Progress 10/01/11 to 09/30/12
Outputs
Progress Report Objectives (from AD-416): Extend the productive life of citrus plantings that would otherwise fall victim to HLB and not reach economic viability via: 1) Improved management of Asian citrus psyllid and 2) Improved control and management of HLB. Approach (from AD-416): 1. Analyze data to determine if intercropping citrus with guava can be an effective method under Florida grove and nursery conditions. If successful, examine various citrus/guava interplanting densities and planting arrangements. 2. Isolate, characterize, and test guava volatiles against psyllid populations in lab and greenhouse choice tests to determine most effective repellent guava volatiles. 3. Effective guava volatile deployment methodology - volatile compounds identified as repellent to psyllids will be formulated and deployed under field conditions to determine if a similar level of repellency can be achieved by the deployment of formulated guava volatile compounds compared to interplanting citrus with guava. This research is related to inhouse objective 3: Verify if Murraya paniculata is, or is not, a preferred reservoir of huanglongbing (HLB) pathogens, whether it can be used as trap plants for the control of citrus HLB. This project was designed to examine the potential disease control of citrus HLB by interplanting citrus with guava. In Vietnam guava has been shown to be an effective deterrent to HLB, slowing the disease and keeping plantings alive for up to 15 years that normally succumb in 2-3 year. For all plots and experiments, Guava trees, (Vietnamese white cultivar) were propagated and grown to appropriate size requiring ~1 year. Both nursery and field citrus trees are assayed for HLB every 60 days, and have been assayed multiple times. Psyllid populations are also being monitored continuously every 2 weeks within interplanted plots to document any repulsion of the vector due to guava. Guava vs no guava nurseries: Two nursery sites, a guava protected citrus nursery versus an unprotected nursery, have were established with disease free, PCR-negative citrus trees (2 sweet orange and 1 grapefruit cultivars) in June 2009 and were located in the protected and unprotected plots. The guava trees were grown to appropriate size as indicated in Vietnam prior to outplanintg. To date HLB appears to be progressing more slowly in nursery plots interplanted with guava that non interplanted plots. Citrus/guava interplantings: 3 commercial plantings with multiple replications were established. This required 1 year to grow the guava transplants and a second year to become established in the field before interplanting with citrus per Vietnam protocols. One trial was established in a commercial orchard with collaborators in Southern Gardens Citrus, but two years of freezes and replanting prompted the grower/collaborator to abandon the planting. A second was established in grove in Martin county but the plantation was sold and removed before data could be collected. A third trial planting was established at the USHRL Picos Farm in Fort Pierce. The Picos plot was interplanted with citrus in August 2009. Severe frosts during 2008/2009 and again during Dec 2010 winters continue to affect the USHRL plots and have caused a delay in the experiment. To date, several HLB+ (PCR+) plants have been identified in the USHRL plots after multiple assays. The majority of these positives have occurred as the result of an edge effect. That is, treatment plots closest to an existing HLB+ planting of Valencia were affected. There continues to be no significant difference among the treatments thus far, however this data is insufficient to draw any conclusions at this point. Research using a Y-tube olfactometer to investigate guava volatiles as repellents of the psyllid has been challenging and resulted in no clear psyllid attraction or repulsion. The best response was 1-wk-old psyllids with C. macrophylla shoots, although psyllid attraction to this odor source was weak. Research with white guava (germplasm from Vietnam) did not lead to any improvement. We will continue to investigate repellency of guava alone or in combination with citrus and refined methods to achieve more sensitivity.
Impacts
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Progress 10/01/10 to 09/30/11
Outputs
Progress Report Objectives (from AD-416) Extend the productive life of citrus plantings that would otherwise fall victim to HLB and not reach economic viability via: 1) Improved management of Asian citrus psyllid and 2) Improved control and management of HLB. Approach (from AD-416) 1. Analyze data to determine if intercropping citrus with guava can be an effective method under Florida grove and nursery conditions. If successful, examine various citrus/guava interplanting densities and planting arrangements. 2. Isolate, characterize, and test guava volatiles against psyllid populations in lab and greenhouse choice tests to determine most effective repellent guava volatiles. 3. Effective guava volatile deployment methodology - volatile compounds identified as repellent to psyllids will be formulated and deployed under field conditions to determine if a similar level of repellency can be achieved by the deployment of formulated guava volatile compounds compared to interplanting citrus with guava. This project is related to inhouse objective 3: Develop or improve comprehensive integrated disease management strategies. This project was designed to examine the potential disease control of citrus huanglongbing (HLB) by interplanting citrus with guava. In Vietnam guava has been shown to be an effective deterrent to HLB, slowing the disease and keeping plantings alive for up to 15 years that normally succumb in 2-3 years. For all plots and experiments, Guava trees, (Vietnamese white cultivar) were propagated and grown to appropriate size requiring ~1 year. Both nursery and field citrus trees are assayed for HLB every 60 days, and have been assayed multiple times. Psyllid populations are monitored continuously every 2 weeks to document repulsion of the vector. For Guava vs. no guava nurseries: Two nursery sites, a guava protected citrus nursery versus an unprotected nursery, have were established with disease free, polymerase chain reaction (PCR)- negative citrus trees in June 2009 and were located in the protected and unprotected plots. The guava trees were grown to appropriate size as indicated in Vietnam prior to outplanting. To date HLB appears to be progressing slowler in nursery plots interplanted with guava than in non interplanted plots. The freezes discussed below did not adversely affect these nursery plots. For Citrus/guava interplantings: 2 commercial plantings with multiple replications were established but due to freezes and property sales these plantings are no longer viable. A third trial planting was established at the USHRL Picos Farm in Fort Pierce. The Picos plot was interplanted with citrus in August 2009. Severe frosts during 2008/2009 and again during 2009/2010 winters affected the U.S. Horticulture Research Lab plots and caused a delay in the experiment. A final hard freeze during the 2010/2011 season killed most of the guava trees. Data analysis to date indicates no differences were observed among treatments, i.e., guava interplanted vs. non-interplanted plots prior to the final demise of the plots. Our interpretation is that Florida is actually a subtropical environment, prone to intermittent freezes and cool or cold temperatures; whereas, Vietnam and Indonesia, where the guava effect seems to work, are truly tropical without such broad temperature swings. It is the new flush of guava which appears to be the best at producing Asian citrus psyllid (ACP) repellent volatiles. Cool or freezing temperatures inhibits volatile production and thus the citrus crop is left unprotected from ACP. While guava not be a viable deterrent as an intercrop, it still may be possible to identify individual volatiles from guava that might be useful under field applications as chemical applications. We are now switching direction slightly to investigate other more temperate Myrtaceous plant species that are more cold tolerant and might be useful as intercrops. Research continues using a Y-tube olfactometer to continue to investigate guava volatiles as repellents of the psyllid as well as to investigate the feasibility of other Myrtaceous plants.
Impacts
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