Autumn is the perfect time to seed new and damaged areas. Given heavy golf schedules or inclement weather, seeding may be delayed until October, when expected frosts could delay or prevent good establishment. After mid-October, covers generally are advisable to hasten establishment of bentgrass seeding’s of tees, approaches and other important areas. Many common soil fungi can parasitize seeds and seedlings, but Pythium and Rhizoctonia spp. are among the most common causes of damping-off. Recently, we have experienced warm, humid, and overcast weather, which has been conducive to Pythium and Rhizoctonia damping-off. After the predicted hurricane, weather will likely cool, but bentgrass seedlings grown under covers could be affected by not only the aforementioned, but also Microdochium patch.
Damping-off often appears patchy with severely thinned-out areas non-uniformly distributed throughout areas of turf with good density. Stands also may appear spotty with small patches of yellow, orange or collapsed plants distributed non-uniformly. Pythium and Rhizoctonia blight progress rapidly (24 to 48 hours) during warm and humid weather, initially causing seedlings to appear darkened and water-soaked. Gray or brown-colored foliar mycelium may be present. Infected seedlings quickly shrivel and collapse, turn brown and die. Dead seedlings may be matted and have a greasy appearance and/or a soapy feel. In the case of Microdochium patch, blighted areas usually are circular and bronze-colored. While Pythium and Rhizoctonia are most active when average night temperatures are above 68oF; Microdochium can be active when average night temperatures range from 45 to 65oF.
Other factors that can enhance damping-off include: old and slow to germinate seed; seed planted too deeply; poor seed to soil contact; excessive nitrogen fertilization; excessive irrigation; poor surface and/or internal water drainage; poor air circulation; not mowing when needed; and leaving heavy clipping deposits.
Covers are helpful in promoting mid-to-late October bentgrass seeding’s in high profile areas. The goal is to get seed out of the ground, but if it starts to cool-down dramatically, keeping covers on is commonly done to promote full coverage. Superintendents have to make sure they are well protected against damping off, because it can be devastating under covers. Monitoring temperatures under covers can provide some helpful insights. Managers need to look under covers in the morning every two or three days, and check the temperature at that time. Some mangers make the mistake in thinking that one application of a Pythium-targeted fungicide is all that is needed. Indeed, it is best to apply both a Pythium-targeted fungicide along with a broad-spectrum fungicide to preventively control Rhizoctonia and Microdochium damping-off, and other potential pathogens. It is best to apply a tank-mix of both a Pythium– targeted and broad-spectrum fungicides just after most seedlings appeared to have emerged, but another application may be needed in 14 to 21 days if night temperatures don’t chill consistently. It is very important not to ignore the need for mowing. Remember the one-third rule, and mow before seedlings get too high and lanky. Mowing actually promotes growth, tillering and the filling-in process. Mow when the canopy is dry and the seedbed is firm enough to support equipment and foot traffic. Blow or otherwise remove excess clipping.