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COASTAL GARDENER – August 7, 2001
Franklin Laemmlen, Ph.D.
Q:
I just planted seeds in my garden so I can have a fall harvest. Only a small
percentage emerged and some of those have died. Can you help me with the
plague in my garden?
A:
Now that summer is here and soil temperatures have warmed up somewhat, plants
grow more quickly, but the organisms that eat plants are also more active. The
following are some causes for the poor seed germination and dead seedlings in
your garden. (1) Cutworms. I talked about cutworms a few weeks ago. The adult
is a brownish-gray moth about one inch long (head to tail) with a two-inch wing
span. The larvae is a gray, brown, pale pink with black specks worm which lives
in the soil. Cutworms feed at night and can destroy emerging seeds and seedlings.
Baits containing Bt, carbaryl or diazinon can be used to manage this pest.
Cutworms usually curl up into a figure 6 shape when disturbed. If you see one of
these while working in the garden or flower beds, kill it to help reduce further
damage. (2) Darkling beetles. These are dull gray beetles (several species) that
live in the soil and feed on plant roots and seedlings. The beetles may be
anywhere from a quarter to three-quarters of an inch long. They do not like light,
so will quickly seek cover if disturbed. They feed at night and seek shelter in the
soil during the day. Carbaryl or diazinon bait can be used for control. Darkling
beetles (dull gray to black) should not be confused with predaceous ground
beetles, which are shiny brown to black and often similar in size to darkling
beetles. Predaceous ground beetles are the good guys that eat cutworms, and other
soil insects. (3) Flea beetles. These come in several sizes and colors. All are small,
anywhere from one-sixteenth to three-sixteenth of an inch long. The one thing
they have in common is that they hop when disturbed. They quickly leave the
plant and seek a hiding place. They are also nocturnal in their feeding habits, so
early (sunrise) morning (or at night with a flashlight) is the best time to check for
flea beetles. If present, they will usually be feeding on young leaves where they
make small holes or windows in the tissues. A single spray of chlorpyrifos or
carbaryl usually controls flea beetles for the duration of that crop. (4) Seed
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maggots. These are the larval stage of a fly. Eggs are laid on the soil at the base of
the seedling, and the larva feed on roots and stem tissues. They can also destroy
germinating seeds. The maggot is white and about three-eights to a quarter of an
inch long at maturity. Keeping a loose layer of soil at the surface, so there are no
soil cracks, discourages adult egg laying. Chlorpyrifos applied to the soil surface
around young plants is also effective in suppressing seed maggot activity. (5)
Garden Symphylans. These animals are also called “garden centipedes.” They are
white, multilegged, live in the soil, and move quickly to hide if exposed to light.
They are from a quarter to half an inch long and feed on roots and stems of
seedlings. One way to test for symphylans is to take a cylinder (three-pound
coffee can with both ends removed or something similar) and push it into the soil
where symphylans are suspect. Fill the cylinder with water. If symphylans are
present, they will float to the surface of the water after several minutes.
Symphylans are hard to control. A soil drench of diazinon will help to suppress
this pest.
Send your landscape and garden questions to: The Coastal Gardener, 624-A
West Foster Road, Santa Maria, CA 93455.
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