Corn producers may notice something a little different as they open bags of corn seed this spring. For more than two decades, Captan alone was the standard corn seed treatment in the United States. Last year, much of the corn seed was treated with Captan plus Apron (metalaxyl). Gradual trends toward earlier planting, more reduced tillage, and a string of bad weather has fostered a desire for better protection of corn seeds and seedlings against Pythium. Apron is more effective against Pythium than Captan, and the systemic activity of Apron potentially will be more persistent during those long, cold Iowa springs.
Another change is occurring this year. This is the first year that a large proportion of corn seed has been treated with a new seed treatment fungicide, Maxim. We have been hearing about this product for a few years, but it was only recently registered, and only a small amount of Maxim-treated seed was available last year. This year, several large and small seed companies will be using Maxim. Novartis, the manufacturer, estimates that Maxim will be used on over 32 million acres of corn in the U.S. in 1997!
The active ingredient in Maxim is fludioxonil, a new fungicide developed by Ciba-Geigy (now Novartis). It is very effective against Fusarium and other corn seedling pathogens, but not against Pythium. Therefore, Maxim is always applied in combination with Apron. So this year nearly all corn seed will be treated with either Captan/Apron or Maxim/Apron.
||Corn seedling infected by soilborne fungi.
||Seed treatment experimental plots: nontreated seed plot in foreground, treated plot in background.
Will producers see a performance difference between Maxim/Apron and Captan/Apron? Maybe. Many field tests have compared these products; sometimes Maxim/Apron is superior, and sometimes Captan/Apron is superior. In 1995, Iowa State University researchers planted two experiments to compare these products and others. All seed treatments caused dramatic increases in emergence (see photo) but there was little difference among treatments; in one experiment, Maxim/Apron was slightly better and Captan/Apron was slightly better in the other. The difference was not statistically significant in either experiment.
Overall, my opinion is that the two combinations are very similar in performance. In certain conditions (I don't know which ones), individual producers may find one product to be superior. The primary advantage of Maxim is probably not as much with performance as with handling. It is applied at a much lower rate than Captan (2.5 grams per 100 kilograms of seed versus 55 grams per 100 kilograms of seed), and does not tend to dust-off like Captan. It appears to be a safer and easier product for seed producers to use, and it may be more pleasant for corn producers to handle.
Planter-box seed treatments can be used in addition to the commercially applied treatment. If insect control is the goal, this can be an effective practice. It is unlikely that planter-box treatments will improve disease control for already-treated corn seed.
This article originally appeared on pages 43-44 of the IC-478 (6) -- April 28, 1997 issue.