Vol. 51—1997 - NorthEastern Weed Science Society

57
Weed Interference in Full Season, No-Tillage
Soybeans at Two Row Spacings
A. Para, B.H. Marose, T.W. Patton, and S. Glenn'
ABSTRACT
ent was initiated in 1996 to evaluate interactions offull season no-tillage
on cocklebur (XanthiumstrumariumL.), velvetleaf(Ahutiion theophrasti
Medicus), pitted orningglory (IpomoealacunosaL.), and fall panicum (PanieumdichotomiflorumL.).
S ybeans (glyphosate resistant) were planted in 7.5- and 15- inch rows in 1O-footx
50-foot plots. Fi weed seeds of one species were planted in three locations five feet apart
inbetween the ce ter rows of the plots for yield analysis. In the back half of each plot five seeds
of the $3.11lespeci s were planted in nine, evenly spaced locations for bioassays. Upon emergence
of the weeds, e planting was thinned to one plant. There were eight replications for each weed
and each row sp . g and the study was arranged in a split block design. Control plots were
included to evalu te soybean growth. Desired weeds were covered and the entire study area was
treated with 1.0 I ailA glysphosate to control unwanted weeds when necessary. Samples were
obtained starting hree weeks following weed emergence for five consecutive weeks from the
bioassays area. amples included the weed and the closest soybean plant. Leaf area index (LA!)
and dryweight ere measured for the weed and the soybean. In the fall, the weeds in the harvest
area were m ed for height, clipped at the base, dried, and weighed. Soybean plants in an
adjacent row w e harvested in e-inch increments extending in both directions from the weeds up
to 60 inches for lant counts and harvest analysis. The LA! of soybeans 9 weeks after emergence
was always lowe when competing with weeds compared to the LA! of soybeans growing in
weed-fre plots. e LA! of cocklebur, morningglory and fall panicum was 96, 24, and 26%
higher.in IS-inc soybean rows compared to 7.5- inch rows. The LA! of soybeans in IS-inch
rows compared 7.5- inch rows was 27 and 38% lower when competing with common
cocklebur and pi ed morningglory, respectively.
lUnivers of Maryland, College Park, MD 20742