Where do thrips come from? YOUR MUM(s).

Thrips damage on mums.

Hopefully my bad attempt at a “Your Momma” joke will get your attention, because this is an important post.

Ongoing research by Rose Buitenhuis’ Lab at Vineland has shown that an incredible number of thrips and spider mites come in on imported mum cuttings. Here’s the scoop and what you can do about it.


The Issue:

To look for pest problems arriving from the U.S., the Buitenhuis team washed mum cuttings imported from Florida and California (supplied by Judy Colley, Plant Products) at 1 day post-receipt and then 7 days post-receipt, to catch any insects that needed time to hatch out.

Out of the 13 batches of mum cuttings tested, 12 of these (i.e. 92%) were infested with either spider mites or thrips (or both), with numbers as high as 76 thrips/100 cuttings (see Fig. 1, below).

graph for June 7 blog.jpg
Fig. 1. Number of pests (thrips or spider mites) found on imported mum cuttings 1 or 7 days after receipt.  Data courtesy of R. Buitenhuis, VRIC. Each bar represents a different source or batch.  Batches were tested on May 5 and 17th, 2016.

What it Means:

Damage from two-spotted spider mites.  We now know that these pests come in on infested mum cuttings imported from the U.S.

Just think if you import 10 thousand cuttings/week for your mum program, you might be walking almost 8000 thrips straight into your greenhouse each week.

Similarly, you could be bringing in up to 2000 spider mites/week, which can be just as difficult (or even more difficult) to control than thrips.

Can we just chalk this up to a “bad pest season” by the propagators or something?  Unfortunately, no, because this is not a new finding.  In 2011, student Wendy Romero found similar high numbers of thrips on imported mum cuttings as part of her graduate thesis work.

I say we need to see this as an ongoing threat to our industry, especially considering both these pests are likely arriving with a high degree of resistance to pesticides.  

So what to do?

The only way to really protect yourself is to ASSUME YOUR CUTTINGS HAVE THRIPS AND SPIDER MITES – LOTS OF THEM – and that they are already resistant to all chemical control options.

Echoing  last week’s post, this means starting preventative biological control programs immediately.  This includes dipping cuttings as soon as they come in the door to remove thrips/spider mite larvae and adults, and  releasing biological control agents right on the rooting bench to catch the “newborns” right away.  Bios should be continued out into the crop until finishing, since petal damage can occur quickly.

More information on thrips biocontrol can be found here and here; more information on spider mite biological control can be found here.




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