Cooperative Extension
No. 7
Community-Wide Lygus Action Plan
The University of Arizona • College of Agriculture
June 30, 2000
Most seed alfalfa fields in our area are either dry
or harvested. The remaining fields, however, are
harboring large populations of Lygus. These populations are dominated by nymphs, as developing
adults appear to be exiting these fields in search
of more favorable habitat. Cotton is squaring
heavily, and growers should prepare to treat for
Lygus as densities exceed threshold but no sooner.
period of seed alfalfa decline and associated adult
movement, it is important to maintain as many
patches (fields, blocks, benches or strips) of actively growing and well-watered forage alfalfa at
all times. These areas will serve to attract any locally dispersing Lygus to this crop which is unaffected by Lygus presence. At the same time, this
will limit movement of Lygus to cotton fields.
Crop Progress & Lygus Trends
The majority of seed alfalfa fields have been dried
down or harvested by this past week (Fig. 1). This
reduces the potential habitat for Lygus as long as
re-growth is kept to a minimum. So fewer fields
are contributing to the area’s production of Lygus.
Unfortunately, some unharvested fields continue
to build in Lygus numbers (Fig. 2). On average,
these seed alfalfa fields are harboring more Lygus
than in previous weeks and more than for any other
host monitored. Interestingly, adult numbers are
declining in seed alfalfa. This trend could represent the dispersal of adults from these declining
fields towards more suitable hosts. The challenge
now is to complete all seed alfalfa production before the growing numbers of nymphs mature into
dispersing adults.
Cotton continues to grow quickly and most fields
are in early to peak bloom, a period that is very
sensitive to Lygus damage. Lygus numbers remain
low in cotton, and there have been no reports of
sprays for Lygus so far. Timing of Lygus sprays
can be critical for yield and quality protection.
Furthermore, a Lygus spray may be the first insecticide application made in many fields this year.
Because of this and the broad spectrum nature of
our Lygus control arsenal, it is important to reserve
use until absolutely necessary. This will help conserve the rather diverse and generous supply of
natural enemies needed to keep Lygus and other
pests in check. Lygus sprays can typically serve to
release whiteflies, mites, or armyworms from
stable natural controls.
Forage alfalfa continues to actively grow throughout the local community. As we move through this
Fields (% of those sampled)
60
50
40
30
20
10
0
24-May
3-Jun
7-Jun
20-Jun
27-Jun
Figure 1: Percentage of seed alfalfa fields in the area (of those that we
sample) that are unsuitable for Lygus production (dry or harvested).
Timing Lygus Sprays in Cotton
Lygus chemical controls in cotton should be used
once there are at least 15 total Lygus with 4 nymphs
per 100 sweeps. Sprays sooner than this or for
adults only have resulted in less than maximum
yields and lower economic returns in recent research (Ellsworth, 2000). Infestations will typically
begin as adult-biased populations, sometimes far
exceeding the ‘15’ level before nymphs are detected. The ‘15:4’ threshold requires the presence
of at least 4 nymphs per 100 sweeps before spraying. Adults are not readily killed by our insecticides. Fortunately, yield protection is largely related to control of the nymphs. A large beneficial
insect community may enable growers to postpone
control even longer.
Internet Access to Newsletters & Cotton Info
Did you know that you can download, print, and
read (in color) each of these newsletters directly
from the internet! Each issue is placed on the Arizona Cotton Information Site, a series of Web pages
that house all cotton production and protection information for Arizona growers. Point your browser
at: http://ag.arizona.edu/cotton for our home
page and http://ag.arizona.edu/cotton/ipm.html
for this and prior issues of our newsletter.
Weeds
Hay
25
Sd Alfalfa
20
Cotton
15
10
5
30-Jun
23-Jun
9-Jun
16-Jun
2-Jun
26-May
19-May
5-May
12-May
28-Apr
References
Ellsworth, P.C. 2000. Lygus control decision aids for Arizona cotton. In J.C. Silvertooth, [ed.], Cotton, A College of Agriculture
Report. Series P-121, Publ. No. AZ1170. University of Arizona,
College of Agriculture, Tucson, AZ. pp. 269-280.
60
60
Weeds
Cotton
30-Jun
23-Jun
9-Jun
16-Jun
24-Mar
30-Jun
23-Jun
9-Jun
16-Jun
2-Jun
26-May
19-May
5-May
12-May
28-Apr
21-Apr
14-Apr
0
7-Apr
0
31-Mar
10
2-Jun
20
10
100
140
90
Weeds
80
Hay
Weeds
120
70
Total Lygus / 100
Sd Alfalfa
60
Cotton
50
40
30
20
Hay
100
Sd Alfalfa
80
Cotton
60
40
20
10
Figure 2: Number of Lygus per 100 ‘cotton-style’ sweeps in various crops
in the western Pinal County area. Each chart represents an average of
multiple sites in multiple fields each week. Due to differences in the
number of sites each week, these numbers are for general information
only. No sample was taken from seed-alfalfa on 28 March. Each site is resampled each week unless it has been recently sprayed, cut or otherwise
removed, or watered. Each chart shows the results for the entitled life
stage. Small Nymphs are instars 1–3; Large Nymphs are instars 4–5; All
Nymphs is the sum of these 2 nymphal categories; Total Lygus is the sum
of all stages of Lygus including adults.
Peter Ellsworth, IPM Specialist1
Steve Husman, Area Extension Agent2
Dave Langston, MAC Farm Superintendent1
1
2
30-Jun
23-Jun
16-Jun
9-Jun
2-Jun
26-May
19-May
12-May
5-May
28-Apr
21-Apr
14-Apr
24-Mar
30-Jun
23-Jun
16-Jun
9-Jun
2-Jun
26-May
19-May
12-May
5-May
28-Apr
21-Apr
14-Apr
7-Apr
31-Mar
0
24-Mar
0
7-Apr
All Nymphs / 100
30
26-May
20
Sd Alfalfa
19-May
Adults / 100
Cotton
30
40
5-May
Sd Alfalfa
Hay
12-May
40
50
28-Apr
Hay
21-Apr
50
24-Mar
Large Nymphs / 100
Weeds
14-Apr
21-Apr
14-Apr
7-Apr
31-Mar
24-Mar
0
7-Apr
30
31-Mar
35
31-Mar
Small Nymphs / 100
40

Department of Entomology, Maricopa Agricultural Center, Maricopa, AZ
Pinal County Cooperative Extension Office, Casa Grande, AZ
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