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grubs in plant roots

Posted by LNMCA z9 CA (My Page) on
Sat, Nov 19, 05 at 15:15

This is my first time on the forum and I came here because am having a hard time finding information on the internet, specifically, about grubs in the roots of my plants (not in the turf). We planted some fortnight lilies (Dietes spp)at the beginning of last summer and some lived, some died. I was digging up the ground to replace the dead ones and came across several (about 50 per 5-gal plot) thick grayish-white grubs, about 1 inch long with orange-brown heads feasting on the roots of these dead plants. I dug up all I could find while removing the dead plant material, but now I am worried that they will return and kill my new plants. Are these problem creatures? Any suggestions?

Follow-Up Postings:

RE: grubs in plant roots

Grubs which feast on plants roots are certainly a problem, but the infestation may or may not repeat. Grubs are simply one stage in a bug's life. These grubs will mature into beetles or some other bug and leave.

They (the adults) may decide the area is good and move in if they feed on the plant as well in which case they will likely reproduce and the grubs will return again.

So, what to do?

Well, really there are many control strategies you can try and see what happens. There are biological controls such as BT strains which will kill grubs as well as chemical controls. For the most part these products are only effective applied in the summer when the grubs are actively feeding and soil temps are right. Just do a google search on 'grub control' and you will find various techniques/products that can be used.

An alternate approach is to not kill the grubs, but to treat plants with neem oil around the time you start to see above ground plant damage from feeding insects. Among it's other properties neem oil is a life cycle inhibitor than prevents adults from laying eggs and prevents larva (grubs) from pupating and becoming adults. You can use neem as a spray on the plants as well as a soil drench.

Hopefully you just had one bad year with the grubs, but if you have a problem next year you will do well to try and identify the actual insect and learn specific control stragegies for it.

Another option, assuming your lillies were the only plant affected, would be to not plant them in the same area for a year to see if that would get the adults to move on to someone else's yard ;-)

RE: grubs in plant roots

  • Posted by jean001 z8aPortland, OR (My Page) on
    Sat, Nov 19, 05 at 22:33

When it comes to the Bt formulation against beetle grubs, it's worth knowing that it doesn't work for the kinds of grubs that live in California.

RE: grubs in plant roots

I didn't know that there was a Bt for grubs. I'm only familiar with Bp.

RE: grubs in plant roots

There are also predatory nematodes and milky spore.

RE: grubs in plant roots

rhizo wrote:
"I didn't know that there was a Bt for grubs. I'm only familiar with Bp."

Bt san diego works against Colorado potato beetle -- a leaf eater.

But yep, there's also a Bp -- Bacillus popilliae.

But still holds that it doesn't work against the grubs in CA.

For anyone who wants to know more -- lots and lots more -- go to "The Bt Primer" which also mentions Bt tenebrionis, another form active against certain beetles.

The primer is at

Here is a link that might be useful: Bt Primer

RE: grubs in plant roots

Has anyone had any experience with grubs in the soil eating flower bulbs & roots specifically, daffodil bulbs? The bulbs bloomed relatively well for one Spring season then almost overnight disappeared completely from the garden spot. The planting was sizable so it would seem likely that something was amiss beyond a simple explanation of overcrowwding (unlikely after only one blooming season) or poor horticultural practices in general. Any help (thoughts, ideas & remedies) with this would be greatly appreciated.

RE: grubs in plant roots

Milky Spore Disease is "Bacillus popilliae" and that is what is used to control grubs. There is no "Bacillus thutingiensis" strain, that I am aware of, that works on grubs.

RE: grubs in plant roots

If you read the link that Jean attached, you'll learn something new today! How great is that??

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