|
1
| 2 | 3 | 4
| 5 | 6 | 7
| 8 | 9 | 10
| 11 | 12 |
13 | 14 | 15
| 16 | 17 |
18 | 19 | 20
| 21 | 22
Alfalfa Interplanted
with Cotton: How does it work? |
17
Lygus is a key insect pest in California cotton. They pierce
the stems and suck plant juices, causing damage to flower
buds, young bolls, and terminal buds.
Cotton is not the preferred host of lygus,
but once the surrounding vegetation starts to dry up, they
will move into irrigated cotton and feed on the plants.
Through habitat manipulation it has been demonstrated that
lygus can be kept away from the cotton during critical square
formation. Alfalfa is a preferred host to lygus and can
be grown in strip intercrops with cotton to assist in lygus
control. (ATTRA Organic Cotton Production, 2003)
It is important to manage Lygus before they
move into a cotton field and cause damage. Once they have
migrated into the cotton, it often requires chemical treatment
to control them, which results in the reduction of natural
enemies and potential disruption by secondary pests.
In a paper written by UC Cooperative Extension Specialist
Pete Goodell and J.W. Eckert* they found that “this
disruption can lead to multiple pesticide applications,
excessive production costs, and destabilization of the cotton
ecosystem.”
The use of alfalfa strips in cotton fields
was introduced in the 1960’s as an alternative method
to broad spectrum insecticide applications. (Stern et al,
1969). Alfalfa is favored by lygus and can also serve as
a refuge for natural enemies. Widespread adoption of the
practice has not occurred, probably because of the difficulty
in maintaining production practices for the two different
crops.
How it’s done
BASIC growers Frank Williams and Mark Fickett were
intrigued by the idea and thought the benefits of interplanting
alfalfa might outweigh the management aspects. They decided
to give it a try. The following is a brief outline of the
practices they used on their cotton in 2003:
Planting Scheme
Six rows of alfalfa and two rows of fava beans (on the outside
of the alfalfa) were planted on December 10, 2002, at a
rate of 5-6 pounds to the acre. The alfalfa was planted
between two 80 acre cotton fields. The planting was done
using standard equipment.
Irrigation
When the alfalfa was planted there was no pre-irrigation
done, the rain took care of the germination process. However,
during the season, the alfalfa habitat was irrigated four
times. The first irrigation took place while pre-irrigating
for cotton planting, on February 19; second irrigation took
place with the first irrigation of cotton on June 10, third
on July 10, and the final irrigation on August 4. Sprinkler
irrigation was used for the alfalfa habitat trial.
Mowing
A mowing scheme was set-up to keep the alfalfa green and
lush. This was done by using a rotation system. Only a portion
of the habitat was mowed at once, leaving a strip of alfalfa
as a hosting zone. Every 30 days a portion of the habitat
was mowed. When the alfalfa habitat was mowed, D-vac samples
were taken, from the habitat as well as the cotton adjacent
to the habitat. The volume and number of beneficial species
were sizeable.
Monitoring
Throughout the season BASIC field staff monitored
the WindFall alfalfa habitat along with the cotton. Using
a D-vac, they took 17 samples during the season; starting
from May 26th through September 12th. Each sample consisted
75 sucks from the D-Vac.
Pest Pressure. The cotton adjacent to the alfalfa strips
had no significant changes in pest pressure from the rest
of the field and most importantly there were no signs of
pests moving out of the habitat.
Conclusions
The alfalfa habitat was considered a success since
there were no significant changes in pest pressure coming
into the cotton. The habitat provided a ready food source
and refuge for the lygus which had no reason to move out
of their preferred host. As the season progressed, we saw
increasingly diverse species and large numbers of beneficial
insects in the D-vac samples.
next article
|
