Possible root weevil infestation (Redbud Tree, Echinacea, Daisy)

(Question)

Nearly 3 years ago I had my small 14’x14′ front garden landscaped with new soil, bark etc. also a 3′ Redbud tree, and various scrubs and plants (echinacea, daisy among others). With this came an infestation of Root weevils. The weevils almost killed the tree in the first year and in the second year too. It took me most of the first year to realise what the issue was. At the end of the first year in the autumn I tried using nemotodes to deal with the problem but the issue came back the second year (last year). During the summer at night I could take off about 20 of these weevils from the tree. The tree iteself was reduced to almost no leaves as I wouldn’t always be diligent in my checking and harvesting. The weevils also attacked the daisies and echinacea in similar numbers the plants looked dreadful and lost nearly all of their petals. Everything online seems to say that these weevils generally don’t killl plants but mine certain are trying and being pretty sucessful and there are hundreds of them. I would welcome advice on getting ride of them this coming year. I was hoping for an earth friendly solution but think the goal now is for something that will be fast and effective without having to torch the whole garden. Your help would be greatly appreciated!!

(Answer)

Well it sounds like you may have an infestation of the dreaded root weevil. Do you know for certain that that is the pest causing havoc in your garden? Did you have it professionally diagnosed? If not this might be the Japanese root weevil, earwigs or some other creature. The first thing to do is to know exactly what pest you are dealing with to know how to treat the problem. Did you have your landscape done by a reputable professional? If so perhaps you could ask them to explain the problem, and suggest the solution. Often the work of professional landscapers is guaranteed. They may have inadvertently brought in contaminated soil and would certainly want to be made aware of the problem.

You mentioned you are looking for cultural control practices for whatever the creature is.  Ensure that you don’t mulch over the root crowns where the pests are situated as it encourages the pests to linger and nibble.  Certainly keeping your gardens clean of all infected debris is crucial. You could also apply a sticky barrier (such as Tanglefoot) or a Teflon barrier on the trunk to help prevent the pest from creeping up the branches of the redbud. Coffee grounds might also be a deterrent, applied around the base of the smaller plants.

Nematodes are a great solution when there are larvae in the soil. That said nematodes must be applied properly to work. Ensure that they are bought from a reputable source, are stored properly before application and that the soil is moistened before application and again afterwards to keep these helpers alive. Several applications of the nematodes might be necessary. They also should only be applied when the temperature is above 13 degrees C and properly timed with the pests development.

If you have tried all of these cultural practices without effect, it may be too late for  your plants. You may need to replace the soil in your garden where the infestation has occurred. You may also need to replace the severely infected plant material.

If you know for sure that the pest is the obscure root weevil, here are some excellent resources: https://www.ces.ncsu.edu/depts/ent/notes/O&T/shrubs/note66/weevilguide.pdf

https://www.ext.colostate.edu/pubs/insect/05551.html

I hope that you can finally rid yourself of whatever the pest is and enjoy a trouble free garden.