Locust tree dying

[Fudog]

Our ornamental locust tree is about seven years old and with every year the attack is stronger and stronger. Now it is covered with what I think are spiders. After the leaves are destroyed a silk strand blows in the wind from every limb. At first the course of action was a rose poison, the thinking was we wanted it to go through the roots and kill every little bug. That slowed them down, but this year it was the worst. I felt guilty using poison because the birds were having a field day eating the bugs. Now that is time for the leaves to drop I applied a poison that was mild. It was also a liquid, but the dirt was turned over to make the penetration quick. Sorry I can't remember the name of the poison. Then it was covered with thick mulch. We have two dogs so we have to be careful. Can anyone tell me what attacked our tree and how we can attack back? Chris

 

[Ed Roland]

At first the course of action was a rose poison, the thinking was we wanted it to go through the roots and kill every little bug. That slowed them down, but this year it was the worst.

Merit can exacerbate spider mite problems by increasing fertility and by killing their predators.

http://www.arboristsite.com/showthread.php?t=78319

 

[Urban Forester]

Were the leaves of this tree encased in webbing in small bunches? What time of year was the damage first noted? Were the leaves twisted/curled or did they have the look of being sucked dry (i.e. yellow/biege) Have you ever actually seen one of the insects that you suspect of doing the damage? Single strands can indicate the presence of cankerworm, but Locust is not one of their favorite targets. This may be Locust mite, if it is, large populations are most often the result of pesticide reducing predator populations.

 

[Fudog]

Thanks to the both of you. The damage began in the spring after the leaves were out, the tree looked beautiful for a very short while. It is difficult to determine the color effect on the leaves since this specific tree is supposed to turn from the green to yellowish orange sunset colors. The leaves are covered with the web in small bunches, but the webbing is not as tight as the webbing from a tent worm. I have never witnessed any bug, insect or worm. The tree has grown over azalea bushes that seem to be immune, but a arborvitae has been attacked by something in only spots, which I have cut out. I wish I still had the poison bottle that was used most recently, but it was worthless anyway. Is there any hope that spraying can be avoided? We have dogs and occasionally we take our bunnies out for a romp in the grass. The more I write the more ignorant I feel on the subject or the cure.

 

[Ed Roland]

"Try the tap test, by placing a white piece of paper under the suspect foliage and whack the branch with a pencil 2 times. A magnifying lens comes in handy for distinguishing these reddish-brown, 1/50th inch long critters. Look for webbing (a very fine cob web appearance) on new growth. Mites also feed near the mid-vein on the underside of the leaf. This may cause an upraised interveinal swelling with hibiscus. Mites suck the chlorophyll, which causes a minute flecking which can expand to an overall bronzing-yellowing or graying of the foliage. This leads to premature leaf drop and possibly death."
http://collier.ifas.ufl.edu/CommHort/CommHortPubs/Southern Red Mites.pdf

In the field, lisenced pros, are looking through goggles and faceshield trying to apply chemical at pressure. Imagine a line of carpet juniper 120' long draped over a south facing brick kneewall. During the spray app. I might take a co. form, turn it over and perform the tap test here and there. Instead of trying to remove all my ppe to get a view under scope, i swipe my dry, chem. gloved, hand over the debris that lies on the paper. The tiny reddish smears represent individual mites. This gives me a fair understanding of the population @ that spot in the row @ that time. If applying oil, this can help reduce the amount of material applied.
If applying Avid, it stands to reason, you would be better off getting even coverage.

 

[Fudog]

Aha there is a reddish color and one red little red bug that is seen with a magnifying glass. We had a hard rain last night and it wiped out most of the leaves on the tree, but the small groupings of leaves on the bottom branches just had a few leaves to tap. Are these bugs living in the tree or on the outside of branches? We live in West Virginia in Weirton about 30 minutes from Pittsburgh, PA.

 

[Urban Forester]

Webbing incasement by Locust mite is rare. They are not great web builders. If there is significant web encasement in small groups on individual terminals (ends) then I would suspect Mimosa Webworm. The fact they appeared in spring is also a clue. They tend to drop out of the tree in late summer and over winter in the ground below the tree. Every once in a while they will pupate in bark crevices also. The little red guy MAY have been a predator mite. Was he a "fast mover" when you saw him? Predators tend to be quicker than plant damaging pests, they have to be to catch their dinner. Check this link for problems of locusts:
http://kentcoopextension.blogspot.com/2007_07_01_archive.html
P.S. 'Woodweasels' "tap + smear" test w/a 10X lens is by far the best way to determine population density and mite type.

 

[Fudog]

locust tree

Yes you are correct, that little guy really moved fast. I will check out the link you provided now. Thanks, Chris