Cornbelt Update: Crop Scouting – July 13 2015

This excerpt is from Cornbelt Update July 13, 2015 vol 16 no 47. Subscribe to Cornbelt Update and receive 52 weekly updates of timely, relevant information and data for only $75 a year. Contact Stu Ellis at StuAgNews@aol.com

Crop scouting refreshers are provided by TX and TN entomologists who say scout early and often, particularly beans which are most susceptible to insect damage from full bloom to maturity. Visually inspect the edges, middle and corners of their fields, and walk the field diagonally. Monitor fields for stand loss, defoliation and significant changes in insect density. Insects should not be treated until thresholds are reached, preserving beneficial insects. Use a sweep net during scouting, and sweep in a figure-eight pattern while walking down the row.

Soybean Plant with Mystery Root Disease

Soybean Plant with Mystery Root Disease


Crop scouting #1. Just when you really don’t need another soybean disease, a new one has appeared which agronomists are calling a soybean “mystery root disease.” It has been identified in a limited area of AR, but should be on a Cornbelt scouting checklist. Plants appear stunted and the leaves are yellow between the veins. Some plants are dead or exhibit yellow foliar symptoms with necrotic “flashing,” and if the taproot is extracted and still attached to the plant, it is dead or dying, soft, and black. It is not sudden death syndrome.

Soybeans Yellow Leaves

Soybeans Yellow Leaves


Crop scouting #2. Soybeans are supposed to be yellow, but not leaves, and many farmers are finding yellow leaves, which KS St. agronomist Dorivar Ruiz Diaz could result from several issues. Wet soils delayed development of rhizobial nodules, resulting in N deficiency, a situation that may change as soils dry out. Wet soil with a high pH may also create a temporary problem with iron chlorosis (green veins in yellow leaves). Another potential is K deficiency, which shows up late in the season.

Soybeans Septoria Brown Spots

Soybeans Septoria Brown Spots


Crop scouting #3. Due to wet, warm weather septoria brown spot is appearing in minimum till fields of continuous beans. Spots begin on lower leaves and develop later on upper leaves. Small dark brown spots develop on both surfaces of leaves, and may grow together to create irregular brown patches. Minor yield loss can be managed with rotation to non-legume crops and tillage, with fungicides warranted under some conditions.

Soybean Yellowing

Soybean Yellowing


Crop scouting #4. The same may be said for soybeans that are yellowing at an early stage in their maturity process. With soybeans needing to generate nitrogen, and doing that with their nodules of nitrogen-fixing bacteria, those yellow plants may have been in saturated soil long enough for the bacterial to die and the nodules to be ineffective. It is possible for new nodules to be generated and resuming their work after soils dry out.

Bugs In Your Soybeans

Bugs In Your Soybeans


Crop scouting #5. If you have bugs in your beans, they may have begun their life on a weed in the soybean field. TX entomologist Mo Way says, “Pests often build up on alternative host plants, such as weeds, and then bail off onto soybeans when they start to bloom. Some insect populations may have up to three generations built up on weeds before the soybeans are vulnerable.” He and others urge weed control to avert any increase in insect populations.

Northern Corn Leaf Blight

Northern Corn Leaf Blight


Crop scouting #6. Foliar disease symptoms are exploding in many cornfields, including gray leaf spot and northern corn leaf blight (right), both of which like wet conditions, particularly if temperatures are within the favorable range like they have been (70 to 90 F for GLS and 66 to 80 F for NCLB). While they typically show up after pollination, they are more responsive to environmental conditions this year and have been attacking corn at various stages of development. Fungicide treatments are
recommended if hybrids are susceptible.

Pinholes Left by The Larvae of The European Corn Borer

Pinholes Left by The Larvae of The European Corn Borer


Crop scouting #7. With the increased acreage of non-GMO corn, comes the increased prevalence of European corn borer. Pinholes left by the larvae are increasingly being found, and just because you have used a Bt hybrid for a number of years does not mean they will avoid your cornfields in a year when you cut back on the trait to save expense. Anecdotal reports indicate some fields may have 75% of the corn plants infested with corn borers. Scout for 2nd generation.

Corn Rootworm

Corn Rootworm


Crop scouting #8. Have you been digging corn roots to gauge performance of your corn rootworm control strategy? You might have found success, but was it your strategy or was it environmental conditions. If CRW larvae hatch in saturated soils, they have difficulty finding corn roots, since the roots are not taking in oxygen and emitting carbon dioxide. The larvae follow CO-2 emissions from the roots to know where to burrow and find root tissue.

Corn Self-Consuming Nutrients

Corn Self-Consuming Nutrients


Crop scouting #9. Donald Trump has not been firing your corn, but a combination of factors may be causing it to mature before it is ready, or in the alternative dying before it is matured. Despite all of your best efforts at N-application and placement, water-induced leaching and poor nutrient uptake by roots have combined to cause the corn plant to begin consuming its own nutrients to fill the grain on the newly-formed ear. That results in early tissue death as those
nutrients are translocated to other parts of the plant.

Water-Logged Corn Fields

Water-Logged Corn Fields


Crop scouting #10. As you walk through your water-logged corn fields which are yellowed and rated poor, will supplemental nitrogen save that crop or be a waste of money? Purdue’s Bob Nielsen says poor root growth is your current problem, but, “As soils begin to dry, new root growth begins near the soil surface and “follows” the downward drying of the soil with time. It is the rate and extent of that fresh root development that largely determines whether a waterlogged field will recover “strongly” or not.” Leaves need sunlight to spur the root growth, and cloudy, cool days are not friendly. He urges patience
and says, “It may recover well enough to produce an acceptable grain yield at the end of the season. Much depends on what weather we receive from this point forward.”

This excerpt is from Cornbelt Update July 13, 2015 vol 16 no 47. Subscribe to Cornbelt Update and receive 52 weekly updates of timely, relevant information and data for only $75 a year. Contact Stu Ellis at StuAgNews@aol.com

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