**3.2 Effectiveness of delaying the latent period (LP), and of removing infectious (IP) trees, in suppressing the spread rate of HLB in an orchard**

We estimated the effectiveness of delaying the latent period (*LP*) and removing infectious (*IP*) trees in suppressing the spread rate of HLB in an orchard, compared with the default situation. The field was defined according to the default conditions above. Then, 100 virulent vector insects were distributed at the center of the *H* field. We set the model calculation period for 84 months.

First, we changed the number of time steps required to transition from *LP* to *IP* from the default (3*t*) to 6, 12 and 24*t*, respectively, in order to estimate the effects of delaying the latent period. The model estimation suggested that the spread rate of HLB in the orchard slowed as the time from *LP* to *IP* increased (Fig. 7). The theory that mean generation time has more affect on the intrinsic rate of natural increase than the reproductive rate, would account for this result. Our estimation suggested that cultivars in which the transition from *LP* to *IP* is delayed might show resistance to HLB and thus suppress the rate of disease spread.

Black dotted line, 3*t* to change from *LP* to *IP* (default parameter); red dashed line: 6*t;* green dash-dotted line: 12*t*; blue dash-dotted line: 24*t.* Black dashed line is number of initial *H* trees in the simulated field (1,681 trees). No. of newly infected trees = *LP+IP+D* (excluding initial *D* trees).

Fig. 7. Effects of delaying the transition from latent period (*LP*) to infectious period (*IP*).

Second, we estimated the effects of removing infectious (*IP*) trees. We assumed that the *IP* trees were removed at 24, 12 and 6*t*, respectively, after their status had changed from *LP*  (default: trees were removed at 45*t*, when their status changed to *D*), and we compared the spread rates of HLB. Under the no-removal scenario (default), the number of newly infected

We estimated the effectiveness of delaying the latent period (*LP*) and removing infectious (*IP*) trees in suppressing the spread rate of HLB in an orchard, compared with the default situation. The field was defined according to the default conditions above. Then, 100 virulent vector insects were distributed at the center of the *H* field. We set the model

First, we changed the number of time steps required to transition from *LP* to *IP* from the default (3*t*) to 6, 12 and 24*t*, respectively, in order to estimate the effects of delaying the latent period. The model estimation suggested that the spread rate of HLB in the orchard slowed as the time from *LP* to *IP* increased (Fig. 7). The theory that mean generation time has more affect on the intrinsic rate of natural increase than the reproductive rate, would account for this result. Our estimation suggested that cultivars in which the transition from *LP* to *IP* is delayed might show resistance to HLB and thus suppress the rate of disease

20 40 60 80

Black dotted line, 3*t* to change from *LP* to *IP* (default parameter); red dashed line: 6*t;* green dash-dotted line: 12*t*; blue dash-dotted line: 24*t.* Black dashed line is number of initial *H* trees in the simulated field

Second, we estimated the effects of removing infectious (*IP*) trees. We assumed that the *IP* trees were removed at 24, 12 and 6*t*, respectively, after their status had changed from *LP*  (default: trees were removed at 45*t*, when their status changed to *D*), and we compared the spread rates of HLB. Under the no-removal scenario (default), the number of newly infected

Fig. 7. Effects of delaying the transition from latent period (*LP*) to infectious period (*IP*).

(1,681 trees). No. of newly infected trees = *LP+IP+D* (excluding initial *D* trees).

*t*

**3.2 Effectiveness of delaying the latent period (LP), and of removing infectious (IP)** 

**trees, in suppressing the spread rate of HLB in an orchard** 

calculation period for 84 months.

No. of newly infected trees

spread.

250

500

750

1000

1250

1500

1750

2000

trees was more than 1,000 (Fig. 8). When we removed the *IP* trees 24*t* after their status change, the number of newly infected trees was almost same as under the default condition. However, when we removed the *IP* trees 9*t* after their status change, the number of newly infected trees decreased relative to the default condition. Moreover, when we removed the *IP* trees 6*t* after their status change, the number of newly infected trees barely increased. We may thus predict that the removal of infectious trees will be efficacious in preventing the spread of HLB in a field.

Black dashed line: no removal; red dashed line: removal 24*t* after infection; green dash-dotted line: 12*t*; blue dash-dotted line: 6*t.* Black dashed line is number of initial *H* trees in the simulated field (1,681 trees). No. of newly infected trees = *LP+IP+D* (excluding initial *D* trees).

Fig. 8. Effects of infectious tree (*IP*) removal in the field.
