Weeds

Weed of the week – Giant Ragweed

Giant Ragweed

Family: Asteraceae (Composite family)

Life cycle: Annual

Description: Erect summer annual that may reach 16 feet in height. Leaves are large and distinctively 3-lobed.  Primarily a weed of agronomic crops that thrives in fertile soils. Found throughout the U.S. except the Pacific Coast, areas of the Southwest, and portions of Florida and Maine.

Seedlings: Cotyledons round to oblong, thick, and 3-4 times larger than those of common ragweed. The stem below the cotyledon (hypocotyl) is often purple. The first pair of true leaves is unlobed and lanceolate in shape, with toothed margins.

Roots: Taproot

Stem: Erect, freely branched, hairy

Leaves: All leaves subsequent to the first pair of true leaves are 3-lobed. Lobes arise from the same point (palmately lobed), and each lobe is lanceolate in shape with toothed margins. Leaves are opposite, hairy, occur on long petioles and are large (4-8 inches wide by 6 inches long).

Flower: Occur in long slender racemes at the ends of branches (male) or in the leaf axils of the upper leaves (female). Individual flowers are small and greenish.

Special identifying characteristics: Large, 3-lobed leaves and crown-shaped achene. The first true unlobed leaves of giant ragweed may lead to the confusion of this weed with Common Cocklebur (Xanthium strumarium). However, the leaves of cocklebur are alternate.

Giant Ragweed Control in Corn

Giant Ragweed Control in Beans

Soybean Postemergence Weed Control – Broadleaves

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.

Table 16 below from the 2023 OSU Weed Control Guide compares the relative effectiveness of herbicides on individual weeds. Ratings indicate the level of control of weeds present at the time of application, and are based on labeled rate and weed size or growth stage.

Click on table to enlarge

Soybean Postemergence Weed Control – Grasses

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.

Table 15 below from the 2023 OSU Weed Control Guide compares the relative effectiveness of herbicides on individual weeds. Ratings indicate the level of control of weeds present at the time of application, and are based on labeled rate and weed size or growth stage.

Click on table to enlarge

Field Observations Thru July 7

Alfalfa

Recent weather has delayed 2nd cutting in many fields.  Potato leafhoppers are very active.  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

Plenty of moisture and some welcome warm weather – What a difference a week makes!

Warmer weather has slowed slug activity and the rapid corn growth is helping these plants escape (outgrow) this damage.

Our corn growth varies greatly throughout the county.  Most of the county is between V6 and V12. However, there are some fields at V12 and beyond.

V10 to V11 – The corn plant begins a steady and rapid increase in nutrient and dry-matter accumulation. The time between the appearance of new leaves is shortened, with a new leaf appearing every two to three days.  Demand for soil nutrients and water are relatively high to meet the needs of the increased growth rate. Moisture and nutrient deficiencies at this stage will influence the growth and development of the ears markedly. Fertilizer, especially phosphorus and potassium, is needed near the roots, which do not move appreciable distances in most soils. Dry soils also may make needed nutrients less available.

I have received a few questions about postemergence herbicide applications.  Click the links below for OSU Postemergence Herbicide Ratings.

Table 5. Postemergence Herbicides in Corn – Grasses

Table 6. Postemergence Herbicides in Corn – Broadleaves

Soybeans

Ok, many soybean fields just don’t look good, especially for this time of year.  While scouting your bean fields, check for seedling diseases and water-logged roots.

Warmer weather has slowed slug activity however beans are still growing slowly and may not be able to outgrow the feeding yet – Continue to monitor your bean fields for slug feeding.

Click here for slug information

Our Soybean  growth varies throughout the county.  Most of the county is between V3 and V6. However, there are some fields at and approaching R1.

V3 through V6 – The third trifoliolate (V3) stage takes place when three trifoliolates are unrolled. In case of damage to the growing point, axillary buds permit the plants to compensate for yield or final productivity.  The unrolling of six trifoliolates indicates the V6 stage. The root system continues to grow, even expanding across a 30-inch row spacing.  The V growth stages continue as long as a plant continues to produce trifoliolates. Determinate soybean plants complete most of their vegetative growth when flowering begins. Indeterminate plants produce trifoliolates until the beginning of the seed formation stage (late reproductive period).

Wheat

When, When, When will the wheat be ready??  Wheat harvest is just getting started.  A little sunshine and continued warm weather would certainly speed up the process.

Planning on planting beans after wheat? 

Click here for the Double Crop Soybean Production Guidelines from Dr. Laura Lindsey.

Click here to view herbicide restrictions prior to planting.  Table 23 from the Ohio Weed Control guide lists these restrictions.

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!

County Rainfall Update

 

Weed of the week – Common Pokeweed

Common Pokeweed (AKA – Pokeberry)

Family:  Pokeweed Family

Life cycle: Perennial

Description: A large, 3 to 10 ft tall, perennial weed with thick, reddish-purple branched stems and dark purple to black berries. All parts of the plant are poisonous to cattle, horses, swine, and humans, especially the roots.

Seedlings: Cotyledons 7-33 mm long, 6-11 mm wide, egg-shaped but pointed at the apex. Stems below the cotyledons (hypocotyls) are without hairs, succulent, and often purple-tinged. Young leaves alternate, egg-shaped but pointed at the apex, and without hairs. Cotyledons and young leaves are pale green in color, with reddish tinted petioles.

Roots: Large, white tap root up to 6 inches in diameter.

 

 

Stem: Branch from the root crown at the base of the plant, erect, large, smooth, purple-tinged.

Leaves: Alternate, 3 1/2-12 inches long, 1-4 inches wide, egg-shaped, petiolated, without hairs, and are smaller in size toward the top of the plant.

Flower: Individual flowers small (6 mm wide) with 5 white to pink-tinged sepals.

Fruit: A berry, 7-12 mm, green when immature, dark-purple to black when mature. Contain a dark red juice.

 

Special identifying characteristics: Large, tree-like plant with egg-shaped leaves, purple-tinged stems and dark purple berries.

Pokeweed Control in Corn and Soybeans

 

Weed of the week – Poison Hemlock

Family: Parsley, Apiaceae.

Habitat: Wet sites, gardens, roadsides, wastelands, pastures, and meadows.

Life cycle: Biennial, forming a rosette the first year and producing flowers and seed in the second.

First Year Growth Habit: Basal rosette of finely divided leaves with a pungent odor.

Second-Year Growth Habit: 2-7 feet tall, branched plant with flowers.

Leaves: Alternate, pinnately compound, finely divided, toothed, and glossy green.

Stems: Branched, waxy with purple blotches; hollow between nodes and grooved.

Flower: June – August (second year). Clusters of small white flowers with 5 petals in a loose, umbrella-like cluster, 2-7” across.

Root: Fleshy taproot.

Similar plants: During the first year, poison hemlock resembles wild carrot, but has a strong, pungent odor. Further, young leaves of wild carrot are more finely divided and its stem is hairy. At maturity, poison hemlock can be difficult to distinguish from water parsnip and water hemlock. Look for purple blotches on the stem to identify poison hemlock. Water hemlock (Cicuta maculata), which is also highly poisonous, has a magenta-streaked stem and lanceolate leaflets with sharply-toothed edges. Water parsnip (Sium suave) is not poisonous and has toothed lanceolate leaflets.

The problem is….This plant is highly poisonous to both humans and animals. Poison hemlock is a large and impressive plant which has been planted as an ornamental in some areas. It grows quickly in fertile soils.

Seedling

Leaves

 

 

 

 

 

Stem – Note distinctive purple speckling

Flower

 

 

 

 

 

Click here for control options

 

Weed Management in Dry Conditions

Source: Dr. Alyssa Essman

Finally, some much needed rain.  It looks like most of the County received around .5 inches Sunday night.  A welcome relief, but more is needed.  Hopefully that happens tomorrow and Wednesday.

This article is written with the hopes that relaying some information about management in a dry pattern will bring on some rain. If that doesn’t work, below are some reminders and considerations for weed control in dry conditions.

  • To wait or not to wait – one consideration is whether it’s better to apply POST herbicides when weeds are small or to hold out for some rain. Weeds are most effectively controlled when actively growing and drought stress can impede control to some degree. However, large weeds are more difficult to control especially if the stress-inducing conditions persist. For this reason, and the fact that herbicides generally work across a range of conditions, it might be best to go ahead and spray when weeds are small unless there is some definite rain in the forecast.
  • Weed emergence – dry conditions can delay the later emergence of weeds, especially those that are in the upper portion of the soil and have small seeds. The emergence of large-seeded species and those at lower depths will be less affected. Weed emergence flushes can occur periodically following rainfall events.
  • Residuals – residual herbicides will not be properly incorporated, and thus not available for uptake by weeds, to help control those that do emerge before we receive a decent rain. Mark Loux talked about this and the use of a rotary hoe in an article a couple of weeks ago, which can be read here. A layered residual strategy for control of waterhemp is still recommended, especially where crops were planted early. Rain will still be needed to incorporate later-applied residual herbicides into the soil profile.
  • POST applications – plants respond to drought stress in part by increasing cuticle thickness to preserve water. This can decrease herbicide absorption, and translocation within the plant is also affected. Optimizing the use of adjuvants can help to increase absorption by improving coverage and uptake. Follow the label and herbicide/adjuvant manufacturer recommendations to determine the best type and rate. Also, be aware that an increase in activity can lead to crop injury in some instances, and that applications early or late in the day may reduce the risk of injury.
  • Antagonism – dry conditions can exacerbate antagonism issues, especially when using POST grass and broadleaf herbicides together. Control can be reduced especially for larger grasses with substandard root systems (hanging on by a few roots). Sequential applications can help overcome this antagonism. Wait seven days between applications when the broadleaf herbicide is applied first, and about one day when the grass herbicide is applied first.

For more information on weed control in a variety of conditions, check out the Weed Control Guide for OH, IN, IL, and MO available for purchase here.

Meet Your New Weed Science Extension State Specialist- Dr. Alyssa Essman

Currently, Alyssa is a Visiting Assistant Professor in Weed Science with responsibilities in research, teaching, and Extension on a two-year appointment. We are happy to announce that Alyssa will be continuing in the Department of Horticulture and Crop Science as a tenure-track Assistant Professor on August 15. She will have responsibilities in Extension as the Weed Science State Specialist and will be conducting applied research in weed management.

Alyssa’s time in weed science dates to April 2014 when she worked as an undergraduate student for Dr. Mark Loux’s weed science program. She received her MS in Weed Science in 2018 followed by her PhD in 2022. Congratulations to Alyssa on this major accomplishment, and we are excited to have you as a permanent AgCrops Team member!

Weed Response to Postemergence Herbicides in Small Grains

When determining your herbicide program for spring applications, the stage of the wheat crop should be considered.  The majority of wheat herbicides labeled for application at certain wheat growth stages have very short windows in which they can be applied.  The popular broadleaf weed herbicides 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring.  Wheat growth stages and herbicide timing restriction are outlined in a in a post last week (Herbicide Applications on Winter Wheat).

Another consideration you should take into account when planning a spring herbicide application is the plant back (or recrop) restrictions to double crop soybeans.  Many of the herbicides listed in Table 19,  have soybean plant back restrictions greater than the typical three month time period between spring applications and double crop soybean planting.  The soybean plant back restrictions greatly reduce the number of options available to wheat producers who double crop soybeans after wheat.

Herbicide Applications on Winter Wheat

When determining your herbicide program for spring applications, the stage of the wheat crop should be considered.  The majority of wheat herbicides are labeled for application at certain wheat growth stages and some commonly used herbicides have very short windows in which they can be applied.  The popular broadleaf weed herbicides 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring.  Wheat growth stages and herbicide timing restriction are outlined in Figure 1.