Q. My desert willows in Kingman, Arizona, are being eaten up
by worms. The web-like pods are all over the branches, but I have not
found anything inside. I certainly do not want to spray as the trees are over
one of my gardens and close to some windows.
A. I did some quick checking but could not
find this critter mentioned anywhere. How do you k now they were being eaten
up? It is possible they have done their damage and now have moved on leaving
their webbing behind.
.JPG) |
| Sphinx moth found dead on sidewalk in May in Las Vegas. |
Desert willow is used in butterfly gardens but
it is usually for the adult butterfly rather than the immature larva (worms) or
caterpillar. If they are causing a great deal of damage then they should be
controlled.
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| Tent caterpillar webbing |
Worms or caterpillars that do cause damage to
desert willow are the Sphinx moth larva or “worm” and relatives of tent
caterpillars. The larva of the Sphinx moth is gigantic with the horn coming off
of its rear end. You would've recognized that one if you had seen it.
 |
| Sphinx moth to give you perspective on size of the moth. |
 |
| Bt formulation from Monterey |
The other caterpillar is much smaller, along
the sizes you're talking about, but they usually form a webbing one or 2 feet
across and they feed inside this webbing or tent. That's why they call these “tent
caterpillars”. Tent caterpillars reproduce quickly and do a lot of feeding over
a short period of time.
My guess is that these critters will not last
very long and be on their way for the season. The desert willow will respond
and survive. But in the meantime that tree will have some damage.
You could use a spray of BT, called usually
either Dipel or Thuricide which is an organic control. It will only target
“worms” that become moths or butterflies. Also Spinosad will work as well. This
way you could avoid more poisonous conventional sprays.
A few years ago I sent you some pics of worms that were chomping on my desert willow trees. I have finally been able to identify them as fall cankerworms. They did not come back in 2015, but reappeared last fall in 2016. I guess the severity of each winter determines whether or not I will see them each year. Up in the high desert areas we do see a lot of tiny moths...almost like snow sometimes. My trees do recover so I am not as upset as I used to get. Thought you would like to know. Sue in Kingman Arizona
ReplyDeleteThanks for this update, Sue. I seldom get them from readers so it is appreciated and informative. If it is fall cankerworm then I would guess that Bt and Spinosad would work on them. I tracked it down and I see it is called both fall and spring cankerworm and reported mostly in the east. I did find University references to it from Colorado and Texas. I liked the Colorado one best.
ReplyDeletehttp://csfs.colostate.edu/media/sites/22/2014/04/franktown-Fall_Cankerworm-USFS.pdf
http://texasinsects.tamu.edu/cimg293.html