Weeds

Field Observations Thru September 1

They are here!  Palmer Amaranth and Waterhemp are prevalent in MANY Knox County fields.  One female plant can produce 1,000,000 seeds.  If you find Palmer Amaranth or Waterhemp you should do whatever you can to prevent these devastating weeds from going to seed, including removing the entire plant from the field.

Continue to remain vigilant!  

Click here for tips on identifying pigweed, palmer and waterhemp.

Corn

Growth & Development

Most of the corn that I have seen this week is in either the R3 (Milk) or the R4 (Dough) growth stage.  Some of our early maturing hybrids have reached the R5 dent stage.

Scouting

Disease pressure throughout the county continues to be very low. Continue to scout for:

  • Foliar diseases – Gray Leafspot, Tar Spot, Northern Corn Leaf Blight.
  • Weed escapes (especially Palmer and Waterhemp).

Soybeans

Growth & Development

Most of the corn that I have seen this week is in the R6 (Full Seed) growth stage.  Some of the early maturity beans are entering the R7 (Beginning Maturity) stage soon.

Scouting

Disease pressure throughout the county continues to be very low.  As you continue to scout your bean fields, look for:

  • Foliar diseases – Sudden Death Syndrome, White Mold, and Frogeye Leaf Spot.
  • Insect feeding – Grasshoppers.
  • Weed escapes (especially Palmer and Waterhemp).

County Rainfall Update

Field Observations Thru August 25

Corn

Growth & Development

Last week I highlighted the R3 (milk) growth stage.  R4 is the next stage, occurring approximately 26 days after silking.

R4 – Dough

  • This stage is about 26 days after silking.

 

  • The kernel has thickened to a pasty (doughy) consistency from the earlier milky state (starch has continued to accumulate and kernel moisture content has decreased).
  • The embryo of the seed is growing while the kernels are just beginning to dry at the top (dent).
  • Kernels have accumulated 50 percent of their dry weight and have about 70 percent moisture.
  • Unfavorable environmental conditions or nutrient deficiencies still can result in unfilled kernels and “chaffy” ears.

Scouting

Disease pressure throughout the county continues to be very low. Continue to scout for:

Chaffy Ears

  • Foliar diseases
  • Weed escapes (especially Palmer and Waterhemp)
  • Head smut
  • European corn borer
  • Barren stalks, poor pollination
  • Nutrient deficiencies

 

Soybeans

Growth & Development

Soybeans are continuing to mature.  Recent rains will help with seed fill.  Last week I highlighted the R5 (Beginning Seed) growth stage.  R6 is the next stage, occurring approximately 10 days after R4.

R6 – Full Seed

R6 Full seed

Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf

 

  • Beans of many sizes can be found on the plant
  • Total plant pod weight is maximized
  • Large amounts of nitrogen are still being accumulated from the soil and remobilized to the seed
  • Root growth is complete between R6 and R7.

Scouting

As you continue to scout your bean fields, look for

  • Foliar diseases – Sudden Death Syndrome, White Mold, and Frogeye Leaf Spot.
  • Insect feeding – Grasshoppers.
  • Weed escapes (especially Palmer and Waterhemp).

Click here for tips on identifying pigweed, palmer and waterhemp.

County Rainfall Update

Weed of the week – Cocklebur

Every year it seems as if we have one weed that that hasn’t really been a problem for a while suddenly pop up everywhere.  This year Cocklebur wins the 2023 award for Comeback Weed of the Year!

Family:  Asteraceae (Composite family)

Life cycle:  Annual

Description: Erect plant reaching heights of 6 to 7 ft.  Stems are rough with dark spots.  Leaves are rough, triangular in shape with wavy or toothed margins and long petioles.  Inconspicuous flowers produce egg-shaped burs with two beaks at end. Seedling has long, fleshy cotyledons.

Seedlings:  The stem below the cotyledons (hypocotyl) is purple at the base and often green in the upper portion. Cotyledons are linear to oblong in outline, waxy, smooth, fleshy, thick, approximately 3/4 to1 3/4 inches long and usually no more than 1/2 inch wide. The first true leaves are opposite, while all subsequent leaves are alternate.

Roots:  Taproot

Stem: Mature stems are green, 1-4 ft. tall, highly branched, hairy, and flecked with maroon to black spots.  Ridges are present on the stem.  Upright hairs cause leaves to feel abrasive and gritty.

Leaves:  The first true leaves are opposite, all subsequent leaves are alternate. Leaves are triangular to ovate in outline, have stiff hairs, and are approximately 2 to 6 inches long. Leave are irregularly lobed with leaf margins that have relatively inconspicuous teeth. Leaves occur on long petioles and also have three prominent veins on the upper surface of the leaf that arise from the same point.

Flower/Seedhead:  Inconspicuous, greenish in color, arising from the area between the leaf petioles and the stems (axillary flowers) and at the ends of the erect stems (terminal flowers).

Special Identifying Characteristics:  The relatively large, linear to oblong waxy cotyledons helps to distinguish this weed in the early stages of development.  Additionally, the long-petioled triangular leaves, stems with maroon to black stem lesions, and the distinctive prickly cocklebur fruit are all features that help in the identification of this weed.In the early stages of development, this weed might be confused with Giant Ragweed (Ambrosia trifida), however the cotyledons of common cocklebur are much longer and more linear than those of giant ragweed. Spiny Cocklebur (Xanthium spinosum) is a closely related and similar species, however, unlike common cocklebur, this weed has very distinctive 3-parted spines that arise at the base of each leaf.

If you have a dog, you will now if you have cocklebur! 

Field Observations Thru August 18

Corn

Growth & Development

Corn development continues to vary throughout the county.  Last week I highlighted the R2 (Blister) growth stage.  R3 is the next stage, occurring approximately 20 days after silking.

R3 – Milk Stage

  • Occurs approximately 18‐20 days after silking.

  • The  kernel is colored yellow with the inside containing ‘milky’ white fluid.
  • Kernel moisture  content is approximately 80%
  • Starch is beginning to accumulate in the kernel.
  • Stress is not as severe at R3 as at R1; however, yield reduction can occur due to a reduction in the number of kernels that ultimately develop and to the final size and weight of the kernels.
  • Very little root growth occurs after R3.

Scouting

Disease pressure throughout the county continues to be very low.  At this stage of growth, with little to no disease pressure, and new crop corn under $5 can we justify at least $25 per acre for a fungicide application?

Read more on disease scouting here.

Soybeans

Growth & Development

Like corn, soybean development continues to vary throughout the county.  Beans are looking much better than they were a few weeks ago. Last week I highlighted the R4 (Full Pod) growth stage.  R5 (Beginning Seed) is the next stage, occurring approximately 10 days after R4.

  • Seed is 1/8 inches long in the pod at one of the four uppermost nodes on the main stem with a fully developed leaf .

  • Rapid seed filling begins, while root growth slows.
  • Dry weight and nutrients begin redistributing through the plant to the developing seed.
  • 50% defoliation can decrease yield by 15-17%.
  • Symptoms of many diseases, including white mold and SDS begin to show up at this growth stage.
  • This is a good growth stage to determine the severity of disease.
  • Treating most diseases with fungicides is not recommended at this time.

Scouting

All of the bean fields that I have seen this week look very similar to this one.  I am seeing very little (if any) disease pressure.  Current and projected weather conditions may change  this.  As you continue to scout your bean fields, look for Sudden Death Syndrome, White Mold, and Frogeye Leaf Spot.

Weeds

It’s that time of year when weeds are beginning to show their ugly heads above the soybean canopy in many fields.  During your scouting, if you find Palmer Amaranth or Waterhemp you should do whatever you can to prevent these devastating weeds from going to seed, including removing the entire plant from the field.

Click here for tips on identifying pigweed, palmer and waterhemp.

County Rainfall Update

Is it Pigweed or Palmer? – Hope it’s not Waterhemp!

It’s that time of year when weeds are beginning to show their ugly heads above the soybean canopy in many fields.  During your scouting, if you find Palmer Amaranth or Waterhemp you should do whatever you can to prevent these devastating weeds from going to seed, including removing the entire plant from the field.

Each of the last 3 weeks I have included a post highlighting the different characteristics of Pigweed, Palmer Amaranth and Waterhemp.  These posts also included a step by step video to help with the identification process for these weeds.

Depending upon the growth stage, identifying these weeds in the field can be challenging. If a seedhead is present, most weeds are easier to identify, including pigweed, palmer and waterhemp. If you have seen a mature palmer seadhaed you will never forget it!  (see pictures above)

When trying to differentiate between these weeds I look for the following 3 plant characteristics:

1.Hair

Pigweed has hair the others do not.  Rub the stem and leaves checking for a “rough” texture.  Palmer and waterhemp will be smooth.

 

2. Leaves

Long Lanceolate Leaves

Waterhemp has long, slender leaves (lanceolate). While pigweed and palmer are more oval in shape.  Pigweed is wider in the middle and palmer is wider near the base of the leaf (this is usually hard do differentiate in the field).

 

 

3. Petiole

The petiole is the part of the plant that connects the leaf to the stem.  The petiole on palmer plant is as long or longer than the leaf.  Pigweed and waterhemp have much shorter petioles (often less than 1/2 the length of the leaf).

These weeds are here, they best way to prevent the spread is by preventing them from developing a seedhead.  One mature female plant  can produce up to 1,000,000 seeds.

 

Weed Identification Videos

 

If you  are still not sure about the identification, do not hesitate to call 740-397-0401) or send (barker.41@osu.edu) me a picture!!!

Weed of the week – Palmer Amaranth

Palmer Amaranth

Family: Pigweed, Amaranthaceae.

Life cycle: Summer annual.

Description: An erect summer annual that may reach 6 1/2 feet in height. Palmer amaranth closely resembles many other pigweed species,

Seedlings:  Stems below the cotyledons (hypocotyls) are without hairs (glabrous), and are often red in color. Cotyledons are narrow and green to reddish in color on the upper surface. Lower surfaces of cotyledons have a reddish tint. First true leaves are alternate, ovate in shape, and are slightly notched at the tip of the leaf blade

Roots: Taproot that is often, but not always, reddish in color

Stem: One central stem occurs from which several lateral branches arise. Stems are without hairs and can appear glossy.

 

 

Leaves: Alternate, without hairs (glabrous), and lance-shaped or egg-shaped in outline. Leaves are 2 to 8 inches long and 1/2 to 2 1/2 inches wide with prominent white veins on the undersurface. Leaves occur on relatively long petioles.

Flower/Seedhead: Small, green, inconspicuous flowers are produced in dense, compact, terminal panicles that are from 1/2 to 1 1/2 feet long. Smaller lateral flowers also occur between the stem and the leaf petioles (leaf axils).  Male and female flowers occur on separate plants. Each terminal panicle contains many densely packed branched spikes that have bracts that are 3 to 6 mm long; can produce 500 thousand to 1 million seeds per plant.

Similar Plants: Loosely resembles many other pigweed species. Palmer’s petioles are as long or longer than the actual leaf. This plant is hairless and has elongated seed heads. Leaves are typically more diamond shaped than other pigweed species, and occasionally has one hair at the tip of the leaf.

The Problem is……..Palmer amaranth is one of the most difficult weeds to control in agricultural crops.  It developed a major glyphosate resistance problem in the southern US from 2006-2010, and has been spreading in the midwestern US since, causing crop loss and increases in weed management costs. Characteristics that make it a successful annual weed include: rapid growth rate; wide window of emergence (early May through late summer); prolific seed production (upwards of 500,000 seeds/plant); tendency to develop herbicide resistance; and tolerance to many post-emergence herbicides when more than 3 inches tall.

Weed of the week – Common Waterhemp

Common Waterhemp

Family: Amaranthaceae (Pigweed)

Lifecycle: Annual

Description: Erect plant up to 8 feet tall.   Leaves are glossy, alternate, ovate to lanceolate.  A dioecious species, thus plants are either male or female.  Highly variable in shape and color, ranging from yellowish green, dark green to reddish green.  Stems are hairless.

Seedlings: Seedling leaves are oar shaped, first true leaves appear lance-shaped and have a minute notch at the tip of the leaf.

 

Roots: Fibrous root system from a well developed tap root.

Stem: Stems are brightly colored and range in color from murky red or pink to green. Stems are without hairs and appear glossy.

 

Leaves: Leaves are without hairs are oval to lanceolate in shape and have a waxy appearance. Common waterhemp leaves are alternate and measure 1-15cm in length and 0.5-3.0cm in width.

Flowers/Seed head: Common waterhemp is dioecious having male and female parts on seperate plants. Flowers and bracts are green to reddish pink and have spikes that are densely packed.

Special identifying characteristics: A long petiole, Waxy and hairless stems, and leaves are prime characteristics of common waterhemp. This summer annual produces a large seedhead and commonly reaches 6 feet in height. Seeds are difficult to see with the naked eye and measure 1mm in diameter.

Weed of the week – Pigweed

Redroot Pigweed

Family: Amaranthaceae

Lifecycle: Annual

Description: An erect summer annual that may reach 6 1/2 feet in height. Redroot pigweed is an abundant seed producer that may be found throughout the United States in horticultural, nursery, and agronomic crops, landscapes, roadsides, and also in pastures and forages.

Seedlings: Hairy, often red in color, especially near the base. Cotyledons are narrow and green to reddish in color on the upper surface. Lower surfaces of cotyledons have a reddish tint. First true leaves are alternate, ovate in shape, and are slightly notched at the tip of the leaf blade (apex). Hairs may occur on the leaf margins and along veins, especially along the lower leaf surfaces.

Roots: A shallow taproot that is often, but not always, reddish in color.

Stem: Stout, erect, branched, and reaching 6 1/2 feet in height. Stems usually have short hairs, especially near the upper portions of the plant.

 

Leaves: Alternate, ovate in outline, with petioles that reach 1/2 inch in length. Leaves have wavy margins and hairs that occur along the veins of the lower leaf surfaces.

 

 

Flowers: Small, green, inconspicuous flowers are produced in dense, compact, terminal panicles that are approximately 3/4 inch wide and from 2 to 8 inches in length. Smaller inflorescences also occur between the stem and the leaf petioles (leaf axils). Male and female flowers occur on the same plant (monoecious). Each terminal panicle contains many densely packed branched spikes that have bracts that are 4 to 8 mm long and 2-3 times longer than the sepals.

Special identifying characteristics: Dense, compact terminal panicles and relatively tall plants with alternately arranged leaves. Redroot pigweed is often confused with other similar pigweed species. For example, Smooth Pigweed (Amaranthus hybridus) is very similar, however this species has terminal panicles that appear less dense, compact, and bristly than those of redroot pigweed. Additionally, the bracts of smooth pigweed are only slightly longer than the sepals, unlike those of Redroot Pigweed (Amaranthus retroflexus). Palmer Amaranth (Amaranthus palmeri) also resembles redroot and smooth pigweed, however the terminal panicles of this species are much longer and narrower than the other pigweed species. These species may also resemble Common Lambsquarters (Chenopodium album) in the cotyledon stage, however common lambsquarters cotyledons often have a mealy gray cast, and the first true leaves are alternate, unlike any of the pigweed species.

Click here to watch pigweed ID video

 

Preharvest Intervals for Soybean Herbicides Applied Postemergence

Preharvest intervals indicate the amount of time that must elapse between the herbicide application and crop harvest. Failure to observe the preharvest interval may result in herbicide residue levels in the harvested portion of the crop in excess of established limits. Also, livestock grazing or foraging treated soybean is not allowed on the labels of many postemergence soybean herbicides. Table 1 contains information regarding preharvest intervals and grazing restrictions for a number of postemergence soybean herbicides.

Table 18 from the OSU Weed Control Guide shows the PHI and feeding restrictions for postemergence soybean herbicide applications.

Field Observations Thru July 14

Alfalfa

2nd cutting is well underway.  Potato leafhoppers are very active. If you haven’t cut yet, continue to monitor, where damage is increasing, cut as soon as weather permits.

Click here for alfalfa insect scouting calendar

Click here for more information on Potato Leafhopper

Corn

Our corn growth varies greatly throughout the county. Some fields are beginning to tassel and some field are at V8.

V12 to V13 – Six weeks after the plant emerges, V12 begins. Moisture or nutrient deficiencies may reduce the potential number of seeds, as well as the ear size, seriously. These two components of yield have key development during the period from V10 to V17. The length of time for the plant to develop through these stages affects harvestable yield.

Early maturity hybrids normally progress through these stages in less time and have smaller ears than later hybrids. Higher plant populations are needed for earlier hybrids to produce grain yield similar to normal-maturity hybrids in the adapted region. Cultivation of plants at this time will destroy some of the plant roots. Brace roots are developing from the fifth node and the first above-ground node.

V14 to V15 – Seven weeks after the plant emerges, V14 begins. The corn plant at V15 is only 12 to 15 days (around one to five V stages) away from R1 (silking). This vegetative stage is the most critical period of seed yield determination. The number of ovules that develop silks, and thus the number of kernels, is being determined. Any nutrient or moisture deficiency or injury (such as hail or insects) may seriously reduce the number of kernels that develop.

The tassel is near full size but not visible from the top of the leaf sheaths. Silks are just beginning to grow from the upper ears. Upper-ear shoot development has surpassed that of lower ear shoots. A new leaf stage can occur every one to two days.

Brace roots from the sixth leaf node are developing, and the permanent roots have continued to elongate and proliferate, eventually reaching a depth of about 5 to 8 feet and spreading several feet in all directions. In some hybrids, brace roots also will develop from the eighth and ninth leaf nodes or even higher. Some corn plants in North Dakota may only develop 16 leaves.

Critical corn growth stages

Table 5. Postemergence Herbicides in Corn – Grasses

Table 6. Postemergence Herbicides in Corn – Broadleaves

Soybeans

Soybeans are starting to look a little bit better, however, there are still a lot of “yellow” beans throughout the county.  Two possible reasons are Yellow Flash and Soybean Cyst Nematode.  Other possibilities are seedling diseases and water-logged roots, more information on these topics next week.

After planting, the second biggest challenge we face is timely weed control.  If you haven’t already made a postemergence application, it might be time to check your fields.  Most beans (and weeds) are at stage that might warrant an application.  The links below will contain OSU Herbicide rating for postemergence applications.

Soybean Postemergence Weed Control – Grasses

Soybean Postemergence Weed Control – Broadleaves

Soybean Growth & Development – R1: Beginning Bloom

 

  • Open flower at any node on the main stem
  • Flowering begins at 3rd to 6th node (V6 to V10 stage)
  • Flowering period is 3 to 4 weeks
    –Begins ~6 to 8 weeks after emergence
    – Peaks R2 to R3; ends ~R5
  • Vertical root growth rates increase rapidly
    – As much as 1.3 to 3.2 in/day

Wheat

Wheat harvest has come to an end and most of the straw is in the barn.  From what I hear, wheat yields were pretty good with little to no disease issues.

If you removed the straw, remember to account for the additional fertilizer removal when planning for fertilizer needs next year.  Read more here.

Double crop beans have been, or are being planted now.  Click here for the Double Crop Soybean Production Guidelines from Dr. Laura Lindsey.

Misc. – Something you don’t see everyday.

I can honestly say that I have never seen one of these before! Click on the picture to see the video. If you know what it is, put your answer in the comment section.  Be sure to check back next week for the answer!

… AND THE ANSWER IS – Horsehair Worm

https://entomology.ca.uky.edu/ef613

County Rainfall Update

Corn Water Requirements

Soybean Water Requirements