Corn Rootworm or Crow Damage?

Last summer, I saw two cases where corn seedlings pulled by crows were misdiagnosed as western corn rootworm (WCR) damage. In the first case, the grower guessed wrong. Possibly, he had recently read a lot in the popular press about WCR moving into the Northeast. By getting a correct diagnosis from Extension, this grower may have avoided the costly mistake of including unnecessary soil-applied insecticides for rootworm control in future plantings for years to come. In the second instance, the damage was misdiagnosed by a pesticide salesman, who then recommended the wrong cure. The salesman seemed genuinely surprised and thankful to find out what crow damage to corn seedlings could look like. The grower was relieved to find out he could drop the $17 per acre treatment. It is crucial to be able to correctly diagnose such problems on your farm to protect your future profitability and the environment.

With the withdrawal of mesurol as a seed treatment, crow damage after planting has become much more common. Crows will not restrict their corn seed feeding to the pre-germination or pre-emergence stage. They will pull up small corn plants to feed on the remains of the attached seed. When the birds drop the plant, most of the roots are left exposed to the air and simply stop growing. These stunted (1/8 to 1 inch long) roots remain in contact with the soil and continue to grow. A single root can keep the plant alive, lying on the soil surface for a week or longer, until the corn is more than a foot in length (Fig. 2). Obviously, this type of damage is limited to seedlings, during or shortly after the corn planting season (May to early July).

The larvae of northern corn rootworm and WCR usually feed on the corn roots for about three weeks from mid-June through mid-July. Lodging (rare in the Northeast) does not occur until the corn is full grown in late summer, when high winds blow the root-pruned plants over. Rootworm injury leaves the feeder and brace roots brown to black in color and chewed off almost flush to the stalk.

A 1992 Animal Plant Health Inspection Service (USDA-APHIS) survey found WCR in all six New England states, but at extremely low population levels. One researcher reported that WCR composed only three to four percent of the total rootworm population. The New England site with the highest number of beetles in the survey had less than 1/10 the population found in Maryland. The populations at all sites were far, far below economic thresholds. Is WCR anything to worry about in New England? Not yet!

If you receive a sales pitch expounding rootworm as a reason for applying soil-applied chemicals, keep in mind that this is simply a new twist on an old theme. In the past, soil-applied insecticides have been promoted for European corn borer control or cutworm control. Ironically, the three worse cases of cutworm damage to corn and peppers that I have ever seen or heard of (directly from the grower) were treated with three different soil-applied chemicals. While teaching people to scout these crops in IPM programs, I have demonstrated to growers that there is no reduction in the infestation of these pests in treated versus untreated fields. While the benefits of many of these chemicals are questionable, there are possible environmental costs.

Most of the materials traditionally used for soil applications are rated as potentially high or moderate leachers. Due to their direct application to the soil, such insecticides are also considered more of a risk to reach groundwater than foliar-applied materials with similar leachability ratings.

There are also the possible adverse effects on predators, parasites and soil microorganisms which compete with, or feed on disease spores, insects, mites and nematodes. There is more and more evidence accumulating that it is the diversity of the soil from fauna and flora which suppress insect pests. These pests include white grubs and diseases like damping-off caused by Pythium and Rhizoctonia, and Phytophthora. In short, applying an unnecessary preventive soil insecticide does not eliminate risk and may not help your bottom line.

Bird Control Options

As for crow damage, bird-shot, in-season hunting, hawk-kites/balloons, shell crackers (fire- works for 12 gauge shotguns) and propane canons may provide some relief, but are usually less than perfect solutions. A combination of bird-scare devices, each used for a short duration, will generally be more effective than relying on one technique.

Thiram (fungicide) seed treatment is supposed to function as a bird repellent to some degree. Some growers think it works well. If your seed companies do not use Thiram, you might request that it be used on all your corn and vine crop seeds or treat them yourself. The chemical 4-amino pyridine (Avitrol) is a restricted-use pesticide that may only be used by individuals trained in bird control (in Connecticut) by the Department of Environmental Protection Wildlife Division. The label states that “Avitrol is a poison with flock alarming properties” . . . and “birds that react and alarm a flock usually die.” Growers who have tried this product report inconsistent results. One article published in the Journal of Wildlife Management compared Avitrol with propane exploders and visual hawk-kites for control of red-winged blackbirds and grackles on field corn. The author found that the latter two were much more effective than the chemical and that the canon was the most cost effective and functioned almost as well as the kites.

Another possible control device that may fit into some growers’ management systems is an electronic bird-distress system called BirdGard. This system has up to three species-specific distress calls recorded on a microchip and is supposed to be more effective than older auditory devices which rely on a generic bird-distress sound. It is often advertised in American Fruit Grower magazine and sells for around $300. In Connecticut, you must obtain a permit from the Department of Agriculture to operate any noise-making device to control wildlife.


  • Conover, M. 1984. Comparative Effectiveness of Avitrol, Exploders, and Hawk-kites in Reducing Blackbird Damage to Corn. J. Wildlife Management. 48(1):109-116.
  • Hollingsworth, C. New England Western Corn Rootworm Survey. 1992. University of Massachusetts Cooperative Extension System.
  • Quarles, W. and J. Grossman. 1995. Alternatives to Methyl Bromide in Nurseries – Disease
  • Suppressive Media. The IPM Practitioner. Vol. XVII. No. 8:1-13.
  • USDA-APHIS Wildlife Services. Shell crackers for Bird Control. 463 West Street, Amherst, MA 01002.

Jude Boucher, Vegetable Crops IPM Program Coordinator, University of Connecticut Cooperative Extension System, Reviewed 2012.

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