Tiny worms take on cucumber beetles
Scientists with Agriculture and Agri-food Canada are working on ways to try to help farmers who grow squash, cucumbers and watermelons deal with the ravaging of their crops by spotted and striped cucumber beetles, but without the need for chemical applications.
Suzanne Blatt at the Kentville Research and Development Centre is working with tiny worms to deal with the beetles.
And like so many other problems, it’s an issue connected to climate change.
“It’s been an increasing issue since about the mid 20-teens, that’s when summers started to get warmer and stay warmer,” Blatt said.
The beetles are native to North America, but have worked their way north.
As if that wasn’t enough, in 2020 researchers noted that it was now warm enough that was a second flush, or emergence, of new beetles.
“They appear on your crop, they mate, they lay their eggs, the larvae hatch and feed on the roots, so that causes problems, the adults will feed on your flowers and your leaves, which causes problems, and the adults can vector a bacterial wilt, so there are three hits that they can do,” Blatt said. “But there is so much heat that those larvae had time to pupate, become adults and then appear and start the process again.”
‘IF YOU CAN HIT THOSE, YOU’RE FINE’
That created new problems, because normally there is only one generation and “if you can hit those, you’re fine.”
It meant an updated strategy to what was being tried in 2019, which was crop trapping. That involves planting something more appealing to the beetles than the crop a grower wants to protect, such as putting zucchini or a hubbard variety of squash around buttercup squash. The trap crop is smaller and planted near the cash crop.
“The idea is that you’re planting a line around the rows you’re trying to protect, so (the beetles) would spend their time there,” Blatt said.
THE SECOND WAVE
That experiment was looking good in the first year, until that second wave showed up.
So in 2021, the team transplanted a second trap crop at about the time the new beetles would have been emerging.
“The next thing we ended up thinking about was, ‘now that we have them there, how can we stop them from getting even to that second generation?’”
Enter the nematodes. Or, more specifically, entomopathogenic nematodes. That’s a group of carnivores that feed on the eggs, pupae, or often the larvae of insects.
BEETLE MEET WORM
The team introduced the microscopic worms to the trap crop in 2022 after the first flush of beetles.
“Now when the larvae come out, the nematodes are eating them,” Blatt said. “So, we should be able to stop that second flush.”
Ideally, that interrupts the cycle and reduces the numbers in a particular area.
There are companies that are producing the nematodes commercially, but one of the hindrances to a grower trying to use them on a large scale is that the recommended application is 2.47 billion nematodes per hectare.
“That is a lot,” Blatt said. “A packet of 50 million can run from $50 to $150 dollars.”
That would be $2,500 per hectare.
“The cost to apply it to everything is just prohibitive,” she said.
That’s why the research is on attracting the beetles the trap crops and eliminating them there.
“The idea is to keep the cost down,” Blatt said “When you’re applying it to just the trap crop, you can take your 50 million package and it goes a lot further than if you’re trying to apply it to every plant in every row.”
THE DIP SOLUTION
Another method under trial is to dip transplants into a solution with the nematodes to infuse it directly into the plant ball before planting.
Part of the issue there is that they’re on the plant long before the beetles shows up, and may start to move away in search of food.
While it would be ideal if the nematodes just reproduced and expanded their hunting grounds to provide wider protection, Blatt said, many of the ones being produced commercially may not be adapted to Nova Scotia’s climate and able to survive the winter. So for now, the expectation is that the research will show that plastering the trap crop will work for one year.
As part of the research, the team also planted nasturtiums. While that doesn’t seem to be effective at driving the beetles out, it did repel squash bugs to lay their eggs further away, Squash bugs are another pest that arrive after the cucumber beetles.
“For the home gardener, I would argue it’s going to be a benefit,” she said. If you’re planting your own stuff in, start your trap crops inside about a week ahead of the others, so when you put everything in the garden your trap crop is about to flower. That will pull them off anything that doesn’t have flowers. If you’re an early riser, go out first thing in the morning and shake the flowers out into soapy water.”
That will remove the beetles, she said. The best thing for the squash bug for home gardeners is to look under the leaves for the bronze-coloured eggs and squish them.”