Vol. 54—2000 - NorthEastern Weed Science Society

EFFECTS OF DROUGHT ON THE INTERFERENCE OF REDROOT PIGWEED,
LARGE CRABGRASS AND SMALLFLOWER GALINSOGA IN PEPPER
R. Fu l and R. A. Ashley'
ABSTRACT
This is the second year of a two-yearreplicatedstudyto determinethe influence of emergence
time anddensity of redrootpigweed Armaranthus retroflexus L., large crabgrassDigitarta sanguinaiis
(L) Scop. and smalltlower galinsoga Galinsoga ciliata L. on the yield loss of bell pepper Capsicum
annuumL. The earlygrowing season of 1999 was particularlydry.The monthlyprecipitationwas 5.44,
7.40 and 3.27 inches in May, June and July in 1998, while in 1999, the monthly precipitation was only
3.97 and 0.13 inches in May and June, 5.44 inches in July. Although there was more rain in July than
last year, the evaporation and transpiration was large due to the high temperature (The degree days was
818.5 Fahrenheit in July of 1999, and 726.5 in July of 1998 with base temperature to be 47 degree
Fahrenheit). The establishmeot of the plants was seriously retarded by the unfavorable weather.
Compared to last year, the peppers were transplaoted to the field II days earlier, but the harvest was
started 9 days later. The overall yields of all treatments decreased dramatically with weed-free yield
decreasedas muchas 50010.
The experiments were conducted on the research station of Departmentof Plant Science,
Uoiversity of Connecticut at Mansfield, CT in 1999. Weed densities of 0, 1,2,4, 8, 16, 32 plants m'
were establishedwithin15cm on eitherside of the croprow for each weed species. The effectsof two
emergence times - weed seedlings emerged right after lransplanting of pepper and weed seedlings
emerged two weeks after transplanting were studied.
Generally,the weeds showedmorecompetitiveabilityunderthe dryweather.Forcrabgrass,low
densitieslike I or 2 seedlings molcaused37.3%and41.8%yield loss forearlyemergencetime thisyear,
and the percentagelosses were 25.0% and 26.2% respectively last year. The maximum yield loss
decreased from the 97.7% oflast year to 93.1% under the highest weed density of the first emergeoce
time, and increased from 61.4% to 74.1% for the highest weed deosity for the late emergence time.
Redrootpigweed turnedout to bemost competitivespecies this year. Onepigweed m-Iemerged
right after transplanting could cause more than 40% of yield loss while this number was 7.3% last year.
The highest deosity of early emerged pigweed caused a yield loss up to 98% and the maximum yield
loss was only 66% last year. The impactof late emergedpigweed on yield loss was just very slightly
less severe.
Low deosities of smalltlower galinsoga had less effect on yield loss in percentsge than last year
when the seedlings emergedrightaftertransplanting.Oneor two galinsoga m'' caused about25%yield
loss last yearandthis year the yield loss was about 13%.The converse was true for the lateremerging
weeds. Lastyearthe late emergedweeds hadno significanteffect on the pepperyield, and this yearthe
yield loss showeda steadyincreasewhenthe weed densities get higherwith the highestyield loss to be
47.50/0.
I GraduateAssistant,Dept. of PlantScience, Universityof Connecticut. Stom, CT06269
2 Professorof Horticulture, Dept. of Plant Science, Universityof Connecticut, Storrs.CT06269
123