Research progress on huanglongbing management and other citrus dieases

Huanglongbing (HLB) is the most important disease in Indonesia however, most farmers keep the infected plants growing in their orchards for harvesting more although with low quality and quantity of fruits. In the infected orchards farmers usually apply some fertilizers since temporary recovery of infected plants gave some expectation of farmers to harvest some fruits in the next season. Element analysis of HLB infected citrus leaves suggested that significantly low concentration of iron and zinc was found. In the green house experiments the application of recommended full iron fertilization every 2 weeks resulted on better growth and less symptom appearance on the infected plants up to 6 months, however the symptoms were developed further after 7 months of application. The infection of Candidatus Liberibacter asiaticus (Las) was still detected at 8 months after application with clear bands of amplified DNA on the prominent symptom using standard PCR and thin bands using nested PCR were resulted on less severe symptoms. In the field citrus relative trial at the age of 2.5 year after planting we found that JC (Japanese Citron) and Siem mandarin grafted on JC with HLB symptom appearance resulted on the detection of Las on some samples, citrus tristeza virus (CTV) on the other samples and double infection of Las and CTV were also found. Another field trial on thiamethoxam application at 2 and 4 months intervals on Siem mandarin grafted on JC all plants were quite healthy and free of HLB and CTV symptom appearance 1.5 year after planting however, some psyllid and aphids population were found on all treatments. The application of 10% thiamethoxam for bark brushing with 2 months interval gave the most limited psyllid and aphid population found and promote the plant phenology growth compared to that of 4 months interval of application and the control treatment without any thiamethoxam application.