Wireworms are occasionally a concern to farmers planting corn. Stand loss occurs in a very small percentage of Iowa cornfields, but where the problem does exist, it may persist for several years. Prevention of stand loss caused by wireworms can only be accomplished with the use of an insecticide. In the March 20 ICM newsletter, data from Missouri were presented that measured the percentage of healthy plants in several insecticide treatments. In this article, Iowa data are presented but the numbers measure the percentage stand increase over the untreated check. The Missouri and Iowa data cannot be compared because each is using a different method of evaluation.

Wireworm and damage to a corn seed.

Data from several Iowa experiments are shown in Table 1, below. Only those tests in which the wireworm population caused substantial injury (injury rating scale rated 2.0 or higher) to the untreated check plots are included. The wireworm injury scale is

1. seed or seedling undamaged;
2. seed or seedling damaged, but plant established;
3. seed or seedling damaged, plant showing some signs of stress; and
4. seed or seedling damaged, no plant or questionable establishment

Selecting the "best" product may be difficult because of the small number of times a product was evaluated or because of variability in performance over the years. A ranking of the products based upon their performance may be a convenient way of judging which products are most likely to provide the best seed and seedling protection.

Table 1. Comparison of efficacy of registered insecticides for control of wireworms in corn measured as percentage stand increase over the untreated check.

* Granular insecticides listed as oz(AI)/1,000 row-ft.

** 1 GPA water carrier.

*** Rating scale as described in text.