Plant Biodiversity
and Pest Management in a Northern California
Vineyard*
- Clara I.
Nicholls Department of Entomology, UC
Davis
- Michael
P. Parrella Department of Entomology,
UC Davis
- Miguel A.
Altieri Center for Biological
Control, UC Berkeley
One of the
consequences of the trend toward expansion of
large-scale monocultures is the loss of
habitats for natural enemies, which results
in increased pest problems. Emerging research
shows that one way to reverse this trend is
by increasing plant diversity within and
around agroecosystems. Some studies have
shown that there is enhancement of natural
enemies and more effective biological control
in vineyards and orchards with cover crops or
where wild vegetation remains at field edges.
Flowers in such habitats provide pollen,
nectar and overwintering sites for a number
of predators and parasites.
The goal of
this study is to investigate the influence of
a 0.3 mile wild flower corridor composed of
66 different flowering plants that cuts
across a northern California organic
Chardonnay vineyard on the diversity,
distribution, abundance and dispersal of key
insect herbivores (leafhoppers and thrips)
and associated natural enemies. The goal is
to test whether changing the landscape layout
of the vineyard with this natural flower
corridor and the presence of cover crops
breaks the monoculture nature of the
vineyard, and whether it enhances functional
natural enemy biodiversity. The first year of
research was directed at determining the
species diversity and abundance levels of
arthropod fauna associated with the various
corridor plant species and at assessing if
the corridor influences diversity and
abundance of natural enemies in the adjacent
vineyard. Arthropod population parameters
measured in this vineyard (herein called
Block A) were compared to trends observed in
a neighboring vineyard that contained no
corridor (Block B). Both blocks are managed
organically with half of the area of each
block planted to summer cover crops
(buckwheat and sunflower) which are also a
source of flowers.
From May 18 to
August 28, 1996 and also during the 1997
growing season, intensive weekly monitoring
of herbivorous insects and associated natural
enemies was conducted using several sampling
methods: yellow and blue sticky traps placed
in the corridor and within the vineyards at
varying distances from the corridor; direct
counting of leafhopper nymphs on leaves;
branch shaking; D-vac of vines; sweep netting
the covercrops and malaise traps placed
across "flight paths" between
vineyards and adjacent edges.
Data collected
during the 1996 summer shows that leafhoppers
and thrips exhibited a clear density gradient
reaching lowest numbers in rows close to the
corridor and increasing in densities in rows
away from the corridor. Predaceous insects
such as Orius and generalist predators
in the families: Coccinellidae, Chrysopidae
and spiders also exhibited and abundance
gradient. Leafhoppers were less abundant in
vines with cover crops beneath than in vines
with bare ground, and this may due to the
fact that predators were more numerous and
diverse in vines with cover crops.
Data analysis
suggests that the corridor serves as a source
of natural enemy biodiversity affecting the
abundance and distribution of predators in
the adjacent vineyard, thus impacting
densities of leafhoppers and thrips in vines
close to the corridor. Cover crops complement
the ecological effects of the corridor by
serving as a source of natural enemies, which
in turn determine lower pest densities in
vines with cover crops beneath. Timing the
mowing of cover crops forces movement of Anagrus
and Orius and other predators to
the adjacent vineyards resulting in further
reductions of leafhoppers and thrips.
* Abstract
distributed to participants in field day held
at Kohn Properties, Hopland, California.
August 15, 1997
