Abstract
Occurence and coverage of under cover plants (UCP) in herbicide-free citrus fields of the University of Tokyo (UT) were observed for three years.
The data was compared with data from other herbicide-applied orchards reported in literature. The purpose of the observation was to obtain data to assist in the development of techniques for ecological weed control.
In the observation of the orchard at UT, fifty five UCP species were found in the nursery tangerine (Citrus unshiu) field, and fifty seven in the hassaku (C. hassaku) field. About sixty percent of the species were common in the two fields. About twenty percent of the species were common in the two fields. About twenty percent were unique to each field.
Climbing plants, plants with high occurence and coverage, and tall plants are harmful to citrus trees, especially to nursery trees. Climbing plants including vines, were difficult to control only by mowing several times a year. Other plants seemed to be well controlled by three to four mowings per year.
Fifteen UCP species in the tangerine field and eight in the hassaku field were common to species in other citrus orchards in literature. Fifteen UCP species were unique to the UT orchard.
Among the UCP species invading the UT fields, some were considered as major weeds in fields throughout the world. No weeds common in paddy fields were seen in the two UT citrus fields.
