Return to the Iris Forum | Post a Follow-Up

 o
TB Iris Borer Attack

Posted by achang89 Central NJ Z6b (My Page) on
Wed, Jul 9, 14 at 13:52

I have had the two Iris beds for several years and they had been care-free for the years. But this year, it finally catches up with me.

This spring, the Irid beds did not send many blooms. I thought they are just too crowded and should be divided. But this is worse. The beds never come out and completely overran by the weeds.

I just cut down the weeds and removed the old leaves. No surprise, it is the Iris Borer attack. Both beds, in very bad shape. See photos:

 photo 20140709_132513.jpg

 photo 20140709_132529.jpg

 photo 20140709_132437.jpg

 photo 20140709_132455.jpg

They should be still viable. I plan to dig them up, clean and soak them in bleach. Then replant them.

My question is that, what should I do with the old beds? Should I treat the beds? Or I can safely plant other things, like corn and tomato etc?

Then how long can I plant Iris again in the same beds?


Follow-Up Postings:

 o
RE: TB Iris Borer Attack

The website this was taken from is no longer but it came from University of Nebraska Department of Entomology and I copied it when Dan M. posted. A search may turn up the original post. And others with more information. Cygon is considered the truly effective treatment. Good Luck.

RE: iris borers
Posted by: Dan M - MA (danmc77@juno.com) on Wed, Jun 21, 00 at 15:07

This insect is the most serious insect pest of iris in Nebraska and is found virtually everywhere in the state. Damage is characterized by dark, streaked, or watery areas and ragged edges on the developing leaves of iris in May and June and extensive destruction of the insides of the rhizomes in July and early August. Examination late in summer will reveal a large white to pinkish caterpillar from 1 1/2 to 2 inches long in the rhizome, usually accompanied by a foul-smelling soft rot.

Life History

Adults (moths) emerge in September and October from the soil, mate, and deposit eggs on the dead leaves, particularly those that are dried and crinkled. Eggs usually are laid in crevices or rolled areas of the leaves, in groups of three to five or more. A single female moth is
capable of depositing up to 1,000 eggs in her lifetime.

The egg overwinters and begins to develop in early spring. Eggs hatch during April and May and the young larvae begin to feed on young, rapidly growing iris leaves.

After feeding on leaf surfaces, causing scars from which sap runs down the leaf, the larvae assume a boring habit, entering the leaves and gradually mining downward. Leaf mining injury is characterized by dark, water-soaked areas or slits in the leaves. Some chewing also occurs on leaf margins.

When about half-grown (one-half to three-fourths inch long), iris borers reach the rhizomes, where they feed until late July or early August. As the borers feed, bacteria infect the rhizome, initiating the soft rot.

When fully grown, iris borer larvae are about 2 inches long, cylindrical, smooth, and plump with whitish to pinkish bodies and dark brown heads. Shortly after this stage is reached the larva leaves the iris rhizome and constructs a "cell" in the soil where the pupa stage is passed.

The pupa is a non-feeding transition stage between the larva (or worm) and the adult moth. Pupae are dark brown to black and are usually found in the top 2 inches of soil. After two to three weeks in the pupa stage, the iris borer moth emerges and the cycle is completed when the eggs are deposited. Moths are typical millers--dark grey to brown, with a wingspan of about 2 inches. There is only one generation per year.

Prevention

One key to iris borer prevention is removal and destruction of the previous year's dead foliage before April 1. This sanitation practice will reduce the problem by destroying overwintering eggs in the residues.

Control

Insecticide sprays of dimethoate (Cygon), lindane, malathion, or chlorprifos (Dursban) can be applied in late April through early May to kill larvae feeding on the leaves. At least two applications should be made, two weeks apart, to obtain satisfactory control. Many larvae can be
killed by hand in May and June by squeezing infested leaves between the thumb and forefinger in the vicinity of the feeding injury. Destroy heavily infested rhizomes, along with the larvae. Some borers in the rhizomes can be killed by poking them with a piece of wire.

When resetting your iris beds, it is important to trim away damaged or rotted areas. To eliminate soft rots caused by bacteria, cut off the damaged parts of the rhizomes and dip the undamaged portions in a solution of 1 part of household chlorine bleach and 10 parts of water.


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Iris Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here