Mixtures of annual weeds emerging 1 week after and competing all season with potatoes (Solanum tuberosum L.) reduced tuber yields by an average of 54% compared to 16% in comparable treatments in which weeds emerged 3 weeks after potatoes. Weeds reduced tuber yields 19% 8 weeks after potatoes emerged and 25 to 45% 10 weeks after emergence. After full-season competition, for each additional 10% of the total dry biomass represented by weeds, there was a decrease of 12% in fresh tuber yield. This relationship was not valid if potatoes were harvested early, which reduced the deleterious effect of weeds on potato yields. Weed competition reduced both size and number of tubers, but had little effect on specific gravity of tubers. In some instances, the reduction in tuber size by weeds reduced the percentage of tubers that were marketable.

Major differences in above- ground biomass and tuber production of yellow nutsedge (Cyperus esculentus L. # CYPES) were not observed when corn (Zea mays L. “CO-OP S265”) was seeded on different dates (1st, 2nd, 3rd and 4th week of May; and 1st week of June). The final seedbed was prepared just prior to each seeding date and this cultivation stimulated dormant tubers to sprout. As a result, a large population of yellow nutsedge emerged with the corn at all seeding dates. Because fertilizer was banded near the corn row, yellow nutsedge biomass, tuber dry weight and number of tubers were higher within corn rows than between rows. Tuber size was affected by seeding date and shifted toward smaller tubers within corn rows and larger tubers between the rows as the corn was sown late. The optimum seeding date of corn was in the 3rd week of May when the highest corn yield was obtained and yellow nutsedge growth was generally reduced.

Increasing the corn (Zea mays L. “CO-OP S265”) population from 33 300 to 133 300 plants per hectare in the field significantly reduced yellow nutsedge (Cyperus esculentus L. # CYPES) above-ground biomass, tuber number, tuber weight and yellow nutsedge height at the end of growing season, and significantly increased corn yield. Photosynthetically active radiation below corn canopies decreased with increasing corn population and corresponded to reductions in yellow nutsedge above-ground biomass, tuber weight and tuber number. These results demonstrate that available light is a major factor in yellow nutsedge competition with corn. The size of yellow nutsedge was also reduced at high corn densities. These results support the use of crop manipulation in an integrated yellow nutsedge management system in corn.

Growth and reproductive potential of individual yellow nutsedge plants were examined under two nitrogen levels and three soil moisture regimes. Irrigation levels were selected on the basis of irrigating at soil water potentials of −20, −50, and −80 kPa. Yellow nutsedge patch expansion was measured using digital images to determine ground cover, while plots were subsampled to estimate total shoot and tuber production. High nitrogen increased shoot production in 2004. When plots were irrigated at a soil water potential of −20 kPa, a single yellow nutsedge plant produced 3,000 and 1,700 shoots and 19,000 and 20,000 tubers in 2003 and 2004, respectively. Patch expansion at −20 kPa was exponential, with the greatest expansion occurring between the middle of July and mid to late August. This research demonstrates that the vegetative and reproductive potential of yellow nutsedge is greatly influenced by irrigation level. With such extensive growth and reproductive potential, management strategies for yellow nutsedge should focus on prevention, early detection and containment, early treatment, and integration of control strategies to reduce its competitiveness and spread.