Wacky Winter Weather Worries

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 maybe things are going to enter a more “normal” weather pattern (whatever that is) for the next couple of months.  The abnormally warm winter temperatures for much of December and early January (resulting from a strong El Niño 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.  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 warm 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 concerns with warm-season grasses primarily because many of them across Virginia (and especially in the Piedmont and Tidewater regions) had not entered full dormancy as of mid-January (Picture 1.  Caption:  Notice the bright green stem of this bermudagrass plant that was harvested from the Turfgrass Research Center in Blacksburg in early January).  If temperatures stay above average and we dodge extended Arctic cold (consecutive nights where the temperatures bottom out in the low to mid teens), a mild winter could be highly advantageous to warm-season grasses as well.  We can always have significant turf loss in the winter due to cold temperature extremes. However, experience has shown that “spring kill” is often as likely to occur as “winter kill” 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 for these types of weather patterns.  Athletic field managers might have turf blankets they can use 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?

BRANDON TO SUPPLY A COUPLE OF PARAGRAPHS HERE.

What about weeds?   Our winter annual weed complex (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:
• Roundup at 12 oz/A does not kill bermudagrass and will only slow spring greenup slightly, regardless of dormancy state.
• DO NOT SPOT TREAT ROUNDUP on semi-dormant turf, rather, use uniform blanket sprays instead.
• Apply the half rate (6 oz/A) in two directions to avoid “streaking” caused by Roundup overlaps that may delay greenup for 20+ days.
• Alternative herbicides are available that are safer than Roundup on semi-dormant turf but control less weeds or need repeat treatment and may be much more expensive.  These include, but are not limited to, diquat (Reward), trifloxysulfuron (Monument), simazine (Princep), foramsulfuron (Revolver), metsulfuron (Manor), sulfosulfuron (Certianty), carfentrazone (Quicksilver) and several broadleaf herbicides that contain two- and three-way combinations of 2,4-D, dicamba, MCPP, and similar active ingredients.

What about insect activity this spring?   Dr. Youngman sent his research assistant 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.  You can find more detailed information on insect management for this season in an article by Dr. Youngman in this issue.

Conclusions?  Hopefully this article will better equip you to educate your clientele about the expectations (or lack thereof) with our turfgrasses following record winter warmth.  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!  However, 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 father of our Constitution had issues with the weather.