Managing Cover Crops Profitably - Valley Crops Home

insects. This approach has been used successfully
by California almond and walnut growers participating
in the Biologically Intensive Orchard
Systems (BIOS) project of the University of
California (142).
The level of ecological sustainability depends
on the grower’s interests, management skills and
situation. Some use no insecticides while others
have substantially reduced insecticide applications
on peanut, cotton and vegetable crops.
• In Georgia, Mississippi and South Carolina,
minimally tilled crimson clover or cahaba vetch
before cotton planting have been successful in
reducing fertilizer N up to 50 percent and insecticide
inputs by 30 to 100 percent.
• Many farmers are adopting a system of transplanting
tomatoes, peppers and eggplant into a
killed hairy vetch or vetch/
rye cover crop. Benefits
include weed, insect and disease
suppression, improved
fruit quality and overall lower
production cost.
• Leaving “remnant
strips” of a cover when most of the crop is
mowed or incorporated provides a continuing
refuge and food source for beneficials, which
might otherwise leave the area or die. This
method is used in orchards when continued
growth of cover crops would cause moisture
competition with trees.
• Insect movement is orchestrated in a system
developed by Oklahoma State University for
pecan growers. As legume mixtures senesce,
beneficials migrate into trees to help suppress
harmful insects. Not mowing the covers from
August 1 until shuck split of the developing
pecans lessens the unwanted movement of stink
bugs, a pest which can damage green pecans
(209). In California, lygus bugs on berseem clover
or alfalfa are pests of cash crops. Be careful that
cover crop maturity or killing a cover doesn’t
force pests into a neighboring cash crop.
Disease Management
Growers traditionally have been advised to turn
under plant debris by moldboard plowing to
Cover crops can enhance the
soil and field environment
to favor beneficial insects.
minimize disease losses (259, 260, 331, 333, 334).
Now we realize that burying cover crop residues
and disrupting the entire soil profile eliminates
beneficial insect habitat and weed control benefits.
The increased use of conservation tillage
increases the need to manage crop disease without
burying cover crops.
Plant infection by microorganisms is rare (254).
A pathogen has to cross many barriers before it
can cause a disease to roots, stem or leaves.You
can use cover crops to reinforce two of these
barriers.
Plant cuticle layer. This often waxy surface layer
is the first physical barrier to plant infection.
Many pathogens and all bacteria enter the plant
through breaks, such as wounds, or natural openings,
such as stomata, in this
cuticle layer. This protective
layer can be physically damaged
by cultivation, spraying
and sand-blasting from wind
erosion, as well as by the
impact and soil splashing
from raindrops and overhead irrigation. In welldeveloped
minimum-till or no-till crop systems
with cover crops, you may not need cultivation
for weed control (see below) and you can minimize
spraying.Organic mulches from living,dying
or killed covers that hold soil and stop soil splashing
protect crops from injury to the cuticle.
Plant surface microflora. Many benign organisms
are present on the leaf and stem surface.
They compete with pathogens for a limited supply
of nutrients.Some of these organisms produce
natural antibiotics. Pesticides, soaps, surfactants,
spreaders and sticking agents can kill or disrupt
the activities of these beneficial microorganisms,
weakening the plant’s defenses. Cover crops can
help this natural protection process work by
reducing the need for synthetic crop protection
materials. Further, cover crop plant surfaces can
support healthy populations of beneficial
microorganisms, including types of yeasts, that
can migrate onto a cash crop after planting or
transplanting.
MANAGING PESTS WITH COVER CROPS 29