ASK THE AGRONOMIST BLOG

Stine’s Ask the Agronomist blog is your source to the latest information from our expert team, including advice and insight on field practices, product recommendations, planting and harvest updates, new technologies, crop management, innovative research and information about how to keep your farm operation running smoothly year round. 

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    Part Three: Herbicide Issues to Look for in a Late Planting Year (Like This One)

    July 17, 2019

    Posted by Stine Seed in Crop Management

    Next up in our series of what to be on the lookout for in a late planting year (like this one), we discuss why plants are growing slowly and what chemicals are showing a greater crop response this year.

    Why are plants growing slowly? And why are chemicals showing a greater crop response this year?
    In reality, these are two separate issues that are closely related. Slow-growing plants in many areas of the country are not a result of subpar seed, fertility or any other input but rather poor environmental conditions. Many areas of the country are too wet, which causes saturated soils.  Water drives out the air in the pores of the soil and, in turn, leads to a lack of oxygen. Oxygen is required for photosynthesis and for microbial activity, such as nitrobacteria, which make nitrogen available for soybean nodulation. 

    Some areas are too dry, and this leads to a lack of soil solution bringing nutrients to plants through mass diffusion, so plants may show signs of nutrient deficiency. Adding nutrients is not necessary, as these plants will either grow to interact with available nutrients or soil moisture (from rain) will bring the nutrients to the plants. In both cases, this can lead to slow-growing, chlorotic plants.

    The second issue has to do with why we are seeing a greater crop response from traditional chemistries that are used annually. As plants grow at a slower pace, all the functions of life (metabolic) are slowed as well. We might think of this in terms of when we are sick with the flu, we tend to have less energy and have less of an appetite than when we feel 100 percent. Some of the chemistries that we have seen issues with are listed below.

    *Note: Cool and wet early-season growth conditions will favor slow plant metabolism of the pre-emerge herbicides. Warmth and humidity with fast-growing conditions in early summer will affect the plants when applying post-emerge herbicides. We have seen herbicide injury in corn and soybeans that have shown up in the following:

    Photosynthesis inhibitors or Group 5 mode-of-action herbicides. Active ingredients include Metribuzin and Atrazine, which have been applied in slow, cool-growing conditions. The soils that have been most affected are high pH or sandy soils. Leaves or the whole plant may turn yellow and stunted, with the veins remaining green.

    Pigment inhibitors and mainly the Group 27 site of action. Consists of products like Balance Flex®, Callisto®, Impact® and Laudis®. Leaves will become chlorotic or have a bleached white banded appearance and can become necrotic. Usually seen on the older leaves, and most plants grow out of it, but slow-growing conditions could lead to yield loss or even death of individual plants or field areas.

    ALS inhibitors or the Group 2 site of action. Products include First Rate®, Python® and Hornet®. They usually cause the beans to have reddish veins on the underside of the leaf with some yellowing and stippled leaves. These products can lead to bottle brushed roots in both corn and soybeans. These products can carryover in the soil from one season to the next.

    As the post-applying season gets into full swing, you may see more damage from the following:

    Cell membrane inhibitors, mainly the Group 14 site of action. This includes products like Cadet®, Flexstar®, Cobra®, Sharpen®, Authority® and Valor®. Applied pre-plant, these products can expose the hypocotyl or cotyledons to high rates on soil surface or rain splashed onto the stems. This can cause plant loss or brittle stalks later in season. Post-applied herbicides cause bronzing and speckling of leaves if sprayed too late in the season. Carryover can become an issue if dry conditions persist late into the growing season.

    Finally, the one herbicide that growers especially need to be on the lookout for:

    Plant growth regulators. This is a Group 4 site of action that includes active ingredients Dicamba, 2,4-D and Clopyralid (Stinger®). Symptoms may include twisting and downward bending of stems. You may also see cupping and curling of leaves or buggy whipping of corn plants. Corn can become brittle, and green snap is definitely a concern. There has also been a lot of leaf burn lately due to certain surfactants added to post-applied herbicides. This is mainly because of spraying during the heat of the day with high humidity, so make sure you are following the label rates of surfactants. Most plants will grow out of this with a favorable extended weather forecast.

    Management Tip: In all of these instances, an improvement in growing conditions will enhance the plant’s ability to metabolize these herbicides and will, therefore, improve the appearance of the plants in question. Normal fertility practices should be maintained, so if you plan to side dress with supplemental nitrogen or micronutrients, procedures should be followed according to soil samples and plant nutrient requirement according to yield goals.

    For questions, please contact your local Stine sales agronomist.

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    Part Two: Insects to Watch for in a Late Planting Year (Like This One)

    July 11, 2019

    Posted by Stine Seed in Crop Management

    Late planting and preventive plant acres will bring new challenges to agriculture in 2019, which is why we need to stay diligent and do our best to plan ahead. Last week we discussed diseases to scout for this growing season, this week we’re continuing our conversation but exploring insect pressure. Here are some tips for scouting symptoms of insect activity in growing crops.

    What issues will delayed planting, slow growth and development cause for the 2019 season? 
    While we covered this question in more detail last week, it’s important to remember that delayed planting will ultimately lead to delayed harvest with decreased yields. It will also lead to a greater prevalence of insect pressure.

    Why more insect pressure?
    The issue is not so much that insect pressure is necessarily higher, but there are two critical factors that will exacerbate its effects this growing season:

    1. Less margin for error from decreased yields due to the late-planted crops. Knowing the insect species, growth habit and potential damage as well as diseases they may vector to the crop will become more important this year.
    2. The second issue is having more green tissue growing throughout the “insect season” due to late planting, which may lead to more potential issues. Plants will mature at a slower pace due to cooler, wetter conditions in their growing environment, so we may have to weigh decisions on treating insects that we normally wouldn’t worry about.

    So how do we determine when to spray?  This information from Iowa State University provides guidance:

    “The most effective way to make treatments decisions for pests with chewing mouthparts (e.g., Japanese beetle, bean leaf beetle, caterpillars, and grasshoppers) is to estimate defoliation…Replicated data over multiple growing regions consistently shows economic thresholds for soybean are 30% in the vegetative stages and 20% in the reproductive stages. This threshold applies to the entire field. Sometimes these pests cause significant injury along field margins and perimeter treatments may be more cost effective if practical.”

    Determining Percentage Defoliation of Soybean Leaves
    Gather 10 to 15 trifoliates from random plants, making sure to pick the first from the bottom of the plant, the second from the middle and the third from the top, then repeat that process. Choose the worst defoliated leaf from each trifoliate. Repeat this process in three to four areas of the field and then estimate the percentage of damage for the entire field. For reproductive damage, choose and estimate pods. 

    Northern Region Insects (Corn)
    Wireworms
    White grubs
    Black and dingy cutworms
    Armyworm
    Corn earworm

    Southern Region Insects (Corn)
    Japanese beetles
    Corn earworm
    Western bean cutworm
    European corn borer (conventional hybrids)

    Management Tip
    In corn, look out for root and stalk feeding, silk clipping and grain feeding. For growers who have planted conventional hybrids, watch for boring insects and be ready to harvest early if you have damaged fields. Spraying insects can be tricky because they are able to move and find protection.

    Northern Region Insects (Soybeans)
    Aphids (leaf feeder)
    Bean leaf beetle (leaf feeder, also vectors diseases)
    Soybean gall midge (root and leaf feeder, may vector diseases)
    Thistle caterpillar (leaf feeder)
    Soybean podworm (pod feeder)

    Southern Regions Insects (Soybeans)
    Aphids (leaf feeder)
    Grasshoppers (leaf feeder)
    Stink bugs (pod feeder)
    Soybean podworm (pod feeder)

    Management Tip
    In soybeans, watch for leaf feeding and pod feeding. Leaf feeding can be deceiving to the eye when it comes to the extent of damage. Pod feeding insects will cause more significant damage and should be given priority. Utilize local extension service traps for moth flights, egg hatches, etc. Know the enemy that threatens your crop. Remember, 30 percent vegetative defoliation is the economic threshold for chewing insects damaging leaves, and 20 percent pod damage is the economic threshold from piercing and sucking insects. Presence of insects does not mean treatment is warranted. Only when the population becomes unmanageable and economically destructive is treatment necessary.

    For more information, contact your local Stine regional sales agronomist or university extension office. Stay tuned next week for Part Three of our series as we explore chemicals showing good crop response in corn and soybeans.

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    Diseases to Watch for in a Late Planting Year (Like This One)

    July 02, 2019

    Posted by Stine Seed in Crop Management

    This tough growing season will not leave us soon enough. The disease triangle is setting up with the cool and wet conditions we’ve had. The three elements of the disease triangle are a host plant (corn or soybeans in this case), the right environment and a pathogen. This triangle sets the stage for diseases to flourish.

    The best way to stay ahead of diseases is to scout and look for symptoms and/or insect activity in growing crops. In addition, there are times when sending plant samples to labs for testing will be necessary. In many situations, especially early plant growth stages (through V6 in corn and 3-4 trifoliates in soybeans), it is best to dig and send whole plant samples. The lab can then examine the whole plant from roots to foliage.

    Late planting adds another dimension to the disease triangle because plant maturities are pushed back farther into the summer. With much more green plant material available, diseases continue to attack plants. If cool, wet conditions continue into summer, this will slow growth habits and make younger plant tissue even more vulnerable.

    So, what issues will delayed planting, slow growth and development cause for the 2019 season?  This question pops up every year in areas that experienced a wet spring. However, this year, the wet area encompasses such a large swath of the central U.S., we should consider all of these potential hazards:

    Delayed harvest with decreased yields

    • With late-planted crops, we know yields decrease but harvest can also be delayed in scenarios where cooler, wetter conditions prevail past normal dates.
    • Greater prevalence of insect pressure
    • Yields can also decrease due to other factors
      • Nitrogen loss
      • Greater prevalence of disease pressure
      • Greater prevalence of insect pressure

    Less vigorous plants

    • Due to saturated soils, oxygen can be depleted from soils
    • Oxygen is necessary for plant respiration
    • Plants deprived of oxygen may grow more slowly and be less healthy

    We will discuss these issues in greater detail over the coming weeks to help you prepare for the worst possible scenarios and protect this year’s crops. We will break our discussion into issues to watch for in northern and southern latitudes for your convenience.

    A word about nitrogen
    Nitrogen loss is a concern in all areas every year, especially when we have excess moisture.  Nitrogen is mobile within the soil and therefore has the ability to leach through the soil profile with moisture or be carried off fields with erosion. However, nitrogen loss may not be the only factor contributing to yellow, stunted plants. Cool growing conditions combined with a lack of sunlight contributes to slow growth, poor photosynthesis and stunting. Nitrogen may be available, but plants may not be accessing the depth the nitrogen has moved to.

    Management Tip:  Compare current soil samples from 6-, 12- and 24-inch depths to applied nitrogen to see if the nitrogen has been driven deeper in soils. As plants grow, roots will eventually reach these depths and interact with soil nitrogen. Supplemental applications may be made in the intervening periods, but at lower rates to sustain the plants until they reach deeper sources of nitrogen.

    Corn Diseases (Northern Region)
    Root rots from Pythium, Fusarium and Rhizoctonia
    Tar spot
    Common and southern rust
    Eyespot
    Northern corn leaf blight

    Corn Diseases (Southern Region)
    Anthracnose leaf spot
    Gray leaf spot
    Eyespot
    Goss’s wilt (bacterial infection)

    Crazy top is a distortion or stunting of the plant with a bushy tassel appearance and excessive tillering caused by prolonged flooding or intense rain periods. No treatment is necessary.

    Stalk rots will be a major concern with saturated fields and flooding. These will be covered in a later blog.

    Management Tip: All of these diseases are controllable through timely identification and treatment with fungicides in a timely manner. However, treatment is not always necessary based on timing and level of infection. Goss’s wilt will not respond to treatment as it is a bacterial infection. Therefore, proper identification is key at an early stage along with severity and attention to future potential for disease spread.

    Soybean Diseases (Northern Regions)
    White mold
    Frogeye leaf spot
    Septoria brown spot
    Bacterial leaf blight

    Soybean Diseases (Southern Regions)
    Poor emergence or slow-growing soybeans 
    Bacterial leaf blight
    Septoria brown spot
    Frogeye leaf spot

    Management Tip: Frogeye leaf spot is the only issue on this list that can be effectively treated this year. Septoria brown spot rarely makes it to the upper canopy to do yield-robbing damage; however, if it does infect the upper third of the canopy, treatment may be necessary. Fungicide selections should always include Strobilurin and Triazole (curative and preventative).