For quantifying corn ear yield, two (fall 2010 and spring 2011)
and four (summer 2011) rows of corn plants were randomly
selected in each treatment plot. In the fall 2011 experiment, continuous
rain on the week of harvest made harvesting difficult thus
only one row of corn was selected for ear yield. Corn ears were harvested
at the appropriate maturity for sweet corn production at the
Waimanalo site (70 days after seeding) and seed corn production
at the Mililani site (120 days after seeding). Total number and
weight of harvested ears from each row were recorded and estimated
in tons per hectare.
Further, quality of corn ears in terms H. zea infestation was
assessed in the spring 2011 and summer 2011 experiments by randomly
sampling 40 corn ears from the harvested corn in each treatment
plot. Yield was lost in the Trichogramma release treatment in
fall 2011 trial as a result of severe virus infection in the plot. Corn
ears were assessed qualitatively by grading on the basis of depth of
H. zea larvae that bored from the tip of the ear. Here, ‘‘undamaged’’
indicated an ear with no evident larval presence, ‘‘moderately
damaged’’ indicated up to 5 cm of kernels from the tip of the ear
were damaged by H. zea larvae, and ‘‘damaged’’ indicated more
than 5 cm of damage from tip. Thus percentage of each category
of corn ear was calculated for each treatment plot.