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Re: CULT-Borer--other plants attacked (long)

  • To: Multiple recipients of list <iris-l@rt66.com>
  • Subject: Re: CULT-Borer--other plants attacked (long)
  • From: mikelowe@tricities.net (Mike Lowe)
  • Date: Sat, 13 Sep 1997 12:24:47 -0600 (MDT)

Bill writes...
>I think I'll try to pursue this through the entomological and agricultural
>literature.  Meantime, I'll ask Anner if there are any references to borers
>in the bibliography of the Cornell publication....?

Here is an excerpt from a later Cornell Bulletin [July 1935 (again no
bibliography!)] that may give you a starting point.

The control measures use chemicals no longer in use or, for that matter,
even legal!

Cheers,

Mike
____________________________________________________________________________
__

35
                        CORNELL EXTENSION BULLETIN 324

                              INSECT PESTS OF IRIS

                                Grace H. GRISWOLD

Until recent years iris has been thought to be comparatively free from the
attacks of insects.  With the spread of the iris borer and the increasing
damage caused by this pest, iris growers are becoming conscious of the
injuries which insects may inflict.  In the following paragraphs some of
the more common insects that attack iris are discussed and measures for
controlling them are suggested.

                                The iris borer

The iris borer (Macronoctua onusta Grt.) is probably the most injurious
insect that attacks iris, causing more damage to this popular plant than
all of its other insect foes combined. Not only is this borer an enemy on
its own account, but the tunnels it makes in a rhizome are ideal places for
the  development of a serious iris disease (page 28). The iris borer
attacks practically all kinds of iris, including the Japanese and the
Siberian, although it appears to be more common in home gardens than in
large field plantings.  The injury is most evident during July and August.
It is not always easy, however, to tell where the borers are at work. If
the infestation is a heavy one, entire plants will be killed; but if there
is only one borer in a rhizome, the damage may not be evident aboveground.
There are several ways in which one can tell that borers are present. A
plant may have leaves that are loose and rotted at the base, so that they
can be easily pulled off.  A rhizome may be exposed, showing holes in the
top which the borers have made. The leaves of the new growth may be small
and poorly developed.  Some of the leaves may have badly eaten places along
the edges.
A careful study of the iris borer is being carried on at Ithaca and it is
planned to publish a detailed report on this work in the near future.  The
adult borer is a medium-sized, night-flying moth, quite inconspicuous, for
its coloring is mostly dark brown marked with black.  The moths usually
appear about the second or third week of September and are on the wing
through October and even into November.  They mate, and the females lay
eggs which do not hatch until the following spring.  The egg is a tiny
object only about 1/50 of an inch across and less than half as high.  When
first laid the eggs are creamy-white, but eventually they become distinctly
lavender.  The eggs are laid in groups or clusters and are carefully glued
down.  In our studies, eggs have been found pasted to practically
everything in the cages that had a roughened surface-twigs, dead leaves,
rusty nails, cloth, bits of wood, and wire screen.  Only in one instance
were any eggs laid on fresh green iris leaves.  A single female may lay as
many as 600 or 700 eggs in 24 hours and a total of more than 1400.
As previously stated, the eggs do not hatch until the following spring,
usually about the last of April or the first week in May in the vicinity of
Ithaca.  The newly hatched larvae are tiny creatures, only about 1/16 of an
inch in length.  Almost at once they crawl up the iris plants and make
small holes, like pin pricks, in the leaves.  Then each larva gnaws out the
soft tissue between the upper and the lower surface of the leaf, crawls
inside, and becomes a leafminer.  From the small holes made in the foliage,
droplets of sap exude.  Later the larva bores down towards the base of the
plant, chewing the edges of newly developing leaves.  Finally, it gets to
the rhizome where it makes great tunnels.  At this time the larva is about
1 1/2 inches long, has a reddish-brown head and a body that is distinctly
pinkish.  It eventually leaves the rhizome and goes into the soil to
pupate.  Pupation lasts for about five weeks and, as previously stated, the
adult moths begin to appear about the middle of September.
                                Control
Iris plants should be carefully watched during the summer months. If there
is any evidence that borers are at work, the plants should be dug up, the
borers removed and destroyed, and the rhizomes carefully cleaned before
being reset.  Any rhizomes that are at all rotted should be given special
attention, as explained on page 30.
In fighting the iris borer a thorough clean-up of the garden late in the
fall and again early in the spring is most essential.  (See page 26.)
Since egg clusters are glued to dead leaves and other debris, all possible
trash should be removed and burned.  Some growers have found it effective
to burn over their iris plantings late in the fall or early in the spring.
This should be done with a quick, hot fire.  An old broom dipped in
kerosene will make a good torch which can be swung back and forth over the
ground about the plants; or one can cover the plants with a light coating
of dead leaves or straw and then apply a match here and there.
Unfortunately, burning-over the plants seems to injure certain types of
iris.
Another method of control is to spray the iris foliage early in the spring
with a stomach poison such as arsenate of lead.  Many of the tiny,
newly-hatched larvae will be killed by the poison when they crawl up the
plants and chew holes in the sprayed leaves.  If the spray solution also
contains a contact insecticide, then any small larvae that are hit by the
mixture will be killed.  The following combination makes a good spray: 1
ounce (about 4 level tablespoonfuls) of lead arsenate, 2 teaspoonfuls of
nicotine sulfate, 1 tablespoonful of mayonnaise dressing, and 1 gallon of
water.  The mayonnaise dressing helps greatly to make the mixture cover and
adhere to the glossy leaves of the iris plants.  Treatments should start
when the eggs begin to hatch, about the first of May in the vicinity of
Ithaca, and earlier in the southern part of the State.  A second
application should follow a week or so later.







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