Winter Kill - 2010 - Part 2

Winterkill 2010?
With colder than normal temperatures in Arkansas this winter, we are anticipating that some of our turfgrasses around the state may suffer from winterkill. To help prepare for this we are publishing a four part series on this topic to help turfgrass managers prepare for what may await them in the spring. Look forward to the following topics over the next four weeks.

Part I: Predicting the damage: What causes winterkill and how can we estimate our losses?
Part II: Preparation and recovery: What should you do or not do this spring to help your turf?
Part III: Planning and planting improved cultivars for a better future.
Part IV: Practices to enhance winter survival.

January 22, 2010

Part II: Preparation and recovery: What should you do or not do this spring to help your turf?
Spring management practices including whether or not to apply spring preemergence herbicide applications should be based upon your winterkill likelihood estimates.

Damage not likely
Minimal damage expected
Moderate damage expected
Severe damage expected

Damage not likely. Some may have little fear of winterkill including those who have zoysiagrass (almost all cultivars are winter hardy in Arkansas), a cold-hardy variety of bermudagrass, or those growing cool-season grasses such as tall fescue or Kentucky bluegrass. If you fall into this group consider yourself lucky or wise for making a good planting decision previously. Those who have little fear of winterkill may go ahead as usual and make their scheduled preemergence herbicide applications this spring.

Minimal damage expected. Those who manage areas of bermudagrass that are partly shaded, common bermudagrass stands known to thin in previous winters, or those growing St. Augustinegrass in southern Arkansas should expect some minimal damage. See below for preemergence herbicide strategy for areas anticipating winterkill.

Moderate damage expected. Those who manage shaded bermudagrass lawns in northern Arkansas and those growing St. Augustinegrass in central Arkansas. Additionally, those golf courses growing bermudagrass greens in central Arkansas may experience some damage. It is too early to tell whether this damage will be minimal, moderate, or severe, but some level of winterkill should be expected. See below for preemergence herbicide strategy for areas anticipating winterkill.

Severe damage expected. Bermudagrass putting greens, bahiagrass, centipedegrass, St. Augustinegrass in northern or north central Arkansas will likely suffer moderate to severe damage. See below for preemergence herbicide strategy for areas anticipating winterkill.

Preemergence herbicide strategy for areas anticipating winterkill. Early spring preemergence herbicides are often necessary in Arkansas to prevent troublesome annual grassy weeds such as crabgrass and goosegrass. Additionally, these applications help to prevent the emergence of some broadleaf weeds. Most preemergence herbicides work to kill weeds by preventing cell division causing death to weed seedlings shortly after they germinate. These products can also affect the rooting of established turfgrasses, especially when new stolons begin to initiate roots. Ronstar (oxadiazon) is the only preemergence herbicide that will not affect the rooting of stolons. Additionally, all preemergence herbicides work to prevent the emergence of turfgrass seeds as well as weed seeds, so do not reseed areas treated with a preemergence herbicide or do not apply a preemergence herbicide if you plan on seeding.

Therefore, if you expect some level of winterkill then it is advisable to skip or delay your preemergence herbicide application this spring. First, allow all of your turf to greenup this spring.

If little winterkill is noticed, then you may go ahead and apply your preemergence herbicide application after greenup. You may consider tank-mixing a postemergence herbicide in the tank as well to control any emerged crabgrass.

If moderate winterkill is noticed after greenup then you will either need to regrow these areas either by 1) waiting the for existing turf to recover or by 2) reestablish these areas from sod, sprigs, or seed depending on the species and cultivar present. If you choose to wait for the existing turf to recover then you could either apply Ronstar to control weeds not yet germinated or you could control existing weeds with postemergence herbicides. If you need to replant from sod, sprigs, or plugs then you should control weeds postemergently or use Ronstar as your preemergence source. Turf established by sod, sprigs, or seed are more susceptible to herbicide injury than established turf so please consult herbicide labels to see when these products may be applied after planting. Two extension publications (MP 476, establishing seeded zoysiagrass; MP 477, establishing seeded bermudagrass) provide detailed instructions on establishing bermudagrass or zoysiagrass from seed.

If severe winterkill is noticed after greenup then you will either need to reestablish these areas from sod, sprigs, or seed depending on the species and cultivar present. If you need to replant from sod, sprigs, or plugs then you should control weeds postemergently. Turf established by sod, sprigs, or seed are more susceptible to herbicide injury than established turf so please consult herbicide labels to see when these products may be applied after planting. Two extension publications (MP 476, establishing seeded zoysiagrass; MP 477, establishing seeded bermudagrass) provide detailed instructions on establishing bermudagrass or zoysiagrass from seed.

If plugs pulled from areas are not recovering at all and severe winterkill is expected, another strategy to get ahead of the problem in the spring is to dormant seed bermudagrass into areas where damage is expected. The basic approach is to scarify the areas with a verticutter or core-arefier and apply seed while temperatures are still cold (February or March). When soil temperatures warm in April, those seeds will germinate and hasten the establishment of bermudagrass. Be sure to irrigate in mid-April if there is no rainfall and control weeds using a postemergence herbicide after bermudagrass has emerged. See MP 477 for more information on dormant seeding bermudagrass.

Drs. Aaron Patton and Mike Richardson