Damage from last summer is reconfirmed as turf is greening up with Spring. Repairing these damaged areas may require complete reseeding of the area or at least overseeding the remaining surviving turf. Unfortunately, spring seeding of cool-season turf like Kentucky bluegrass or tall fescue is difficult because of pending summer, weed pressure, and/or disease issues. Late summer (August) is easily the best time to seed cool-season grasses, but sometimes turf must be seeded in the spring. The following should help improve the success of spring seeding:
Seed as soon as possible to maximize the amount of time seedlings have to establish before summer weather. Mid-May is usually the cut-off for spring seedings and later seeding dates increase the chances for having to do it over in August.
Improve the seed-soil contact by aerifying, power raking, and/or hand raking before seeding. After seeding, a light raking will further mix the seed and soil or a light rolling will push the seed into better contact with soil.
Water lightly and often to keep the seedbed moist. Mulch will also work to conserve water, but use sparingly and so at least 30-40% of the soil is still visible through the mulch. Additionally, straw mulch often brings in weed seeds which may become problematic.
Avoid any preemergence crabgrass herbicides over the top of the seedings and if they have already been applied, wait to seed in August unless products containing siduron were used. Weed control is important because weeds will quickly take advantage of the thin turf. Following are general guidelines, but check the label of your product for specifics:
o Mesotrione (Tenacity ) or siduron (Tupersan ) can be used in the seed bed and will likely provide three to four weeks of PRE control of crabgrass.
o SquareOne (quinclorac+carfentrazone) can be applied within 7 days after emergence (DAE) of tall fescue or Kentucky bluegrass for POST control of crabgrass and broadleaf weeds.
o Mesotrione (Tenacity ) can be applied POST to Kentucky bluegrass or tall fescue at 28 DAE to control crabgrass and some broadleaf weeds.
o Dithiopyr (Dimension , Dithiopyr ) can be applied once the root system is well established and after at least two mowings for PRE/POST control of crabgrass.
o Quinclorac (DRIVE XLR8 , Quinstar , Quinclorac , and others) can be applied PRE or 28 DAE of Kentucky bluegrass or anytime over tall fescue for POST control of crabgrass and some broadleaf weeds
o Carfentrazone (QuickSilver ) can be applied at any time after seeding for POST broadleaf weed control
Since the seedlings will not develop a good root system until next fall, low rates of fertilizer applied frequently will be most effective. Applying 0.5 to 0.75 lbs N/1000 sq ft every 4 to 6 weeks until mid-June should help the grass fill in.
Again because of poorly developed root systems, keep the newly seeded areas well-watered all summer.
Mow as soon as the first few seedlings reach the mowing height for the area. Early and frequent mowing will encourage the seedlings to spread.
If hot and humid weather is in the forecast, a fungicide application maybe needed to minimize damping off, pythium, and/or brown patch. Night temperatures >68F are conducive to these diseases, but hopefully will not occur for a couple of months.
Zac Reicher, Professor of Turfgrass Science, zreicher2@unl.edu