Whacky Winter Weather Worries

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Virginia Cooperative Extension - Knowledge for the CommonWealth

Whacky Winter Weather Worries

Crop and Soil Environmental News, January 2007
Mike Goatley, Shawn Askew, Brandon Horvath, Rod Youngman, and Erik Ervin

This article is being prepared during the third week of January, 2007 so you will have to cut the VT Turf Team a little slack if our crystal ball turns out to be not quite as clear as it should have been. As we write, Blacksburg has just come out of its first winter storm of the season and at month’s end, the coldest weather of the year. The abnormally warm winter temperatures for much of December and early January (resulting from a strong El Nino in the Pacific) have caused lots of turf managers to scratch their heads and wonder just what this means later when spring officially arrives in late March. Long-range temperature forecasts from the National Weather Service’s Climate Prediction Center suggest continued above average temperatures through April and generally normal precipitation amounts. However, other forecasts indicate that El Nińo has dissipated and that we will have a colder than normal late winter period (and with the temperatures of late January, we’re starting to believe maybe THIS is the most accurate forecast). There is nothing more unpredictable than the weather, but what the heck -- we’ll take a stab at some of the things that you might be seeing from a turf manager’s perspective as a result of this winter’s whacky weather.

What’s going on with our turfgrasses?

Late-season plantings of all grasses (both warm- and cool-season) have generally done very well due to moist soils and abnormally warm temperatures. Warm spring soils can promote a strong spring root system in cool-season grasses maintained under a responsible N fertility program. Warm soils will also promote recovery from spring cultivation events. Many of our turfs need a lot of recovery potential this year. Depending on your perspective, the winter warmth was either a blessing (more revenue potential) or a curse (lots of play during what is traditionally a “down” time for your turf) for outdoor sporting activities.

There are special concerns with warm-season grasses this winter, especially in the Piedmont and Tidewater regions of Virginia. As this article is being prepared, the immediate concern is what is going on with our warm-season grasses during the extreme cold of late January when temperatures dipped into the teens in the Richmond area and into the low 20s along the coast. Most warm-season grasses had not gone fully dormant through mid-January across the state. (Insert Picture 1. Caption: Much of the bermudagrass at the Turfgrass Research Center in Blacksburg still had bright green stolons as of the first week of January, 2007.) We have no intent of being alarmists, but these extreme cold events on grasses with varying levels of winter hardening are worrisome and demand some attention. Degrees of winterkill are virtually impossible to predict, but it is certainly logical that extreme temperatures are a major contributor. Also remember that other limiting factors (inadequate physical or chemical properties of the soil, disease, moisture extremes, traffic, etc.) often compound winterkill, so pay attention to your traditionally weakest turf as you assay potential turf damage this spring.

If temperatures generally stay above average and we dodge extended Arctic cold, a mild winter can be highly advantageous to warm-season grasses IF they can make it into a desirable growing period in the spring and escape late freezes. Our experience indicates that “spring kill” is often as likely to occur as winterkill during seasons when our warm-season grasses get an early start on spring growth and then get heavily damaged by a late freeze. When this happens, all the new shoot tissue that was developed by utilizing most of the carbohydrate reserves is destroyed and the plant can’t make enough food by photosynthesis to meet its needs. These plants literally can starve to death under repeated spring frosts.

Unfortunately, there is not a lot you can do on a large scale basis to protect your turf during winters like 2006-07. If you are trying to ascertain possible winterkill severity this spring, there are numerous ways you can check your turf. Remove plugs and look for pliable, fleshy stems and roots that have healthy color (creamy white for rhizomes and roots, and very light green for stolons). Bring numerous plugs indoors and see how completely they green. Another field assay technique on a larger scale basis is to promote greening by applying clear plastic to the turf. After just a few days under the plastic you will have an idea of how much turf is alive.

To combat late-season freezes, athletic field managers might use turf blankets on their bermudagrass fields for freeze protection, but for the rest of us the most important factor will be to keep away from encouraging too much spring shoot growth by way of heavy N fertilization. Review expected “last freeze dates” in your area to help make sound agronomic decisions this spring regarding fertility and chemical options. (Note: This information can be found in the climate section of your county soil survey map that you can access at your local Virginia Cooperative Extension office.) Let the turf grow as Mother Nature is prompting it, but be careful not to promote excessive late winter/early spring growth when there is still the potential for a freeze event.

What about diseases?

The major concern is going to be spring dead spot (SDS) severity on bermudagrass. Unfortunately, we don’t know what effect temperatures have on the activity of SDS. So, this winter could be either great or devastating for warm-season grasses. SDS is incited by a soil-borne pathogen that infects bermudagrass roots, and some reports suggest a mild, moist winter results in less SDS damage. Conversely, highly variable weather patterns that oscillate from warm to extreme cold can promote SDS damage. There is nothing that can be done about SDS at this time, so if wide scale damage is evident this spring, be prepared to regrass or to encourage regrowth with appropriate N fertility programs.

There also was quite a bit of dollar spot pressure being reported on cool-season grasses during the record warmth of December and January. It is likely the cold snap of late January will put a cease to this activity, but if above average temperatures return in late winter/early spring, anticipate that you will have to initiate your preventative treatment programs a little earlier than usual to get the jump on this disease. Similar strategies apply to managing summer patch and Rhizoctonia blight: they will show up a little earlier if the weather is warmer than usual.

What about weeds?

Our winter annual weeds henbit, chickweed, lawn burweed, etc.) like a mild winter just as well as our turfgrasses and there are some great stands of winter weeds already in place. Warmer temperatures are conducive to their control with most of our standard two and three-way postemergent herbicides labeled for this use. Remember that thick populations of winter weeds go hand in hand with heavy summer annual grass pressure following the death of the winter weeds later this spring.

And speaking of annual grasses? What effect does a mild winter have on annual bluegrass and crabgrass populations? There was no doubt a sacrificial population of crabgrass that emerged and was then killed by the cold in eastern Virginia this January. But will this sacrificial crabgrass event make a big difference in your crabgrass population later this spring? NO. There is plenty more seed where that came from. A healthier, thicker stand of grass resulting from a warm winter will provide the best weed control possible, so warm weather might actually help us in terms of germinating weed pressure. It is also likely that higher than average winter temperatures will move our PRE herbicide application dates up a week or two as compared to average years, but the only way to really know this is by charting growing degree days. Growing degree days are calculated as the average of the maximum and minimum temperature for a given day minus the base temperature for crabgrass germination (50 F). Thus, a maximum of 75 and minimum of 27 gives us one growing degree day. If the value is negative, zero growing degree days are added to the running total. Crabgrass starts emerging when the running total reaches 70 to 140 units. You can also keep an eye on soil temperatures and expect emergence after 4 to 5 days of temps reaching 55 to 58 F. Forsythia bloom is usually a good indicator in northern climates with crabgrass emergence occurring at 50% bloom drop but plants like Forsythia, dogwood, and daffodil will probably be less useful this year due to the sporadic warming trends in December and January. Finally, when thinking about your crabgrass preemergence program this year you might also think about any bermudagrass winter kill and your subsequent strategy for renovating damaged areas. Newer seeded bermudagrasses give us an excellent option for rejuvenating damaged areas, but these seeded grasses are sensitive to crabgrass herbicides and may not be seeded for as much as four months following treatment with a crabgrass preemergence herbicide. If you expect winter kill, consider using postemergence crabgrass herbicides such as quinclorac (Drive) or MSMA until after new bermudagrass has become established and then follow with a preemergence treatment.

We already know that the warm winter has resulted in an early flush of annual bluegrass. This plant was flowering in early January all across Virginia. More normal temperatures have likely slowed flowering somewhat, but if you are using Growing Degree Day models to time plant growth regulator applications you will probably see that they will be going out earlier in 2007 as well. Plants will be larger this year and seedhead production will be discontinuous with some plants already initiating seedhead production earlier in the winter. Expect seedhead suppression to be more difficult this year. If you find your chemical seedhead controls lacking, remember that vertical mowing and increased mowing frequency can drastically improve putting green conditions but the effects are short lived.

The increase in winter weeds due to warm temperatures has increased our desire for broad-spectrum vegetation control on dormant turf. Much concern has been voiced recently over use of glyphosate (Roundup) on semi-dormant bermudagrass and zoysiagrass. If you plan to “burn down” winter weeds and your turfgrass is not as dormant as you like, keep the following points in mind:

What about insect activity this spring?

Dr. Youngman and staff went to the field to scout for white grub activity in mid-January to determine if the warm weather had caused them to begin migrating upward in the soil to feed on grass roots. This sampling showed that the grubs were still at a 5 to 6 inch depth and had not begun their ascent in the root zone. Hence, he feels that our standard grub control programs and timing will likely be appropriate again in 2007.


Hopefully this article will better equip you to make informed decisions regarding your turfgrasses this spring and educate your clientele about the expectations (or lack thereof) with our turfgrasses following a roller coaster of a winter. The weather continues to be one of the best ways to make conversation, and if you really want to liven up your parties start talking about global warming! Virginia’s climate has long presented challenges to its agriculturists. For instance, consider this bit of recorded information:
May 4. the blue ridg of mountains covered with snow.
[May] 5. a frost which destroyed almost every thing. it killed the wheat, rye, corn, many tobacco plants, and even large saplins. the leaves of the trees were entireley killed. all the shoots of vines. at Monticello near half the fruit of every kind was killed; and before this no instance had ever occurred of any fruit killed here by the frost. in all other places in the neighborhood the destruction of fruit was total. this frost was general & equally destructive thro the whole country and the neighboring colonies.

This comes from Thomas Jefferson’s Garden Book of 1774. Even the author of the Declaration of Independence had issues with the weather.

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