Q. I grow a lot of different plants in nursery containers
in my yard. This past spring I found
three white grubs in the soil in one 5-gallon container! I also found
them in the soil in my yard when planting new roses and trees. I’ve been
manually picking them out and tossing them on the driveway for the birds to eat
when I see them. Are they a threat to my flowers and veggies? Should I take any
action against them?
A. Finding large white grubs in the landscape where soil
has been improved is normal during the spring months. However, finding a lot of
white grubs in landscape soils is not a good thing because they can eat the
smaller young roots of plants as well. Personally, I wouldn’t be overly worried
if I found one white grub in a 5-gallon nursery container full of soil but
three is excessive. I would take some action.
the immature grub of a scarab beetle, sometimes called a June beetle. When
temperatures begin to warm they pupate in the soil and emerge in summer as a
flying adult seeking the opposite sex and a place to lay its eggs if it’s
female. Your landscape sounds like it’s a playground for these guys!
 |
| Green metallic june beetles devouring Kadota fig |
one of the most frequent “June beetles” we see flying in the summer months is
the metallic green June beetle. When flying out and about they love to eat
white Kadota figs and just about any soft fruit that’s ripe! But we also see during
summer months the brown June beetles as well which are another type of scarab
beetle.
 |
| Ten lined June beetle in the orchard another chafer or scarab beetle |
female beetles lay eggs in mid-summer. The female picks spots to lay her eggs where
there’s plenty of food for her young to eat. She hones-in on soils that have
been amended with compost since these young white grubs favor ripe or decaying
organic plants mixed in the soil. Young tender roots of plants are mingled with
decaying soil organics and they’ll feast on both. That’s the problem.
 |
| Another June beetle picture sent to me by a reader |
pesticides like Sevin insecticide applied to the area as a soil drench will
easily kill these grubs if you lean in that direction. Sifting through the soil
when you’re planting and handpicking them like you’re doing will get rid of
most of them if you are organically inclined. Using Milky Spore bacterium for
biocontrol only works if these white grubs are related to Japanese beetles.
Most of our white grubs are not.
preventive measure for future years is mixing beneficial nematodes into the
soil that pursue various types of white grubs and not just the Japanese beetle.
Your local garden center may carry beneficial nematodes, but they should be
refrigerated when buying them. The best time to apply them is usually around
August after egg laying has finished and the young grubs are starting to gain
some size.
nematodes should be kept in the dark and in the refrigerator until they are
ready to be mixed in the soil. They will have directions for their use on their
label.