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ISSUE 6   June 18, 2009

MIGRATORY INSECTS ARRIVE IN NORTH DAKOTA

Cereal aphids were observed in wheat at the NDSU Agricultural Experiment Station Farm in Fargo this past week. With the late-planted wheat and barley crop this year, it will be important to scout for cereal aphids. Late planted spring cereal crops are at high risk for aphid infestation and barley yellow dwarf virus, which is vectored by aphids. For now, it is still early in the season.

Potato leafhopper was also observed in alfalfa at the NDSU Agricultural Experiment Station Farm in Fargo this past week. Newly seeded alfalfa fields are most at risk for economic infestation of potato leafhopper. Right now, populations are still low.

 

SPRAYING FOR WHEAT STEM MAGGOT IN WHEAT

Inquiries have been coming into the NDSU Extension Entomology office about whether to tank mix an insecticide with herbicide when spraying 4-6 leaf wheat for controlling wheat stem maggot. Here’s a summary of what we know to aid your decision-making.

Emergence: Based on preliminary research data collected from six sites in North Dakota in 2008, the first emergence of wheat stem maggot occurred at an average of 1240 accumulated growing degree days (AGDD), and the peak emergence occurred at an average of 1560 AGDD using a base of 32 F (wheat growing degree day base). Currently, most of the southern tier of North Dakota is at first emergence (or 1240 AGDD), while the northern tier has yet to reach 1240 AGDD (Fig. 1). As of June 12, Pat Beauzay of NDSU Extension Entomology observed the first adult wheat stem maggots in 4-6 leaf wheat at Fargo using a sweep net. It appears that adult wheat stem maggots are emerging right on schedule in the Fargo area. If we warm up to 70-80 F this week, we will accumulate about 20-30 GDD units per day. So, we should anticipate peak emergence in 10-15 days depending on the weather.

Sampling & Economic Threshold: It is easy to sample for adult wheat stem maggots using a sweep net in wheat fields. Adult flies are small (1/4 inch) long with a yellow-green thorax, black stripes on thorax and abdomen, square face and bright green eyes. The hind tibia is greatly enlarged. Although we are typically more concerned with spring wheat infestation by wheat stem maggot, winter wheat development is delayed this year and wheat stem maggot can also cause injury to winter wheat. So, consider scouting winter wheat as well as spring wheat this year. Unfortunately, no economic threshold for wheat stem maggot has been developed.


Photograph by P. Beauzay

Biology: Wheat stem maggot attacks cereal crops including spring wheat (preferred), winter wheat, rye, barley, oats and native grasses. This pest has two to three generations per year. Wheat stem maggot passes the winter in the larval (maggot) stage in the lower parts of the stems of wheat and other wild grass hosts. They pupate in the spring and adults emerge in June. Females lay 30 eggs per individual on the leaves and stems of wheat and other grass hosts. Newly hatched maggots of this generation enter the leaf sheaths and tunnel into the tender tissues of the stem. Maggots feed for about three weeks before pupating. Another generation of flies emerges in midsummer to lay eggs in wheat or other grass hosts. The fall generation emerges in late August to early September and lays eggs in native grass hosts.

Control: Optimal insecticide spray timing is prior to peak emergence of adult flies, since insecticides should be directed against adults and newly hatched larvae before they enter the leaf sheaths and stems. Insecticide timing data indicate that spraying is effective at controlling wheat stem maggot from the 4-6 leaf stage through the flag leaf stage in 2008 (Table 1) based on white head counts. However, when populations of wheat stem maggot were low (average of 6% infested plants per field, source – 2008 NDSU Extension IPM Survey) as in 2008, there was no yield gain from spraying an insecticide regardless of spray timing (Table 2). In 2007, populations of wheat stem maggot were higher (average of 17% infested plants per field, source – 2007 NDSU Extension IPM Survey) and a yield gain of 10 bushel/acre was observed from spraying wheat at either 4-6 leaf or flag leaf.

Figure 1.

Table 1.

Treatment

Rate

Wheat Stem Maggot

Average White Head Count Per Plot

Hettinger

Fargo

Makoti

Minot

Cruiser 5FS (high rate)

50 g AI/100 kg

15.0 a

14.3 a

10.5 a

16.8 b

Check

---

13.8 a

22.0 a

9.8 a

24.5 a

Cruiser 5FS (low rate)

39 g AI/100 kg

9.3 a

20.8 a

7.3 a

20.8 ab

Warrior II (flag leaf stage)

1.28 fl oz/acre

3.4 b

4.3 b

1.0 b

5.3 c

Warrior II (4-6 leaf stage)

1.28 fl oz/acre

0.3 c

3.3 b

0.5 b

4.5 c

Cruiser 5FS (low rate) +
Warrior II (4-6 leaf stage)

39 g AI/100 kg
1.28 fl oz/acre

0.3 c

0.3 c

0.5 b

2.8 c

Means followed by the same letter are not significantly different (Fisher’s LSD, P 0.05).

Table 2.

Treatment

Rate

Yield (bu/acre)

Hettinger

Fargo

Makoti

Minot

Cruiser 5FS (low rate) +
Warrior II (4-6 leaf stage)

39 g AI/100 kg
1.28 fl oz/acre

20.2 a

75.5 a

26.3 a

55.0 ab

Warrior II (flag leaf stage)

1.28 fl oz/acre

19.7 ab

82.4 a

26.5 a

60.7 a

Cruiser 5FS (low rate)

39 g AI/100 kg

19.5 ab

74.8 a

26.9 a

47.9 b

Check

---

19.1 ab

80.5 a

25.2 a

60.6 a

Warrior II (4-6 leaf stage)

1.28 fl oz/acre

18.0 bc

78.9 a

26.3 a

55.1 ab

Cruiser 5FS (high rate)

50 g AI/100 kg

17.1 c

74.1 a

26.4 a

58.9 a

Means followed by the same letter are not significantly different (Fisher’s LSD, P 0.05).

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

TENT CATERPILLARS ACTIVE IN NORTH DAKOTA AND MINNESOTA

Tent caterpillars are active in southeastern North Dakota and western Minnesota. This past weekend I observed eastern tent caterpillar defoliating chokecherry seedlings, and also forest tent caterpillar on several hardwood tree species, especially near Pelican Rapids, Minnesota. I have not observed any new tent construction by eastern tent caterpillar yet this year, but tents should begin appearing as the weather warms. Homeowners, arborists, and park managers should be on the lookout for tent caterpillar activity.

Three species of tent caterpillar occur in our area: eastern tent caterpillar (Malacosoma americanum), forest tent caterpillar (M. disstria), and prairie tent caterpillar (M. californicum ssp. lutescens). Host plant damage by these moth species is caused by the larvae, or "caterpillars." Several hardwood hosts may be used, depending on the species.

Eastern tent caterpillar prefers chokecherry, though it will feed on other hardwood species occasionally. Larvae of eastern tent caterpillar are gregarious and construct tent-like nests of silk in the forks of branches and smaller trees (Figure 1). Tents are used for shelter or as resting places. Larvae forage during the day in new foliage on nearby branches. Larvae feed for 6 to 8 weeks and are about 2 inches long when mature. Larvae (Figure 2) are black and rather hairy, with a whitish-yellow stripe down the middle of the back, narrow broken orange stripes just to either side of the whitish mid-stripe, and lateral white and blue markings. Larvae disperse when mature and spin cocoons in sheltered places. Adult moths appear in late June and early July. Females lay eggs in a band-like cluster of 150 to 350 eggs around a small twig and cover the eggs with a frothy excretion called spumaline. Eggs overwinter and larvae emerge in the spring; thus, there is one generation per year. Larval feeding disfigures ornamental plants but usually does not result in permanent damage unless the feeding is severe. Tents and masses of larvae are unsightly. Eastern tent caterpillar populations usually peak every 10 years.


Figure 1. Tent of eastern tent caterpillar
(photo by P. Beauzay)


Figure 2. Eastern tent caterpillar
(photo by P. Beauzay)

Forest tent caterpillar utilizes a wide variety of hosts, including ash, aspen, basswood, birch, cottonwood, elm, maple, and oak. Larvae emerge in the spring from overwintered eggs. Emergence coincides with the flush of host plant foliage. Larvae feed for 5 to 6 weeks and are about 2 inches long when mature. Larvae are identified by keyhole-shaped spots along the midline of the back and by broad bluish lateral bands (Figure 3). Unlike other tent caterpillars, forest tent caterpillar does not form a tent. Instead, larvae gather and spin silken mats on branches. Larvae tend to feed in wandering masses. Mature larvae form silken cocoons, and adult moths emerge about 10 days later. Females deposit 150 to 200 eggs around small twigs and cover the eggs with spumaline. Light defoliation has little effect on tree growth, but severe feeding can affect growth and cause twig mortality. In ND, outbreaks of forest tent caterpillar typically last for 2 to 4 years.


Figure 3. Forest tent caterpillar
(photo by P. Beauzay)

Prairie tent caterpillar can utilize a variety of hardwood host, though chokecherry is its preferred host. Prairie tent caterpillar is the most common tent caterpillar species in North Dakota. Praire tent caterpillar overwinters in the egg stage and larvae emerge in the spring with the flush of their host plant foliage. Larvae feed for 6 to 8 weeks and are about 2 inches long when mature. Larvae are black with a white mid-line stripe broken into dashes, and light blue lateral stripes also broken into dahses. Like eastern tent caterpillar, larvae of prairie tent caterpillar form silken tents in the forks of branches and small trees and feed on nearby foliage. Mature larvae spin cocoons in curled leaves or in leaf litter. Adult moths emerge in mid-summer. Females lay eggs near the base of the host plant in the ground. Larval damage is similar to that of eastern tent caterpillar.

Control of all tent caterpillar species should target larvae. Actively feeding larvae are easily controlled with conventional foliar insecticides including acephate, carbaryl, imidacloprid, or any of several pyrethroids. Biorational treatments include Bacillus thuringiensis (Bt), insecticidal soap, and pyrethrin. Boiling water can also be poured directly on tents that contain larvae. Tents may also be physically removed and destroyed.

Patrick Beauzay, Research Specialist
Extension Entomology
patrick.beauzay@ndsu.edu

 

SUGARBEET ROOT MAGGOT FLIES EMERGING

The first sugarbeet root maggot (SBRM) flies detected in the NDSU trapping network this season were collected from traps in North Dakota in the Hillsboro, East Grand Forks, and Drayton sugar factory districts on June 12. As suggested previously, flies are expected to emerge later than normal this year due to the spring’s persistently cool temperatures.

The NDSU root maggot development model is used to monitor degree-day (DD) accumulations and predict peak fly activity in current-year sugarbeet fields. Peak fly usually occurs on the first warm (80 F or above), dry, low-wind (10 mph or less) day following the accumulation of 600 air DD. Weather conditions during the next few days will have a major influence on the exact date of peak activity. Cold, windy, or rainy weather will delay the actual peak, even if adequate DD units have been accumulated for adults to emerge from soil.

Air temperatures in most Red River Valley locations were slightly above 5-year averages during the past 5 days. This is accelerating root maggot larval development to faster rates than was occurring the past few weeks. As a result, peak fly activity is expected to be slightly earlier than the long-range forecast published in last week’s Crop & Pest Report. Current DD accumulations and the updated forecast for peak fly activity at representative locations in the Red River Valley are presented in the following table:

Degree-day (DD) accumulations for sugarbeet root maggot development and peak fly forecast as of June 16, 2009

Site

Soil temperature

Air DD1

Peak fly activity forecast

Fargo

64

517

June 20 + 1st 80° day

Hillsboro

69

480

June 22 + 1st 80° day

Grand Forks

68

448

June 23 + 1st 80° day

Grafton

70

369

June 27 + 1st 80° day

Cavalier

73

354

June 28 + 1st 80° day

Raw data provided by the North Dakota Agricultural Weather Network (NDAWN).
1Peak fly activity occurs in current-year beet after 600 air DD.

Postemergence additive insecticide applications are recommended in areas of moderate to high risk for damaging root maggot infestations this year. This is a major concern this year because many fields were planted much later than normal, and plants in such fields will be smaller and more vulnerable to root maggot feeding injury. The high percentage of fields planted using seed treated with Poncho Beta insecticide is also of concern because Poncho Beta is a moderate-performing product for sugarbeet root maggot control. Postemergence insecticide applications are strongly advised in late-planted fields and/or those treated with Poncho Beta in SBRM problem areas. Poncho Beta should not be relied on for stand-alone protection in such areas.

The 2009 risk map for sugarbeet root maggot infestations in the Valley is presented in Figure 1. Growers in areas of moderate to high risk of damaging maggot infestations should be vigilant at monitoring fly activity in their fields, and plan on applying an additive postemergence insecticide to ensure adequate control.


Fig. 1.
2009 Forecast map for sugarbeet root maggot
populations in the Red River Valley (based on fly activity
and root maggot feeding injury ratings at 40 monitoring
sites during the preceding growing season)

Postemergence Control Tips: If a granular insecticide is preferred for postemergence control, apply it between 5 and 14 days before peak fly activity. If a liquid insecticide will be used, make applications between 3-4 days before or within 3 days after peak fly. NDSU research indicates that control can be optimized by splitting full rates of Lorsban 4E (and other chlorpyrifos-containing liquid materials labeled for use in sugarbeet) in to two applications: make one application a 3 or 4 days before anticipated peak fly and repeat it about 7 days later. More detailed information can be found in the "Insect Control" section of the 2009 Sugarbeet Production Guide or the "Sugarbeet Insects" section of 2009 Field Crop Insect Management Recommendations. Online versions of these publications are located at:

www.sbreb.org/Production/production.htm &

www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm

Mark Boetel
Research & Extension Entomologist
mark.boetel@ndsu.edu


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