ISSUE 7 June 12, 2003
SUGARBEET ROOT MAGGOT: PEAK ACTIVITY EXPECTED IN COMING WEEK
The cool and rainy weather patterns that prevailed during the past 2 weeks have slowed development and hindered movement of sugarbeet root maggot populations in the region. However, moderate to high numbers of emerging sugarbeet root maggot flies (12 to 54 per stake day) were captured by NDSU personnel on sticky stakes in previous-year beet fields during the past weekend. The extended weather forecast suggests that several warm days are likely into the early part of next week. The root maggot developmental model suggests that peak fly activity in current-year beet fields should occur sometime between Tuesday and Friday of next week, depending on latitude (northern areas later than southern).
Growers in high-risk areas for significant root maggot infestations, especially Pembina and northern Walsh counties of North Dakota, should consider application of a postemergence insecticide. Those preferring to use a granular product should apply it as soon as possible - it is better to err on the early side of peak activity with a granular formulation. Liquid insecticides can kill the adult flies so those products should be applied within 2 to 3 days (either before or after) the projected peak to get the best results. A sudden, unanticipated flare-up of fly activity will also be best handled by applying a liquid insecticide. For more information regarding postemergence control of the sugarbeet root maggot and for more specific product recommendations, refer to the "Insect Control" section of the 2003 Sugarbeet Production Guide or the "Sugarbeet Insects" section of the 2003 Field Crop Insect Management Recommendations. The respective WWW locations for online versions of these publications are:
Research & Extension Entomologist
The IPM survey scouts are having little trouble finding grasshopper nymphs. The survey counts across the state are numbering in the 1 to 24 nymphs per square yard. Other people, particularly in the north central and western counties, are reporting higher numbers. Grasshopper numbers found in the survey are likely to increase in the next two weeks.
A few corrections to last weeks list of insecticide options by crops. It appears I was editing some of the information on pulse crops and must have been interrupted. Here are the (hopefully) correct options:
Asana, Baythroid, Mustang Max, Sevin
Baythroid, Mustang Max
Asana, Mustang Max, Sevin
CEREAL APHIDS MAKE EARLY APPEARANCE
The IPM crop survey program detected aphids in wheat and barley fields with some of the first field scouting efforts. Cereal aphids arrive in the region from May to July, but detections prior to mid-June have been few. The scouts have found aphids primarily in the eastern edge of the state, fewer fields have had them in the west. The populations had been generally low, coming in below the 25% infested plant range. However, scouting reports coming in at press time indicate aphid levels in Sargent and neighboring counties are actually approaching some 70% infested stem levels.
One caution, the aphids have frequently been Bird cherry oat aphids. This aphid is commonly associated with infections of Barley Yellow Dwarf Virus transmission. The other cereal aphids (English grain, Greenbug, and Corn leaf) are also vectors, however bird cherry oat has been associated with more virulent forms of the virus.
Encircled area represents locations where aphids have been found at low levels
The greatest risk of yield loss from aphids feeding on grains is in the vegetative to boot stages. Significant yield reductions after the onset of flowering (or heading) could not be demonstrated in research published from South Dakota in 1997 (Voss et al., 1997. J of Economic Entomology 90: 1346-1350). Reasons for these conclusions were that:
Other components of yield are determined earlier (number of spikelets - determined at jointing; number of seeds - determined at flowering).
To protect small grains from yield loss due to aphid feeding, the treatment threshold is 85% stems with at least one aphid present, prior to complete heading. Fields should be monitored for aphids from this point to determine if colonization and population increases occur.
SOYBEAN INSECTS GETTING SOME ATTENTION
By now, soybean aphid should be an insect we have become familiar. Currently, surveying efforts for the aphids have focused on inspecting buckthorn in an effort to detect overwintering/first generation aphids. So far, the effort has turned up nothing in our area . . . but this was the same result obtained last year. Soon, the survey effort will start shifting to soybeans. They have found soybean aphid on soybean in southeast Minnesota, the earliest it has been detected in these first three seasons of experience.
Initial surveys of soybeans are for detection of early colonization only, not for making treatment decisions. Treatment decisions are still going to be made in the late vegetative, early flowering , and early pod set stages.
Another soybean insect that we are watching for a little more closely is the Bean leaf beetle. This insect has not been an issue in North Dakota soybeans. In fact, the North Dakota Insect Reference Collection housed in the NDSU Entomology Department has no official record of collection of this insect from our state. There have been casual observations reported for ND, most recently last week. The Minnesota Department of Agriculture Crop Pest Survey detected low levels of damage attributed to bean leaf beetles as close as Traverse County (Wheaton, MN).
The bean leaf beetle has caused problems in southern Minnesota, Iowa, southeastern South Dakota, and other areas to the south. Populations of this insect have been increasing in these areas due to favorable weather conditions, e.g., mild temperatures and/or snow cover. In these areas, high numbers of bean leaf beetles have prompted concern about direct losses from beetle feeding and transmission of bean pod mottle virus in the spring.
|Graphic source: Bradshaw and Rice. Bean leaf beetles: a current and historical perspective. Integrated Crop Management, Iowa State University, Ames, Iowa. (3/17/2003)|
We would not expect any concerns with bean leaf beetle during plant emergence this spring. Treatment thresholds published by Iowa State University indicate that cotyledon stage soybeans require about 3 to 4 beetles per plant to justify control with an insecticide. The number of beetles per plant increases as the plants reaches the V1 and V2 stages. It is worth noting if beetles are found this season and how the population may progress.
For more information on bean leaf beetle, the entomologists at Iowa State University excellent discussions over the years in their newsletter, Integrated Crop management which can be found at:
Honey Bee Facts
Never spray a crop in bloom unless it’s absolutely necessary. If spraying a crop in bloom is necessary, do the spraying when there is minimal bee activity, preferably during the evening hours. During most summer evenings, honeybees leave fields by 8 PM and do not return until 8 AM or later the following day. Most fungicides and herbicides (except 2,4 D) pose little threat to honeybees. Protect our important pollinators!
Grasshopper Management Tidbits
INSECTICIDE RATES – Lower rates are recommended for the nymphs (young grasshoppers) on small plants or sparse vegetation. The higher rates are suggested for adult grasshoppers or when materials is applied to crops requiring greater coverage.
EFFECTS OF WEATHER ON INSECTICIDES– Cold temperature prolong the residual of insecticide while warm temperatures break down insecticides more rapidly.
GRASSHOPPER BIOLOGY AND EFFECTS OF WEATHER
Grasshoppers overwinter in the egg stage. The majority of the eggs are laid in late season crops like flax, sunflower, dry beans, for example. If you find crop damage during hatching period and 33-45 grasshopper nymphs per square yard in field or 50-75 nymphs per square yard in field edge, an insecticide treatment is recommended. Remember, grasshopper nymphs are easier to kill than adult grasshoppers. The nymphs will remain in grassy areas or roadsides for a long time before moving into fields, so spray ditches/field edges or just "hot" spots in ditches/field edges. It takes about 35-50 days for the nymphs to go through the five or six nymphal stages before becoming a winged adult.
Temperature, rainfall, and snowfall are all important in determining the severity of grasshopper infestations. A warm, extended fall will result in larger number of eggs being laid. The same condition supports greater embryonic development before winter. This results in an earlier and more even hatch of young grasshoppers the following spring. Extremely dry conditions in the fall and spring will limit embryonic development within eggs. Very cold winter temperatures (soil temperature of <5 degree F) with little snow cover can result in up to 90% mortality of the eggs. Unfortunately, most grasshoppers lay their eggs in areas where snowfall will accumulate. Spring temperatures will have only a minimal effect on the survival of grasshopper that hatch. Young grasshoppers are hardy enough to tolerate below freezing spring temperatures for a short period. Spring temperature will affect grasshopper development and plant growth.
If the spring is hot, grasshoppers will hatch early and develop quickly. Cool spring temperatures will slow grasshopper development. Under hot dry conditions, a small grasshopper can do as much damage as a large grasshopper under cool, wet conditions. Rainfall will only have an effect if a heavy downpour occurs immediately after an extensive hatch. A cool, wet June will NOT seriously affect grasshopper populations. However, a warm humid summer will increase the potential for diseases in grasshopper populations, which will help reduce the densities the following year.
Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center