Effects of seed treatments on Iowa corn yields

click image to zoomFigure 2. Mean number of plant-parasitic nematodes in soil samples collected at the V5 corn growth stage in the experiment in central Iowa (near Ames) in 2011. “misc.” = miscellaneous plant-parasitic nematodes present in very low numbers. Bars with different letters above them had significantly different total numbers of plant-parasitic nematodes (P=0.10). Nematode results

• There were no significant differences in numbers of plant-parasitic nematodes in the soil among the treatments at planting in any experiment or in the soil at the V5 to V6 corn growth stage in the experiments in northeast, southeast, and southwest Iowa.
• In the experiment in central Iowa, there were significant differences in total number of plant-parasitic nematodes in the soil among the treatments at the V5 sample date, with fewer total nematode numbers in the Counter and Votivo treatments (figure 2).
• In the experiment in northwest Iowa, spiral nematode numbers and total numbers of plant-parasitic nematodes in the soil were lower in the treatments with Avicta, Counter, and Votivo and the Cruiser + Maxim Quattro treatment (minus Avicta) than in the treatment with Poncho + Acceleron fungicides (minus Votivo) (figure 3).
• The numbers of spiral, root-lesion, lance, dagger and pin nematodes in all experiments at planting and at the V5 to V6 corn growth stage were well below established damage thresholds for those nematodes.
• Very few nematodes were recovered from the root samples; those data were not used.

click image to zoomFigure 3. Mean number of plant-parasitic nematodes in soil samples at the V6 corn growth stage in the experiment in northwest Iowa (near Sutherland) in 2011. Bars or segments of bars with different letters are significantly different (P=0.10). Corn yield results

• There were no significant differences in yield among the treatments at any of the five experiments.
• Overall mean yields for the experiments were 195 bushels per acre in northwest Iowa, 205 bushels per acre in northeast Iowa, 151 bushels per acre in central Iowa, 154 bushels per acre in southwest Iowa, and 129 bushels per acre in southeast Iowa.
• Corn yields were low in central, southwest and southeast Iowa experiments. There was some hail damage and gray leaf spot developed in the experiment in southwest Iowa. In the experiment in central Iowa, there were wind lodging problems later in the season, possibly related to poor stalk health.

Summary
The nematode management products did not consistently reduce numbers of plant-parasitic nematodes or corn yields in the experiments that were conducted in 2011.

The low population densities of plant-parasitic nematodes that were present in the field did not affect corn yield in the experiments. The numbers and types of nematodes in the experiments were similar to those frequently found in samples submitted to Iowa State University for testing for nematodes that feed on corn from 2000-2010 (see ICM News article).

The nematode management products may have a much more pronounced beneficial effect in fields with very damaging nematode species (like needle nematodes) and in fields with much greater plant-parasitic nematode population densities.

For more detailed information about the methods used and results of the experiments, contact the first author or consult the 2011 annual reports of the ISU Research and Demonstration Farms.