Phoenix Gardening Tip: Black Specks on Yellow Bells

Leaf Skeletonizing Damage on Tecoma stansThose of you who are growing Tecoma stans (Yellow Bells) or one of its many cultivars (such as Orange Jubilee) in your desert garden may notice some black specks or leaf skeletonizing on your plant.  I just received a bulletin from the Desert Botanical Garden who, in conjunction with the University of Arizona, have identified the speck-depositing culprit.  It turns out that this is the excrement of the caterpillars that are feeding on the leaves.

Sometimes those guys just roll up in a leaf and go to town.  As you can see, they can do quite a bit of damage.

According to a page on the ASU site, these caterpillars like to do their work following a wet monsoon season.  And we’ve had some pretty good rains in the Phoenix desert this summer, so they’re right in their element.

So what can you do about it?  According to the DBG, your best bet is to wait and see what happens.  The caterpillars could be killed off in a freeze or they could just disappear.  If you feel better about applying a chemical control, go with the least toxic alternative–the DBG suggests Bt (Bacillus thuringiensis) at the maximum labeled rate.

The other option is to wait until the danger of frost has passed (late February-March) and then prune your shrub down to about a foot.  I usually do this every couple of years anyway, both to remove any frost damage and to encourage new growth.  Then just make sure to throw the infected parts into the trash (not your compost bin).

 

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