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ISSUE 10   July 15, 2010

SOYBEAN APHID CONTINUE AT LOW LEVELS

Soybean aphids continue to be at very low levels in most soybean fields in North Dakota (Fig. 1). However, it is easy to find many beneficial insects eating soybean aphids in fields now. Some beneficial insects observed: lady beetles, minute pirate-bugs, damsel bugs, lacewings, and more. So, avoid any early season ‘insurance’ insecticide applications that may kill these beneficial insects. You will end up doing more harm than good by killing off the beneficial insects and causing the soybean aphids to increase!


Fig. 1.
Soybean Aphid IPM Survey map (J. Walker, NDSU)

 

GRASSHOPPER ALERT IN LENTILS FOR NW ND

Montana State University has received reports of grasshoppers infesting lentil fields in eastern Montana. Grasshoppers can damage lentil flowers and pods when present within the field during bloom resulting in significant crop damage. When grasshoppers are found within lentil fields shortly before bloom, economic damage thresholds are very low; only two grasshoppers per square yard may require treatment. (Source - K. Wanner, Extension Entomologist, MSU)

  

WATCH FOR GRASSHOPPERS IN SUNFLOWERS AND OTHER CROPS INTO LATE SUMMER

Grasshopper nymphs and some adults are being reported in sunflower field edges causing defoliation. Grasshopper infestations in sunflowers are often heaviest on the field margins. As cereal crops are harvested in late July, adult grasshoppers will start to migrate into other late season ‘green’ crops like sunflower, flax, and soybean.

An insecticide application is justified when grasshopper populations reach the following Action Threshold in agricultural crops (except lentils, see above): 

Grasshopper Life Stage

Field margins
(non-crop areas)

Within the field

Nymph

         50-75

        30-45

Adult

         21-40

         8-14

For a list of insecticides registered for grasshopper control, please consult the NDSU 2010 Field Crop Insect Management Guide at: http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm.

 

CONTINUE TO SCOUT FOR CEREAL APHIDS IN LATE PLANTED WHEAT AND BARLEY

Late planted wheat is at higher risk for cereal aphid infestation than early planted wheat. There are often more aphids around and they may be vectoring Barley Yellow Dwarf Virus, which also increases the risk to late planted cereal crops. Cereal crops are susceptible up to the completion of heading. Be sure to continue to scout and treat any wheat/barley fields that are above the economic threshold of 85% incidence or 12-15 aphids per stem prior to the completion of heading.

 

SCOUT FOR BANDED SUNFLOWER MOTH EGGS AT R3 CROP STAGE

Pheromone trap catches indicate that adult banded sunflower moth numbers are increasing (Fig. 2). Egg laying has just started on sunflowers in R2-R3 crop stage in southeast North Dakota. Scouting for eggs should start on crops in the preferred egg laying stage (R2-R3).

 
Figure 2. Banded sunflower moth pheromone trapping map
(T. Mittelsteadt, NSA)

Egg Scouting Method and How to Calculate the Economic Threshold:  The potential for banded sunflower moth damage is determined by counting eggs on floral bracts in the field (Fig. 3).


Figure 3.
Banded sunflower moth eggs on bracts
(Ext. Entomology, NDSU)

Because the eggs are very small a magnifier is needed to accurately count the small eggs. We recommend using a head-mounted 3.5X magnifier (Fig. 4) to leave both hands free for manipulating the bud being observed.

 
Figure 4.
Magnifier to finding banded sunflower moth eggs
(Ext. Entomology, NDSU)

Egg counts should be made when most of the plants in the field are at plant stage R3 (Fig. 5, distinct bud elongated ¾ inch above the nearest leaf, yellow ray petals not visible).

 
Figure 5.
R3 sunflower bud (side view on right and top view on left)
(L. Charlet, USDA-ARS)

 Sampling for banded sunflower moth egg populations in commercial fields should be conducted as follows:

1) Divide each side of the field into two sections.
2) Sample the center of each section at 20 feet into the field from the field edge.
3) Randomly select five buds.
4) From each bud, randomly select six bracts from the outer whorl and count the eggs on each bract.
5) Average the egg counts from the five buds and then map the average egg counts from each sample site to a diagram of the field.

Next, compare the average egg density at each sampling site to the calculated economic injury level.  The economic injury level (EIL) considers treatment cost ($/acre, market price ($/lb), and plant population per acre.

EIL =

TC

V * PP * 0.00078

V = Market value per lb
PP = Plant population per acre
TC = Treatment cost

For oil sunflowers (TC = $8/acre, V = $0.13/lb, and PP = 20,000 plants/acre), the EIL is 3.4 eggs per six bracts. For confection sunflowers (TC = $8/acre, V = $0.26/lb, and PP = 18,000 plants /acre), the EIL is 2.2 eggs per six bracts.

A spreadsheet is available at the NDSU Extension Entomology website to automatically calculate your egg EIL. Click on “Banded Sunflower Moth Calculator for Egg Sampling.”  http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/index.htm#Sun

Alternative pest management strategies like host plant resistance are being studied for banded sunflower moth. Resistance to the banded sunflower moth has been identified in some sunflower germplasm and in some native sunflower species. The nature of the resistance mechanisms resulting in reduced seed damage is currently being investigated. Future efforts will focus on bringing these identified resistance genes into cultivated sunflower through conventional breeding.

For more information, please see the revised factsheet from NDSU Extension Service on Banded sunflower moth, E-823.  http://www.ag.ndsu.edu/pubs/plantsci/pests/e823.pdf

Insecticides registered for control of banded sunflower moth are listed in the sunflower section of the NDSU E-1143 2010 North Dakota Field Crop Insect Management Guide.  http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm

  

SCOUT FOR LYGUS BUG IN FLOWERING CANOLA

Some insecticide spraying for Lygus bug in flowering canola has been reported near Pillsbury and Oriska in Barnes County, North Dakota and in Red Lake Falls in Red Lake County and Thief River Falls in Pennington County, Minnesota. Both immature and adult Lygus bugs feed on growing points, buds, flowers, and green pods. Lygus bugs inject a toxic saliva with their piercing sucking mouthparts during feeding, causing blasting of flowers or buds and shriveled seeds. Blasted flowers turn white within 24 hours and quickly fall to the ground. The small seeds or damaged seeds are lost during harvest.

Scout for Lygus bugs from just prior to bud formation through flowering until seeds within the pod have become firm. Lygus populations can increase suddenly. For example, when alfalfa (preferred host) is cut, Lygus will migrate quickly into nearby canola fields and often in high numbers. Use a 15-inch sweep net and make 10 180-degree sweeps at several sampling sites. The economic thresholds developed in Canada are: 15 Lygus bugs per 10 sweeps from bud stage through petal drop, and 20 Lygus bugs per 10 sweeps after petal drop. If soil moisture is good, canola plants usually can compensate for Lygus bug feeding injury to plants in the bud and flowering stages. However, if populations are high, control during the early pod ripening stage is usually the most economical.

 

 

WHERE IS THE EUROPEAN CORN BORER MOTH?

Traditional corn producing states like Illinois and Iowa that have an annual survey for European corn borer (ECB) are reporting all-time record lows for ECB densities. In North Dakota, we are seeing fewer and fewer fields infested with ECB as well. It seems clear the 2010 flights of ECB will continue to be low due to the wide scale and increasing use of Bt hybrids and new pyramid genes expressing multiple Cry proteins with decreasing refuge size.

To assist with the timing for ECB scouting for egg masses and shot holing, a degree day model has been developed to predict the univoltine flight of ECB moths in July. The degree day model predicts the proportion of moths that have emerged using a degree day base of 50 F. To determine current degree day accumulation, go to the NDAWN website and select Applications, and then select Corn Growing Degree Days. For the planting date, enter ‘2010-03-01.’ http://ndawn.ndsu.nodak.edu/corngdd-form.html

The current map (Fig. 6) indicates that the southeast region is 90% emerged to 50% emerged in the central region to only 10% emerged in the northwest region of North Dakota.


Figure 6.
European corn borer degree day map (NDAWN)

Accumulated Degree Days

Proportion of Emerged
ECB Moths

911

10 %

986

25 %

1078

50 %

1177

75 %

1274

90 %

 Please see the ECB factsheet for more information: http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/ecb/mngborer.htm  

 

WHAT INSECT CAUSES THESE DAMAGED SUNFLOWER HEADS  IN FIG. 7?

 
Figure 7. Damaged sunflower heads (J. Nitschke, Allied Agronomy)

This damage is caused by the sunflower seed maggot, Neotephritis finalis (Fig. 8). Adult flies and damaged sunflower heads have been observed in eastern North Dakota (Cass and LaMoure Counties).

 
Figure 8.
Adult sunflower seed maggot
 
(Neotephritis finalis) (P. Beauzay, NDSU)

Adults emerge during the first week of July and egg laying occurs on the corolla of incompletely opened sunflower inflorescences. The larval stage lasts about 14 days. Larvae feed within undeveloped ovaries of the flowers, often completely consuming the floret before the seed is fertilized. The first generation pupates in the head and the second generation overwinters as pupae in the soil or as adults. The small, brown pupae can sometimes be found on the face of sunflower heads, usually surrounded by a small number of damaged florets. Unlike the other two species of sunflower maggots (Strauzia longipennis and Gymnocarena diffusa), the sunflower seed maggot has two complete generations per year in North Dakota.

The sunflower seed  maggot appears to cause more bud/head damage than the other two species of sunflower maggots. Seed sterility occurs when newly emerged larvae tunnel into the corolla of young blooms. Observations indicate that a single larva feeding on young flowers will tunnel through 12 ovaries. Mature larvae feeding on older sunflower heads will destroy only one to three seeds. The magnitude of damage to sunflower seeds by sunflower seed maggot larvae depends largely on the stage of larval and seed development.

A field monitoring scheme for this insect has not been developed and an economic threshold has not been established. Insecticide use has not been warranted for control of this fly, although recent injury to sunflowers has been noted in a number of locations in North Dakota. Research is currently being conducted by NDSU Extension Entomology and the Sunflower Unit of USDA-ARS to determine an Economic Injury Level and the potential for planting date and insecticides and timings to reduce damage. Preliminary research suggests that early planting dates are infested heavier than late planting dates. This research is supported by the National Sunflower Association.

 

MYSTERY INSECT:  WHAT IS THIS INSECT THAT FEEDS ON VINE CROPS (SQUASH AND PUMPKINS) IN HOME GARDENS?

 
Figure 9.
Mystery insect (M. Simmer, NDSU)

This is the squash vine borer, Melitta curcurbitae, a common clearwing moth in home gardens in North Dakota and Minnesota. It can be a serious pest destroying squash, pumpkins, cucumbers and melons when populations are high. Gardeners often notice the wilting plants infested by the borer. Look closely for holes near the base of the plant filled with moist green to orange frass from the tunneling larva. Several borer larvae may feed inside a stem causing it to collapse, rot and die. For pest management of the squash vine borer, monitor for the presence of adult borer moths during late June through July. These moths are easy to detect because they fly during the day and make a loud conspicuous buzzing sound. A yellow water pan trap can also be used to detect moths that are attracted to the yellow color and drown in water. Place a teaspoon of dish soap in water to help reduce the surface tension of water. If insecticides are needed, be sure to target the base of plant starting late June and repeat every 7-10 days through July. Some insecticides labeled for use in home garden include: carbaryl, permethrin, bifenthrin and esfenvalerate. Read and follow all insecticide labels very carefully and observe the number of days between insecticide application and when you can harvest vegetables.

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu


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