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On mango, symptoms are black and raised leaf spots with an angular shape (Pitkethley, 2006) and sometimes a chlorotic halo (Pruvost et al., 2011b). Several months after infection, leaf lesions dry and turn light brown or ash grey. Severe leaf infection may result in abscission. Black and cracked twig and stem lesions can appear (Pitkethley, 2006) which act as sources of inoculum and weaken the branches. On the fruit, symptoms are seen as small, water-soaked spots on the lenticels which later become star-shaped, erumpent and exude an infectious gum (Pruvost et al., 2011b). Often, a 'tear stain' infection pattern is observed on the fruit. Severe fruit infections will cause premature fruit drop. According to Ah-You et al. (2007), mango leaves inoculated with pathovars mangiferaeindicae sensu stricto (group I) and anacardii (group II) exhibited lesions with different morphologies. Group I strains produced black, raised lesions on mango leaves, whereas group II strains produced brownish, flat lesions. Group I was able to infect both mango and cashew, while group II multiplied markedly in cashew leaf tissue, but did not cause significant disease in mango (Ah-You et al., 2007; Pruvost et al., 2011c).
Symptoms on cashew in the field were described by Viana et al. (2007) as angular, water-soaked, dark-to-black spots on the leaf and at the mid-rib vein surrounding the leaf veins. In young, green fruits, symptoms were large, dark, oily spots surrounded by conspicuous water-soaked areas. Ah-You et al. (2007) described group III strains as producing a unique syndrome on ambarella (Spondias dulcis) and mombin (S. mombin) and termed them pv. spondiae.
In mango, bacteria may be present epiphytically on juvenile tissue without visible symptoms (Pitkethley, 2006; Pruvost et al., 2009). Bacteria then gain access through stomata or wounds where they become endophytic and eventually cause disease (Pruvost et al., 2009). Liu et al. (2009) measured an average latent period of 6 days after artificial infection, however this differed with susceptibility of the cultivar.
Regular scouting means control can be started before disease levels become too high. Use disease-free planting stock; prune to remove infected branches (sources of inoculum) and to improve aeration within the tree; practice hygiene such as sterilization of pruning and harvesting implements; provide windbreaks to minimize wind damage (creation of infection sites) and the spread of the bacterium by wind; use resistant cultivars where possible (Pitkethley, 2006). Control weeds; epiphytic populations of X. campestris pv. mangiferaeindicae were found on 18 of 36 weeds common in and around mango orchards (Kishun and Chand, 1994). Where possible, cultivate varieties with some resistance. In China, bronze leaf cultivars were more resistant to this disease than pale-green or dark-green leaf cultivars (Liu et al., 2009).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
Several commercial cultivars of mango are very susceptible, and losses can be serious if environmental conditions are favourable (Willis, 2009; Pruvost et al., 2011a). On susceptible mango cultivars, namely Keitt, Kent and Tommy Atkins, trees may be weakened through loss of foliage, which eventually leads to lower yields (Kotzé and Visser, 1997).