ISSUE 11 July 22, 2010
GET
READY TO SCOUT FOR RED SUNFLOWER SEED WEEVILS
Adult red sunflower seed
weevils have been observed in the southeast region of North Dakota. These fields
are R3 to R4 and will be blooming by the end of the week. Red sunflower seed
weevil adults (Fig. 1) are reddish brown and ⅛ inch long. Adult weevils begin to
emerge in mid-July and continues through mid-August. Peak emergence occurs in
late July. Start counting adult seed weevils when the yellow ray petals
are just beginning to show. Counts should continue until the economic threshold
level has been reached or most plants have reached 70% pollen shed. A plant that
has reached 70% pollen shed has few seeds still suitable for red seed weevil egg
laying. Fields where most plants are at the 70% pollen shed stage should no
longer be susceptible to further significant damage.
Figure 1. Red sunflower seed
weevil adult
(Ext. Entomology, NDSU)
When sampling, use the X
pattern and begin counting at least 70 to 100 feet into the field to avoid field
margin effects. Count the number of weevils on five plants at each site for a
total of 25 plants. The ideal plant stage for treatment is when most plants are
at 40% pollen shed. However, we recommend that treatment be considered when
three out of 10 plants are at 10% pollen shed (or R5.1) (Fig. 2).
Figure 2. R5.1 or 10% pollen shed on flowering
sunflower head (L. Charlet, USDA-ARS)
Economic Threshold for
Oilseed Sunflowers:
To decide whether to use an
insecticide treatment to control red sunflower seed weevils, it is necessary to
determine the economic threshold for this year. The economic threshold (ET) is
based on: 1) the cost of insecticide treatment per acre, 2) the market price of
sunflower in dollars per pound and 3) the plant population per acre. The ET can
be calculated using the following formula:
Oilseed ET (Weevils per head) =
|
Cost of Insecticide Treatment
|
|
(Market Price x 21.5) (0.000022 x Plant Population + 0.18) |
|
Table 1.
Economic Threshold for Oilseed Sunflowers - Number
of adult red sunflower seed weevil per head when the cost of control
equals $8 per acre. |
||||||||||||
|
Market Price |
Sunflower Plants per Acre (x 1,000) |
|||||||||||
|
$ per lb |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
21 |
22 |
23 |
24 |
25 |
|
0.07 |
12.4 |
11.8 |
11.3 |
10.8 |
10.3 |
9.9 |
9.5 |
9.1 |
8.8 |
8.5 |
8.2 |
7.9 |
|
0.08 |
11.3 |
10.7 |
10.2 |
9.7 |
9.3 |
8.9 |
8.5 |
8.2 |
7.9 |
7.6 |
7.4 |
7.1 |
|
0.09 |
10.3 |
9.8 |
9.3 |
8.9 |
8.5 |
8.1 |
7.8 |
7.4 |
7.2 |
6.9 |
6.7 |
6.4 |
|
0.10 |
9.5 |
9.0 |
8.5 |
8.1 |
7.8 |
7.4 |
7.1 |
6.8 |
6.6 |
6.3 |
6.1 |
5.9 |
|
0.11 |
8.8 |
8.3 |
7.9 |
7.5 |
7.2 |
6.8 |
6.6 |
6.3 |
6.0 |
5.8 |
5.6 |
5.4 |
|
0.12 |
8.2 |
7.8 |
7.4 |
7.0 |
6.7 |
6.4 |
6.1 |
5.8 |
5.6 |
5.4 |
5.2 |
5.0 |
|
0.13 |
7.7 |
7.3 |
6.9 |
6.5 |
6.2 |
5.9 |
5.7 |
5.4 |
5.2 |
5.0 |
4.8 |
4.7 |
|
0.14 |
7.2 |
6.8 |
6.5 |
6.1 |
5.8 |
5.6 |
5.3 |
5.1 |
4.9 |
4.7 |
4.5 |
4.4 |
|
0.15 |
6.8 |
6.4 |
6.1 |
5.8 |
5.5 |
5.2 |
5.0 |
4.8 |
4.6 |
4.4 |
4.2 |
4.1 |
|
0.16 |
6.5 |
6.1 |
5.8 |
5.5 |
5.2 |
4.9 |
4.7 |
4.5 |
4.3 |
4.2 |
4.0 |
3.9 |
|
0.17 |
6.1 |
5.8 |
5.5 |
5.2 |
4.9 |
4.7 |
4.5 |
4.3 |
4.1 |
3.9 |
3.8 |
3.7 |
|
0.18 |
5.8 |
5.5 |
5.2 |
4.9 |
4.7 |
4.5 |
4.2 |
4.1 |
3.9 |
3.7 |
3.6 |
3.5 |
|
0.19 |
5.6 |
5.2 |
4.9 |
4.7 |
4.5 |
4.2 |
4.0 |
3.9 |
3.7 |
3.6 |
3.4 |
3.3 |
|
0.20 |
5.3 |
5.0 |
4.7 |
4.5 |
4.2 |
4.0 |
3.9 |
3.7 |
3.5 |
3.4 |
3.3 |
3.1 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Table 2.
Economic Threshold for Oilseed Sunflowers - Number
of adult red sunflower seed weevil per head when the cost of control
equals $10 per acre. |
||||||||||||
|
Market Price |
Sunflower Plants per Acre (x 1,000) |
|||||||||||
|
$ per lb |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
21 |
22 |
23 |
24 |
25 |
|
0.07 |
15.5 |
14.8 |
14.1 |
13.5 |
12.9 |
12.4 |
11.9 |
11.4 |
11.0 |
10.6 |
10.3 |
9.9 |
|
0.08 |
14.1 |
13.4 |
12.7 |
12.1 |
11.6 |
11.1 |
10.7 |
10.3 |
9.9 |
9.5 |
9.2 |
8.9 |
|
0.09 |
12.9 |
12.2 |
11.6 |
11.1 |
10.6 |
10.1 |
9.7 |
9.3 |
9.0 |
8.6 |
8.3 |
8.0 |
|
0.10 |
11.9 |
11.2 |
10.7 |
10.2 |
9.7 |
9.3 |
8.9 |
8.5 |
8.2 |
7.9 |
7.6 |
7.3 |
|
0.11 |
11.0 |
10.4 |
9.9 |
9.4 |
9.0 |
8.6 |
8.2 |
7.9 |
7.5 |
7.3 |
7.0 |
6.8 |
|
0.12 |
10.3 |
9.7 |
9.2 |
8.7 |
8.3 |
7.9 |
7.6 |
7.3 |
7.0 |
6.7 |
6.5 |
6.3 |
|
0.13 |
9.6 |
9.1 |
8.6 |
8.2 |
7.8 |
7.4 |
7.1 |
6.8 |
6.5 |
6.3 |
6.0 |
5.8 |
|
0.14 |
9.0 |
8.5 |
8.1 |
7.7 |
7.3 |
7.0 |
6.6 |
6.4 |
6.1 |
5.9 |
5.7 |
5.4 |
|
0.15 |
8.5 |
8.0 |
7.6 |
7.2 |
6.9 |
6.5 |
6.3 |
6.0 |
5.7 |
5.5 |
5.3 |
5.1 |
|
0.16 |
8.1 |
7.6 |
7.2 |
6.8 |
6.5 |
6.2 |
5.9 |
5.7 |
5.4 |
5.2 |
5.0 |
4.8 |
|
0.17 |
7.7 |
7.2 |
6.8 |
6.5 |
6.1 |
5.9 |
5.6 |
5.4 |
5.1 |
4.9 |
4.7 |
4.6 |
|
0.18 |
7.3 |
6.9 |
6.5 |
6.1 |
5.8 |
5.6 |
5.3 |
5.1 |
4.9 |
4.7 |
4.5 |
4.3 |
|
0.19 |
7.0 |
6.5 |
6.2 |
5.9 |
5.6 |
5.3 |
5.1 |
4.8 |
4.6 |
4.5 |
4.3 |
4.1 |
|
0.20 |
6.6 |
6.3 |
5.9 |
5.6 |
5.3 |
5.1 |
4.8 |
4.6 |
4.4 |
4.2 |
4.1 |
3.9 |
Economic threshold for
Confection or Hulling Sunflower Market
Red sunflower seed weevil
control on confection sunflower is based on a need to keep seed damage below
0.5% due to industry standards. Treatment is recommended when 1 to 2 weevils
(ET) are found per plant. The banded sunflower moth, seed weevil
and Lygus bug have all impacted quality of these sunflowers the past
seasons. So, it is recommended at this time that sunflowers grown for these
markets be treated a minimum of two times, once at early flowering and again
5 to 7 days later. With this type of program, a window of protection should be
provided to minimize impact from all three of these seed damaging insect pests.
Growers should plan
treatment schedules early. When flowers begin blooming across the region,
competition for access to aerial applicators increases.
SUNFLOWER MIDGE DAMAGE OBSERVED
It is a good time to get
out and inspect sunflowers for the presence of small (about 0.9 inch) cream to
yellow sunflower midge larvae (Fig. 3), and to determine if infestations are
confined to field margins or throughout the field, and also the extent of the
injury (bract only or floret damage).
Heavy infestations of sunflower midge have been reported near Thompson
and Grand Forks in Grand Forks County, North Dakota. It may be too early to
determine the amount of damage to sunflower heads (Fig. 4), which is affected by
the midge densities present, bud size at the time of infestation, and sunflower
hybrid being grown.
Figure 3. Sunflower midge larva (P.
Beauzay, NDSU)
Figure 4. Deformed sunflower head from
sunflower midge damage (G. Endres, CREC)
Remember, insecticides will
not control sunflower midge. The best management strategy has been rotation
to crops other than sunflower in the vicinity of severe infestations. Staggering
planting dates to promote different budding periods between fields aids
in reducing risk of damage to all fields in the same geographic areas. Sunflower
hybrids have recently been evaluated for their tolerance to sunflower midge.
Selecting hybrids for their ability to tolerate infestations should be
considered when choosing a hybrid for the upcoming season.
SCOUT
FOR LYGUS BUGS IN FLOWERING CONFECTION SUNFLOWERS
Lygus bugs (Fig. 5 & 6) are
noted for being a pest of seed production to many crops. Their feeding
preference is meristematic tissue or embryonic tissue. Lygus bugs
insert their mouthparts into the host, start a "pre-digestion pump" to
inject saliva and start digestion, then suck the fluid into the stomach.
Figure 5. Lygus bug adult (S.
Bauer, USDA-ARS)
Figure 6. Lygus bug nymph (S.
Bauer, USDA-ARS)
This is where the seed
injury originates, because the saliva is toxic to plant tissue. This injury
causes a brown to black spot (Fig. 7) resulting from tissue death at that
feeding site. The damage has been named “kernel brown spot.”
Figure 7. Kernel brown spot caused by
Lygus bug feeding (L. Charlet, USDA-ARS)
To minimize the damage
which results in a quality reduction, a general approach to protecting sunflower
from Lygus and other seed-feeding insects is
recommended. Sunflower is susceptible to Lygus damage, from flowering
through seed hardening. Lygus can be treated at the same time confection
sunflower is treated for other insect pests, such as the red sunflower seed
weevil and banded sunflower moth. The action threshold is one adult or nymph
Lygus bug per 9 heads. This population level could result in economic loss to
the producer through the reduction of seed quality. Two treatments are
recommended to sufficiently protect confection sunflower heads from Lygus bug
feeding: one application at the onset of pollen shed, or approximately 10%
bloom, followed by a second treatment 7 days later. This program should
adequately control any insect pests on confection sunflower throughout
flowering, minimizing the potential feeding damage. Oilseed sunflower are not
believed to be at risk to damage from Lygus feeding at this time.
Janet Knodel
Extension
Entomologist
janet.knodel@ndsu.edu
