Disease Susceptibility of Brown Midrib (BMR) Silage Corn

Judith M. Kolkman1 , Rebecca J. Nelson1, 2, and Gary C. Bergstrom1
Sections of Plant Pathology and Plant-Microbe Biology1, and Plant Breeding and Genetics2 – School of Integrative Plant Science – Cornell University

What to know about BMR silage corn and diseases

Brown midrib (BMR) corn is a market class within silage corn that is desirable due to its significantly decreased lignin content.  As the name suggests, midrib veins of BMR corn leaves have a distinctive brown color.  Decreased lignin is desirable in corn silage because it increases feed digestibility for ruminant animals.  BMR corn carries naturally derived mutations in single genes that affect the plant’s lignin biosynthetic pathway.

The biosynthetic pathway that produces lignin also makes compounds that contribute to active plant defense mechanisms.  Some of these active defenses include small molecules called secondary metabolites that confer resistance against pests and diseases.  Structurally, lignin is a major component of the cell wall and serves as a barrier against fungal pathogens.  Lignin is also actively produced to strengthen cell walls that are being attacked.

To date, six BMR mutations have been identified in corn, and are designated as bm1 through bm6.  The causal gene has been identified for five of the BMR mutations.  Lines carrying two of these mutations, bm1 and bm3, are used as inbred parents for the production of commercially available hybrids known as BMR1 and BMR3, respectively.  Commercial BMR silage corn hybrids have been gaining in popularity.

There is concern that the same bm gene(s) that confer greater digestibility to BMR silage hybrids may also confer increased susceptibility to fungal diseases.  Some of these hybrids are more vulnerable to stalk lodging.  Northern leaf blight severely affected commercial BMR hybrids in 2013 and other recent growing seasons.

To determine the effect of the brown midrib mutations on disease susceptibility, we used replicated trials across multiple years to test the reaction of bm1 – bm4 mutants in a uniform inbred line background, W64A, to leaf, stalk and ear diseases (Fig. 1, Fig. 2 and Fig. 3).  Corn lines containing the four BMR mutations were all found to have heightened susceptibility to foliar fungal diseases, including northern leaf blight, gray leaf spot and anthracnose leaf blight (Fig. 1 and Fig. 2).

diseased corn leaves
Figure 1. Examples of lesions of (left to right): northern leaf blight, anthracnose leaf blight, Stewart’s bacterial wilt and gray leaf spot in corn.
graphs of corn disease reactions
Figure 2. Reactions to foliar fungal (NLB, GLS and ALB) and bacterial (SW) diseases in W64A inbred lines containing bm1, bm2, bm3 or bm4 mutations in comparison with W64A which does not contain a BMR mutation.
Graphs of disease reactions in corn
Figure 3. Reactions to anthracnose stalk rot and Gibberella ear rot in W64A inbred lines containing bm1, bm2, bm3 or bm4 mutations in comparison with W64A which does not contain a BMR mutation.

Figure 4 depicts a dramatic increase in W64A with the bm3 mutation.  The lines were also found to be more susceptible to the foliar bacterial disease, Stewart’s bacterial wilt (Fig. 2).  After two years of trials, our evidence suggests that BMR corn inbreds have higher susceptiblity to anthracnose stalk rot as well (Fig. 3).  Additionally, the bm1 and bm3 containing inbreds were more susceptible to Gibberella ear rot, caused by Fusarium graminearum, when compared to their non-BMR counterparts (Fig. 3).

diseased corn comparison
Figure 4. Increased severity in an inoculated trial of northern leaf blight in a W64A corn inbred with the bm3 gene (right) compared to a W64A inbred lacking the mutant gene (left).

The benefits of BMR silage corn are huge for the dairy industry.  While individual hybrids may vary, BMR corn, appears to be more susceptible to diseases than non-BMR corn. The degree of susceptibility does vary by bm mutation and specific pathogen (Fig. 2 and Fig. 3).  Breeders are constantly working to improve disease tolerance, and disease ratings should be factored into hybrid choices.  BMR hybrids in the market show a wide range of suceptibilities to individual diseases.

How to manage diseases in BMR silage hybrids

Knowing that BMR silage corn can be more vulnerable to foliar, stalk, and ear diseases means that a proactive and integrated strategy is needed to maintain optimal plant health in these hybrids.  Elements of integrated management include:

Be aware of corn diseases on your farm and in your area.  Scout your fields annually for foliar diseases from tassel emergence through grain formation.  Check for ear rots (by pulling back husks) and stalk rots (squeeze lower stalks or attempt to push stalks over) prior to harvest.  Seeing diseases even late in the season gives you an indication of what pathogens may survive in corn residues into the next growing season and helps you to plan rotations and select hybrids.

Fungi that cause anthracnose, gray leaf spot, northern leaf blight, and Gibberella ear rot and stalk rot survive between crop seasons in corn residues on the soil surface; therefore rotation of corn with non-host crops can help to reduce the spore inoculum potential for these diseases.  Northern leaf blight has been the most widespread and injurious foliar disease in New York in the past decade and can be a problem anywhere in any given year.

Consider disease susceptibility when selecting BMR hybrids. Select BMR hybrids with the least susceptibility to specific diseases that have been problematic on your farm or in your region. If disease risk is extreme, e.g., in a humid river valley with a history of severe gray leaf spot, it may be preferable to grow non-BMR hybrids with documented resistance.

BMR hybrids, especially BMR1 and BMR3, have the potential to have severe ear rot and mycotoxin contamination in years with persistent moisture during silk emergence.  Be sure to check seed company guides for the latest disease ratings for BMR hybrids.

Apply foliar fungicide based on disease detection and forecast risk. There is a wide choice of foliar fungicide products labeled for control of fungal leaf blights in New York.  Table 3.5.1 in the 2020 Cornell Guide for Integrated Field Crop Management (https://www.cornellstore.com/2020-PMEP-Guide-for-Integrated-Field-Crop-Mgmt) notes the relative efficacy of labeled fungicides against different corn diseases.  To slow down the development of resistance to fungicides in pathogen populations, it is best  to use products with different modes of action (FRAC groups) in alternating years or to apply combination products with more than one mode of action.

The optimal timing for applying foliar fungicides is between tassel emergence (VT) and brown silk (R2) stages.  Observation of foliar fungal diseases in the middle leaf canopy (at lowest ear level) and a forecast of significant precipitation in the following week are the best indicators that fungicide application will be result in disease suppression and yield increase.  Suppression of foliar diseases also helps to preserve stalk health, standability, and quality, including lower levels of fungus-produced mycotoxins.

Consider longer term and regional effects of growing BMR hybrids. Year after year of growing a susceptible BMR hybrid can increase the disease inoculum load in a particular field and locale, thus affecting neighboring fields of non-BMR silage, dent, and sweet corn.  Occasional rotation out of BMR corn should be considered.


BMR silage corn is increasing in popularity and acreage as it provides a high quality, digestible feedstock for dairy nutrition.  Its positive attributes need to be balanced with proactive disease management to insure plant health and sustained productivity in dairy cropping systems.


This work was supported by the USDA National Institute of Food and Agriculture Hatch accession #1004040.

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What’s Cropping Up? Volume 30, No. 3 – May/June 2020

The full version of What’s Cropping Up? Volume 30 No. 3 is available as a downloadable PDF on issuu. This issue includes links to COVID-19 resources on the back page. And as always, individual articles are available below:

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Meadow Fescue-Alfalfa Mixtures in Northern New York

J.H. Cherney1 and D.J.R. Cherney2
1Soil and Crop Sciences Section, School of Integrative Plant Science; 2Animal Science Department; Cornell University

Over 90% of the alfalfa acreage in northern NY is seeded with a perennial grass. Meadow fescue is becoming increasingly popular for mixtures with alfalfa in New York. Most meadow fescue varieties were developed in northern Europe or at higher elevations in southern Europe. Meadow fescues are very winter hardy and tolerant of wet soils, they have been popular for both grazing and hay in Canada for decades. They have also been shown in NY and WI trials to be higher in fiber digestibility than other grasses more commonly used in mixture with alfalfa in the northern USA.

One concern in the Northeast has been the seeding rate for meadow fescue with alfalfa. This grass is very aggressive when grown with alfalfa, particularly if soil conditions are not optimal for alfalfa production. We evaluated one diploid (SW Minto) and one tetraploid (Tetrax) meadow fescue at 5 seeding rates with either a reduced-lignin alfalfa (HarvXtra) or a conventional high-quality alfalfa (Hi-Gest 360).


In May, 2018, we planted field trials on farms near Copenhagen in Jefferson County, NY (Site 1) and near Lowville in Lewis County, NY (Site 2). HarvXtra and Hi-Gest 360 were seeded at approximately 15 lbs/a, with the same number of pure live seeds per sq. ft. for both alfalfa varieties. Tetrax meadow fescue was seeded at 0.5, 1, 2, 3, and 4 lbs/a, with the same number of pure live seeds per sq. ft. for SW Minto. Tetraploid meadow fescue seed is up to three times greater in weight per seed compared to most diploid varieties.

Plots at both sites were mowed to control weeds during the seeding year, and no data was collected. In 2019, three photographs were taken per plot (covering >70% of the plot area) prior to each harvest and were visually evaluated for grass percentage. Site 1 was harvested four times in 2019, on 6 June, 10 July, 12 August, and 18 September. Site 2 was harvested three times on 31 May, 15 July, and 14 August. At each harvest, forage quality and dry matter samples were collected prior to harvest, and forage quality samples were separated into alfalfa and grass components for laboratory analysis.

Forage Yield

Dry matter yield for Site 1 averaged 5.1 dry tons/acre and was 67% greater than Site 2. Site 2 had a soil pH of 6.4 at spring harvest in 2019 and had been adequately fertilized, but alfalfa never looked reasonably healthy and had a stunted appearance throughout the season. There was insufficient regrowth to justify a fourth harvest at Site 2. Yield at both sites was primarily attributed to spring growth. Site 1 yield distribution was 41%, 29%, 18%, and 12% for four cuts, while Site 2 yield distribution was 61%, 28%, and 10% for three cuts. Yield at both sites was influenced by grass seeding rate (Fig. 1).

Graph 1
Fig. 1. Yield of alfalfa-meadow fescue as related to grass seeding rate.

Grass Percentage in Mixtures

Struggling alfalfa resulted in very high grass percentages at Site 2 (Fig. 2). Although alfalfa was normal in appearance at Site 1, grass percentage was also high for the year after seeding. SW Minto was considerably higher in grass percentage of mixtures than Tetrax at both sites (Fig. 3). Grass percentage consistently agreed with grass seeding rate, but plots with the 0.5 lb/acre grass seeding rate were less uniform than at higher seeding rates. Visual estimation of a majority of the plot area provided more consistent results than calculating a grass percentage estimation based on a small, separated sample of alfalfa-grass that may or may not be representative of the entire plot.

Graph 2
Fig. 2. Grass percentage in mixtures for Tetrax meadow fescue in 2019 at two sites, averaged over harvests, weighted for dry matter yield.
Graph 3
Fig. 3. Grass percentage in mixtures in 2019 for two meadow fescues averaged over two sites, and averaged over harvests, weighted for dry matter yield.

Grass Quality

Grass crude protein (CP) was related to the proportion of alfalfa in the mixture, as alfalfa provides grass with nitrogen (Fig. 4). Grass quality was very similar between sites. Across sites and harvests, Tetrax averaged 51% NDF, while SW Minto averaged 55%. Tetrax averaged 2.5% greater fiber digestibility (NDFD48h) than SW Minto across sites. NDF, ADF, and lignin tended to increase with increased grass seeding rate, while in vitro digestibility and NDFD decreased with increasing grass seeding rate. Grasses were harvested prior to heading, so we lack relative maturity information, however, these two grasses had the same spring heading date in Ithaca, NY in 2019. Meadow fescue averaged 82% NDFD over variety, site and harvest, while alfalfa averaged 56%.

Graph 4
Fig. 4. Crude protein in meadow fescue as influenced by grass seeding rate in alfalfa-grass mixtures in 2019. Average of two meadow fescue varieties and two sites. Harvests were also averaged, weighted for yield.

Alfalfa Quality

With less than ideal sites for alfalfa production, grass dominated stands at all but the lowest grass seeding rates. Typical forage quality differences between reduced-lignin alfalfa and conventional alfalfa were not observed at these sites. HarvXtra was significantly lower in lignin (but only 2.7% lower) than Hi-Gest 360 at Site 2, and varieties did not differ for lignin at Site 1. HarvXtra had 4.2% greater NDFD than Hi-Gest 360 at Site 1, while alfalfa varieties did not differ for NDFD at Site 2. Alfalfa composition was not affected by grass seeding rate.

Harvesting grass with reasonably good forage quality in mixtures in the spring in NY often results in alfalfa harvested at relatively immature stages. For example, mixtures were harvested on June 6, 2019 at Site 1, and alfalfa averaged 30% NDF, while grass averaged 58% NDF. A common rule of thumb for alfalfa is harvesting in the spring at approximately 40% NDF after accumulating 750 growing degree days (GDDbase41F). The two sites reached 750 GDD on June 15 and June 17.


Meadow fescue is well adapted to colder environments and to somewhat marginal soils. Meadow fescue also is generally high in fiber digestibility compared to other cool-season grasses typically sown with alfalfa in the Northeast. It is very competitive with alfalfa under such conditions. If the goal of a mixed seeding for dairy forage is to produce a stand with 20-30% grass on soil not ideally suited to alfalfa, meadow fescue seeding rate should probably not exceed 1 lb/acre. While seeding rates can be controlled, climatic conditions cannot. Grass percentage in alfalfa-grass mixtures can be greatly affected by soil moisture, particularly for the first month after seeding. Shallow-rooted young grass seedlings are much more susceptible to drought than alfalfa seedlings.

Reduced-lignin alfalfa may not perform as well on more marginal soils, as it generally does on good alfalfa soils. In these trials and other studies conducted in NY, Tetrax meadow fescue has been less aggressive with alfalfa than most meadow fescues evaluated and is often higher in fiber digestibility. There are over 120 meadow fescue varieties certified for sale in Europe; few are currently sold in North America. Optimum seeding rate for meadow fescue with alfalfa may vary for different cultivars and for different regions in the Northeast; more research on meadow fescue varieties is warranted.

This research was supported by the Northern New York Agricultural Development Program.

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Wheat spindle streak mosaic in spring: A reminder to plant a resistant wheat variety in fall

Gary C. Bergstrom, Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University

The Disease

Wheat spindle streak mosaic (WSSM), caused by wheat spindle streak mosaic virus (WSSMV), is a disease that attracts little attention today because most of our widely grown, winter wheat varieties have significant levels of resistance to it.  Yet WSSMV persists in New York soils in its protozoan vector ready to infect the roots of susceptible winter wheat varieties soon after planting.  Swimming spores (zoospores) of the vector move through films of water in the soil and thus root infection is favored by moist conditions in fall. Plants remain infected over the winter dormant period but do not develop typical leaf symptoms until spring following a number of weeks of cool weather which favors virus replication and virus movement from roots into shoots. Temperature, not moisture, is what drives symptom development in spring since plants were already infected in the fall. Only winter wheats, not spring wheats, are affected by WSSMV because of the time it takes to build up virus levels in the roots and then the shoots.


Symptoms of WSSM first appear in late April or early May and are characterized by long, light green, spindle-shaped streaks with dark centers (Fig. 1). As leaves age, these streaks can become necrotic and resemble lesions of Septoria tritici blotch but without dark fruiting bodies, i.e., pycnidia of Zymoseptoria, in evidence under a hand lens. Symptoms of WSSM fail to develop on new leaves that emerge when average daily temperatures exceed 60 F, though symptoms can reinitiate at later growth stages if persistent cool conditions occur during stem elongation, head emergence, and even grain-filling. Conditions have been ideal in April and May 2020 for development of WSSM.  Symptom development is extremely sensitive to warm temperatures such that we have seen very little WSSM in years with high temperatures in early spring.

wheat leaves
Figure 1. Characteristic symptoms of wheat spindle streak mosaic on wheat flag leaves at boot stage (A) and close-up of spindle streaks (B).


What should a wheat producer do if she/he observes characteristic symptoms of WSSM this spring?  There is no action that can be taken to mitigate WSSM in a growing crop – the yield damage, which can exceed 30% of the crop’s potential, has already occurred. However, diagnosis of the disease is a sure reminder that the variety they are currently growing is susceptible to WSSMV, and they need to choose a variety with at least moderate resistance for planting in the coming fall.  This should elicit a conversation with your seed supplier about varieties resistant to WSSMV; some companies include that information on their website and in their seed catalogs but others do not.  While the majority of available varieties express resistance to WSSMV, susceptible varieties appear in the seed market from time to time. Scores for WSSM also are included in winter wheat variety trial tabular results (https://blogs.cornell.edu/varietytrials/small-grains-wheat-oats-barley-triticale/small-grains-cultivar-trial-results/) from Cornell’s Small Grains Breeding Program in years when symptoms are observed.

If you find more pronounced mosaic and fewer distinct streak symptoms in a variety designated to be WSSMV-resistant, your wheat could be infected by another soilborne, protozoan-transmitted virus called soilborne wheat mosaic virus (SBWMV), which we have diagnosed occasionally in isolated fields in southern areas of the Finger Lakes Region.  Resistance to SBWMV is independent from resistance to WSSMV, though it is also available from wheat seed suppliers in a choice of adapted varieties.

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Burndown Herbicide Options in No Till Soybeans

Mike Hunter, CCE North Country Regional Ag Team

plants in field
Resistant marestail in a field of soybeans in Jefferson County

Glyphosate resistant and multiple resistant (Group 9 and Group2) marestail is spreading across New York State and may already be on your farm.  If you don’t have it on your farm today the chances are you will at some point in the future.  The presence of herbicide resistant marestail, tall waterhemp and palmer amaranth in New York is changing the way we manage weeds.  We need to use burndown herbicide programs with more than one effective site of action to delay the development of resistant weeds and provide the best control.  The use of glyphosate alone should no longer be considered a viable burndown herbicide program.

In no-till, strip-till and very minimum till (i.e. one pass with a vertical tillage tool) situations burndown herbicides will be necessary to control emerged weeds prior to planting.  Marestail can be either a summer annual or winter annual.  The winter annual marestail rosettes are present right now and as it warms up these will begin to bolt and grow tall quickly.  Once resistant marestail gets any taller than 6 inches it becomes very difficult to control.

Xtend, Enlist and Liberty Link traited soybeans are the choices that allow for effective postemergence control of multiple resistant marestail.  In Roundup Ready or conventional soybean fields we have no effective herbicides for the postemergent control of multiple resistant marestail.

Burndown herbicide programs for no till soybeans will include either glyphosate, glufosinate or paraquat tank mixed with 2,4-D and/or Sharpen (saflufenacil).  The addition of metribuzin or Valor SX (flumioxazin) or both to the burndown program will provide residual control of marestail.

If dandelions are also a problem in the field, consider using one of the listed programs that include 2,4-D ester.  Don’t substitute 2,4-D amine formulations for the ester formulation.  Apply 1 pint per acre of 2,4-D ester (4 lb gal formulations) to keep the preplant interval to 7 days, rates higher than that will lengthen the planting interval.

If using a burndown option that includes Sharpen, apply 1 oz/acre for no preplant restrictions (except for coarse soils with 2% or less organic matter where the preplant restriction is 30 days).  If Sharpen (used at 1 oz/ac) is included in the burndown program and tank mixed with a flumioxazin product the preplant restrictions will be a minimum of 14 days in no till (except for coarse soils with 2% or less organic matter where the preplant restriction is 30 days) and 30 days in conventional till regardless of the soil texture and organic matter.

Here are choices that include more than one effective site of action for the control of resistant marestail in soybeans:

    • Sharpen (1 oz) + glyphosate + metribuzin
    • 2,4-D ester (1 pint) + glyphosate + metribuzin (7 days prior to planting)
      • Can include a flumioxazin product (Valor SX, Valor XLT, Envive, Surveil)
      • Or a premix containing metribuzin + flumioxazin (Trivence WDG or Panther Pro)
    • 2,4-D ester (1 pint) + Sharpen (1 oz) + glyphosate + metribuzin (7 days prior to planting)
    • Sharpen (1 oz) + glufosinate (Liberty)
    • Sharpen (1 oz) + glufosinate + metribuzin
    • 2,4-D ester (1 pint) + Sharpen (1 oz) + glufosinate + metribuzin (7 days prior to planting)
    • paraquat (Gramoxone) + metribuzin
    • 2,4-D ester (1 pint) + paraquat (Gramoxone) + metribuzin (7 days prior to planting)
    • Sharpen (1 oz) + glyphosate + dicamba (must use one of these: XtendiMax, Engenia, FeXapan, Tavium (dicamba + s-metolachlor)) In Roundup Ready 2 Xtend (dicamba tolerant) soybeans only
    • Sharpen (1oz) + Enlist One + glyphosate (or Enlist Duo (2,4-D choline + glyphosate)) In Enlist soybeans only

Here are choices that include only one effective site of action for the control of resistant marestail in soybean:

    • 2,4-D ester (1 pint) + glyphosate (7 days prior to planting)
    • Sharpen (1 oz) + glyphosate
    • glyphosate + dicamba (must use one of these: XtendiMax, Engenia, FeXapan, Tavium (dicamba + s-metolachlor)) In Roundup Ready 2 Xtend (dicamba tolerant) soybeans only
    • Enlist One + glyphosate or Enlist Duo In Enlist soybeans only

Resistant tall waterhemp has been found in 12 counties in NYS.  If resistant tall waterhemp is present on your farm the herbicide program will be slightly different from a multiple resistant marestail program.  It is highly unlikely that a one pass, preemergence herbicide application will provide adequate control of resistant tall waterhemp in soybeans.  It will require a two pass (Pre and Post) herbicide program to provide season long control to minimize the spread of seed.

If Roundup Ready or conventional soybeans are planted, make a preemergence application of a Group 15 herbicide (Dual II Magnum, Warrant, Outlook, EverpreX) + metribuzin and consider including flumioxazin in this tank mix as well.  The postemergence herbicide choices will be limited to Reflex, Flexstar, Flexstar GT (if RR soybeans), Prefix (Dual Magnum + Reflex) or Warrant Ultra (Warrant + Reflex).  If necessary, a late postemergence rescue treatment of Cobra can be used.

If Xtend, Enlist or Liberty Link traited soybeans are planted, make a preemergence application of a Group 15 herbicide (Dual II Magnum, Warrant, Outlook, EverpreX) + metribuzin and consider including flumioxazin in this tank mix as well.  In Roundup Ready 2 Xtend (dicamba tolerant) soybeans apply a postemergence application of XtendiMax, Engenia, FeXapan, Tavium.  If Enlist soybeans are planted, apply Enlist or Enlist Duo.  If Liberty Link soybeans are planted apply Liberty.

Always read and follow label directions prior to using any herbicide.  If you have any questions or would like more information regarding burndown herbicide programs for soybeans contact your local Cornell Cooperative Extension office.

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NYS IPM Field Corn Pheromone Trapping Network for 2020 Caught Moths in Mid-April!

Ken Wise and Jaime Cummings – NYS IPM Program

The NYS IPM Field Corn Pheromone Trapping Network has started trapping black cutworm (BCW) Agrotis ipsilon and true armyworm (TAW) Mythimna unipuncta moth flights in NYS. While it seems like it might be early, we have caught BCW and TAW moths this week in Western, NY in pheromone bucket traps. These moths migrate north on weather fronts from the southern US every year. Both BCW and TAW prefer feeding on grasses, such as grassy weeds, hay fields, small grains and corn.

Even though the number of moths caught this week were low, it indicates that they have arrived. From this point forward, we can set the “Biofix Date”. The biofix date is the point where we start to calculate the number of BCW and TAM degree-days. We can predict when the eggs that were laid by moths will hatch. Degree-days are calculated by taking the high and low temperature each day and averaging them from the biofix date. Next, subtract the base temperature of 50 degrees Fahrenheit, and this will give you the daily degree-days. Each day, add the number of BCW degree days and this will give you a total. When this reaches 90 BCW degree-days and 113 TAW degree-days, the eggs will start to hatch.

High Temperature + Low Temperature/2 – 500 F = daily BCW degree days

The easy way to calculate this is to use the NEWA Degree Day Calculator. This will calculate the degree-days from a weather station near your farm. Below is the information on degree-days for the lifecycle of BCW and TAW.

Black Cutworm Degree Days (Base 500 F)

Degree Days               Stage                           Feeding Activity

0                                  Moth Capture              Egg Laying

90                                Eggs Hatch

91-311 1st to               3rd Instar                     Leaf Feeding

312-364                       4th Instar                     Cutting Begins

365-430                       5th Instar                     Cutting Begins

431-640                       6th Instar                     Cutting Slows

641-989                       Pupa                            No feeding

Source: University of Minnesota Insect Pest of Corn-Stand Reducers Black Cutworm

True Armyworm Degree Days (Base 500 F)

Degree Days               Stage                           Feeding Activity

0                                  Moth Capture              Egg Laying

113                              Eggs Hatch

612                              Larval stages               Leaf Feeding

909                              Pupa                            No feeding

Source: Scouting for True Armyworms Is Highly Recommended in Small Grains and Early Corn-University of Kentucky

A large number of moths in a trap does not necessarily mean there is going to be damage in your corn. It will depends on where the moths lay eggs. If a trap near your farm has a large number of moths, it would suggest it is time to scout for larvae and signs of feeding damage.

A good time to start scouting is when you take plant population counts. BCW damage is easy to identify. The larvae will cut the plant near the base at the soil surface, while TAW will feed from the edge of the leaf to the mid rib.

black cutworm armyworm control tableBCW and TAW larvae are primarily nocturnal or night feeders. Normally, you will not see them during the day. BCW larvae are ½ inch to 2 inches. They appear as greasy gray with darker raised spots on each segment. They normally hide in the soil near the base of the corn or under residue that might be on the surface.

Black Cutworm
Photo by Ken Wise, NYS IPM

TAW larvae range from ½ to 1.5 inches long. They have orange and white strips running along the side. They also have a white strip running down the back. TAW will hide under surface residue, in the whorl of the plant or in cracks in the soil.

True Armyworm
Photo by Keith Waldron, NYS IPM

If you are at threshold, and the larvae are still small, try to treat only the infected corn and a 20 to 40 foot border around the area. When the larvae are large (1.25 inches +) they are harder to kill with an insecticide, and they will pupate soon. When pupating, they will stop feeding.

One of the issues with BCW and TAW is that there can be multiple flights on different weather fronts throughout the spring. This can cause multiple infestations with different sizes of larvae in a field. Still follow the economic threshold, and manage if needed.

Our pheromone-trapping network has 25 traps of each BCW and TAW placed in 19 counties across the state. The counts and degree-days for many locations across NY will be published weekly starting later in April in the NYS IPM Field Crops Pest Report .


University of Missouri-True Armyworm

University of Minnesota Insect Pest of Corn-Stand Reducers Black Cutworm

Cornell University Field Crop-Armyworm

Purdue University-Armyworm

Purdue University-Black Cutworm

Cornell University Guide for Integrated Field Crop Management

Scouting for True Armyworms Is Highly Recommended in Small Grains and Early Corn-University of Kentucky

This work is funded by the NYS Corn and Soybean Growers Association.
NY Corn & Soybean Growers Association logo

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