ISSUE 14 AUGUST 5, 1999
RED SEED WEEVILS IN SUNFLOWER
Many decisions are being made this week on treating for red seed
weevil. Reports from the southeast
to the north central counties indicate that threshold levels have been reached in many confectionary
sunflower fields. The treatment threshold is one weevil per head in confection fields.
This should serve as a wake-up call for watching oilseed sunflowers
closely as they bloom. Seed
weevil populations have remained low during the 90's. Most problem spots have been very localized in
North Dakota. These early reports from a number of areas might be an early warning that the population
is increasing and many more oilseed fields could require treatment than in the past five seasons.
BANDED SUNFLOWER MOTH AND HEAD MOTH
Banded sunflower moths have been out and laying eggs for over
a week. From McLean County,
a report of large numbers of BSM moths in field borders was received late last week. As reported two
issues ago, the BSM lays eggs on the bracts, so they arrive during late bud stages. When BSM are
present in sunflower fields, treating early in the flowering stage has proven the most effective at reducing
larval populations. The threshold used over the years has been one moth per two plants when scouting
near dusk. The same insecticides used against seed weevil should provide control of BSM larvae.
There have also been two reports of sunflower head moth from
the region. One report was in the
east from the Wahpeton-Breckinridge area, the second was from the west in Beach, ND. Sunflower
moth migrations from the south central United States normally appear in North Dakota in early to mid
July. The moths are highly attracted to sunflower that is beginning to bloom. Eggs are deposited by
female moths on the surface of open sunflower heads. Newly emerged larvae feed on pollen and florets.
The larvae begin tunneling into seeds upon reaching the third instar of the larval growth stage. The young
larvae of the sunflower moth feed primarily on florets and pollen. Older larvae tunnel through immature
seeds and other parts of the head. A single larva may feed on from three to 12 seeds and forms tunnels
in both the seeds and head tissue. The economic threshold for sunflower moth is one to two adults per
five plants at the onset of bloom or within seven days of the adult moth's first appearance. Fields that
are in bloom or that bloom two weeks or more after the first adult moth appearance have very low
potential for damage despite the presence of moths in threshold numbers. When scouting sunflower,
look for the adult moth, which is a shiny gray to grayish-tan moth, just under ½ inch long, and a dark
dot near the center of each forewing. When at rest, the wings are held tightly to the body, giving the
moth a slender cigar-shaped appearance.
CORN BORER UPDATE
The flush of moth activity in northern and western areas did not
last very long. The numbers of fields
in the state being treated will be much lower this year than the previous three seasons. If significant activity
has not been observed in fields by now, the likelihood of problems developing should be low.
PREPARATION OF GRAIN BINS AND PLANNING FOR LONG TERM STORAGE
Sanitation is an important program for preventing insect
infestations. It is also critical to be thinking
about storage of grain and things necessary to keep insects and other storage problems to a minimum.
Last year, there were many problems associated with insects in stored grain that can be avoided with
proper planning and handling.
1. Clean outside around the bin, beneath perforated floors and inside ducts in addition
to cleaning the
bin. Sweep or vacuum grain dust and old grain from floors, walls and ceilings where hiding places exist
for stored grain insects. If you can tell what has previously been in the bin, it is not clean. In bins where
the perforated floor cannot be easily removed, chloropicrin grain fumigant can be applied to control
insects in the sub-floor area. Chloropicrin is a highly toxic chemical and as such, all label instructions
and safety measures must be carefully adhered to. Debris and grain spills outside the bin also encourage
rodents and insects which can then move in through openings.
2. When possible, avoid filling bins with new grain where some old grain is already
present. This creates
an ideal situation for insects in the bran bug group (sawtoothed grain beetles, flour beetles and the like).
3. Roof leaks commonly lead to columns of spoiled grain. Check for these leaks by
looking for light
coming into the bin. Moisture coming into the bin through the seal between the bin and concrete will
cause spoilage around the perimeter of the bin at the base. Check the seal since sealants do deteriorate.
Water will run away from the seal at the base of the bin wall if the concrete is sloped away from the bin.
Also check the seals around the doors and hatches.
4. After cleaning and repairing, use a residual bin spray to treat the insect surfaces
of the bins at least two
weeks prior to filling. Recommended bin sprays are methoxychlor 2 lb EC, Reldan 4 lb EC or Tempo,
applied according to label directions.
5. If grain is to be held in storage for a year or more, it should be treated
with a grain protectant
such as malathion or Reldan. Be aware, however, that malathion will not control Indian meal moths,
which commonly infest stored commodities in the state, and neither Reldan nor malathion will control
lesser grain borers. Bacillus thuringiensis (Bt) sold as Dipel can be used as a surface treatment to control
Indian meal moth, but it will not have any affect on beetle infestations (e.g., red flour beetle, sawtoothed
grain beetle, granary weevil, etc).
Note: The American Malting Barley Association has a policy that does not allow for the use of
any residual insecticide on malting barley. This would include the products malathion, and
Reldan. These insecticides are allowable for use as residual bin sprays in bins that will be
filled with malting barley. According to AMBA policy, the only chemical allowable for use on
malting barley is phosphine (aluminum phosphide) fumigant to control an existing infestation.
6. In the fall, aerate to cool the crop and create a better storage environment in any
bin larger than 2,000
to 3,000 bushel capacity. Determine if the aeration system in your bins will provide at least 1/10 cubic
foot per minute (cfm) airflow for each bushel of crop being stored. Check the condition of the entire
aeration system. You'll also need at least one square foot of opening in the bin for each 1000 cfm of
airflow to allow the air to enter or exit from the bin. By gradually cooling the stored grain through the
fall, temperatures below 50EF should be achievable. At these temperatures, insect activity is reduced.
The target temperature for stored grain should be 25EF for the winter. At this temperature, insect
activity ceases and some mortality will occur for a number of our stored insect pests.