WINTER INJURY TO WEEPING LOVEGRASS AND OLD WORLD BLUESTEMS

Death of some plants and greatly reduced number of tillers on others was common on weeping lovegrass and some varieties of Old World bluestems in western Oklahoma in the spring of 1985, 1990 and 2001. The winter damage appears to be caused by two different weather patterns.  The damage in 1990 was preceded by a severe cold snap in December 1989 during which minimum temperatures reached -15 to -20 F.  The damage in 1985 and 2001 was preceded by very dry conditions during the previous August and September and then extended periods of cold temperatures in December and January (minimum temperatures 0 to -5F)

Weeping lovegrass was severely affected with 80 to nearly 100% stand loss in northwestern Oklahoma. Damage on Old World bluestems, ranging from none to severe, was dependent upon the variety, age of stand, management history, soils, and locality. Since these species are a major forage resource in the region, we attempted to document by field observations the extent of damage and recovery over the spring and summer of 1990 and with additional observations in the spring of 2001..

RECOVERY MECHANISMS. Recovery of weeping lovegrass or Old World bluestem pastures from freeze damage is by:

1. Surviving tillers on old plants. A mature plant has many tillers (commonly 30 to 60). Each tiller emerging in the spring has the potential to become a plant with its own root system. Thus, several surviving tillers per clump are adequate to reestablish a stand. Protection from grazing and use of a herbicide to control annual broadleaf weeds will speed pasture recovery by tillers.

2. Seedlings. Weeping lovegrass and Old World bluestems are prolific seed producers. Thus stands, with the exception of those heavily used, contain some to an abundance of shattered seed. Establishment of seedlings in a depleted stand is aided by reducing a light-limiting dead overstory by grazing, beating, or burning; using a herbicide to control broadleaf annual weeds; and protection from grazing.

WEEPING LOVEGRASS. Weeping lovegrass was so severely damaged in the winter of 1989-90 that little or no forage was available for grazing on this species during the spring of 1990. Damage in our experimental pastures ranged from severe (most of the plants putting out a few tillers) to nearly all plants dead.  Damage during the 2000-2001 winter was less marked and ranged from moderate to moderately high.

No differences were seen in damage as related to degree of use the previous growing season. Apparently the climatic conditions were so severe that the recommended practice of non-use later in the growing season had no effect on survival.

Portions of stands with a few live tillers per plant recovered well. Seedlings were abundant in open unshaded areas between old plants in early June and some survived the summer. Mortality was apparently due to summer drought and competition for water by marestail (an annual broadleaf weed). Seedlings were not found in areas where a dead lovegrass canopy covered the soil surface.

Overall, winter damage must be recognized as a problem that occurs every 5 to 10 years in weeping lovegrass. Stands usually recover - the nearly complete die out in some pastures in 1990 is an exception. Weeping lovegrass, with good management, has been a valuable forage resource on very sandy soils. There is no other species available that is as productive on these sites. We believe weeping lovegrass should continue to be used in western Oklahoma - however, farmers and ranchers should not be unduly dependent upon any one forage species.

OLD WORLD BLUESTEMS. Varieties of Old World bluestem were affected differently by the severe climatic stress. 'Caucasian' and 'Ganada' had little or no damage. 'WW-Iron Master' had none to moderate damage. 'WW-Spar' and 'Plains' had moderate to severe damage with a greater number of dead plants in Plains.  Extensive damage has been observed in the spring of 1985, 1990, and again in 2001.  

The most severe damage was in heavily grazed pastures, especially those heavily grazed or hayed in September. Our most severely damaged WW-Spar pastures were then treated with 'Ally' to control broadleaf weed seedlings and not grazed. By September 1990 these stands had recovered well. Surviving tillers and seedlings both contributed to the recovery. Check strips not treated with Ally will probably require another growing season to develop the plant density now present in the treated areas.  Light rates of 2,4-D, 1/4 to 1/3 lb a.i. per acre, could be used after the new Old World bluestem seedlings reach the 3 to 5 leaf stage.

Damage to Old World bluestems was most severe on very sandy hilltops. Here exposure and pedestalling of plants were apparently significant factors contributing to damage. Old stands (8 years) were more affected than younger stands (3 years).  More damage to Old World bluestem can be expected if weather does not allow regrowth following grazing or haying in late summer.

Fewer plants were dead in heavily grazed nitrogen-fertilized WW-Spar pastures (20%) than in heavily-grazed unfertilized WW-Spar pastures (40%). This is contrary to our observation that more plants were dead in nitrogen-fertilized WW-Spar plots after the cold winter of 1983-84.