Leaf Strip

Other Iris Pests and Diseases

Root Rot: Outbreaks of bacterial soft rot usually occur when excessive moisture is present. It is often associated with some sort of injury to the rhizome, as caused by insects or cultivation. Over watering and over fertilizing are potential causes of this foul smelling problem. Often it appears first at the base of the leaves where they join the rhizome, and is manifested by a yellowing of the fans. Keep a sharp eye out for such signs during wet weather. The sooner the problem is detected the more successful your treatment will be. The soft mushy tissue must be removed. If soft rot occurs in established clumps, it is easiest to cut out the affected rhizomes, thus minimizing the injury to the healthy rhizomes that remain.

If you are not dealing with an established clump, you may remove enough soil from around the rhizome to expose just the affected area, leave the roots that anchor the plant in place. Then, using an old spoon or knife, carefully scoop out all the mushy tissue. If the problem seems extensive, you may elect to dig the plant up to remove all the rotten tissue.

The wound made to the rhizome while removing rotten material should be disinfected. Some gardeners dust with sulfur, we suggest drenching with a bleach solution (1 part bleach to nine parts water) after the wound has been disinfected, allow the sun to dry and heal the wound several days before covering with soil.

Leaf Spot: This common fungal problem appears with wet conditions: rain, high humidity, fog or even overhead irrigation. Small yellow and brown spots appear near the tops of the leaves and eventually spread downward, consuming the leaves. In most cases this disease is unsightly and destroys some leaves. In extreme cases, if allowed to progress unchecked, the rhizomes may rot.

The spores that cause leaf spot can live over the winter on garden debris. It is important to keep a clean garden. Be sure to remove old dead iris leaves. Keep an eye out for the onset of leaf spot during wet weather. Cut off and destroy any leaf or part of a leaf that is affected. Not only does your garden look better, but you are also removing the fungal spores.

Starting in the spring when conditions for leaf spot are favorable, a regular biweekly spraying program is recommended. Start spraying when the leaves are 6 to 8 inches tall. Spray less often if the weather is dry, more often if rain washes it off. Most fungicides are helpful in the control of leaf spot, however Daconil. And Triple Action 20 are two that do not seem to lose their potency. Triple Action 20 biodegrades in approximately 48 hours after spraying and is environmentally harmless. Daconal is available at most garden supply centers. Triple Action 20 is only available through Spray-N-Grow P.O. box 2137 Rockport, TX 78381. www.spray-n-grow.com

Orthacheta Bud Fly: The bud fly lava is a hybridizer’s nightmare, it is a small white maggot that bores into the side of an iris bud to eat the pollen in side. The standards and style arms are usually destroyed in the process. When the blossom opens it is disfigured. They like siberian irises best, but will attack other irises including louisiana iris. When you see a small hole in the side of a bud or a disfigured blossom, remove it and check the stem. If there is no sign of passage, then you have it. Carefully break the bud or blossom apart, look for the maggot and destroy it. You can also put them into a zip lock bag for destruction. If the stem shows sign of passage, then the maggot has gone down the stem to change into the fly. Another good way to control an out break of the Orthacheta Bud Fly is to spray with a systemic when the buds have formed, this can be done when spraying for iris borers.

Other Pests: Sucking insects such as aphids, thrips and white flies can damage iris and spread diseases. Control these pests by spraying a pesticide such as Isotox or Malathion. Check the registration of which chemical you use, and follow the manufacture’s recommendation for rate and timing of application. Insecticide soaps are effective control of most pests, while not harming beneficial insects. Bacillus thurgingiensis (b.t.) is an environmentally safe and effective control for chewing insects such as caterpillars.

Slugs and Snails: Other chief enemies of iris are slugs and snails. They love to chew on iris leaves causing damage which is unsightly. Diseases can get into the rhizomes through the damaged areas left by these land mollusks. Keeping a clean garden by removing protective cover for snails and slugs is a good beginning. In early spring when evidence of slug or snail damage is present, bait for these pests is a good method of control. You can choose the type of bait that you think is best for your environment. Bug-Geta (pellets), Deadline (liquid), and Deadline Force II (dust free meal) are some that you can spread. Terminator Turtle and beer in a cup are baits that work in small areas. Copper tape will keep them out of an area because they will not cross it. Diatomaceous Earth also controls earwigs, silverfish, beetles, and crawling insects in addition to slugs.
Gardening Tools: Trowel
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