The true armyworm – not to be confused with the fall armyworm – can pose a threat to corn stands and overall yield as an early season pest. Armyworm larvae are characterized by alternating light and dark bands.
The larvae feed primarily on seedling leaves and are associated with causing defoliation. When feeding, armyworms start at the base of the corn plant and work their way up, primarily feeding on softer leaves and during the nighttime. During the day, armyworms will migrate to the whorlof the corn plant as well as inside of soil cracks.
Cool and wet weather in the springtime supports the development of armyworms and fields with a heavy presence of weeds and grasses are conducive for allowing them to thrive. Armyworm moths migrate up from the south and look for the grassy fields or areas with lush vegetation. Therefore, winter rye cover crops have been associated with a higher prevalence of armyworm infestation.That is why it is important to terminate cover crops at least two weeks prior to corn planting.
Treatment and Mitigation
Death in corn plants from armyworm is not common, but if the armyworm feeds on a budding corn plant, this can lead to poor stands and significant loss in yield. When armyworm infestation causes defoliation in more than 25% of corn plants, it is advised to begin using an insecticide. Additionally, when armyworms are still developing and larvae is only ¼ to ¾ inches in length, treatment is considered economical and is advised.
Controlling excess grass growth will prevent moths from laying eggs and will offer protection from future infestation. If herbicides are applied, the loss of a weed habitat can drive armyworms to feed predominately on corn plants.
Treating an armyworm infestation with small corn plants requires quick decision making because large populations of armyworms can spread quickly across a field. Keep an eye on those fields that have a cover crop or are close to armyworm habitat. Be prepared to act if conditions warrant treatment!
Cutworms are insects that show up during the earliest growing stages of the season. The presence of cutworms can pose a threat to the well-being of corn plants, but their severity is highly variableand depends on the species. Delayed planting and corn plants shorter than 18 inches are most susceptible to undergoing severe damage from cutworms.
Black Cutworm
Black Cutworm
Black cutworms are the most common species found in corn throughout the Midwest. The larvae of black cutworms can be up to 1¾ inches long with their appearance characterized by a dark-gray segmented body. Black cutworms are most likely to be seen between stages VE – when the shoot first emerges from the soil and V5 – when the first five leaves exhibit visible collars. The sets of paired spots unequal in size that run along the length of the black cutworm make it distinct in appearance. Black cutworms cause damage by chewing holes in leaves and larvae will cut the lower portions of the corn plant just above the soil line. The youngest larvae will feed on leaves whereas older cutworms will feed exclusively below ground level. The first generation of black cutworm will cause the most damage, though three to four generations can be produced in a year.
The black cutworm thrives best in wet and weedy fields with poor drainage. Cover cropping can make conditions conducive for the growth of laid eggs, especially if weeds are prevalent. Insecticide is advised if cutting is evident across 2-3% of corn plantsand larvae do not exceed ¾ inch in length.
Dingy Cutworm
Dingy Cutworm
Similar to the black cutworm, dingy cutworms can form larvae up to 1¾ inches long and often emerge in fields with heavy crop residue. However, unlike black cutworms, the pairs of black dots running along the segmented back appear to be equal in size. When fully grown, dingy cutworms reach a size of one inch in length. Dingy cutworms typically only feed on leaves and do not cut plants.
Glassy, Bronzed and Sandhill Cutworms
Glassy Cutworm
These three classes of cutworms are characterized predominately by the color of their larvae. Glassy cutworms have a white, translucent segmented body with a solid orange head and cause damage primarily to seedlings.
Bronzed cutworms are colored with light orange, bronze and brown stripes running the length of their body.
Like glassy cutworms, sandhill cutworms have a translucent, light brown body that is uniform in color, including the head. Glassy cutworms are known to cause cutting damage in addition to chewing and feeding damage exhibited by other cutworms.
Sandhill CutwormBronzed Cutworm
What to Look for When Scouting
Corn plants succeeding soybeans or legumes are most susceptible to hosting cutworms. With shorter corn plants having the greatest vulnerability to cutworm damage, scouting should begin once seedlings first emerge and continue until plants achieve a height of 18 inches tall. Look for signs of cutting, wilting and irregular holes on leaves. Uneven stand or inconsistencies in cutting across rows are also signs of cutworm damage.
Cutworms gravitate toward moist soil for burrowing. When looking for signs of infestation, dig around the base of plants to look for burrows ranging in size from three to four inches. When soil is dry, digdeeper to three inches below ground to identify burrows.
Treatment
As cutworms are associated with reduced stand resulting from cutting or wilting, yield can subsequently be decreased. However, replanting is not usually necessary and is only advised if the presence of cutworms is not under control and stand has been severely impacted.
Controlling weeds can reduce overwintering and can remove an environment favorable for hosting cutworms. Tilling practices that reduce weeds and field residue will deter moths looking to lay eggs in the fall. Reduced tillage or no-till, delayed planting and overwintering cover crops are all management practices that increase chances of cutworm damage.If you see cutworm damage on 2-3% of plants and they are smaller than ¾ inch, it’s time to spray. When pre-applying insecticides to dry or crusted soils, it is advised to work the treatment into the soil so it is able to reach cutworms and burrows housed below ground.
Photo Credits
Black Cutworm: Iowa State University Extension and Outreach
Dingy Cutworm: Purdue University
Glassy Cutworm: University of Minnesota Extension
Sandhill Cutworm: Iowa State University Department of Entomology
Bronzed Cutworm: Iowa State University Department of Entomology
Frost damage occurs in corn and soybeans when plants are exposed to freezing or below-freezing temperatures. Damage can occur to the plants above and below the soil when temperatures range from 28 to 32°F and colder. Corn and soybean plants exposed to air temperatures below 28°F are often lethal and prevent plants from undergoing full recovery from injuries.The key in assessing frost damage is waiting five days to allow for any potential growth recovery or rehabilitation to occur.
Spring Frost in Soybeans
If frost damage occurs below the soybeans’ cotyledons – the first leaves that emerge above ground – the plant will mostly likely fail to recover. Wilted and dried leaves will often remain on the plant after a frost event. In recovering soybeans, new leaves will emerge at the site of cotyledons – the first pair of embryonic leaves that appear above ground. If auxiliary buds growing at the juncture of the plant’s stem and cotyledons are not frozen, the plant is on track for recovery.
Spring Frost in Corn
Since corn plants are protected by soil for a longer period of time relative to soybeans, they are less susceptible to lethal frost injury. However, temperatures below 28°F can cause damage below the soil and compromise growth, leading to poor stands. Once the growing point is above ground, corn plants exposed to 32°F for a few hours and 28°F for a few minutes can be lethal. After an initial frost, continued cool temperatures can decrease yield due to the onset of stalk rot diseases.
If frost occurs before V6, yield loss is minimal. In recovering corn plants, you should see new leaf growth emerging from whorls. Yellow-colored tissue that exists above the growing point is a sign of regeneration.
For corn and soybean plants before and after emergence, flooding and saturated soils can jeopardize yield. Germinating seedsrequire oxygen to survive. After the first 48 hours following a heavy rain or flooding event, oxygen levels in the soil will become entirely depleted and prevent seedsfrom germinating and continuing to grow.
Yield loss for corn and soybeans depends on the duration of the flooding event and at what growth stage it occurs. The longer a plantis submerged or growingin saturated soil, the less likely it is to survive. Generally, smaller seedlings with lower stamina are less likely to survive following a heavy rainfall event compared to larger seedlings.
Warmer temperatures are associated with higher growth rates, and as a result, a higher amount of oxygen is used. When temperatures exceed the mid-70° range, survival may not exceed 24 hours following the heavy rainfall event.
Effects on Corn Plants
Before V6, the growing point is below ground and damage from flooding ismore likely to impact yield or kill the plant. After V6, corn plants fair better in saturated conditions if some of the plant is out of the water. However, the higher temperatures can speed up respiration and oxygen requirements, leading to more plant damage compared to cooler temperatures during a flood event.
Nitrogen loss is another way flooding impacts corn yields. Corn consumes two-thirds of its nitrogen by the start of the reproductive stage and relies on a functional root system. If a flooding event compromises plant roots, yield can be reduced significantly. Research from Iowa State University found that a 30-inch corn plant that had been flooded for 48 hours with minimal nitrogen uptake experienced a 20% reduction in yield. Flooding can also promote seed decay, crazy top that exhibits proliferated tassels, stunted ears or completely barren plants
Impacts on Soybeans
For soybean plants at stages V2 or V3, survival is possible. However, nitrogen fixation can be restricted and reduced yield is still likely. For soybeans submerged for less than 48 hours, yield loss is rarely observed.
Once the first bloom appears at stage R1 the number of pods per node will be greatly decreased if sitting in saturated conditions. Wilting, stunting and yellow-leaves will be expressed in damaged or dying soybean plants. Further, research has found that greater yield reduction has been observed in soybean plants grown in heavy clay soils as opposed to silt loam soils.
Assessing Outcomes
Flooding and prolonged saturated soils pose the greatest threat to young plants that have yet to emerge above ground. As water recedes, any remaining residual mud on corn and soybean plants can reduce photosynthesis. For plants that survive a flooding event, they will be more vulnerable to diseases and stresses over the course of the growing season.
The survival outlook for saturated seeds and germinating plants will not exceed four days. Plants that surviveafter water levels recede will continue to grow within three to five days.
Everyone is vitally aware of how brittle the farm economy has been, yet it seems like every agriculture periodical that I read discusses all the challenges. This movie quote illustrates the current state of our industry,
“I’m drowning and you are describing the water.”
We don’t need ag magazines and experts to “describe the water.” We need someone to toss us a life vest, or a plausible solution! That’s why I’m concentrating on solutions to help create stability.
Granted, these solutions don’t come easy. You must be being willing to do something that you may not have done in the past. Another quote comes to mind,
“For things to change, you need to change. For things to get better, you need to get better.”
This quote has some personal and professional reflective value. Th e world agriculture market is becoming more competitive and aggressive. We must get more efficient domestically, and we must find ways to differentiate our products on a global scale. We must look beyond quantity of the crop produced to qualitative components, such as amino acids, fatty acids, omega 3, 6, 9 composition and more. This resonates deeply with the consumer. Not only does increasing the quality of our corn add value, it also helps us build “marketing muscle.”
For years, research has looked for corn silage products that are stable on the acre. Then researchers looked into delivering the very best nutritional matrix. The delicate balance is so important that early adopters are designing on-farm experiments to test their management systems. I’m excited that Phil Long is merging technology with a vision of the future with Latham’s Seed-2-Soil precision agriculture program services. Little details like better starch and fiber digestibility in grain also make big differences.
The image below illustrates the value of feeding hybrids with softer starch. We continually provide good data to help you make better seed product selections and transform research into useful on-farm results.
2018 corn silage data is available on Latham’s website. Feel free to contact me if you have any questions about setting up an on-farm research trial for forage products. In 2019, be open to exciting possibilities – and to trying something new on your farm!
Nitrogen rates can be the most powerful yield influencer when it comes to corn inputs. Other management practices including fungicide, starter fertilizer and seeding rate also can significantly impact yield.
In a previous post, I discussed the results of our Climate FieldView (CFV) study. We compared a recommendation from Climate’s Nitrogen Advisor tool of 135 pounds per acre (lbs/A) total Nitrogen (N) to our typical yield goal (YG) approach of 170 lbs/A total N. We didn’t see significant yield differences between the two nitrogen programs. In this post, I’m going to focus on the other 10% of the
study.
Seeding rates don’t always influence yield as expected because many of our hybrids have outstanding ear flex and the plant compensates for the additional space. Our planting rates were around 31,500 and 37,500 seeds per acre in our study, but weather greatly affected this. Several severe storms hit during the early growing season, and winds of 70+ mile-per-hour hit during the period of rapid growth for most of our corn. Corn fields throughout our area saw quite a bit of greensnap; the corn we planted 10 days later had no greensnap. Unfortunately, timing was not on our side. I took stand counts before harvest. Our final plant stands were 25,000 and 29,000 plants per acre (ppa) for the low and high seeding rates. We had approximately a 4,000-plant difference between the two seeding rates, which made a significant yield difference.
Our CFV nitrogen test had 135 total lbs/A of N yielded 198 bushels per acre (bu/A) at the low seeding rate, and 210 bu/A at the high seeding rate. Our YG approach with 170 lbs/acres total nitrogen yielded 206 bu/A at the low seeding rate and 213 bu/A at the higher seeding rate. We saw both a 12 bu/A and 7 bu/A advantage with the higher seeding rates in the CFV and YG systems. After subtracting the cost for higher seeding rates, the additional yield resulted in additional revenues of $23.48/A (CFV) and $5.80/A (YG). We used LH 5245 VT2 PRO, which has a semi-flex ear. This means that even at the low seeding rate of 25,000 ppa, that hybrid had the late-season ability to flex enough in ear length and kernel depth (weight) to make up for lost bushels. The question is, “Does it pay to plant at higher rates?” It did for us in 2018, but there’s a good chance our results will differ in 2019.
Results for LH 5245 VT2 PRO with planting populations at 15,000 ppa on the left (resulting in girth of 16 kernels and length of 38 kernels on the left-most ear) and 58,000 ppa on the right (girth 18, length 33 on the right-most ear).Cross Section split of LH 5245 VT2 PRO from Latham Hi‑Tech Seeds stress wheel research study 2018.
Our nitrogen test didn’t show a yield difference despite the 35 additional pounds in our YG approach. Given the abnormally high amount of rainfall and above-average growing degree units (GDUs) for the season, we likely saw an increased grain-fill period and some additional loss of nitrogen through leaching. Above-average temperatures and good soil moisture means we also likely had higher mineralization rates, so the soil may have saved us because this particular soil organic matter is 5.0 percent.
All things considered, our YG approach won out in terms of revenue this year, but will it hit the mark every year? Consistency is what we want to see when trying to manage such a variable nutrient in the soil. In the future we plan to expand our research on the CFV Nitrogen Advisor tool to bring meaningful information on seeding rates to our dealers and customers.
Join us this morning on understanding your yield variability. Phil Long helps us identify the types of variability and importance of knowing the difference. #AskTheAgronomist
The true armyworm – not to be confused with the fall armyworm – can pose a threat to corn stands and overall yield as an early season pest. Armyworm larvae are characterized by alternating light and dark bands. 
