This article was published originally on 9/15/2010
The following are highlights and updates about samples and questions recently received in the Clinic:
Calls and samples continue to come in concerning lawns that look "blotchy" to "terrible." See the earlier newsletter article for information for the effect of summer stress on lawns.
White grubs should be obvious by now if these common root-eating insects are the cause of unthrifty or dead grass. Obvious that is, if you are on your hands and knees, pulling up the dead turf and looking for the three-quarter inch long grubs at or just under the soil surface. See the photo below. If grubs are not present, then grubs are not the cause of the dead grass and insecticides will be wasted if applied.
If you do have white grubs, you are very limited to what is effective for curative control (treatment after grubs are present), and time is growing short. Treatments after mid-October are not effective and to be effective the insecticides MUST be immediately watered into the soil with at least 0.5 inch of irrigation, putting them out of reach of children and pets. Modern insecticides used for white grub curative treatment are trichlorfon for homeowners and Acelepryn and clothianidin for commercial applicators. Read more online at the Iowa Insect Information Note.
Lawn rejuvenation by seeding should be completed by mid-September in northern Iowa. Gardeners in southern Iowa can sow grass seed up to October 1. A late summer to early fall seeding has several advantages over spring seeding. The seeds of cool-season grasses germinate quickly in the warm soil of late summer. The warm days and cool nights of early fall promote rapid turfgrass growth. The growing grass also has less competition from weeds as few weed seeds germinate in the fall.
The wet weather has been hard on many tree species. We are getting many reports of leaves falling prematurily. This could be due to stress or the many fungal leaf diseases that have plagued trees this summer. Although it is unfortunate to loose the leaves early, especially if the tree normally has good fall color, there is nothing to do to reverse the problem and there is no need for any treatments with pesticides or fertilizers. This late in the season the leaves of deciduous trees have done their jobs and are no longer necessary for the health of the tree. The more important thing will be how well the tree leafs out next year. If foliage is sparse or there is branch dieback then it is time to contact the Plant & Insect Diagnostic Clinic so we can help you figure out what is going wrong.
Oaks have had a particularly rough time this year with some freeze injury to leaves from the late frost and anthracnose. Anthracnose and freeze symptoms appeared early in the year, but in the past month or another fungal disease has been causing leaves to brown - Tubakia. Researchers in the Plant Pathology Department are studying this disease and there are as many questions as answers. One Tubakia sp. fungus on Bur oak has been dubbed Bur Oak Blight. For more information on this Tubakia caused disease on only the Bur oaks please see this article.
Also be aware oaks can suffer from oak wilt, a serious vascular disease that will eventually kill the tree. For more information on the symptoms of oak wilt and how to test for it please see our pamphlet Oak Wilt - Identification and Management.
Mole crickets are an occasional invader found inside homes and other buildings. They are only moderately common in Iowa. The name describes the insect well. The back end looks like a cricket and the front legs look like they came from a mole. See the photo below.
Mole crickets live in the ground (they dig like a mole) but cause no real damage to Iowa lawns, gardens or landscapes. As a harmless accidental invader, they need only be swept up and discarded. See our Iowa Insect Note for more information.
Mole crickets look alien but are moderately common throughout Iowa. Photo by Deb Christiansen.
White grubs are found on or near the soil surface under damaged turfgrass. Photo by Larry Ginger.