- HUANGLONGBING: DEVASTATING DISEASE OF CITRUS 327
HLB intensified in Florida, it became readily apparent that the disease
was widespread throughout commercial citrus production regions in
the state. By 2008, citrus orchards in all 32 commercial citrus-producing
counties in Florida had been confirmed to contain trees infected with
CLas. At the time of this writing, it is generally agreed that at least 90%
of all commercial orchards are affected by HLB, and in some orchards,
100% of the trees are affected. In a field trial, the incidence of CLas
infection increased from 30% at the beginning of the study to 95% in
only 18 months (Stansly et al. 2014) showing how fast an epidemic
can develop on an orchard scale. The pathway of long-distance CLas
spread likely involves infected psyllids migrating from citrus tree to
citrus tree as well as hitchhiking on infested ornamental plants such as
Murraya, a preferred host (Manjunath et al. 2008). AlthoughMurraya
has been shown to be a host of CLas, its role or importance in HLB epi-
demics is unknown. Based on observations of localized HLB secondary
spread, much movement is presumed to be of a series of short distances
(Gottwald 2010).
Regardless of how HLB was spread, CLas was confirmed in Louisiana
(2008), South Carolina (2009), Georgia (2009) and has also been con-
firmed in Cuba, Belize, Jamaica, Mexico, and other countries in the
Caribbean (da Grac ̧a et al. 2015). In 2012, CLas was confirmed present in
Texas (Kunta et al. 2012) and in California (CDFA press release, March
30, 2012; Kumagai et al. 2012). The initial HLB find in Texas was in
a commercial citrus orchard, but soon thereafter HLB was confirmed
in residential trees. HLB is now widespread throughout Texas citrus. In
California, the initial HLB find was a single residential tree in Los Ange-
les County. Following the initial confirmation of CLas infection in 2012,
no additional finds were made in California until July 2015. In August
2015, nine additional CLas-positive residential trees were identified in
the San Gabriel area of Los Angeles County, approximately 15 miles
north and west of the original 2012 find (CDFA 2015b). At this time,
no CLas-positive citrus trees have been confirmed in commercial citrus
orchards in California. However, ACP have been found in commercial
citrus orchards in California and the threat of CLas movement into the
orchards is significant. Although ACP have been found in Arizona, at
the time of this writing, HLB has not been found in Arizona.
In Florida, it was 7 years after the discovery of ACP that HLB was
confirmed in the state. In Texas, it was 11 years after the discovery of
ACP that HLB was confirmed.
In Brazil, it was 62 years from the appearance of ACP until HLB
was confirmed. The lengthy time for HLB to appear following ACP
in Brazil suggests that the introduction of CLas came much later than