Reducing flea-beetle feeding wounds on canola seedlings with foliar insecticide failed to improve blackleg control

In earlier studies, it was found that <i>Leptosphaeria maculans</i> could readily infect canola via fresh wounds but would require extended leaf wetness to infect intact tissues. We hypothesized that flea beetle feeding wounds might facilitate <i>L. maculans</i> infection under field conditions. Multi-year plot trials were conducted in western Canada to assess the effect of reducing flea beetle feeding wounds on canola seedlings with in-crop insecticide on subsequent blackleg infection. The experiment encompassed susceptible and resistant cultivars seeded into canola stubble from the previous year, with pyrethroid insecticide applied weekly commencing at trace feeding (&lt;5%) to mitigate the insect damage. Fluopyram seed treatment was used as an additional treatment against early blackleg infection. Results from eight station years showed moderate feeding damage by flea beetles and generally high blackleg pressure, with the average disease incidence &gt; 80%. Despite reduced feeding damage due to in-crop insecticide treatment, significant blackleg reduction was not observed. A greenhouse study revealed no correlation between puncture wounds on cotyledons and successful stem infection under high-inoculum conditions, suggesting that reduced insect feeding might not effectively counteract the heavy inoculum pressure resulting from canola residue in field trials. Fluopyram seed treatment did not reduce blackleg substantially, while resistant cultivars consistently exhibited effectiveness. Furthermore, harvested seed from plots with lighter blackleg often displayed lower levels of <i>L. maculans</i> inoculum contamination.既往研究表明，黑胫病菌（*Leptosphaeria maculans*）可通过新鲜伤口高效侵染油菜，但侵染完整植株组织则需要长时间的叶片湿润环境。本研究提出假说：田间条件下，跳甲取食造成的伤口可能会促进黑胫病菌的侵染。为评估作物生长期施用杀虫剂以减少跳甲取食伤口对油菜幼苗黑胫病后续发生的影响，我们在加拿大西部开展了多年小区定位试验。试验设置涵盖了播于上年油菜残茬地的感病与抗病油菜品种，在跳甲取食痕迹达<5%时开始每周喷施拟除虫菊酯类杀虫剂以减轻虫害为害，同时增设氟啶酰菌胺种子处理作为早期黑胫病防控的额外处理组。8个试验站年度的试验结果显示，田间跳甲取食为害程度中等，黑胫病发病压力整体较高，平均病株率>80%。尽管作物生长期杀虫剂处理显著降低了跳甲取食为害程度，但未观察到黑胫病发生量的显著降低。温室试验结果表明，在高接种体压力条件下，油菜子叶的穿刺伤口与茎部成功侵染之间无显著相关性，这提示田间试验中减少昆虫取食可能无法有效抵消油菜残茬带来的高病菌接种体压力。氟啶酰菌胺种子处理未能显著降低黑胫病发生，而抗病品种则始终表现出稳定的防控效果。此外，黑胫病发病较轻的小区所收获的种子，其携带的黑胫病菌接种体污染水平通常更低。