DIVERSIFICATION STRATEGIES - The Epidemiology of Plant Diseases - page 269

- mixed inter-cropping - two or more crops are wholly interspersed, maximising

their interaction. The crop is a species or variety mixture. It may also be a
species and variety mixture;

- row inter-cropping - one or more of two or more crop species or varieties are

planted in alternating rows, simplifying management but reducing species or
varietal interactions;

- strip inter-cropping - two or more crop species or varieties are grown in strips;

the strips are wide enough for independent management but narrow enough for
some interaction among the crops;

- plot intercropping - the field is divided into plots or blocks, each of which

contains a single species or variety; interactions will be relatively small.

Table 10.1. Diversification in monoculture and polyculture at the three production levels,
species, variety and resistance character

Level Monoculture Polyculture

Species Diversification still possible at the

variety and/or resistance sub-levels,
either in single or intercropping

Many possible arrangements among
and within species, varieties and
resistances using intercropping

Variety Dangerous unless used as multilines

(i.e. mixed crop diversification at
the resistance level)

Many possible arrangements among
and within varieties and resistances -
includes variety mixtures, multilines
and populations

Resistance The highest risk for losing the

effectiveness of the resistance

Many possible arrangements among
resistances - multilines and
populations

With mixed inter-cropping, the cycles of the crops tend to be similar except in some
forms of intensive hand cultivation or where the crops are so different that their
management is separate (e.g. cereal/clover). In the other forms of intercropping, the
difference in the crop cycles may vary from a few days, in some forms of vegetable
production, to many years, in all forms of agroforestry. A special form of deliberate
mixed cycle cropping is relay inter-cropping , a form of polyculture intermediate
between rotation and intercropping. It is often applied as a form of strip-
intercropping; two or more crops are grown simultaneously during part of the life-
cycle of each.
Different forms of intercropping can be combined, not only together but with
sole cropping; for example, where an intercrop vegetable enterprise is considered as
one element in a farm rotation. Such complex systems can have a major influence in
limiting diseases, pests and weeds.