Standard GB 9194-88 for the Control of Tea Geometrid
This standard applies to the control of the tea geometrid (Boarmia obliqua hypulina Wehrli) in mature plucking tea gardens.
1 Terms and definitions
1.1 Control threshold The pest population density at which, under the specified optimal control period, the incremental economic loss equals the incremental cost of preventing that loss.
1.2 Infestation center Larvae hatched from the same egg mass gather on the same plucking surface to cause damage. One aggregation point constitutes one infestation center.
2 Control threshold
2.1 Optimal control period Based on the characteristics of young larvae, namely low leaf consumption and strong aggregation, the late peak stage of second-instar larvae is determined as the optimal control period, that is, when second-instar larvae account for
60% of the total.
2.2 Control population density When tea geometrid larvae cause damage in mature plucking tea gardens and the population density reaches 4500 larvae per mu or 10 larvae per meter of tea row, the tea garden should be sprayed for control.
3 Investigation of population density
3.1 Investigation time
3.1.1 The occurrence period of each generation of tea geometrid larvae.
3.1.2 On sunny days, before 10 a.m.; on cloudy days, at any time of the day.
3.2 Investigation method
3.2.1 For tea gardens with high population density where infestation centers cannot be distinguished, sample along parallel lines, taking 20-40 points per mu according to tea rows, taking 1 m of tea row at each point, checking the number of larvae at each point, and using formula (1) to calculate the population density per mu.
d＝444.4a/b……………………………………………………
(1) Where: d -- population density per mu, larvae;
a -- total number of larvae investigated, larvae;
b -- length of tea row investigated, m;
444.4 -- the row spacing of tea rows in a general tea garden is 1.50 m, equivalent to a tea row length of 444.4 m per mu of tea garden area.
3.2.2 For tea gardens with clearly defined infestation centers, the infestation centers and larval numbers may be investigated. Within the investigated tea garden area, first conduct a general survey of the number of infestation centers in the whole garden and mark them, then randomly sample 10%-20% of the infestation centers for larval counts, and use formulas (2) and (3) to calculate the population density per mu.
n＝n0/p0………………………………………………………
（2）d＝Pn/S………………………………………………………
(3) Where: n -- average number of larvae per infestation center, larvae;
n0 -- total number of larvae in the sampled infestation centers, larvae;
p0 -- number of sampled infestation centers, pieces;
d -- population density per mu, larvae;
P -- number of infestation centers in the whole garden, pieces;
S -- total garden area, mu.
4 Control efficacy
For tea gardens that reach the control threshold, during the optimal control period, select pesticides with high efficacy, low toxicity and low residue, and on the premise of ensuring spray quality, investigate 3 days after spraying; the control efficacy should reach 95% or more.
Appendix A
Correction of the control threshold population density
(Supplementary provision)
Since there are many species of natural enemies of the tea geometrid, such as Apanteles sp., Oxyopes sertatus L., nuclear polyhedrosis virus, parasitic fungi, etc., all of which have a relatively strong inhibitory effect on the occurrence of the tea geometrid. Therefore, when applying the control threshold, the following formula may be used to correct the control threshold population density:
I＇＝I/（1-P）
Where: I -- originally determined control threshold population density, larvae/mu;
I' -- corrected control threshold population density, larvae/mu;
P -- predation and parasitism rate of natural enemies, %.