Investigating the Biology of False Blossom Phytoplasma and its Leafhopper Vector to Inform Integrated Pest Management Approaches for Cranberry Growers

View the project final report

Commodities

• Fruits: berries (cranberries)

Practices

• Pest Management: disease vectors, integrated pest management, prevention

Cranberry false blossom disease (CFBD) devastated the U.S. commercial cranberry industry in the 1920’s. The causal agent, cranberry false blossom phytoplasma, is vectored by the blunt-nosed leafhopper (BNLH; Limotettix vaccinii). Through combined efforts of cultivar breeding and chemical controls, CFBD and its vector were seemingly eliminated in commercial cranberry production nearly 100 years ago. In recent years however, localized occurrences of CFBD have been noted, as well as outbreaks of the BNLH vector in North America. The objective of this study is to survey the distribution and diversity of CFBD and leafhoppers in Wisconsin cranberry marshes. Field surveying for CFBD was done by visually identifying uprights displaying characteristic symptoms, including witches’ broom and floral abnormalities, which were collected from farms throughout central Wisconsin in 2022 and 2023. Uprights were dissected by plant organ type for DNA extraction, qPCR analysis, and confirmation sequencing. In symptomatic uprights, all plant organs, from roots to flowers and terminal buds, yielded positive results for the CFBD phytoplasma presence, suggesting a systemic infection. To measure the occurrence of BNLH, weekly collections were performed via sweep net over 20m transects along the bed edges and center lines from May through August, 2021-2023. The BNLH comprised 80% of the adult leafhopper population throughout the entire sampling period, with a nymphal stage lasting until late June and an adult stage ending in August. Additionally, a controlled cage feeding assay was performed to determine the degree of feeding injury done to cranberry uprights by BNLH, both the nymph and adult life stage, feeding at different densities for two weeks. We found that the amount of feeding injury was dependent on the density of BNLH at 0, 1, and 2 weeks post feeding for nymphs, but only at 0 weeks for adults. The findings of this study contribute to the understanding of this re-emerging pathogen and its vector, informing the industry of mitigation strategies for phytoplasma transmission by highlighting key phenological patterns of the vector species. Knowing that infection is systemic also suggests that removal of infected uprights requires total excision of root tissues, a rigorous and costly practice if infection is high, and favors control of the insect vector.

The expected learning outcomes for this project are: 1) researchers and cranberry growers will learn the extent of systemic infection of the CFBD phytoplasma throughout cranberry organ tissues; 2) researchers and cranberry growers will learn the seasonal phenology of the BNLH vector; 3) researchers and cranberry growers will learn when feeding is occurring on cranberries by BNLH; 4) researchers and cranberry growers will learn the difference in feeding injury based on BNLH abundance. The expected action outcomes of this project  can be split into the short and long term, with short term outcomes being: 1) cranberry growers will learn how to identify the symptoms of CFBD, as well as its insect vector; 2) cranberry growers will learn the level of threat of BNLH feeding injury on yield. Long term outcomes are: 1) growers will know when CFBD is coming out of dormancy and adjust cultural controls for CFBD infection removal; 2) cranberry growers will refine chemical sprays to target BNLH populations at key life stage, based on the BNLH phenology, for optimal CFBD transmission prevention and preventing feeding injury from reaching damaging levels.