IPM

Purple Fields Everywhere

While driving through Knox County looking at wheat fields last week, I noticed many, many “purple fields”.  The purple plants are a combination of purple deadnettle and henbit.  This time of year these plants (weeds) can be found in fields, roadsides, gardens, flowerbeds and landscaped areas.

These winter annuals begin to develop in fall, form a small rosette of leaves that overwinter, and complete their development in spring, forming flowers and seeds. They die in late spring and early summer after setting seed.

Purple Deadnettle vs. Henbit

Purple Deadnettle

Purple deadnettle and henbit belong to the mint family and thus have a square stem.  Both have two-lipped tubular flowers, opposite leaves. The leaves of purple deadnettle at the apex of the stems are tinted purple and fade to green as they mature. The leaves have a short petiole (stem) and are heart- or triangular-shaped with rounded teeth on the leaf margin.

 

Henbit

The leaves of henbit are more rounded and scalloped and clasp the stem directly – they do not have a leaf petiole.  Henbit flowers are pink to purple with darker purple spots than those of purple deadnettle. The flowers of henbit are longer and more slender than those of purple deadnettle.

Fall-applied Herbicide Considerations

Now that harvest is finally winding down, our thoughts change to fall weed control.   This is the best time of year to control winter annuals and some of the more difficult to manage overwintering weed species. Biennial and perennial plants are now sending nutrients down to the root systems in preparation for winter. Systemic herbicides like glyphosate and 2,4-D applied at this time will be translocated down into the roots more effectively than if applied in spring when nutrients are moving upward. This results in better control. In addition, the increasingly unpredictable spring weather patterns we have experienced in recent years can influence the timing and efficacy of spring burndown applications. Fall-applied herbicides can lead to weed free situations going into spring until early emerging annuals begin to appear in April, and are an essential component in the control of marestail and other overwintering species.

Here are some reminders when it comes to fall-applied herbicides:

  • Evaluate weed emergence and growth post-harvest to help determine if an application is necessary.
  • Fall-applied herbicides should primarily target weeds that are emerged at the time of application.
  • Species present in large quantities late-season that would necessitate the application of an herbicide include (but are not limited to): marestail, dandelion, wild carrot, poison hemlock, common chickweed, purple deadnettle, henbit, annual bluegrass, and cressleaf groundsel.
  • OSU research has not found much of a benefit from adding metribuzin or other residual products late in the fall. The exception to this is chlorimuron, which can persist into the spring. The recommendation here has generally been to keep costs low in the fall and save those products for spring when you will get more bang for your buck.
  • Herbicides generally work across a range of conditions, though activity can be slower as temperatures drop. Foliar products are most effective when daytime temperatures are in the 50s or higher and nighttime temperatures remain above 40.

Table 1 in the Weed Control Guide for Ohio, Indiana, Illinois, and Missouri provides ratings for various overwintering weed species in response to fall-applied herbicides.

Fall-applied Herbicide Considerations

Harvest is progressing in much of Ohio, though recent rains have slowed field activities in some areas. As crops continue to come off it’s a good time for a reminder about the value of fall-applied herbicides. Rains this past week may stimulate winter annual weed emergence to some extent. This is the best time of year to control winter annuals and some of the more difficult to manage overwintering weed species. Biennial and perennial plants are now sending nutrients down to the root systems in preparation for winter. Systemic herbicides like glyphosate and 2,4-D applied at this time will be translocated down into the roots more effectively than if applied in spring when nutrients are moving upward. This results in better control. In addition, the increasingly unpredictable spring weather patterns we have experienced in recent years can influence the timing and efficacy of spring burndown applications. Fall-applied herbicides can lead to weed free situations going into spring until early emerging annuals begin to appear in April, and are an essential component in the control of marestail and other overwintering species.

Here are some reminders when it comes to fall-applied herbicides:

  • Evaluate weed emergence and growth post-harvest to help determine if an application is necessary.
  • Fall-applied herbicides should primarily target weeds that are emerged at the time of application.
  • Species present in large quantities late-season that would necessitate the application of an herbicide include (but are not limited to): marestail, dandelion, wild carrot, poison hemlock, common chickweed, purple deadnettle, henbit, annual bluegrass, and cressleaf groundsel.
  • OSU research has not found much of a benefit from adding metribuzin or other residual products late in the fall. The exception to this is chlorimuron, which can persist into the spring. The recommendation here has generally been to keep costs low in the fall and save those products for spring when you will get more bang for your buck.
  • Herbicides generally work across a range of conditions, though activity can be slower as temperatures drop. Foliar products are most effective when daytime temperatures are in the 50s or higher and nighttime temperatures remain above 40.

Table 1 in the Weed Control Guide for Ohio, Indiana, Illinois, and Missouri provides ratings for various overwintering weed species in response to fall-applied herbicides.

Check your corn now for stalk strength

As harvest approaches, its time to check our corn plants for stalk integrity.  Time spent tin the field now, may pay huge dividends later this fall.  As stalk tissue becomes compromised below the main ear the stalk may become brittle or weak and be prone to lodging.

There are a number of plant pathogens that can cause stalk rot including, Anthracnose, Bacteria, Charcoal, Diplodia, Fusarium, Gibberella, and Pythium. Some of these stalk rots have very characteristic symptoms that can help identify the specific problem, while others may require laboratory diagnosis (Table 1).  The Purdue Extension Publication Corn Diseases: Stalk Rot has good images to help identify the major stalk rot diseases. (https://www.extension.purdue.edu/extmedia/BP/BP-89-W.pdf ).

Check field by using the Push or Pinch Test by evaluating 20 plants in at least five random areas in a field.

  • Pinch Test – grab the stalk somewhere between the lowest two internodes and pinch between your fingers to see if the stalk is strong enough to handle the force – if the stalk collapses, it fails.
  • Push Test – push the stalk to a 30-degree angle – if it pops back up when released, it passes the test, if not it fails.

Threshold: 10% or more of the stalks fail then consider field for early harvesting to avoid risk for lodging.

What can you do in the future – management options will depend on the specific disease (see table 1). Production practices that promote good plant health including balanced fertilization, appropriate plant populations, and good water management can reduce stresses that might predispose corn to stalk rot. In addition, these key management tools can help mitigate future stalk rot issues.

  1. Properly diagnosis the stalk rot pathogen.
  2. Select hybrids with resistance if available.
  3. Crop Rotation – rotating to non-host crop will help reduce stalk rot potential in a field. Note that Charcoal rot and Gibberella stalk rot can infect other rotational crops.
  4. Tillage – burying infected crop residue will encourage more rapid desiccation and help reduces risk of overwintering in crop residue.
  5. Good soil drainage and reduced compaction.
  6. Foliar Fungicides – applying foliar fungicides can help protect crop from foliar diseases that could predispose plant to stalk rot when present, but devoid of foliar disease pressure fungicides applications have not consistently been found to help reduce stalk rot.

Field Observations Thru September 15

Corn

Growth & Development

Most of the corn that I have seen this week is in either the late R4 (Dough) or the R5 (Dent) growth stage.  A few fields are approaching the final growth stage R6.

R6 – Physiological Maturity

  • Occurs approximately 66‐70 days after silking.
  • R6 is reached  after the milk line disappears and the starch has reached the base of the kernel.
  • Kernels have reached maximum dry weight.
  • Kernel moisture is  about 35% at physiological maturity.
  • Black layer occurs after physiological maturity and  serves as a visual verification that the plant is mature. Black layer typically occurs at 30%  moisture but varies by hybrid and environment.
  • Husks and many of the leaves are no longer green, but the stalk may be green.
  • Only external stress can reduce yield now,  such as plant lodging or insect feeding.

Scouting

At this growth stage look for:

  • Ear rots.
  • Stalk rots.
  • Anthracnose top dieback.
  • Stalk lodging.
  • Abnormal ear fill which identifies periods of stress.
  • Weed escapes (especially Palmer and Waterhemp).

This is also a good time to get an accurate yield estimate.

Soybeans

Growth & Development

Soybeans are continuing to mature.  Last week I highlighted the R7 growth stage, the last growth stage is R8 full maturity.

R8 – Full Maturity

  • 95% of pods reached mature color
  • Mature pod color does not necessarily indicate that beans are ready to harvest
  • 35% grain moisture in freshly matured pod
  • 15% within another 5 to 10 days
  • Below-optimum plant stands cause more branching, low pod heights & can delay maturity
  • Above-optimum plant stands increase lodging.

Scouting

At this growth stage look for:

  • Green stem syndrome.
  • Lodging
  • Sprouting seeds
  • Pod shattering
  • Weed escapes (especially Palmer and Waterhemp).

This is also a good time to check soybean yield potential.

County Rainfall Update

Weed management practices: Fall scouting and equipment cleaning

 

Weed management encompasses more than controlling actively growing weeds. You can be proactive to help prevent the future spread of weeds. Two different management practices are discussed below: fall scouting for weed escapes and equipment cleaning.

Fall scouting can help plan for future control

Weeds that escape control by in-season management practices can cause several problems, including the possibility of reduced harvest efficiency and crop yield. Even if these factors do not justify an herbicide application, it is important to consider the future costs of seeds produced by those escapes – particularly if those escaped weeds produce a lot of seed and/or are herbicide resistant.

Just a few escapes of species such as waterhemp or Palmer amaranth can have a big impact. For example, research conducted in Georgia showed that one female plant in five acres added about two million seeds per acre to the soil. Those seeds can have impacts for many years. It took six years of total palmer amaranth control to deplete the seedbank by 98% in Texas. In some situations, scouting during the weeks leading up to harvest may provide an opportunity to remove these plants by hand to reduce the number of seeds in the soil.

Scouting for weeds at harvest, even if you simply make notes from the combine, is important for planning future weed management.

When scouting, make notes about

  • which weed species are present,
  • where weed escapes are present, and
  • any changes in the size or location of areas with weed escapes.

Some observations might be the result of soil or environmental conditions, while others might suggest problems with the herbicide selection or application equipment. However, some of these escapes might indicate the presence of herbicide-resistant weeds in your field – especially if the same herbicide program has been used for a number of years. Two examples of observations that might indicate herbicide resistance are 1) a growing patch of a particular species, or 2) herbicide failure on a few plants of a single species that is normally controlled.

Stop spreading weed seed during harvest activities

Weeds can spread in a variety of ways, including on farm equipment. As you move harvest equipment from field to field, be aware of the potential to spread weed seed – especially if uncontrolled weeds are known or suspected to be herbicide resistant. Some steps to prevent spreading weeds when moving harvest equipment from one field to another are listed below.

  • Clean new-to-you equipment so someone else’s weeds are not introduced to your farm.
  • If possible, harvest fields with excellent weed control first.
  • Harvest fields where weeds are or might be herbicide resistant last.
  • Harvest around areas with extremely dense weed populations.
  • Slow the combine to ‘self-clean’ between fields.
    • Run the unloading auger empty for a minute or two.
    • Open grain elevator doors, rock trap, and unloading auger sump then run the separator with maximum airflow and suction.
  • Use an air compressor to remove material remaining in the rock trap and grain auger and from the head, feeder house, straw spreader.
  • Take half a day to do a deeper clean when possible.
  • Check fall-tillage equipment between fields.

It is very difficult to completely remove weed seeds from harvest equipment. However, taking a few minutes to reduce the number of seeds on your harvest equipment may save time and money in the future.

FSR Weed ID Quiz

Test your weed identification skills at this year’s Farm Science Review.

  • The quiz is 40 multiple choice questions over 25 different weed specimens.
  • The highest score in each participant category will receive a prize at the conclusion of the 2023 FSR.
  • Categories: Adult, High School/FFA, Youth, Extension Educator.
  • Weed ID Quiz tables will be located at the Ag Crops Tent Plot Area Tuesday thru Thursday.

Field Observations Thru September 8

Corn

Growth & Development

Most of the corn that I have seen this week is in either the R4 (Dough) or the R5 growth stage.

R5 – Dent

  • The second to last stage of corn development.
  • R5 (dent) occurs approximately 31‐33 days after silking.
  • Kernels are dented in at the top with the “milk line” separating the liquid and
    solid (starch) portions.
  • Within R5, kernels are often staged according to the progression of the milk line; i.e. ¼, ½, and ¾.
  • At the beginning of R5, kernels have 60% moisture content.
  • Stresses will reduce kernel weight at this time.

Scouting

I have heard a wide range for projected corn yields this year.  The Yield Component Method is the most widely used procedure for estimating corn yield.  While  you are out checking potential corn yields, also keep an eye out for:

  • Ear rots.
  • Stalk rots.
  • Anthracnose top dieback.
  • Stalk lodging.
  • Abnormal ear fill which identifies periods of stress.
  • Weed escapes (especially palmer & waterhemp).

Soybeans

Growth & Development

Soybeans are continuing to mature.  Last week I highlighted the R6 growth stage  the next stage is R7 the last growth stage prior to maturity.

R7 – Begining Maturity

  • One mature-colored pod anywhere on the main stem.
  • Yellow pods are moving toward maturity.
  • Tan, brown or tawny pods (depending on variety) signal physiological maturity.
  • Seeds at the R7 growth stage are at approximately 60% moisture.

Scouting

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

Estimating soybean yields

It is much more difficult to accurately predict soybean yield.  The process to estimate soybean yields can be found here.

County Rainfall Update