Vol. 54—2000 - NorthEastern Weed Science Society

WEED CONTROL AND YIELD OF CUT FLOWERS TREATED WITH TWO HERBICIDES
E. Jay Holcomb, Tracey Harpster, Larry Kuhns, and Robert Berghage'
ABSTRACT
This experiment was designed. to compare the productivity of four species of cut flowers
treated with either napropamide or dithiopyr to weeded control plots, and to determine the
effectiveness of the herbicides in controlling weeds. Weed control with napropamide and
ditbiopyr was similar for the cut flowers tested. Applications of both napropamide and dithiopyr
had a slight depressing effect on plant quality. However, at harvest only celosia had shorter
stems and reduced fresh weight due to napropamide and dithiopyr application.
INTRODUCTION
Pest infestations are one of the most frequent causes of reduced yield of cut flowers, and
weeds are one of the pests that must be controlled. If weeds are left uncontrolled, yield of many
cut flowers are dramatically reduced. However, manually controlling the weeds can be very
expensive in terms of time and labor and desirable plants are often damaged by mechanical and
hand removal of weeds.
The pre-emergent herbicide that some cut flower growers use is napropamide. In
previous research we determined that napropamide gave good early season weed control but
marginal late season weed control and that one species of cut flower, celosia, was injured by it
early in the season. A new herbicide, dithiopyr, has recently been labeled for ornamentals. This
set of studies was established to compare the productivity of four species of cut flowers treated
with either napropamide or dithiopyr to weeded control plots, and to determine the effectiveness
of the herbicides in controlling weeds.
METHODS AND MATERIALS
Seeds of cockscomb (Celosia cristata L.). Cramers Yardstick (Artemesia annua L.), and
China aster (Callistephus chinensis (L.) Noes) were germinated in the greenhouse in mid March
and were planted to the field on June g, 1999. Two millets, Tapestry (Echinochloa crus-galli
(L.) Beauvois) and Spray (Setaria italica (L.) Beauvois), were sown directly in the field on June
8. In the field lbe plants were grown in raised bedstbat 6 feet long and 30 inches wide with drip
tape running down the center of the bed. There were two rows of plants on each bed and the
plants were spaced about 1 foot apart in the row. On June II treatments in Table 1 were applied
to the celosia, artemesia and China aster. The treatments were applied to both millets on June 29.
All beds were hand weeded before herbicide applications. The first herbicide application
was made on June 11 between 8:00 and 10:00 am. Conditions at the time of the application were
clear and sunny, 67° F with 0 to 3 mph winds. The June 29 applications were applied from 4:00
1 Professor, Research Associate, Professor, and Assistant Professor of Horticulture, Department of Horticulture, The
Pennsylvania State University, University Park, PA 16802.
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