Managing bacterial wilt, caused by Erwinia tracheiphila, on muskmelon with early control of striped cucumber beetle ( Acalymma vittatum (F)), and through varietal selection

Ahmad Shah Mohammadi, Purdue University

Abstract

Muskmelon (Cucumis melo L), is an important vegetable crop in the United States. It is grown throughout the US, and Indiana ranked 4th in production after California, Arizona and Georgia with 12.4 thousand metric tons and market value of $7.6 million in 2015. Bacterial wilt of cucurbits, which is caused by Erwinia tracheiphila (E. F. Smith), and vectored by striped cucumber beetle (Acalymma vittatum (F)), is one of the most serious diseases of muskmelon that influences muskmelon quality and yield. Many cultivars of muskmelon are grown around the United States, especially in the Midwest. Muskmelon cultivars differ in attractiveness to the striped cucumber beetle (SCB) and susceptibility to BW, but no known cultivar resistant to BW has been introduced. The primary method for managing BW is controlling the striped cucumber beetle before it can infect the plant. However, it is not known whether there is a critical stage during early plant growth when muskmelon plants are more susceptible to infection and therefore control of striped cucumber beetle is especially important. We conducted three field experiments at two locations (Lafayette and Vincennes, IN) in 2013 and 2014 to investigate whether there is a critical period for striped cucumber beetle control sometime during the first three weeks after muskmelons are transplanted to the field. We found that using row covers that exclude beetles, seed treatment or soil drenches with insecticide thiamethoxam significantly reduces the beetle numbers and wilt and increases the number of marketable fruits yield compared to not controlling striped cucumber beetle. However, the length of time row covers were left on the plants (for 7, 14, or 21 days after transplanting, DAT), or the period beetles were permitted to feed on plants (0-7, 7-14, or 14-21 DAT), or the time when beetles began to feed on plants (0, 7, or 14 DAT) did not significantly influence disease influence or yield in a consistent manner. This suggests that there is no clear ‘critical period’ during early muskmelon growth when controlling striped cucumber beetles is especially important. The data show that maximum severity of bacterial wilt occurred in June and July, which corresponds to development of disease transmitted by feeding of overwintered beetles plus additional transmission by the first generation of adults to emerge in the summer. We also conducted field studies in 2015 and 2016 with 10 to 12 cultivars at three locations (Lafayette, Wanatah and Vincennes, Indiana) to identify those most and least attractive to SCB and susceptible to BW. Replicated plots of each cultivar were grown and natural populations of SCB allowed to feed. At one location, additional plots of each cultivar were populated with 5 SCB per plant, and row covers applied to keep the SCB near the plants for 3 weeks. Results differed among locations. Without row covers, cultivars ‘Diplomat’, ‘Dream Dew’ and ‘RML 9818’ attracted higher numbers of SCBs than most other cultivars at one location each. ‘Dream Dew’ (at all locations) and ‘RML 9818’ (at two locations) had significantly higher percentages of BW than the least susceptible cultivars. Without row covers, ‘Superstar’, ‘Aphrodite’ and ‘Wrangler’ produced significantly greater yield than the lowest yielding cultivars at all locations. With row covers, early season beetle populations did not differ among cultivars and BW was greatest in ‘Dream Dew’ and least in ‘Superstar’ with other cultivars intermediate. With row covers, ‘Athena’ and ‘Superstar’ produced greater yield than many other cultivars. Over all ‘Diplomat’ and ‘Dream Dew’ were the most attractive to beetles and susceptible to BW. ‘Aphrodite’, ‘Athena’ and especially ‘Superstar’ were less attractive to beetles and showed more tolerance to BW in both 2015 and 2016. We found cucurbitacin A in leaves of ‘Athena’ and ‘RML9818’, and cucurbitacin B only in leaves and stems of ‘Dream Dew’ and ‘RML9818’. All cultivars had cucurbitacin I in both leaves and stems. In leaves the highest level of cucurbitacin I was found in ‘Hales Best’ followed by ‘Afg1’ and ‘Superstar’, and the highest level of cucurbitacin A was found in ‘RML9818’. Stems of ‘Diplomat’ had the most cucurbitacin I, followed ‘Superstar’, ‘Dream Dew’ and ‘Hales Best’. Cucurbitacin B was the highest in stems of both ‘Dream Dew’ and ‘RML9818’. Cucurbitacin E was present at similar levels in the stems of ‘Diplomat’, ‘Hales Best’ and ‘Afg2’.

Degree

Ph.D.

Advisors

Foster, Purdue University.

Subject Area

Horticulture|Agriculture

COinS