NDSU Crop and Pest Report


ISSUE 7  June 13, 2002



Black Fly

Buffalo gnats (or black flies) are usually a problem around mid May. With the late spring, we are seeing this activity start about two weeks late. Expect emergence and activity over the next few weeks.

Buffalo gnats are small, humpbacked flies. They can be a major nuisance due to their buzzing presence and constant crawling, not to mention their irritating bite. Buffalo gnats are active during daylight hours. Their tendency to bite increases towards sunset. They seldom attack indoors or even in a vehicle.

Larvae of these flies develop in flowing waters (rivers and streams). Problems with flies may be worse in areas adjacent to these locations but not limited to them. Black flies can be blown long distances from where they emerge.

Appropriate clothing is the best defense for people. They do not bite through clothing but do have a knack for crawling into hair and under clothing. Tucking trouser cuffs into socks prevents them from getting at the ankles. These flies are attracted to dark colors (example: blue, purple, brown, and black). A light colored shirt is a better choice than darker colors when black flies are active. Blue jeans would be a good choice by helping to attract flies away from the head region. Insect repellents provide some relief when applied to exposed body parts. Repellents applied to clothing remain active longer than repellents applied to the skin.

Buffalo gnats can be annoying to livestock and pets. There is no practical control measure available for herds of livestock. Riding horses may be particularly bothered. They can be treated with different pyrethroid insecticide products (EctrinR, AnchorR, AtrobanR) for temporary relief. For dogs, it may be easier to let them take shelter indoors during the day or treat them with insect repellents for pets available through veterinary supply stores.

In general, area sprays and premise treatments are not regarded as very effective in managing Buffalo gnats.



The IPM Survey scouts have been reporting on grasshopper numbers found in field margins. Sweep net counts indicate low numbers . . . so far. Keep in mind that the cool weather has delayed emergence in many areas. The survey counts are below threatening levels at locations surveyed. Over the next three weeks we may see some changes.

What is important is that growers and consultants now begin assessing local populations to locate sites of significant activity. Of particular interest will be the south central counties where numbers were greatest last year. These areas are also dry, a condition that favors grasshopper survival and contributes to future losses.

Grasshopper map

Future updates will be posted at:




Adult Aster Leafhopper can be found in grassy areas and moving into some small grain fields. They are the greyish looking leafhoppers active in field borders. If you look closely, six spots on the top of the head are visible. The aster leafhopper moves the mycoplasma-like organism Aster Yellows (AYP) to flax, canola, sunflower and other plants.

The Aster leafhopper migrates into the region AND overwinters as an egg in grass leaves. Most of what we are currently seeing are the local residents that hatched this spring. Typically, the migrating population of adults from southern states are the ones with the greatest risk of carrying AYP and they are the primary contributor to AYP transmission to hosts. The local population typically has a lower level of infectivity. Factors that contribute to infectivity are: feeding on AYP infected plant; and, an incubation period of 2 to 3 weeks before the AYP can be transmitted. Adults migrating from southern states are more likely to be AYP carriers because of infected host plants where they originated and they have the necessary time needed for AYP to replicate itself in the insect.

Aster yellow infections are very difficult to predict. Risk of problems relates to the size of the insect population and what level of infection is present. The economics of control to try and prevent AYP are not very good for most field crops. High value vegetable crops, such as carrots, should be monitored and treated when aster leafhopper is present. In this case, the insect is controlled to limit transmission. Once AYP is acquired by a plant, there is nothing that can be done. Symptoms require a week or more to appear in infected plants. Typically, a longer time is required for symptoms to appear in older plants. The later the infection, the less impact on the overall health of the plant. Therefore, later planted crops are at greater risk to AYP.

Over 300 species of plants have been identified as hosts of AYP. The vegetable crops (carrots, lettuce, celery) get most of the attention because of their production value. Other plants infected include grains (oats, barley, wheat, rye) and weeds (quackgrass, lambsquarters, sowthistle, dandelion). The aster leafhopper also moves the Oat blue dwarf virus to small grains.

Because of so much uncertainty about infection and poor economic incentive to control the vector, treatment has not been encouraged for field crops and small grains.

Phillip Glogoza
Extension Entomologist



According to the NDSU sugarbeet root maggot developmental model, peak fly activity in current-year beet fields is just around the corner. However, a achieving a precise estimate of peak activity is especially challenging this year. In addition to slow accumulation of degree-day (DD) units through much of the spring, excessive rainfall amounts and saturated soil conditions in fields are further complicating the picture. A rainfall event can have significant impacts, both positive and negative, on overwintered root maggot populations. A gradual "soaker" rain on a warm soil surface can percolate heat energy into the soil profile and accelerate development; however, excessive rainfall that leads to prolonged saturation can result in substantial levels of mortality.

Sticky stake data from our monitoring program indicates that, as of 11 June, sugarbeet root maggot activity in current-year beet fields was quite low. Degree-day accumulations as of 10 June suggest that, depending on latitude, peak emergence from previous-year fields has either taken place within the past few days or will do so shortly. Peak fly activity in current-year beets is projected to occur on the first warm (80 degrees Fahrenheit or above) day between June 11th and 21st in the Red River Valley.



Current DD*

Projected days to 600 DD

Projected peak
activity date**




21 June + 80E day




21 June + 80E day




17 June + 80E day




11 June + 80E day

Forest River



17 June + 80E day




14 June + 80E day




13 June + 80E day




19 June + 80E day

St. Thomas



18 June + 80E day




11 June + 80E day

*Degree-day unit accumulations based on NDAWN data recorded as of 10 June 2002

**Projections are, in part, based on the extended weather forecast. Peak activity usually coincides with the first 80 day following accumulation of the required 600 DD units.



Although moist soil conditions are typically an asset to using granular products for postemergence control of sugarbeet root maggot larvae, the excessive rainfalls received recently in many fields may make timely application efforts difficult for many growers. In such cases, a liquid product may be a more viable management option. A liquid formulation of an organophosphate product such as Lorsban 4E may provide fly control. Larval control will be most effective if rainfall is received within 1 or 2 days after the application to adequately incorporate it into the soil. A liquid product may also be good choice if unanticipated high fly activity occurs. Research suggests that adult fly control can also be achieved with Asana; however, it and other pyrethroid products are not particularly active against larvae when applied postemergence. Fly activity will dictate if a postemergence insecticide is even warranted. Thus, growers are recommended to assess conditions in their sugarbeets on an individual-field basis. Reference to the root maggot population forecast map may also assist with making the decision on whether to apply a postemergence treatment. Refer to the "Insect Control" section of the 2002 Sugarbeet Production Guide or the "Sugarbeet Insects" section of the 2002 Field Crop Insect Management Recommendations for more detail and specific product recommendations.

Mark Boetel
Research & Extension Entomologist

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