[compost_tea] Cabbage Maggots

From: Merla Barberie <herbnmerla_at_supersat2.net>
Date: Mon, 09 Jun 2003 12:33:37 -0700

Somehow, we managed to get some
       Cabbage Maggot, Diptera: Anthomyiidae, Delia radicum (L.).
They're just starting and we dug up all we could find and I'm making a
BD spray out of the larvae and pupae.

Is there any CT spray that I can do now to stop these babies or any
organic measure we can take? The literature says that we're out of luck
if we can see the larvae eating away on the roots. The Extension agent
says they overwinter here in the roots of wild mustard. The only thing
we did different than we usually do is get manure for next year earlier
than usual. I bet we brought them in there.

IDENTIFICATION: The adult stage of the cabbage and seedcorn maggots is a
small (about 1/4 inch long), dark-grey fly
that is similar in appearance to the house fly. The legless larvae of
both species are white, tapered maggots that reach a
size of about 1/3 inch long when fully grown. Maggots of these species
are virtually indistinguishable from one another
in the field.

LIFE HISTORY: Cabbage and seedcorn maggot adults typically emerge in
April and begin laying eggs. Female cabbage
maggot flies actively seek out and lay eggs on the lower portions of
stems of young host seedlings or in nearby cracks in
the soil. Within a few days the eggs hatch and the tiny maggots burrow
down to the roots and begin feeding. About three
to four weeks later pupation occurs in the soil which is followed about
a week later by the emergence of second
generation adults. Several generations may occur as late as early July,
but the first generation is the most destructive.
Soil-borne pupae of the last generation serve as the overwintering
stage. The life cycle of the seedcorn maggot is similar
to that of the cabbage maggot; however, the seedcorn maggot prefers to
lay eggs in freshly-tilled soil that is high in
moisture and organic matter, and especially in soil where animal manure
has been applied because it is highly attractive to
female seedcorn maggot flies during egg laying. The eggs of the seedcorn
maggot hatch within a few days and the
maggots begin feeding on decaying organic matter or the germinating
seeds of wild or crop plants. Seedcorn maggots are known to be highly
attracted to odors produced by germinating seeds.

CONTROL: No action thresholds or scouting techniques currently are
available for cabbage or seedcorn maggots, thus
control measures typically rely on preventive use of soil-applied
granular insecticides or insecticidal seed treatments at
planting. Ground beetles and other predators may provide some degree of
control, but serious damage can occur if
conditions after planting are cool and wet. Mechanical barriers such as
tar paper, plastic mulch, and foam-rubber collars
placed at the base of plants have been used with some success to prevent
egg laying by cabbage maggots; however,
insecticidal seed treatments or the more expensive granular
insecticides, when used at planting, are considered the best
methods for controlling seedcorn maggots. Because subsequent generations
of seedcorn maggots are not as damaging,
replanting usually is effective, although costly. Also, gardens with a
history of seedcorn maggot problems may benefit
from the application of an insecticidal seed treatment at planting.

* * * * *

Screen cones or a mesh netting over early spring cabbage prevent the
cabbage maggot fly from laying its eggs
at the base of the plant.



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Received on Mon Jun 09 2003 - 18:05:51 EDT

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