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Alfalfa Seed Organic Program Notes PO
Box 1555, Ventura, CA 93002 800-248-2847 *
805-643-5407 fax
805-643-6267 e-mail bugnet@rinconvitova.com web www. rinconvitova.com |
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Lygus – tarnished plant bug, Lygus sp.
Habitat strip to
attract and focus biological control
Alfalfa strip with
Daikon radish, mustard (low growing seed), sequence of bean plantings-such as
black eyed peas to attract lygus.
Succession plantings
every 2 weeks to keep plants available producing seeds in milk stage, which is
most attractive for lygus adults to deposit their eggs and feed their primary
predator the big-eyed bugs Geocoris spp.
Maintain by cutting
older alfalfa, maturing plants as they become less attractive to lygus.
When lygus numbers
high, vacuum lygus using 2 stage screen, 16 mesh (threads/inch) (window screen)
and 90 mesh. Release the wasps and small insects in the 90 mesh and dispose of
insects in 16 mesh, releasing ladybugs and other large predators.
Alternately run
chickens through the strip to harvest insects. You can use cages like a chicken
tractor, or movable electric fencing to keep chickens in, predators out.
As lygus numbers
build in the habitat strip, everything that eats lygus will show up, so you may
not need to do anything. Lacewing can be introduced early in the season to
increase the number of predators.
Diabrotica – cucumber beetle
Tachinid fly,
Celatoria diabrotica, parasite on adult beetles. Plant flowers to attract hover flies and tachinid flies,
especially umbels like dill.
Heterorhabditis sp.,
Hb or Hm or Hi nematodes are parasite on larva in soil known as corn root worm.
Larva lives on the roots of warm season grasses.
As you reduce numbers
of Diabrotica, the percentage parasitized will probably go up. There are records of over 60 percent
parasitism of adult weevils. I find
that general predators in alfalfa reduce the populations of larvae in the
soil. The adults migrate into the
fields from weed in unfarmed areas and when harvesting fields from miles
around. These concentrated populations
migrate to vegetables when hay is harvested.
Alfalfa is a trap for these populations when it is strip cut early in
the spring because they are not driven from the alfalfa when solid field
cutting is routine. It is a little more
trouble but when the process is the paradigm, hay production is increased
because the field must be more quickly harvested in order to irrigate the half
grown strips. Often an extra cutting of
hay results. If you made seed in the
fall, and the seed chalcid was under natural biological control, it would be a
win—win situation.
OF COURSE
AUGMENTATION OF LACEWING AND LADYBUGS FOSTERS BETTER BIOLOGICAL CONTROL AND
GUARANTEES THE MAXIMUM BENEFICAL EFFECTS FROM THESE GENERAL PREDATORS!
Alfalfa weevil
Larva on leaf, in
soil
Collops larvae is
predator of Diabrotica larvae (root worms) and alfalfa weevil
Hooded beetle and
other Anthicidae larvae are predators of flower thrips and weevils
Theravid or stiletto
fly, larva is predator along with
Many species of rove
and ground beetles; Staphlinidae and Carabidae.
Heterorhabditis sp.
Nematodes parasite on larva
Sheep off (graze with
sheep) first cutting, sheep eat larva in top of plant
Look for
overwintering weevils under bark of trees near fields. May be able to use
Heterorhabditis sp. Nematodes to decrease numbers
My
personal experience with biological control of alfalfa seed production
is limited to the low desert of California where seed is generally produced
early in the season using the second cutting.
This is largely chosen to avoid the alfalfa seed chalcid, Bruchophagus roddi (Gussakovsky). This insect is a major pest of seed production but
of little importance in hay production.
There are several generations and they emerge from the seeds in greater
numbers as the season advances.
Making hay and
removing the alfalfa stems before the seed enters the milk stage is physical
control of this pest.
During our work monitoring the
spotted alfalfa aphid, (SAA) and the exotic parasites that were introduced from
the middle east, we focused our attention on strip farming alfalfa hay. Every other land was cut and harvested each
irrigation cycle. This was a way to
keep the parasites active in the participating farmers fields rather than
sending them down wind to the next alfalfa when the fields were solid cut.
We vacuum sampled our fields monthly
and counted every kind of insect that we found and identified them with their
function in the process of making hay.
However one of our farmers decided to go deer hunting in the fall and
dried up his field to make seed. We
continued to monitor the insect populations and discovered that seed chalcid
had many primary parasites attacking them and they were not a serious pest or a
deterrent to making seed profitably.
While the chalcid is extremely difficult to control chemically, it is
vulnerable to natural biological control, at least under this one
experience. Our farmer explained that
he regularly went deer hunting in the fall and this rotation to seed allowed
him to do it. Lygus was also not a
problem because the strip cutting process enhanced biological control of all
alfalfa pests including alfalfa weevil which has benefited from importation and
establishment of several species of
Bathyplectes and parasites of the adult weevils (Microtonus spp.). A fungus
also attacks the weevils when moisture is high.