May 2023 Articles

Cold Soils and Corn

May 5th, 2023

Ron Myer, Golden Plains Area Agronomist

Optimum soil temperatures for corn germination and plant progress begins at 50 degrees F.  Soil temperatures lower than 50 F can cause corn seed to lay dormant, exposing the seed to disease and insect damage.  When corn seed is planted into soils that are too cold to allow adequate germination a condition called imbibitional chilling can occur.  Seed imbibition is a two step process; water is absorbed by the seed and the seed swells.  When seed swelling occurs, imbibition begins which activates enzymatic processes in the seed, including increased seed respiration and cell duplication.  In other words, germination.  This germination activity results in seedling growth and finally emergence.  Cold soils slow this process and can result in lower germination and delayed seedling growth, increasing potential seedling pest issues such as seedling disease problems.  Other issues with delayed emergence include restricted seedling development which restricts nutrient uptake and damaged or aborted sprouting.  Herbicide injury is also a factor with slow seedling growth as this condition exposes seedlings to an applied herbicide for longer periods of time.

Planting corn seed when soil temperatures and conditions are favorable provides the corn plant with the best chance for successful emergence which gives the corn crop the best start.  For current soil temperature information, access the Colorado CoAgMet system at:

Cold Soils and Weeds

May 5th, 2023

Kat Caswell, Washington and Weld Counties Agronomist

The spring season of 2023 is off to a chilly start. Low temperatures and late snows in the spring have kept soil temperatures in northern Colorado lower than we’ve experienced the last few planting seasons. The cooler temperatures are having a noticeable effect on what weeds have started to emerge in the northeast part of Colorado.

Most weed species have a specific time window in which they emerge each year. Kochia is one of the earliest weeds, emerging in late March to early April. By the middle of May, 90% of the kochia will have emerged for that year. As of late April, kochia around the region was only beginning to emerge and form seedling mats. Cheatgrass, another early emerging weed, has been behind the kochia emergence this spring. Weed seed germination is heavily influenced by soil temperature and soil moisture. While soil temperatures remain lower, summer annual weed seed germination will be delayed compared to the normal emergence window.

Despite being delayed, some of the early emerging weed species will still have time to germinate and become a challenge to manage. For example, palmer amaranth can emerge, flower, and produce viable seed through the entire growing season. Weed control options will to be adjusted to match weed emergence in years such as this. Soil applied herbicides are only able to kill weeds that are actively growing. If a soil applied herbicide with a three-week residual activity is applied but weed seeds do not germinate until the last week the residual is effective, there will be a population of weeds that escape control. An additional herbicide application will need to be done later, allowing the crop to establish during the weed free critical period, but adding an additional expense for equipment and chemicals.

In years with varying weather conditions, active scouting and adaptive management will be a necessity for maintaining weed control. Palmer amaranth was identified to have resistance to six different sites of action in March of 2023 in Kansas. Due to the limited efficacy of herbicides during hot and dry conditions, accurate timing of herbicide applications will be both challenging and crucial.

Identifying Imazomox Resistance in Feral Rye

May 5th, 2023

Todd Gaines, CSU Associate Professor of Weed Science

We conducted a survey of eastern Colorado for winter annual grass weeds in wheat. We found no resistance in the samples to quizalofop (Aggressor herbicide in CoAXium) as expected since CoAXium wheat hadn’t yet been introduced, and we found that mostly all the samples were sensitive to imazamox (Clearfield wheat and Beyond herbicide), except for a couple of samples in Weld county. In those samples, we found feral rye resistant to imazamox. Two populations had target site mutations in the ALS gene. A third population had enhanced metabolism of the herbicide. All three populations were collected based on grower and crop consultant observations and concerns about potential resistance, and were not part of the random survey. Growers should monitor feral rye after imazamox application for efficacy and consider submitting samples for resistance testing.

Read the full paper. 

Western Region Updates

May 5th, 2023

Retta Bruegger – Western Regional Range Management Specialist 

Conditions are setting up well for a good year of forage production on the western slope. Cooler spring temperatures, especially at higher elevations, means that grass growth is delayed but soil moisture from a strong winter means it can likely recover. Lower elevations (below 6,500 ft), grass production is strong. Abundant moisture also means the invasive annuals (cheatgrass and others) benefit and in lower elevation areas, there may be a bounty crop of cheatgrass. The next month’s condition’s will be critical for overall forage production on rangelands. Continued wet and mild conditions would greatly benefit the forage crop.

Todd Ballard – Tri-Rivers Area Agronomist

Wheat in the Grand Valley appears to be in good condition. Land prep for summer crops is well underway. The biggest concern at this time in the Tri-River Area is flooding.

North Fork of the Gunnison at flood stage.

Snow pack above the Gunnison River

Regional Updates

May 19th, 2023

Contributors: Ron Myer, Golden Plains Agronomist and Retta Bruegger, Western Slope Rangeland Specialist  

Areas of the eastern plains have received over 2 inches of rainfall. Areas of heavy rainfall have left standing water or have delayed summer crop planting with wet soil conditions. Some wheat fields in the southeast part of the state have been abandoned and will be replanted with a summer crop.

Similar conditions persist on the Western slope as earlier in the month. If current conditions are maintained, it will be a good year for forage production.

Drought ratings have been lowered across the state, with the worst conditions persisting in the southeast corner.

Standing Water and Wet Soils

May 19th, 2023

Kat Caswell, Washington and Weld Counties Agronomist

Good news, according to the UNL Drought Monitor, drought conditions are improving across northeast Colorado. Aside from a few storms, Weld County has been receiving a trickle of rain each day, allowing time for water to move into the soil profile, without leaving any standing water. In other areas, of NE Colorado, storms producing greater rainfall in a short period of time are leaving standing water in fields, and in some cases running off fields.

Slower rainfall can be of benefit to the wheat crop. Wheat conditions have varied field to field based on planting timing. Thinner fields with poorer stands will benefit from the rainfall but are unlikely to yield as well as those with better fall stand establishment. Areas with excessive amounts of moisture may have a negative impact on kernel development, reducing yield.

Wheat can tolerate approximately 24 hours of standing water before there is significant damage. The level of damage will depend on the growth stage of the wheat, but in general, will increase the risk of lodging. With the likely pressure of wheat-stem sawfly, monitoring wheat lodging and considering harvest methods should be planned for.

Cooler moist soils create a greater risk for disease pressure. Root rot has been observed in Kit Carson County, as reported in the Wheat Disease Newsletter.  Although stripe rust has not been observed, wheat fields near I70 are experiencing outbreaks of leaf rust.  Treatment is similar for both rusts.  Continue to scout fields for any new diseases and monitor the Wheat Disease Newsletter for updates.

Corn planting has been slightly delayed this year with the cooler soil temperatures. Standing water on a recently planted corn can kill newly emerging seeds, cause uneven plant emergence, increase disease risk, or nutrient accumulation problems in the stand. Corn seedlings in wet soil are likely to develop only a shallow root system, reducing their ability to access moisture lower in the soil profile during hotter months. Planting into wet soils will lead to soil compaction from equipment and sidewall compaction in the furrow. Sidewall compaction will inhibit root growth, restricting the plant’s ability to access nutrients and moisture. Cool and wet soils can reduce emergence and result in an even stand.

If there is standing water in a recently planted field, wait for the water to drain before scouting or making the decision to replant. Evaluate field conditions before planting any crop. Soils should be at least 50 degrees Fahrenheit at a 2 inch depth. Clay soils that are too wet will produce water when squeezed, much like a sponge. Dryland corn still has limited window for planting remaining, but irrigated fields that are not yet planted should consider changing to a shorter season variety or planting a different crop.

Soils that continue to have standing water or are too wet past the planting windows for common crops still have options for a later planting with a substitute crop Residue management is important for drought resilience and managing heavy rainfalls. Cover crops and annual forages can be planted later into the summer. Both will produce residue and reduce the risk of soil erosion than if a field is fallowed.

With the cool, wet spring, regular scouting of field conditions will be important for any crop. Waiting for soil temperatures and moisture to be adequate is important for any planting, but if conditions are not met for your intended crop, consider other crop options. Fields with standing water should wait until the water has drained and evaluate each field’s stand before making replanting decisions.

Contributions from Ron Myer, GPA Agronomist