ISSUE 5 June 1, 2006
CEREAL APHIDS OBSERVED IN NEIGHBORING STATES!
Cereal aphids (English grain aphid, bird cherry oat aphid, corn leaf aphid) have been observed in southeastern MN and WI at low levels and are expected to be blown into ND soon. Aphids are soft-bodied pear shaped insects with prominent antennae and conspicuous cornicles or "tailpipes." Descriptions of cereal aphids include (see photo):
Greenbug - pale green with darker stripe down back.
Bird Cherry Oat Aphid - olive green, brownish patch at the base of cornicles.
English Grain Aphid - bright green with long black cornicles.
Most cereal aphids cause economic damage to cereal crops through their disease transmission of barley yellow dwarf virus, which affects barley, wheat and oats. The disease is called "red leaf" in oats. Although younger plants are more severely affected, most plants can become diseased at any growth stage. The severity of an infestation will depend upon the number of aphids present, the percent viruliferous aphids, crop growth stage and several other factors. You can't tell a viruliferous aphid from a clean one just by looking at it. When aphid populations are high, the disease can spread through small grain fields. At greatest risk are later planted fields which attract migrating aphids that are moving from more mature fields.
Field scouting for aphids should begin at stem elongation and continue up to the heading stage of wheat. 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. Aphid populations at or above the thresholds during these growth stages will result in economic injury to plants. 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 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: after heading the only major yield component that aphids affected is seed weight. Other components of yield are determined earlier (number of spikelets - determined at jointing; number of seeds - determined at flowering). If Barley yellow dwarf virus is prevalent in area and aphid populations are high, producers should consider lowering the treatment threshold below 85% of aphid infested stem to prevent spread of barley yellow dwarf virus.
Lady beetles, aphid lions, syrphid fly, and parasitic wasps play a major role in reducing aphid populations. When natural enemies are present in large numbers, and the crop is well developed, producers are discouraged from spraying fields.
SOYBEAN APHIDS MAKE A VERY EARLY ARRIVAL!
Researchers from the NWROC entomology project found soybean aphids on V1/V2 soybeans between Crookston and Fisher this week. Populations are very small (nothing to worry about yet!) but this is the earliest date that soybean aphids has been recorded infesting fields in northern MN (and may be one of the earliest dates for them to be found in commercial fields in the state!). These aphids undoubtedly overwintered in the region this year. This is definitely the earliest we’ve ever had soybean aphids in commercial soybean fields in NW MN and is very probably the result of successful overwintering on local buckthorn. The mild temperatures and snow cover during the past winter provided very good overwintering conditions for these aphids.
In the Crookston/Fisher fields, winged females were observed depositing nymphs on leaves and small colonies of several aphids were found on the top trifoliates of several plants. Populations are low at the moment but the weather conditions are conducive for aphid reproduction, and we are expecting these ‘good aphid temperatures’ to continue for at least the next week. Remember, at this time of year all soybean aphids are females and reproduction is parthenogenic – asexual reproduction where female aphids are born ‘pregnant’ and when they mature, give birth to live daughters. These nymphs (young aphids) will mature in 3-10 days and then start having daughters of their own. Aphid populations are usually partially controlled by predation and by fungal diseases. However, our recent hot spell may have negatively impacted the fungal diseases that help keep these pests in check and the lack of rain may impair their ability to get established (like any other fungus, these insect killers need some humidity to establish and grow) We’ll have to wait and see if this is the case.
Bottom line, it's not time to break out the spray rig yet but it is time to think about scouting your fields and keeping an eye on developing aphid populations.
For information on early scouting for soybean aphids, see the link below:
Department of Entomology
University of Minnesota
NW Research and Outreach Center
WEEKLY FIELD SCOUTING TIPS FOR INSECT PESTS
Continue Scouting for Cutworms
Cutworms continue to be a major pest problem on many different crops, especially sunflowers, sugar beets, peas, and other row crops. Be vigilant in scouting fields for injury symptoms of cutworms - cut plants or missing plants. See Crop & Pest Report Issue 1for more information on economic thresholds and scouting tips.
Cropland Grasshoppers Emerging!
Young grasshoppers have been observed in north central and southern regions of North Dakota. Start scouting for these young grasshoppers about the size of a wheat kernel. Remember young grasshoppers are concentrated in hatching sites (grassy ditches), and more susceptible to insecticides. Threatening populations of newly hatched grasshoppers are more than 50-75 per square yard in field margins or 30-45 per square yard in field.
SUGARBEET ROOT MAGGOT: INFESTATIONS HAVE SPREAD & PEAK FLY ACTIVITY EXPECTED SOON
The recent warm weather has accelerated development of sugarbeet root maggot populations in the Red River Valley. Flies were first detected in the northern portion of the Valley (St. Thomas vicinity) during the 3rd week of May. Activity is quite high in central and south central Pembina County, as well as in central and north central Walsh County of ND. Surprisingly, flies have also been observed in fields in the southern portion of the Valley near Moorhead and Baker, MN. Maggot infestations in these areas have been extremely low for over five years.
Degree-day accumulations are being monitored this year and run on the NDSU root maggot model with the help of Emeritus Professor Dr. Robert Carlson. Major levels of adult fly emergence from previous-year fields will occur during the next couple of days, and peak activity can be expected within the next 3 to 10 days, depending on location and weather conditions. Remember, warm (80 F or above) daytime weather is needed for the actual peak to occur. Flies will not be active during cool, windy, or rainy weather. Thus, what would have been the true peak can be delayed, and its intensity can be spread out over a few days.
Growers in all eastern ND sugarbeet-producing areas and those in most adjacent counties of MN should be aware that flare-ups in fly activity during the next 10 days could warrant treatment with a postemergence insecticide. Risk should remain quite low in heavy soil areas of extreme northwestern MN. Infestations of 1 or more flies per plant in sugarbeet fields may be economically justifiable to require a postemergence insecticide application. Vigilance in applying postemergence materials to manage the root maggot in these areas could also help combat the development of damaging populations in these areas for next year.
For guidance on anticipated populations in the region or for specific information on sugarbeet root maggot management, please refer to the "Insect Control" section of the 2006 Sugarbeet Production Guide or the "Sugarbeet Insects" section of the 2006 Field Crop Insect Management Recommendations for more detail and specific product recommendations. The respective WWW locations for online versions of these publications are:
Research & Extension Entomologist
DEFOLIATING WEEVIL DAMAGING AREA SUGARBEETS
Reports of field damage from the sugarbeet leaf-feeding weevil, Tanymecus confusus, have been received from the Southern Minnesota sugarbeet production area.
Adults are about 1/2 inch long and their head narrows slightly toward its tip into a broad snout. They are a mottled brown to brownish-gray in color, and their bodies are covered with minute, gray, hair-like structures (Fig. 1).
Figure 1. Adult leaf-feeding weevil
on damaged sugarbeet leaf
Feeding injury typically occurs in small areas of sugarbeet fields, but damage can be severe enough to require replanting. Adult weevils use chewing mouthparts to feed on cotyledons and leaves of young sugarbeet plants. They generally feed on leaf edges and interveinal areas, and usually leave the midrib intact. Significant feeding damage can result in seedling death.
Weevils are difficult to find because their dark mottled coloring makes them difficult to detect on the ground. Detection is made even harder when they fall to the ground and "play dead" after being disturbed. Careful inspection reveals the insects in plant debris or in the soil immediately surrounding damaged plants.
Field scouting for adult weevils and timely application of insecticides may be necessary to control some populations. No economic threshold exists for this rare insect; however, fields in which major stand reductions are anticipated or occurring should be treated with a foliar insecticide. Materials labeled for use on sugarbeet that have activity as stomach poisons in other beetles, especially weevils, should provide good control of the leaf-feeding weevil. Pyrethroid insecticides will perform best in moderate to cool weather, whereas, organophosphates work best when warm temperatures prevail. For more information on this insect, refer to the following extension circular:
Research & Extension Entomologist