crop and pest report for july 24, 2008 · 7/24/2008 · the larva has a dark head capsule with a...

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No. 11 July 24, 2008

Inside this Issue...Sunflower Bud Moth Damaging to Sunflower Buds . . . 1Banded Sunflower Moth Egg Laying Underway . . . . . . 2New Formulation of Lorsban® for 2009 . . . . . . . . . . . . . 2Soybean Aphids Increasing in Red River Valley . . . . . . 2Impact of Drought Stress on Corn - 2008 . . . . . . . . . . . . 3Hail Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4NDSU IPM Field Scouts Results - July 18 . . . . . . . . . . . 5White Mold in Beans . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Ventenata - New Grass Weed . . . . . . . . . . . . . . . . . . . . 6Why Herbicides Kill Weeds – Why Not the Crop? . . . . 72008 NDSU Horticulture Research Field Day . . . . . . . . 8Weather & Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

SUNFLOWER BUD MOTH DAMAGING TOSUNFLOWER BUDS

Larvae of the sunflower bud moth, Suleimahelianthana (Riley), have been observed damagingsunflower buds in R1-R3 sunflowers. Typically, most ofdamage occurs mostly in the stalk. However, this yearsunflower bud moth emergence is delayed and larvae arefeeding in the bud causing injury to the developing head(see photograph).

The only time yield loss is noticeable is when larvaeburrow into unopen buds, preventing proper headdevelopment. The larvae normally do not feed ondeveloping seeds but confine feeding activities to thefleshy part of the head. The larva has a dark head capsulewith a smooth, cream-colored body and is 0.31 to 0.43inch (8 to 11 mm) at maturity (see photograph).

There are two generations of sunflower bud moth inNorth Dakota. Adults emerge from overwintering pupaebetween the last week of May to mid-June. A few daysafter adult emergence, eggs are deposited on the terminalsof immature sunflower or on the receptacle of maturesunflower. Eggs also are deposited in leaf axils. Thehatched larvae begin tunneling into the sunflower plant.The initial infestation in mid-June is characterized by anentrance hole surrounded by black frass, or insectexcrement. Mature larvae pupate within the sunflowerplant. Pupae move to the opening of the entrance holesformed in the stem or head tissue so that adults canemerge easily. The second generation adults appear inAugust. Infestation by the second generation larvae is noteconomically important.

A field monitoring scheme and economic thresholdhas not been established for this insect since it is not ofeconomic significance most years. Insecticide use is NOTrecommended for control of sunflower bud moth, becausethe larvae are protected when feeding within thesunflower plants. As a result, insecticides will havelimited efficacy.

North Dakota State University CROP & PEST REPORT July 24, 2008

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BANDED SUNFLOWER MOTH EGG LAYINGUNDERWAY

Eggs of banded sunflower moth have been found onR3 stage sunflower fields. Fields should be scouted nowfor egg laying activity, especially R3 sunflower fields.Please refer to Issue 10 of the Crop & Pest Report formore information on scouting. The map from thepheromone trapping in North Dakota indicate increasingpopulations of adult moths, especially in the northern tieralong the Canadian border.

NEW FORMULATION OF LORSBAN® FOR 2009Dow AgroSciences will be releasing a new

formulation of chlorpyrifos called “Lorsban Advanced®”in 2009. It features: lower odor than Lorsban-4E®,comparable efficacy, water-based formulation, and fewerVOCs (carbon-containing substances that, when exposedto air, volatilize into gases that contribute to ground-levelozone formulation). Lorsban Advanced® will be registeredon the same crops as Lorsban-4E®, and listed in the NorthDakota Field Crop Insect Management Guide for 2009.

Janet KnodelExtension [email protected]

SOYBEAN APHIDS INCREASING IN RED RIVER VALLEY

Soybean aphid numbers are increasing in the RedRiver Valley area and eastern counties of North Dakota.Most fields still have low numbers, but a few fields areapproaching threshold. This is the time to scout andmonitor your fields for soybean aphid. The economicthreshold for soybean aphid in the upper Midwest is:

250 aphids/plant in 80% of the field and withsoybean aphid numbers increasing.

The economic threshold of 250 aphids/plant wasarrived at through research conducted over a three yearperiod at 19 locations in the northern US including NorthDakota. The economic threshold was established to givegrowers a seven-day lead time for insecticide applicationbefore aphid populations reach a level where economicloss actually begins. Even though soybean market pricesare high, the 250 aphid/plant threshold is still valid. Thisis because 250 aphids/plant is lower than the population atwhich yield loss can be measured and attributed to aphidinjury. What this means in practical terms is that the leadtime for insecticide application is reduced from sevendays to three or four days. Therefore it is critical thatgrowers monitor their fields closely.

NDSU Extension Entomology has received a fewcalls from growers asking whether they should tank-mixan insecticide with their last glyphosate application eventhough soybean aphid numbers are not at threshold. Wedo NOT recommend this practice, nor do we recommendany insecticide application when the economic thresholdhas not been reached. Applying insecticides too early tocontrol soybean aphid may result in a second aphidinvasion, which will require a second insecticideapplication. Insecticides also kill natural enemies ofsoybean aphid (such as lady beetles and damsel bugs), andre-invading aphid populations can increase very rapidly inthe absence of natural enemies. Some vendors are offeringguarantees on second insecticide applications. While theguarantee covers the chemical, it may not coverapplication costs. There is also the risk of spider miteflare-up in fields that have been treated twice withpyrethroid insecticides because beneficial mites have alsobeen killed. This may require a third application using anorganophosphate insecticide (such as Lorsban) to controlthe spider mites. Natural enemies keep aphid populationsfrom growing rapidly and may even keep aphidpopulations from reaching threshold. Conservation ofnatural enemies is of paramount importance incontrolling soybean aphid - don’t spray unless anduntil you have to!

Most fields are currently in the R1 growth stage(beginning flowering), though some are still in latevegetative (V) stages. The 250 aphid/plant threshold isvalid from late vegetative through the R5 (early seeddevelopment) growth stage. Research has shown thatinsecticide applications at R6 (full seed) and beyond donot give a yield benefit. Therefore, insecticideapplications for soybean aphid are not recommended afterthe R5 growth stage. Pyrethroid insecticides (such asWarrior) offer good control of soybean aphid. Severalpyrethroids are labeled for soybean in North Dakota. Besure to read and follow the label for application rates andpre-harvest interval restrictions.

Patrick BeauzayExtension Entomology Research Specialist

[email protected]

Janet KnodelExtension [email protected]


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IMPACT OF DROUGHT STRESS ON CORN - 2008More than half of the state is now rated abnormally

dry or drier by the US Drought Monitor(http://www.drought.unl.edu/dm/DM_highplains.htm) andnearly a third of the state is under severe drought. Corn isone of the most water efficient crops grown in NorthDakota. Nevertheless, it has a high water requirementbecause of its high yield potential and can be significantlyimpacted by drought. The impact of drought on corngrowth and yield varies considerably depending on itstiming and severity. Research has shown that there islittle impact of drought on corn growth during earlyvegetative stages. During late vegetative development,however, short periods of drought stress (four days ofsufficient stress to cause leaves to curl) during this growthstage can reduce yields by 5-10%. Currently most of thecorn in North Dakota is in the 8 to 12 leaf stage. Kernelsper cob are being set during this stage until just beforesilking, so drought stress now can impact the size of thecob. Drought stress during tassel emergence has thepotential to reduce yields by 10 to 25%. The mostsensitive period for drought stress in corn is during theperiod between silk emergence and the blister stage whereyield losses between 40-50% can occur. Corn is mostsensitive to drought during this stage because the maleand female flowers are separated by a considerabledistance and pollen and silks are sensitive to hot and dryconditions. When corn is severely stressed prior toflowering, silk growth is delayed and pollen shed willoccur before the silks have emerged, resulting inbarrenness. Silks can also dry before they are pollinatedresulting in poor fertilization and missing kernels. Abortion of developing kernels is common, particularlytowards the tip of the ears, with drought stress duringearly grain fill. Since the corn plant has the capacity tostore considerable reserves in the stem, yield losses whendrought stress is delayed until the dough stage usually arein the 20-30% range. These yield losses discussed abovecan be additive if stress occurs at more than one growthstage. With about half the growing season still ahead ofus, the potential for yield losses due to drought appear tobe quite high for a large part of the state unless we getsome timely rains.

How is yield affected by late season drought stress?During the first stage of stress, the upper leaves curl

or roll towards the midrib during the hottest part of theday (see attached photo). If stress continues, prematureleaf death begins at the bottom of the plant and proceedsupward. Leaf death is the first sign of permanent damageto the plant. With severe stress, the upper leaves roll sotightly that they appear like “onion leaves”. With less leafarea capable of photosynthesis, grain filling is slowedeven while maturing at an accelerated pace. Carbohydrates that had been stored in the stem earlier inthe season are moved to the developing ear. Notsurprisingly, drought stressed crops are more prone tolodging because of poor stalk health. There may be somekernel abortion in the tips of the ears, but for the mostpart, kernel numbers are not reduced significantly withlate season drought. Yield losses will largely be due toreduced kernel size and reduction in test weight. Theamount of reduction will be related to the amount of stressprior to harvest.

Joel RansomExtension Agronomist - Cereal Crops

[email protected]


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HAIL DAMAGEEach summer hail damages field crops leaving

producers wondering if the crop will recover and howmuch yield loss will be incurred. Hail events areunpredictable; developing during some summerthunderstorms but not others. Thunderstorms typicallyoccur during the late afternoon and early evening. Thetemperature contrast between the Earth’s surface and theclouds can cause wind turbulence, creating up and downdrafts within the storm cell. When water droplets arepushed upward into sub-freezing air layers the waterfreezes and frozen droplets eventually fall. The ice piecesmay be pushed back up for several cycles increasing thesize of the hail stones. Large hail stones, resulting fromintense storm cells are more likely to cause severe cropdamage compared to hail produced by weaker stormsystems. In addition to hail damage, strong windsassociated with summer storms may cause crops to lodge.The stage of crop growth and development at the time of ahail event is critical in the plant’s ability to recover andstill produce a decent yield. Damage to the leaf tissue mayresults in plant stress. However, if ample moisture andfertility are available, the crop should be able to recoverquicker than crops experiencing drought stress. Haildamage can vary considerably between neighboring farmsor from field to field on individual farms. The variationmay be a result of the different stages of cropdevelopment at the time of the hail event or because theamount of hail produced tends to be inconsistent evenwithin short distances. Researchers at NDSU haveconducted many years of simulated hail research onvarious crops to produce hail adjustment tables to estimateyield reductions that are based on the stage of growth andpercent defoliation.

During a simulated hail study conducted from 2002-2004, researchers investigated soybean yield reductionsbased on different levels of defoliation at the reproductivestages R1 (Beginning of bloom) and R4 (pods are ¾ inchlong at one of the four uppermost nodes on the main stemwith a fully developed leaf). Zero (control), one, two, orthree leaflets were removed from each fully expandedtrifoliate leaf per plant to study the effects on yield (Table1).

Table 1. Soybean yield in % of the check at two growthstages and four defoliation levels. Research conducted atProsper, ND, during the 2002-2004 growing seasons.

Defoliation in %

Growth Stage 0 33 66 100Yield in % of the check

R1 100 99 93 92R4 100 92 87 44

Source: Johnson and Petersen.

When the defoliation took place at the earlyreproductive stage (R1) the plants were able tocompensate during the remaining season. Yield losseswere 1, 7 and 8 percent at 33, 66 and 100 % defoliationrespectively. Yield reduction as defoliation levelincreased was mainly a result of fewer pods per plant.Yields were lower when defoliation took place at the R4growth stage compared with the R1 growth stage.

This research indicates that a plant has the ability tocompensate for loss of leaves but it will depend on thegrowth stage of the plant and the remaining growingseason. If defoliation occurs at an early growth stage,which allows more time to regenerate foliage, yieldreduction will be less. This study was an attempt tosimulate hail injury, however, in a real hail event thestems of the plant may also be damaged further reducingthe plant’s ability to recover.

Although field crops may appear to be heavilydamaged after a storm, the plants will try to recuperateand produce seed. Contact your insurance agent for advicebefore you decide to destroy a damaged crop.

Hans KandelExtension Agronomist - Broadleaf Crops

[email protected]


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NDSU IPM FIELD SCOUTS RESULTS - July 18NDSU field scouts are winding down their survey of wheat and barley in the state, as the crops are rapidly maturing. The

field scouts surveyed 77 wheat fields and 31 barley fields during the week of July 14-18. During that time, the averagegrowth stage of wheat fields surveyed was early milk stage, and the average growth stage of barley fields surveyed was earlysoft dough stage.

Wheat: Wheat leaf rust was observed in 16.8% of thewheat fields surveyed, with an average severity of 5.3%.

Tan spot and Septoria were the most common diseasesobserved in wheat, found in 52% of fields surveyed whichstill had green flag leaves. Bacterial leaf stripe wasobserved in 7.7% of the surveyed wheat fields, and loosesmut was observed in 9% of surveyed fields, with anaverage incidence of infected plants in these fields at11.4%. This incidence of loose smut in symptomaticfields is very high, a level in which infected fields wouldcertainly have received benefit from seed treatments thatcontrol loose smut. Fusarium head blight (scab) wasonly found in 5% of surveyed fields, with a field severityaveraging less than 1%.

Barley: Barley leaf rust was observed in 20% ofsurveyed fields, Septoria leaf blotch in 20%, and Spot orNet blotch also in 20% of surveyed barley fields. Loosesmut levels were lower in barley than in wheat, with onlya 6% incidence in infected fields. Scab was found in lessthan 3% of surveyed fields, at very low severity, less than0.1%.

Marcia McMullenExtension Plant Pathologist

[email protected]


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WHITE MOLD IN BEANSWhite mold is a common problem on edible beans,

and can be found in many soybean fields as well. Yieldloss from white mold is possible in either crop, but whitemold is more frequently a problem for edible beans. Thedisease begins when spores germinate on senescingflower petals, and infection progresses into the stem. Aninfected stem will take on a dried bone color and may beshredded (Figure 1). Sometimes a white fuzzy moldappears (where white mold gets its name), and small blacksurvival structures are produced (sclerotia). Because theinfection begins on the senescing flower petals, the mostimportant time to assess disease rick is at early bloom.

The highest risk for white mold occurs when a fewenvironmental factors come together.

Soil saturation. The disease cycle begins when thesurvival structure of the fungus (sclerotia) germinates andproduces a small mushroom-like structure (apothecia) fullof spores. These spores are then dispersed, and can landon the senescing flower petals which can result in disease. For this to happen, researchers have estimated that the soilmust be saturated for about 10-14 days. I took theapothecia photo in a wheat field near Langdon lastThursday, so there are areas in the state where conditionshave been favorable for development.

Canopy wetness. Once spores are on the petals, asaturated canopy for a prolonged period of time (day ormore) is necessary for the disease process to begin. Rainfall and heavy dews during flowering increase risk ofinfection.

Temperature. When it gets hot, white mold is lessof a problem. Temperatures above 85 F will inhibitapothecia formation and disease development. If you believe you may be at high risk numerousfungicides are available. Application timing is important,an application during the early bloom stage isrecommended. For further information, consult the 2008North Dakota Field Crop Fungicide Guide (PP-622),available at: http://www.ag.ndsu.nodak.edu/extplantpath/fungicide.html

Sam MarkellExtension Plant [email protected]

VENTENATA - NEW GRASS WEEDVentenata dubia is a weedy grass that has been

identified in much of the western U.S. Prairie Provinces ofCanada, and other areas. Confirmed establishment inMontana could mean, as weeds do, movement into NorthDakota. There is not much written about this grass speciesbut a quick goggle on the web (ventenada) will yield somesources of information. Some web sites are:

http://plants.usda.gov/java/profile?symbol=VEDUwww.cnr.uidaho.edu/range454/2004_pet_weeds/ventenata.htmlhttp://www.kew.org/data/grasses_db/www/imp10735.htm

Ventenada control data is also limited. One researchreport from University of Idaho in 2002 shows:

Rate(lb ai/A)

Ventenada Control%

Silverado + MSO 0.0134 + 1.5 pt 49Silverado + NIS 0.0134 + 1.5 pt 66Silverado + MSO 0.0089 + 1.5 pt 58Hoelon 1 2

Fig. 1. White mold in soybean field

Fig. 2. Apothecia produced by the white mold pathogen


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WHY HERBICIDES KILL WEEDS – WHY NOTTHE CROP? - QUICK REVIEW

Selectivity is the ability of a herbicide to kill onespecies and not harm another. We often take selectivityfor granted. We apply herbicides at low rates and expectthem to give adequate weed control but not kill thetargeted crop.

By what processes do herbicides work or what is theirmode of action? Herbicides kill weeds or damage cropsthrough a four step process.

4 Steps in Herbicide Mode of Action1. Contact or Retention - contact of the herbicide with

the roots or retention of spray droplets on a leaf.2. Absorption – uptake of the herbicide molecules into

the leaf, shoot, or root.3. Translocation – movement of the herbicide from the

site of uptake to the location in the plant where it cancause damage such as translocation the roots to theleaves or from sprayed leaves to growing points orroots (contact herbicides don’t need to translocate).

4. Inhibition at the site of action – typically, theherbicide molecule binds to a specific enzyme,blocking the production of essential products such asamino acids or blocking photosynthesis.

Why are crops not harmed by herbicides? Simply,some plants are able to metabolize (or detoxify) theherbicide into non-toxic chemicals before they damage theplant. In most cases, the key to selectivity is a plant’sability to rapidly metabolize the herbicide before it causesdamage at the site of action. In these cases, the plant hasother enzymes that can cleave off a side chain from theherbicide molecule. This often reduces the toxicity of theherbicide molecule because the molecules no longer hasthe right configuration or shape to bind tightly at the siteof action. The next step in herbicide metabolism is oftenbinding of sugars or amino acids to the molecule, whichfurther detoxifies it. Safeners are added to someherbicides like Dual II Magnum, Harness, Option, andLaudis. These safeners trigger the crop to produce moreenzymes to detoxify the herbicides, which increases cropsafety. Under normal weather conditions, a crop plantmay be able to metabolize a majority of the herbicide inseveral hours. On the other hand, a sensitive weed willonly slowly metabolize the herbicide. During this time,the herbicide is able to bind to the site of action and killthe weed.

Herbicide selectivity is based on metabolism in mostherbicide-crop combinations such as with Accent, Dual,Callisto, atrazine, or Banvel in corn or Valor, Pursuit,Cobra, or Sencor in soybeans. The exception tometabolism-based selectivity is when the crop has an“insensitive” site of action, which means the targetenzyme in the crop has a slightly different shape so theherbicide does not bind to it. This is the case with Assure,Select, and Poast Plus on broadleaf crops like soybean and

alfalfa. Since these herbicides cannot bind to the site ofaction, they do not damage these crops.

Roundup Ready corn and soybean are also resistantto glyphosate based on an insensitive site of action. Thegene that was added to these crops produces an altered orinsensitive enzyme that glyphosate cannot bind to.Therefore, the enzyme is not blocked and it keepsproducing amino acids for the corn or soybeans. TheOptimum GAT corn and soybean being developed byPioneer uses a metabolism-based glyphosate resistance. Inthis case, a gene (GAT) was added to the crops, whichproduces a special enzyme to rapidly detoxify glyphosatebefore it damages the crops. Liberty Link corn andsoybean also use metabolism-based resistance where thePAT gene was inserted into the crops, which produces anenzyme to rapidly detoxify Liberty.

This year we have received a larger amount of cropinjury calls. Herbicides from many different chemistriesapplied alone or on tankmix combinations have producedcrop injury. Both soil-applied and post-applied herbicideshave caused crop injury. The cool/cold weather we hadearlier in the season certainly reduced the metabolism inplants causing the plants to be affected by the herbicides.Multiple herbicide/fungicide combinations require plantsto simultaneously degrade pesticide of several differentmodes of action in the presence of reduce metabolism. Inaddition, the cool, wet weather allowed plants to formthinner cuticles on leaf surfaces rather than thick cuticlesin dry/drought conditions. Thin cuticles allow faster andgreater penetration of pesticide active ingredients thusfurther taxing the metabolic system in plants. I am surethere are other factors involved in the crop injury many ofus have seen this year but these are explanations that mayhelp answer why it happened.

Rich ZollingerExtension Weed Specialist

[email protected]


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2008 NDSU HORTICULTURE RESEARCH FIELD DAY

If you are interested in learning more about woodyplant, fruit and vegetable research, then attend the NorthDakota State University Horticulture Research Field Dayon Saturday, August 2, 2008 at 9:45 a.m. at the NDSUAbsaraka Horticulture Research Farm. A walking tourbegins at 10:00 a.m. Participants are asked to bring a sacklunch, but drinks will be provided.

The walking tour will continue after lunch. NDSUtree and shrub selections and introductions, common andexotic species, dwarf conifers and juneberry, grape andvegetable research plots will be toured.

The 80-acre farm includes the 35-acre ResearchArboretum, plus additional plot research areas. Dr. DaleHerman (woody plant selection and introductionresearch), Dr. Harlene Hatterman-Valenti (high-valuecrop research), and research associates at NDSU willconduct the tours.

Come and enjoy nature, plants and the great outdoors.There will be numerous tree and shrub door prizes.

For more information contact Dale Herman [email protected] or Harlene Hatterman-Valenti [email protected]

Directions to Horticulture Research Farm From East: Take I-94 west and turn north at WheatlandExit 322. Follow pavement to the north, which curves towest shortly after passing through Wheatland. Turn north(right) on County Road 5 (paved road, sign posted). AtAbsaraka corner, road changes to gravel at a slight curve. Go north about 3/4 mile (sign posted). Turn east (right)on field road and proceed ½ mile to Horticulture ResearchFarm bordered by trees.

From West:Take I-94 to Buffalo Exit 314. Turn north on Highway 38for seven miles. Turn east (right) on gravel at a dairyfarm (silos). Go through Absaraka to County Road 5(sign posted). Turn north (left) and go about 3/4 mile(sign posted). Turn east (right) on field road and proceed½ mile to Horticulture Research Farm bordered by trees.

From North: Take I-29 south to Argusville Exit 79. Gowest approximately 20 miles on County Road 4 (paved). Turn south on County Road 5 (gravel, sign posted) forapproximately four miles. Turn east (left) prior toAbsaraka corner (sign posted) and proceed ½ mile toHorticulture Research Farm bordered by trees.


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F. Adnan Akyüz, Ph.D.Assistant Professor of Climatology

North Dakota State Climatologisthttp://www.ndsu.edu/ndsco/

Non-Profit Org.U.S. Postage

PaidPermit No. 818

Fargo, N.D.

North Dakota State UniversityCROP & PEST REPORTExtension EntomologyHultz Hall 202Fargo, ND 58105-5346

Sam Markell, Co-EditorPlant Pathology231-8866 phone231-7851 fax

Janet Knodel, Co-EditorEntomology231-7582 phone231-8557 fax

Plant Sciences231-7972 phone231-8474 fax

Soils231-8881 phone231-7861 fax

Weeds231-7972 phone231-8474 fax

Ag Engineering231-7261 phone231-1008 fax

Helping You Put Knowledge To WorkThe information given herein is for educational purposes only. References to a commercial product or trade name is made with theunderstanding that no discrimination is intended and no endorsement by the North Dakota Extension Service is implied.

NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and the U.S. Department of Agriculturecooperating. Duane Hauck, Director, Fargo, North Dakota. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914.We offer our programs and facilities to all persons regardless of race, color, national origin, sex, handicap, age, Vietnam era veteransstatus, or sexual orientation; and are an equal opportunity employer.This publication will be made available in alternative formats for people with disabilities upon request (701) 231-7881.

NDSU Crop and Pest Report http://www.ag.ndsu.nodak.edu/aginfo/entomology/ndsucpr/index.htm

crop and pest report for july 24, 2008 · 7/24/2008 · the larva has a dark head capsule with a...

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