ISSUE 14 August 1, 2002
CRISIS EXEMPTION ISSUED FOR MUSTANG USE IN FLAX FOR GRASSHOPPER CONTROL
The ND Department of Agriculture has issued a crisis exemption for the use of Mustang (zeta-cypermethrin) in flax to control grasshoppers.
"Movement of grasshoppers from maturing small grain fields and other areas into flax fields has become severe in recent days and threatens flax production as well as other late season crops," Roger Johnson, ND commissioner of Ag, said. "The later maturing flax fields will be green and attractive to grasshoppers for a longer period of time than normal because of delayed seeding following the unfavorable spring planting conditions."
The label allows application from July 30 to August 13, 2002. Johnson said he will soon submit a specific exemption request for Mustang to extend use of the insecticide beyond the 15-day period allowed under a crisis exemption.
The crisis exemption allows a use rate of 3.4 to 4.3 fluid ounces of product per acre. There is a post harvest interval of 30 days for this label. All other directions, restrictions, and precautions from the EPA-approved labeling for Mustang must be followed.
Users must have a copy of the label in their possession at time of use. To obtain a copy, contact your local extension office, pesticide dealer, or find it on the NDSU Pesticide Training Program web site at:
GRASSHOPPER ACTIVITY CONTINUES
As small grains ripen or non-crop areas dry down, adult grasshoppers increase their movements to green areas in a region. By now, most people should be aware of the grasshopper infestations around their farms. With the NDSU IPM survey we have been monitoring for grasshoppers during the season at all field sites sampled. Currently, adult numbers found in the survey are finding regions where we are exceeding the 8 per square yard considered a threatening level.
Here is a map of the state with the July survey numbers summarized. As we attempt to do more real-time assessment with pest problems, your comments would be appreciated on the value and perhaps the accuracy of this current map. It appears the southwest quarter of the state may be underestimated at this time. This may be due to a greater survey emphasis on small grains where grasshoppers are now moving away. In other areas, later season crops have been surveyed representing the location where grasshoppers are moving towards.
SOYBEAN APHID - READY TO TAKE FLIGHT ?
Adult aphids can be winged or wingless. When observing field infestations, outbreaks largely consist of wingless adults. However, there are conditions that stimulate production of winged adults. What are all the conditions? They may not be completely known but include crowding in large colonies, declining quality of the food (e.g., plants are maturing), shortening day length, and others.
Last year when soybean aphid populations increased rapidly in late July and early August, the population started to shift to the production of increasing numbers of winged, or alate, aphids. During field scouting last week in North Dakota, winged adults are becoming easier to find.
An inspection of the nymphs provides a clue whether populations in fields are preparing to be winged and take flight. If a nymph has squared shoulders, a closer look reveals the developing wing buds. Nymphs with wing buds become winged adults in a only a few days and take flight. If the majority of the nymphs are alatoid (developing wings) then migration from fields is expected. If the populations is preparing to take flight, insecticide treatments may not be economical.
EUROPEAN CORN BORER UPDATE
Decisions should be finalized on the need to treat the ECB univoltine flight. Larvae are finished hatching and assessment of numbers present in fields should provide an indication of whether infestations are great enough to warrant control.
BANDED SUNFLOWER MOTH FLIGHTS
Field reports have indicated banded moths are moving to and settling in around this years sunflower fields. Check field margins during the day to get an indication of the population around specific sites. The moths will sit in the grassy borders of fields during the day, later dispersing into sunflower fields in the evening hours. Moths have been reported in southeast and east central ND as well as neighboring areas of Minnesota.
RED SEED WEEVIL IS RIGHT BEHIND
Red seed weevils are being found in south central counties of ND. It is time to assess seed weevil populations along with banded moth to determine whether treatable levels are present in oilseed fields. Remember, confection fields and seeds targeted for the dehulling market should be treated to minimize the risk of injury from seed weevil, banded moth, and lygus bugs.
At this time of the season, numerous questions arise regarding the sunflower maggot, Neotephritis finalis. The reddish-brown pupa of this maggot is seen by many as scouting gets underway for banded moth and seed weevil. The pupa is seen in the opening flower, usually in the center of a damaged area where the maggot had fed.
Two complete generations per year of N. finalis occur in North Dakota. Adults of N. finalis emerge during the first week of July. Egg deposition occurs on the corolla of incompletely opened sunflower inflorescences. The total larval period is 14 days. The first generation of N. finalis pupates in the head; the second generation overwinters in the soil as pupae.
The magnitude of damage to sunflower seeds by N. finalis larvae depends largely on the stage of larval and seed development. Seed sterility occurs when newly hatched larvae tunnel into the corolla of young blooms. Observations indicate that a single larva feeding on young flowers will tunnel through 12 ovaries. Mature larvae feeding on older sunflower heads will destroy only one to three seeds.
There has not been an economic threshold established, and insecticide use has not been warranted for control of this sunflower maggot.