You’re dealing with the borer infestation in case your irises are yellow and wilted. Iris borers are a kind of moth that lays its eggs and stalk foundation. Their grubs, which resemble caterpillars that are pink-ish, distribute a bacteria that destroys the plant and tunnel through the soil ingesting rhizomes. Rid your home of the pests by maintaining a clear iris mattress among other techniques.
Remove all natural material which has fallen in to your iris mattress. This contains aged iris stems, leaves and rotted rhizomes, as well as any twigs and other natural matter. Matter that is such produces breeding places for borers. Cleaning beds of the materials is particularly crucial in the drop to prevent a spring infestation of borers, but should be done year round as a precaution.
Check for iris borers by digging rhizomes up and observing them for grubs which are whitish-grey in colour. Rhizomes suffering from borers are slimy, spongy and gentle. Discard infected plants when you they are found by you, or burn them, which is the most efficient technique of destroying borers.
Apply an borer insecticide to impacted divisions in the spring on iris foliage. Follow the maker label instructions for best results. Wear protective clothes and gloves, and use garden sprayer or a spray bottle to apply the insecticide.