Entomology Logo


ISSUE 2    May 12, 2005

WHEAT MIDGE OUTLOOK GOOD FOR NORTH DAKOTA PRODUCERS

A soil survey conducted last year detected low levels of overwintering wheat midge larvae. This predicts the potential for wheat midge problems and is good news for wheat and durum producers. Wheat midge populations ranged from 0 to less than 500 midge larvae per square meter, with most of the state having less than 200 midge larvae per square meter during 2004. Fields with more than 1,200 midge larvae per square meter are considered high risk. At that point, some control tactic must be used to reduce midge populations.

2004 Wheat Midge Larval Survey Map

Although a few fields sampled in 2004 had populations close to 1,000 midge larvae per square meter, a tiny, black parasitic wasp kept the wheat midge in check. The 2004 wheat midge larval also indicated % parasitism by wasp.

2004 Wheat Midge Larval Survey % Parasitism Map

This wasp, Macroglenes penetrans, parasitizes the larvae of wheat midge and will emerge the following spring and kill the wheat midge larvae. Parasitism can range from 0 percent to 100 percent, with the higher rates occurring in areas where midge populations have been high. With the wheat midge population being low for the last few years, producers unfortunately may see a slow decline in the parasitic wasp population in the future.

Weather conditions and the stage of wheat will be important in determining if sporadic outbreaks of wheat midge will cause economic damage this year. Environmental conditions favoring wheat midge development include moist soil conditions prior to emergence in late June to early July, warm, high humidity and light wind conditions during egg laying. Economic injury still can occur if wheat or durum is in the susceptible stage (heading to 50 percent flowering) during wheat midge emergence and egg laying. Damage can reduce crop yields and lower the grade of harvested grains.

The wheat midge survey is conducted by the NDSU Extension Service and supported by the North Dakota Wheat Commission.

 

WHEAT MIDGE DEGREE DAYS USED AS A GUIDELINE FOR HRSW RISK ASSESSMENT

Most of North Dakota is now in the high risk planting period, 200-600 Degree Day (DD), for HRSW to wheat midge infestation (see map). HRSW planted during the 200-600 DD period is when wheat is in the susceptible stage, heading, and this timing coincides with peak wheat midge emergence. Prior to 200 DD and after 600 DD, wheat is at less risk to midge infestation due to the period of heading occurring prior to or after peak emergence of wheat midge. Late planted wheat may also be more susceptible to frost injury. The southern tier of North Dakota entered the 200 DD window around mid-April, whereas the northern tier of North Dakota started around May 1st.

Insect Degree Day map

 

OUTLOOK FOR SEED DAMAGING INSECTS FAVORABLE

Soil temperatures are now above 50F in North Dakota, which is the minimum temperature for feeding activity of most seed damaging insects, such as wireworms or seed corn maggots. Unfortunately, the cool weather has delayed crop emergence and this increases the potential for injury from seed damaging insects. These insects cause stand reductions and reduce crop vigor. Producers often first notice the uneven emergence or bare, patchy areas in fields. Dig up the seed and look for tunneling into the seed or seed that is completely hollowed out. Look around soil next to damaged seed for the insect culprit! Remember there are several other factors that can lead to stand reductions: planter malfunction, seedling diseases, and pesticide damage to seed. If fields need to be replanted due to an insect pest, a soil-applied insecticide or seed treatment should be considered depending on the insect present, is the pest still actively feeding, soil temperatures, and plant growth rate. Where wireworms are a problem, a soil insecticide or seed treatment is usually justified, because wireworms continue to actively feed through June. Control of seed corn maggots depends on the soil conditions and crop growth rate. If soil conditions are cool and moist where seed corn maggots are actively feeding, and crop emergence is slow (over a week), an insecticide seed treatment is critical. If soil conditions are warm, and germination / crop growth rate is fast, an insecticide may not be needed for control of seed corn maggots. The growth of crop may be sufficient to protect it from injury. Remember to read the label to be aware of any restrictions as to the amount of product that can be applied per season.

 

ALFALFA WEEVIL SCOUTING DEGREE DAYS UPDATE

Scouting for alfalfa weevil can be improved by using degree day accumulations to time field visit when weevils are active. Degree days for alfalfa weevil are slowly accumulating; however, we havent yet reached the 250-300 Degree Day (DD) mark (base of 48F), which is used to initiate alfalfa weevil sampling. Currently, North Dakota is in the low to mid 100s. Symptoms of weevil injury are small pin-holes in leaves at growing tip in May. This is the best time to begin scouting. Early detection of tip-feeding injury is critical to prevent yield and quality loss when infestation levels are high.

Future Crop & Pest Reports will address management decisions and accumulated heat units.

Janet Knodel
Area Extension Specialist
North Central Research Extension Center
jknodel@ndsuext.nodak.edu

 

NORTH DAKOTA GRASSHOPPER OUTLOOK FOR 2005

Surveys of grasshopper activity in 2004 suggest that several ND counties will be at risk for development of damaging grasshopper infestations this season. The 2004 survey map of grasshopper activity is shown in Figure 1. These counts can be used as a guide to weigh the risk of major infestations for 2005. As the map indicates, the western 1/3 of the state is at greatest risk. Recent rainfall and cool weather in central ND may help reduce hopper survival in some sites. Areas in southwestern ND that remain dry will likely support more grasshopper survival.


Figure 1.  Survey map of adult grasshopper
activity in North Dakota, 2004
(courtesy, ND IPM Survey)

Refer to the following guidelines to determine the need for control measures:

  Nymphs (Young hoppers)
per square yard
Adults
per square yard
Rating

Margin

Field

Margin

Field

Light
Threatening
Severe
Very Severe

25-35
50-75
100-150
200+

15-23
30-45
60-90
120

10-20
21-40
41-80
80+

3-7
8-14
15-28
28+

Treatment is advised whenever grasshopper populations reach the threatening level. Control is most effective and more economically sound if directed at nymphs.

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

Justin Knott
Plant Protection Specialist
ND Dept. of Agriculture
jknott@state.nd.us

 

INSECTICIDE CONSIDERATIONS FOR RE-PLANTING SUGARBEET

Frost damage may necessitate re-planting of some sugarbeet fields this spring. Re-planted beets will be smaller and more vulnerable to attack by root maggot larvae than older, more established plants. Recent NDSU research has demonstrated that a gross benefit of over $200 per acre can be achieved in high root maggot infestation areas by making a secondary insecticide application beyond the original planting-time treatment in re-planted fields. Therefore, growers re-planting in high-risk areas where significant maggot populations are anticipated are advised to consider two management options:

  • apply another granular material at re-planting of the crop; or
  • apply a postemergence liquid or granular insecticide.
  • It is critical to note that use of Counter 15G and Lorsban 15G is limited to one application per year. If one of these products was applied on a particular field at initial planting, another material must be used for the succeeding application.

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


    NDSU Crop and Pest Report Home buttonTop of Page buttonTable of Contents buttonPrevious buttonNext button