340 G. McCOLLUM AND E. BALDWIN
by severe pruning combined with foliar nutritional sprays could be an
alternative to tree removal due to HLB. Data was only presented for
a single year following treatment, and yield data were not reported,
making it impossible to conclude whether the treatments were of any
economic significance. In contrast, Lopes et al. (2007) reported that
pruning had no effectiveness on control of HLB. Gottwald et al. (2012)
saw no significant effects of several nutritional treatments, typical of
grower practice, on productivity or health of HLB-affected “Valencia”
oranges and according to Bove (2014), nutritional treatments offered no ́
benefit in Brazil.
Stansly et al. (2014) recorded highest yields from 10-year-old “Valen-
cia” on “Swingle” that had received both the Boyd cocktail and vector
control, in four sequential cropping seasons. Production for these trees
in the fourth year was close to the pre-HLB regional average for similar
trees. Nevertheless, at the time the study was reported, the extra revenue
generated from the combined insecticide and nutritional treatments did
not cover the added treatment costs. In fact, increasing the inputs on
declining groves likely results in greater losses than would have oth-
erwise been realized. If production costs exceed returns, orchards are
economically, if not physiologically, no longer viable.
Unlike the inconsistent effects of ENPs on citrus health and produc-
tivity, the data have shown consistently that nutritional treatments have
absolutely no effect on CLas titer in an infected tree or on the rate of
spread of the pathogen at the tree or orchard scale (Rouse et al. 2010,
2012; Gottwald et al. 2012; Rouse 2013; Shen et al. 2013; Stansly et al.
2014). In trees receiving ENPs, incidence of CLas infection rose from
30% at the time of first detection to 95% in only 18 months (Shen et al.
2013; Stansly et al. 2014). There were no differences in the incidence
of infection among any of the treatments which included ENP, insec-
ticide application, combination of ENP and insecticide, and untreated
controls (Stansly et al. 2014). In this study, 100% of the trees tested
were HLB-positive, despite the fact that the ACP populations were con-
sistently lower on insecticide-treated trees than on trees not treated
with insecticide over the entire 4-year period. These results suggest
that insecticide and nutrient applications could not slow the spread of
HLB once the trees were infected by CLas (Chiyaka et al. 2012). Taken
together, these results bring doubt on the value of continued insecticide
applications following a high level of CLas infection.
- Effects of pH and Carbonates.Some evidence indicates that trees
affected by HLB are especially sensitive to carbonates (Graham et al.
2014). High carbonates are associated with high pH irrigation water