural control should be strengthened, citrus orchard management should be improved, and on the basis of cultivating vigorous tree vigor and enhancing tree resistance, winter and spring pruning should be emphasized. The focus of pruning is dead branches and withered leaves, and internal canopy branches, drooping branches, and shaded branches that have high pest population density and cannot bear fruit; these should be centrally disposed of to reduce pest sources and improve control effects. Second, attention should be paid to uniform and careful application. The arrowhead scale body is small, generations overlap, and tree leaves interlock. Therefore, when applying pesticides, it should be uniform and careful, and the pesticide should fully contact the insect body, with even spraying above and below the tree and inside and outside the canopy, with key areas at the base of the tree, the inner canopy, and shaded branches. When spraying for first-generation young scales, old leaves should be the main focus, with new shoots also treated in severe cases; third, the number of applications should be reasonable. For the overwintering generation, generally apply once in conjunction with pruning, and do a good job of winter and spring orchard cleaning. Apply once during the peak occurrence period of the first-generation young scales, and apply once more in severely affected orchards; for the second and third generations, selective treatment should be adopted.

3. Chemical pesticides: because the entire body of the arrowhead scale is covered with wax, general pesticides have very poor control effects, so selecting suitable chemical pesticides occupies an important position in its control. For winter and spring orchard cleaning to control adult scales, use rosin mixture at 100-150 times dilution; to control adult scales of each generation, use 40% Supracide or 48% Lorsban at 1000 times dilution, with very good results.