Entomology Logo


ISSUE 10   July 6, 2006

UNIVOLTINE EUROPEAN CORN BORER EMERGENCE UNDERWAY!

Itís time to scout non-Bt corn fields for European corn borer eggs and larvae. Itís about 2 weeks earlier than last year due to the heat. Look for eggs masses on the underside of leaves and early signs of larval feeding (irregular pinholes in corn leaves or whorl).

European corn borer hatching
European corn borer hatching
(University of Georgia Archives, University of Georgia)

European corn borer larvae
European corn borer larvae
(Clemson University - USDA Coop Ext. Slide Series)

The best time to apply insecticide is when larvae are in the early instars, only a 7-day window, before it enter the corn stalk. Once the larvae is inside the corn plant, no insecticides can kill it. About 10% of the univoltine-type European corn borer have emerged in northern tier of North Dakota, while 25 - 50% have emerged in the southern tier of North Dakota (see map). The following table summarizes the degree day (Base 50 F) model for moth emergence of the univoltine-type European corn borer.

Accumulated
Degree Days

Proportions of Emerged Moths

911

10 %

986

25 %

1078

50 %

1177

75 %

1274

90 %

Accumulated Corn Growing Degree Days

To continue monitoring degree day accumulation in your part of the state, refer to NDAWN, select Applications, then select Corn Degree Days for the nearest town, and enter 2006-04-01 for planting date to accumulate degree days for corn borer.

http://ndawn.ndsu.nodak.edu/corndd-form.html

With high temperatures, heat units will accumulate faster resulting in faster insect development. Control should be considered in field corn when 45 - 50 percent of the plants in dryland corn or 25 - 35 percent of the plants in irrigated corn have shot-holing in the whorl, egg masses on the undersides of leaves or live borers visible in whorls.

Specific economic thresholds (corn borer/plant) are available that factor the crop value and cost of insecticide.

See the following weblink:

http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/ecb/mngborer.htm

European corn borer egg mass
European corn borer egg mass

 

MORE AND MORE APHIDS - PEA APHIDS HIGH!

Reports from the north central and northwest regions of North Dakota indicate high populations of aphids in peas. Pea aphids damage pulse crops by feeding on plant and indirectly by vectoring viruses. Direct feeding on the plants becomes a problem in an aphid outbreak year (like this year)! An insecticide application is needed when there are more than 10 aphids per plant between the 10th node and flowering. One well-timed application before late flowering should give satisfactory control. Insecticide registered for control of pea aphid in peas in ND are:

Pyrethroids - Asana XL, Baythriod 2, Mustang Max, Proaxis, Taiga Z, Warrior

Organophosphates - Dimethoate (Digon, Cygon, ..), Lannate LV, malathion

Dimethoate is one of the more popular and cost-effective insecticides for aphid control. The low rate of 0.125 lb ai per acre is not sufficient for long term aphid control. Using the higher label rate of 0.5 lb ai per acre, losses to aphid are near zero percent. Fortunately, the label for dimethoate was not canceled for use on pulse crops by the EPA yet. See comments about insecticide efficacy and high temperature below.

Pea aphid
Pea apid
(Whitney Crenshaw, CO State University, www.insectimages.org)

 

HOW WILL THE HIGH TEMPERATURES AFFECT SOYBEAN APHID POPULATIONS AND INSECTICIDE PERFORMANCE

There has been a few reports of fields being spraying for soybean aphid in southeastern North Dakota. Continue to scout fields for economic levels of infestation (250 aphids per plant and increasing populations) during late vegetative to R5.

The high temperatures will affect aphid population development as well as insecticide performance. Optimal temperatures for aphid longevity (36 day life span) and reproduction (maximum of 9.5 offspring per day during peak reproduction) is from 68 to 86 F. At 95 F, soybean aphids are under stress. Aphids survived for only about 11 days and no young are produced. (McCornack et al. 2004). In summary, the development rate of soybean aphids peaks and the generation doubling time is fastest when temperatures are near 80 F. The knowledge of how temperatures affect the biology of soybean aphid has profound implications for management. If the temperatures are projected to be hot (in the 90 F and above), soybean aphid population growth will slow, stop, and may even decrease as temperatures stress shortens life span and stops reproduction. Conversely, if temperatures are projected for the mid to upper 70 F range, soybean aphid population growth will reach its maximum.

Insecticide registered for soybean aphid control in North Dakota include:

Pyrethroids - Asana XL,, Decis 1.5 EC, Taiga Z, Warrior, Mustang Max, Proaxis, permethrin

Organophosphates - Lannate LV, Orthene 97 Pellets, Penncap-M, Lorsban 4E

Carbamate - Furadon 4F

The efficacy of pyrethroid insecticides is negatively correlated to high temperatures. So the warmer the temperatures, the shorter the residual and reduced control. The high rate of labeled pyrethroids should provide 7 to 10 days of control. In contrast, organophosphates (OP) are readily biodegradable and do not persist in environment as long as pyrethroids (in other words a shorter residual, usually 3 to 5 days). Under high temperatures, OPs may provide better efficacy since they have a higher acute toxicity (more rapid knockdown). Spider mites are always a threat when we have hot dry conditions in soybeans. Although synthetic pyrethroids have broad insecticidal activity, control of spider mites is limited using pyrethroids. In fact, pyrethroids can often flare spider mite populations.

 

WHEAT MIDGE EMERGENCE ENDING

The hot temperatures are pushing degree day (DD) accumulations, and crop / insect development. Most regions of North Dakota are past 1600 DD when 90% of the female wheat midge have emerged with the exception of the northern border near Canada (see map). The emerging adult wheat midge is also susceptible to dry soil conditions, which can increased adult mortality. This is good news for wheat and durum growers!

Accumulated Midge Growing Degree Days

 

SPOTTED SUNFLOWER STEM WEEVIL - TIME TO SCOUT!

Reports of spotted stem weevil on sunflower have come in from South Dakota. Monitor for adults when sunflower plants are in the V8 to R1, or usually late June to early July. Economic threshold levels are 1 adult sunflower stem weevil per three plants. When scouting, approach plants carefully and slowly to avoid disturbing the adults and look several plants ahead to observe adult weevils on leaves. No reports from North Dakota.

Adult stem weevil
Adult stem weevil

 

BERTHA ARMYWORM TRAP UPDATE

Pheromone trap catches have increased this past week in north central and northeastern regions of North Dakota. The accumulated trap numbers are listed below:

County

Nearest Town

Accumulated Trap Number

Benson

York

6

Benson

Leeds

10

Bottineau

Gardena

216

Bottineau

Lansford

17

Burke

 

61

Cavalier

Munich

105

Cavalier

Alsen

226

Cavalier

Nekoma

88

Cavalier

Hyws 20 & 66

340

Cavalier

Osnabrock

137

McHenry

 

42

McLean

Raub

49

McLean

Washburn

63

Mountrail

 

49

Ramsey

Devils Lake

3

Renville

Mohall

129

Ward

Carpio

65

(Source: NDSU IPM scouts)

Currently all accumulated trap catches for bertha armyworms are below 500 indicating no threat to canola crop.

Janet Knodel
Extension Entomology
janet.knodel@ndsu.edu


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