Thursday, June 22, 2017

Harlequin Bug

By Stephanie Rukowicz

The harlequin bug is a type of stink bug, much more colorful than the brown ones you might find around your house. An invasive species, it is a common insect pest of crucifers in the southern part of the U.S. but in recent years has been reported in PA as well.

2016 brought my first encounter with harlequin bugs. First eggs were sighted on kale around the same time I was noticing leaf miner damage to spinach and beet leaves (early May). At the time, I wasn’t sure what had laid the eggs, but noted their distinguished geometrical grouping and pattern.
 Uncapped (already hatched) eggs.

Side view of eggs, note black striping along side.
As the season progressed,the harlequin bugs made themselves known. Mostly laying on and inhabiting my kale plants, I attempted hand control by picking eggs and both adult and baby bugs, which helped but did not eliminate the population. I noticed as I pulled and destroyed severely infested plants that bugs and eggs could also be found on closely neighboring tomato plants. The warmer winter of 2015/2016 may have played a role in my new familiarity with this insect pest. Also, two plots in our garden use a radish cover crop, possibly providing a nice winter home for adult bugs.
Harlequin bugs on the underside of a collard leaf. Adult top left, youth middle right.
Later this season, I also spotted Harlequin bugs in the Parks and Rec vegetable garden at Columbus Square Park. Is this a new issue for South Philly? I wonder what next year’s gardening season will be like and if we need a more concentrated effort to control this pest population.

Collard leaf with damage from harlequin bugs,
browning and spotting. Also showing
concurrent damage from cabbage lopers
(holes and munching around leaf margins).
“Early in the season populations and damage are often low and you may be tempted to ignore them. But, with two to three generations in a season, by the time fall crops begin to mature their numbers may be one hundred times as high, causing serious damage. Harlequin bugs reproduce quickly, developing from an egg to an adult in about 48 days. Adult males may live up to 25 days and females up to 41 days. During their adulthood they can mate repeatedly laying multiple egg masses of 12 eggs every 3 days. That means a single female can produce 164 eggs. My advice – don’t ignore harlequins bugs; put together a plan to keep their numbers low.”

“Host-free periods without brassicas can help limit the population. Remember brassica cover crops, like forage radish, are known hosts. Harlequin can also feed and reproduce on wild weedy mustards (Shepherd’s purse, wild mustard, pepperweed), pigweed (Amaranthus spp.), lambsquarter (Chenopodium spp.). Keeping these weeds under control in fields and on field edges will limit habitat. Leftover crop residue in the field provides a protected host area for over-wintering adult harlequins. Remove or disk in residue to destroy overwintering sites. Trap crops have been recommended, but I would suggest that you need to rapidly kill the bugs in the trap crop, or destroy the trap crop and follow it with a host-free period, for this to work well. Plant an early crop of horseradish, mustard or kale and try to kill the harlequin bugs concentrated on this favorite host. One grower has successfully controlled harlequin by frequent vacuuming.”

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