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ISSUE 9  June 28, 2001

 

APHIDS IN GRAIN CONTINUE AT LOW LEVELS

Cereal aphids are still at low numbers based on scouting reports from this week. Continue to monitor for the presence of English grain and Bird cherry oat. Past observations of English grain aphid reveal very rapid increases in its number around heading time. This is typically the aphid that moves to the grain head. These population increases are not sustained long enough to cause significant impact on yield and quality, as cited in last weeks newsletter.

 

WHEAT MIDGE EMERGENCE UNDERWAY

The degree day accumulations have reached 1300+ in most of the southeast, valley, and central areas of ND. The warm weekend increased degree day accumulations enough to have emergence begin 1 to 2 days earlier than last weeks projections. Begin scouting heading wheat to determine if populations in your fields and area are reaching treatable levels. Jan Knodel, Plant Protection Specialist - Minot, reported trapping adult midge in the Makoti area on Wednesday, 6/27.

 

ARMYWORM QUIET . . . FOR NOW

There have not been any new reports of armyworm infestations. Black light traps in southeast ND are catching only a few moths at the moment. Numbers reported from southern Minnesota were also less. Some armyworm have been detected with sweep nets in field margins during IPM surveys. Watch fields carefully in the next week.

 

SUNFLOWER MIDGE EMERGENCE BEGINNING

A degree day model for predicting sunflwoer midge emergence has been in development for a couple of seasons. Though we still lack a responsive control measure for managing this insect pest, it is beneficial to know when it is active. We have reached a point in the southeast quarter of the state when SF midge are beginning to emerge. SF midge prefer to lay eggs on the developing bud. Due to late planting of many of the sunflowers, there aren’t going to be many of the preferred places to lay those eggs. The midge will deposit eggs in leaf axils. The hatching larvae will feed at those sites, causing scarring of the outer plant tissue. We do not recommend control of the insect under these circumstances, but it is good to be aware of the potential for some noticeable injury that will be visible later.

 

SUNFLOWER BEETLE LARVAE ARE HATCHING

As larvae hatch, scout fields to determine if the larval threshold has been reached. The treatment threshold is 10 to 15 larvae per plant. Leaf damage will likely be light from larval feeding. However, defoliation will reach the damaging level of 25 to 30% if populations are present at the treatment threshold and are allowed to develop. As the larvae grow in size, their leaf consumption will increase both in quantity and speed. Delaying treatment, though the larval numbers suggest the need for control, only results in a ragged, stressed plant during flowering.

 

EUROPEAN CORN BORER EMERGING

European corn borer moths have been captured in black light traps since June 8. The numbers of moths have been very low. These low numbers in June have been typical for the region. The moths represent bivoltine, or two generation, ECB which have been only a small percentage of our population. A more significant flight is about to get underway.

ECB emergence has been the focus of another degree day modeling project. The univoltine, or single generation, ECB has been the dominant type infesting our region’s corn in the past 10 years. The research project was designed to gain a better understanding of when the univoltine moths are emerging and laying eggs based on temperature. The model can be used to indicate where the region is in terms of the percent of moths emerged. The principle is the same as with the wheat midge model we rely on for scheduling scouting activities.

Degree Day Accumulations for Univoltine
European Corn Borer Moth Emergence

Percent of Moths Emerged

Degree Day Accumulation
(modified Base 50 F)

10

910

25

986

50

1078

75

1177

90

1274

The degree day accumulations are determined using a formula we refer to a as a modified base 50EF. This is the same method of calculating growing degree days for corn. Therefore, one model for monitoring corn growth and its key insect pest in the region.

Currently, we are in the mid-700 to mid-800 degree day totals in southeast, the point where emergence is getting underway with the peak coming later.

 

STABLE FLIES MAKING NUISANCE OF SELVES

Numerous complaints from eastern ND about biting flies. The flies are the stable fly. Stable flies are more often a livestock pest but they will also bite people and pets. Following is some information about stable flies that you may find useful.

Life Stages of the Stable Fly

The house fly and stable fly are similar in size, color and general appearance; livestock producers often refer to them as barnyard flies. On closer examination, these two flies are quite distinct in appearance, feeding habits and in the ways they annoy livestock.

A distinguishing feature, visible to the naked eye, that separates the two species is the distinct stiletto-like proboscis of the stable fly which extends forward beyond the head. This sharply pointed beak is used to pierce the skin and draw blood. The house fly cannot bite since it has sponging mouthparts.

Adults: Both male and female stable flies feed on blood and are persistent feeders that cause significant irritation to host animals. Adults are 7 to 8 mm long and resemble house flies. A "checkerboard" appearance of the top of the abdomen and the stiletto-like proboscis will separate this species from adult house flies.

Eggs: Stable fly eggs are about 1 mm long and are an off-white color. Females deposit clusters of eggs containing up to 50 eggs. Several such clusters of eggs will be deposited during the life of a female fly and a single female can lay up to a thousand eggs during her lifetime.

Larvae: Stable fly larvae have a typical maggot shape. There are three larval stages. The last stage larva is about 10 mm long and is a cream white color.

Pupae: After the third stage larva completes feeding it shortens, hardens and darkens in color. The chestnut brown pupa is 6 to 7 mm long. Stable fly pupae are very similar in appearance to house fly pupae and are difficult to distinguish since, in their natural habitat, they are usually mixed with house fly pupae.

Stable Fly Life History and Habits

Life Cycle: Stable flies will feed on blood from practically any warmblooded animal, including humans, pets and livestock. During periods of high stable fly activity, humans can be severely annoyed and this insect has been called "the biting house fly." Individual flies may feed more than once per day. Peaks of feeding activity commonly occur during the early morning and again in the late afternoon. Stable flies prefer feeding on lower parts of the hosts such as the legs and belly of horses and cattle. Both male and female stable flies feed on blood, and the female requires blood meals to produce viable eggs. Females deposit their eggs in a variety of decaying animal and plant wastes, but are rarely found in fresh manure. This fly prefers excrement mixed with straw, soil, silage or grain but are also found in wet straw, hay, grass clippings, other post harvest refuse and poorly managed compost piles. Large round hay or straw bales, where contacted by moist soil, may serve as larval development sites. Larval development requires 11 to 21 days, depending on environmental conditions. Mature larvae then crawl to drier areas to pupate. The pupal period varies from six to 26 days depending on temperature. The entire life cycle from egg to adult is generally completed in three to six weeks.

Stable flies are active during the summertime in North Dakota and are the most important pests of dairy and feedlot cattle in the state. Stable flies prefer to feed outdoors and rarely are found feeding or resting indoors. These flies are strong fliers and dispersion from one livestock facility to the next is common. They remain active into October, but the larval development slows as autumn temperatures decrease. At temperatures near freezing, larvae survive and continue to develop slowly in habitats such as piled silage or manure where fermentation generates heat.

Applications of residual insecticides to premises are frequently used to control both house and stable flies. Longer residual insecticides provide control for an extended period when sprayed onto sites where the adult flies congregate. Such places as fences, sides of buildings and inside and outside of livestock facilities may be potential day or night resting sites for these flies. For livestock producers, observation of a barnyard situation will rapidly tell the favored resting sites for flies. Flies contact the insecticide when they land on the treated surfaces. Residual insecticides are effective because they control flies over an extended period of time and even will kill flies that emerge after treatment.

Knock-down sprays are effective in killing adult flies present at the time of application. The chemicals used for these applications are short residual insecticides having a quick knock-down and high contact toxicity. Several types of spray or fogging apparatus may be used for these applications. Wind velocities should be low at the time of application and the droplet or particle size should be small.

Other methods of fly control such as baits, electric grids and traps may have some limited use for house fly control but are ineffective for the blood-feeding stable fly.

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu

 

LEAFMINERS INFESTING RED RIVER VALLEY SUGARBEET FIELDS

Leafminers are causing injury in Red River Valley sugarbeet fields this season. Economically significant infestations have been detected in the Becker Co., MN area. Although no formal survey has been carried out, small numbers have also been observed as far north as St. Thomas, ND. However, to date, economically significant infestations appear to be most prevalent in the southern portion of the Valley.

Two species, the Beet Leafminer and the Spinach Leafminer are capable of infesting and causing economic losses in sugarbeet. They are similar in appearance, life history, and the damage they cause to the sugarbeet plant. Adults are small, clear-winged flies with brown or grayish-brown to green bodies that look like small house flies. They also have numerous hairy spines on their backs. The adults observed in Becker County have been dark brown in color. Females lay groups of 3 to 10 white, oval eggs on the undersides of beet leaves. Eggs hatch within 3 to 10 ten days, depending on prevailing air temperatures.

Upon hatching, the larvae (pale-green to whitish colored worms; tapered from front to back [Fig. 1.]) tunnel into and feed between the upper and lower surface of the leaf, creating characteristic serpentine paths, or "mines" which contributes to their common name. As feeding progresses, the mines expand and run together. Eventually the injury results in necrotic leaf blotches (Fig 2). The larvae can be detected quite easily by holding an infested leaf up toward a source of light such as the sun. Although the blotches are most common near the leaf tips they can appear at any point throughout the leaves. These leafminer species are capable of having up to 3 generations per year; however, it is usually the first generation that causes the most significant problems in sugarbeets. We are likely at or near the beginning of the second generation. Although major problems are not expected to develop much further into the season, fields should be monitored immediately to determine if treatment is necessary and for the next few weeks for further flare-ups, especially in fields that were borderline but did not receive treatment.

Figure 1 Color.jpg (223008 bytes)

Figure 1. Full-grown leafminer larva inside "mine."

Figure 2 Color.jpg (198846 bytes)

Figure 2. Necrotic blotch on sugarbeet leaf from leafminer injury.

Field scouting and early detection of leafminer are crucial for effective control. Scouting is important because leafminers may be a significant problem only in certain, isolated fields. Early detection is crucial because insecticides are most effective when applied just before or at egg hatch; however, very good control has been achieved after high proportions of larvae have already tunneled into leaves. To scout a field, sample several sets of 10 random plants in several representative areas within a field. The more samples taken, the more reliable the population estimate will be. The current recommendation is for fields to be treated if 50 percent or more of the plants have egg masses and small mines are visible. Refer to Table 1 for insecticide options. Please note that products without leafminers listed specifically on the label can be used as long as they are registered for use on beets. If planning to tank mix when spraying for leafminer, liquid formulations of insecticides containing oil may increase chance of injury from the herbicides Betamix and Progress. Therefore, it is recommended that the amount of crop oil used be reduced by 50% to minimize the chance of crop injury.

Table 1. Treatment options for controlling leafminers in sugarbeet

Product

Use Rate Per Acre (formulated product)

Re-entry Interval
(hours)

DZN diazinon 50W          RUP

0.75 - 1.0 lb

24

DZN diazinon AG500      RUP

0.75 - 1.0 pt

24

DZN diazinon AG500 WBC (water-based concentrate)
                                       RUP

10.0 - 13.5 fl. oz.

24

DZN diazinon 500AG      RUP

0.75 - 1.0 pt

24

Lannate SP                      RUP

0.25 - 1.0 lb

48

Lannate 2.4LV                 RUP

0.75 - 3.0 pt

48

Lorsban 4E

1 pt (2/3 pt banded)

24

RUP – Restricted Use Pesticide

Mark Boetel
Research & Extension Entomologist
mboetel@ndsuext.nodak.edu

 

FOREIGN INSECTS

Everyone has heard of the Imported cabbageworm (Pieris rapae), the European corn borer (Ostrinia nubilalis) and the Gypsy moth (Lymantria dispar); certainly the introduced ‘C-7' ladybeetle (Coccinella septempunctata) is familiar. More than 100 species of foreign insects have been recorded from North Dakota. Beginning last autumn and now this year, two new foreign insects have made their appearance in the state.

The Multicolored Asian ladybeetle (MAL, Harmonia axyridis) has been introduced unsuccessfully many times into the U.S. An accidental introduction at New Orleans, LA, became established and the species now has a wide distribution in temperate North America. MAL was found in Cass and Richland counties last autumn and has additionally turned up in Grand Forks county this spring. MAL is larger than C-7, and because it may be spotted or unspotted, it can resemble two of our native species. MAL is best recognized by the large black ‘M’ on the thorax. MAL is a beneficial aphid predator, however, it often invades homes in the autumn and can be a nuisance. The Greater yellow underwing (GYU, Noctua pronuba) was first found in North America in Nova Scotia in 1979. This European cutworm has been steadily extending its range south and westward. Specimens of GYU were found in Cass and Richland county light traps during the third week of June. The larvae have a very broad host range including: strawberry, potato, tomato, beets, carrots, cabbage, lettuce, grape, and also assorted weeds and grasses.

Dr. Gerald Fauske
NDSU Department of Entomology


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