Timing of August Seedings Can Protect Alfalfa
Ohio and Indiana farmers who properly time their no-till alfalfa seedings in August can reduce the risk of infection by Sclerotinia crown and stem rot, says Ohio State forage agronomist Mark Sulc.
Sclerotinia causes serious stand and yield losses. The risk of damage is greatest in no-till seedings in fields with a recent crop history of clovers or alfalfa, Sulc says.
He says a recent two-year Ohio State study showed that seeding by certain dates in late summer helps reduce infection better than planting closer to autumn. Make no-till seedings as early as possible in late July or early August to reduce Sclerotinia damage, he says.
For conventional seedings, farmers in northern counties of both states should seed by Aug. 15 to 20. Those in the south have until Sept. 1. In any event, spring seedings are the safest bet of all.
In its field trials, Ohio State made no-till seedings in May, early August, mid-August and late August. Averaged over two years, the proportion of the stand affected by the disease was 4 percent, 12 percent, 23 percent and 41 percent, respective to each of those planting dates.
In addition, the average yield data the year following seeding correlated to the disease severity and planting date. In the order of seeding dates, respectively, yields were 98 percent, 94 percent, 85 percent and 73 percent of non-infected control plots.
Older seedlings apparently have greater resistance during the height of the infection season, mid-October and December. May-seeded plants were over 23 weeks old by then. Seedings in early, mid- and late August were about 10, 8 and 6 weeks old, respectively, by mid-October.
"Infection occurs in late fall when spores are released from tiny, mushroom-shaped structures on the soil," Sulc says. "The white-mold fungus kills plants during the winter and early spring.
"Once producers see stand decline in spring, they can mistake it for winterkill or weed encroachment."
Unfortunately, August's typically dry weather may delay plant emergence. An early-planted crop may become established late, and be more vulnerable to infection. However, resistant varieties will afford some protection in cases of late emergence.
Ohio State's laboratory and field testing is identifying resistant varieties for use in a farmer's total management program.
"We have some varieties coming on the market now that have improved resistance," Sulc says.