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London, UK
rbutrus
May 30, 2020 10:28 AM CST
Hi, as shown in the photos, the bottom of my leaves/stem are turning yellow. I think it's some sort of insect causing this. Any ideas? How should I control it?
Thumb of 2020-05-30/visitor/ddb09a


Thumb of 2020-05-30/visitor/bacaba

[Last edited by rbutrus - May 31, 2020 3:10 AM (+)]
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Name: one-eye-luke US.Vet.
Texas (Zone 8a)
Quitter's never Win
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oneeyeluke
May 31, 2020 3:09 AM CST
I don't think you have anything to worry about at this time. The plant is just adapting to the environment and is not a problem at this time. If you think you have a problem with pests you need to get a magnifier and get a close up look at the areas you are worried about. The most important thing for corn is that you plant enough corn and close enough to insure that they are properly pollinated.
NOT A EXPERT! Just a grow worm! I never met a plant I didn’t love.✌
London, UK
rbutrus
May 31, 2020 6:57 AM CST
oneeyeluke said:I don't think you have anything to worry about at this time. The plant is just adapting to the environment and is not a problem at this time. If you think you have a problem with pests you need to get a magnifier and get a close up look at the areas you are worried about. The most important thing for corn is that you plant enough corn and close enough to insure that they are properly pollinated.


More and more are falling over. It's like they're being eaten at the stem! Look at this:


Thumb of 2020-05-31/rbutrus/4002ad

Name: stone
near Macon Georgia (USA) (Zone 8a)
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stone
May 31, 2020 10:43 AM CST
Are you sure it isn't a fungus? Or a problem with the roots? Too much rain? Too much water from the hose?

If it was a bug or caterpillar, You should have seen it by now.
[Last edited by stone - May 31, 2020 10:43 AM (+)]
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Name: Dr. Demento Jr.
Minnesota (Zone 3b)
RpR
May 31, 2020 2:28 PM CST
Root & Stalk Rots

Root and stalk rots are among the most destructive corn diseases. They are caused by various species of fungi, including Diplodia zeae, Fusarium species, and Colletotrichum graminicola. Infected corn stalks fall over (called lodging) and losses result from unharvested ears and poor ear development on infected plants. Some of these disease-causing organisms enter through the roots and move up into the stalk, while others enter the stalk directly at the nodes. Insect damage can increase infection by wounding the plant and allowing fungi to enter.

Identifying and Managing Stalk Rots

Stalk rots cause damage and yield loss in many corn fields across North America each year. Depending on location, stalk rot organisms may include anthracnose, Gibberella, Diplodia or Fusarium, all of which survive in corn residue and are spread to the next crop by wind and/or rain. Stalk rots can reduce corn yield by killing the plant before physiological maturity. They can also cause plant lodging, increasing harvest losses and impeding harvest progress. If ears from a fallen plant come in contact with the ground for an extended period, grain quality may also be reduced. Each of these 4 diseases is briefly explained and shown below, to help growers identify them correctly. Identifying disease issues at harvest makes growers better prepared to select hybrids for the coming season.

Anthracnose Stalk Rot
Gibberella Stalk Rot
Diplodia Stalk Rot
Fusarium Stalk Rot
Reducing Stalk Rots and Lodging
Pioneer Research for Stalk Rot Resistance
Anthracnose Stalk Rot

Anthracnose is the most common stalk rot disease faced by corn growers worldwide, with yield losses reaching as high as 40% as a result of reduced ear size and stalk lodging. Infection is favored by warm temperatures (70-80 F) and high humidity. Anthracnose has both a leaf and a stalk phase in corn. The infection can spread from leaves to stalk, or the stalk may be infected through the roots or base of the plant, or through insect cavities or other wounds in the stalk. Shiny black blotches which often coalesce are a distinguishing characteristic of anthracnose stalk rot. Removing the leaves and leaf sheaths from the lower stalk is the best way to inspect for anthracnose. Splitting the stalk reveals degenerated pith tissue, often with only the vascular bundles remaining. Diseased tissue is usually dark gray to brown in color.

Gibberella Stalk Rot

Another stalk rot common in most corn growing regions is Gibberella. Wet, cool weather during early ear-fill is conducive to disease development. Infection occurs through the roots or leaf collar of the plant and spreads to the stalk as the plant is weakened by stress. Rotting generally affects the roots, crown and lower internodes. Gibberella stalk rot can best be identified by splitting the stalk. The pith inside is disintegrated and characterized by a pink or reddish color. On the outside of the stalk, small superficial black spots (perithecia) are often evident.

Diplodia Stalk Rot

Diplodia and Gibberella have a similar disease cycle both thriving in warm, wet weather 2 to 3 weeks after pollination. Diplodia stalk rot may first reveal itself when affected plants die suddenly during mid- to late ear-fill. Upon examination, dark brown lesions can be found extending in either direction from the node. Small black spots (pycnidia) may develop just beneath the stalk epidermis near the nodes. The black dots are not easily rubbed off, which distinguishes Diplodia from Gibberella. Diplodia results in rotted stalks that are disintegrated and discolored, allowing the stalk to easily break. The discoloration is brownish in appearance, not pink like Gibberella.

Fusarium Stalk Rot

Fusarium infection is favored by warm, wet conditions following stress. It invades through the roots, wounds in the stalk or leaf scars. This disease can colonize any part of the plant and is commonly found on corn ears. The earliest symptoms of Fusarium stalk rot are wilted plants in the field. Infected plants take on a grayish-green hue, then turn tan. Outward symptoms of the disease are indefinite discolored patches on the lower internodes. Stalks feel spongy as the pith disintegrates, leaving vascular strands intact. A whitish-pink to salmon discoloration of the remaining pith and vascular strands may be observed when stalks are split. In addition, roots take on a reddish-pink discoloration.

Reducing Stalk Rots and Lodging

Stalk rots cannot be entirely prevented but their effects can be reduced through good management practices. The following practices can help reduce stalk rot, lodging and harvest losses:

Soil Fertility. Test soils regularly and apply nutrients based on soil test results and yield goals. Be sure potassium levels are adequate, and manage nitrogen to prevent losses and ensure its availability throughout plant uptake.

Crop stress. Crop stress is never eliminated but can be reduced with good crop, soil and water management. Excessive plant populations increase stress and stalk lodging. Poorly spaced or "clumped" plants create a high population microenvironment similar to overplanting. Maintain planter and planter meters properly and do not exceed manufacturer's suggested ground speed. Calibrate planter meters for optimum plant spacing and monitor rates carefully when planting. Compaction is one of the primary causes of crop stress, and may persist for several years. Avoiding compaction and maintaining soil quality are keys to reducing crop stress. Proper irrigation management is critical to minimizing crop stress in arid regions.

Insects. Manage insects such as corn borer and fall armyworm to prevent plant wounds and stress.
Corn Residue. Stalk rot pathogens overwinter in corn residue. Occurrence and intensity of stalk rots is sometimes related to the amount of inoculum present. A prime example is anthracnose which is prevalent in continuous corn and no-till fields. Rotation to a non-host crop such as soybeans is recommended to reduce corn residue and stalk rot. Disking or otherwise incorporating residue may also be beneficial in some fields. Reduction of stalk rots must be weighed against the advantages of soil conservation and maintaining soil carbon levels when deciding whether to till.
[Last edited by RpR - May 31, 2020 2:36 PM (+)]
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