By Jawwad Qureshi
The Asian citrus psyllid (ACP, Figure 1) is the vector of huanglongbing (HLB) disease associated with the phloem-limited bacterium Candidatus Liberibacter asiaticus. Infected trees start to decline and produce poor-quality fruit, which drops prematurely. Consequently, citrus production has decreased dramatically since the advent of HLB in Florida in 2005. There is no cure for the disease yet. Several strategies, including high-density plantings, are being tested to increase profits in the early years of tree production. There are several unknowns for this concept, including a lack of knowledge on the response of the ACP, natural enemies and pest management in high-density citrus plantings.
The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) conducted experiments to investigate the influence of different planting densities on ACP populations and natural enemies. The experiments were conducted at the Southwest Florida Research and Education Center (SWFREC) on four-year-old Valencia sweet orange trees budded on US-897 rootstock. Six planting densities were investigated at 447, 512, 598, 717, 745 and 897 trees per hectare.
Researchers assessed the incidence of ACP, natural enemies and biotic mortality in ACP populations. There were 54% to 56% more shoots in the planting density of 897 trees per hectare than 447 trees per hectare. The shoot infestation with ACP immatures increased by 6% to 9% with the increase in planting density from 447 trees to 897 trees. There was a positive relationship between the increase in shoot density and infestation rate. However, the effect of high-density plantings on adult ACP was not as consistent as seen with the infestation rate in shoots.
Natural enemies, including lacewings, ladybeetles and spiders, were abundant in all planting densities and showed significant potential in reducing ACP populations. There were no significant differences in the reduction of ACP immatures in developing colonies exposed to natural enemies in different planting densities, which averaged 49% to 99% between five cohorts initiated from eggs or nymphs of ACP at different times of the year. Data is presented from cohorts initiated from eggs or nymphs in June 2022 in Figure 2. Researchers also tested the effects of insecticidal sprays on ACP and natural enemies in different planting densities and found similar levels of their suppression across planting densities.
Jawwad Qureshi is an associate professor at the UF/IFAS SWFREC in Immokalee.
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