Lassoing Loopers: why you NEED to care about caterpillar control

tomato looper 2_Steve hatch

Know which looper species this is? Are you SURE? If not, keep reading, as some species could get your shipments detained at the border.  Photo: Steve Hatch, Bugwood.org.

With spring crops behind us and summer approaching, most of you are probably concentrating on the Big 3: thrips, aphids and whitefly.  But recent alerts put out by the United States Department of Agriculture (USDA), bring a new emphasis to caterpillar control.  Read on to understand what’s happening, how to control occasional pests like cabbage looper, and avoid potential issues at the border.

 

As many of you might have heard from Flowers Canada, the USDA recently informed CFIA that the moth Chrysodeixis chalcites (known as tomato looper, or the golden twin spot moth) is an actionable pest in the U.S.  This means they WILL take action on any shipments from Ontario they even suspect may contain this pest.  Specifically, they may refuse or quarantine shipments, and/or increase inspections on shipments from Ontario.

So why does this matter to us?  It’s a TOMATO pest, right?!?! Well…

The problem is two-fold.  First, technically tomato looper can attack ornamental crops such as carnation and geranium, among others.  But the bigger problem is that TOMATO LOOPER LOOKS JUST LIKE A LOT OF OTHER LOOPERS (e.g. moths in the family Noctuidae)*.  For example, both the larval and adult forms of tomato looper are pretty indistinguishable from cabbage looper (see pictures below), which commonly attacks certain ornamental crops, especially between July and September.

*(Basically all the moths in this family look like indistinguishable stupid brown blobs and their larvae are even worse to tell apart.  I’m pretty sure Noctuidae means “Boring Blob Moth”, but I haven’t actually looked that up).
Looper adults

Tomato Looper (Chrysodeixis chalcites; left) is only slightly less ugly than the Cabbage Looper (Trichoplusia ni ; right).  Photos courtesy of Bugwood.org.

Unfortunately, the only way to accurately distinguish different looper species is by dissecting out the adult moth genitalia and comparing them (Yikes. I almost feel sorry for them; the people that have to do this I mean. Not the moths).  This means that cases of mistaken identity at the border have the potential to occur, or shipments could be held until the identity of the culprit is confirmed.

looper larvae.jpg

Larvae of Tomato Looper (left) and Cabbage Looper (right) are extremely similar in appearance. DNA sequencing is the only way to accurately tell larvae apart.  Photos courtesy of Bugwood.org.

Luckily, the solution to this problem is fairly straight forward:  stay on top of your caterpillar control before you ship!

I’ve been in more than one floriculture operation where caterpillar control (even for Duponchelia) was a bit of an afterthought. But now, we should consider caterpillars more seriously in our pest control programs.  If you’re diligent about your control program, they can be kept to low levels fairly easily.

Caterpillar Control 101:

  • Prevention: Screened vents help prevent the entry of moths and a good inside/outside weed control program will reduce potential infestation sites.
  • Monitoring: Black light traps (UV light) will attract adult moths of many species so you can determine if/when moths are an issue in your crop. You can also use pheromone traps: sex pheromone lures specific to tomato looper, soybean looper or cabbage looper are all available.  However, if the vents are open, moths can be attracted from outside, so traps may be more suitable during the cooler months, OR, traps can be placed a short distance from the greenhouse.  Once you detect the presence of these pests, begin control before small caterpillars start feeding. Signs of an active infestation are webbing, large chewed holes in foliage and pelletized excrement.
  • cabbage looper damage_AM Varela

    Loopers make large, irregular holes in leaves between the leaf veins and leave copious amounts of black excrement. Photo: A.M Valera.

  • Biological Control: Dipel / BioProtec / Thuricide HPC are all registered products with the same active ingredient (the bacteria Bacillus thuringiensis var kurstaki). These are registered for loopers in chrysanthemums as well as leafrollers in roses.  As a weekly foliar and soil surface spray, they form the backbone of effective caterpillar control programs.
  • Chemical Control: Other registered pesticides for loopers include:
    • Confirm (tebufenozide) – is a chemical that’s fairly compatible with biocontrol programs, though it can be hard on A. swirskii (for thrips) and P. persimilis (for spider mites), specifically. Re-introductions of these bios may have to be made after use.  Apply to early caterpillar (larval) stages as needed every 10-14 d.  This product is also registered for other caterpillar pests (e.g. earworm, armyworm; see label).
    • Pylon (chlorfenapyr) – is hard on all natural enemies, with a fairly long residual, so caution will be needed not to disrupt any existing biocontrol programs (so it’s perhaps best saved as a spot spray in infested areas). For caterpillar control, apply early when pests first appear.  This product is registered for cabbage and soybean loopers in ornamentals, but cannot be applied to cut flowers.

Resistance Issues:

When it comes to looper control, we can also learn a few lessons from our friends in the vegetable industry.

We know that repeated reliance on chemicals has resulted in lack of efficacy/resistance in looper pests in crops like tomato.  This has occurred across a wide range of chemical classes, including Pylon (Group 13), Confirm (Group 18) and Coragen (chlorantraniliprole, Group 28; registered for loopers in greenhouse vegetables). So, although chemical control might seem like the quicker fix, generally, biocontrol of this pest is your best long-term bet (especially since we only have two chemical classes to work with in ornamentals!).

The Bottom Line:

Although the potential to have shipments rejected to the U.S. is real, looper pests ARE controllable, so just be on the look out and be prepared to add this pest to your regular IPM program.  OMAFRA continues to work with CFIA, Flowers Canada Growers, and the USDA to keep you posted on this issue.

More information on tomato looper’s biology and pest status can be found here:

http://www.ipm.msu.edu/uploads/files/Forecasting_invasion_risks/goldenTwinSpot.pdf
https://secure.fera.defra.gov.uk/phiw/riskRegister/downloadExternalPra.cfm?id=3849
http://ecoipm.org/wp-content/uploads/2015/05/Chrysodeixis-chalcites-CPHST-datasheet.pdf
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