Field & Feedlot

Field & Feedlot is a monthly newsletter of current educational topics written by Agriculture and Natural Resources Extension and Outreach specialists in Northwest Iowa.


Proper Pruning Time for Oaks by Dawn Henderson

Forages this Fall & Winter by Beth Ellen Doran

Winterizing Your Ventilation System by Dave Stender

Corn Ear Disease Issues by Joel DeJong

Archived Issues


Proper Pruning Time for Oaks

Dawn Henderson, Horticulture Program Coordinator

Colder temperatures are moving in and soon outdoor perennials will be dormant for the winter, including trees. Dormant trees provide the best opportunity for safe and effective pruning by allowing a clear view of unwanted branches. Most deciduous trees should be pruned in late winter from February to March, because of the shortened healing time before spring bloom. Oak trees are the exception. A lethal fungus that targets oak trees is active from April to early-August and is easily transferred through open wounds. Oak Wilt, caused by the fungus Bretziella fagacearum, attacks the vascular tissue of the tree - where water and nutrients are moved through the plant. Due to this restriction, Oak Wilt can kill a tree within a matter of weeks.

Movement of this pest comes in three major ways: root grafts, wind dispersion, and insect movement. Intertwining roots provide direct access for the fungus to move from an infected tree to a healthy one. The only solution here is to divide and remove the affected tree roots, which is rather costly. Spores released from the fungus are also able to be picked up by the wind and moved onto another potential oak host. Again, very little can be done to avoid this. The most effective control of Oak Wilt is removal. Cut down any infected trees as soon as an official diagnosis of the disease is made. Finally, insects move freely between trees and pick up pollen and spores whenever they land. The fungal mat produced by Oak Wilt has a strong, fruity scent that attracts sap feeding beetles to an infected tree where they feed, collect spores, and fly to another tree. These beetles are the main reason pruning oaks in the dead of winter is the safest for the tree.

Oak tree pruning should happen after the leaves have fallen and temperatures are cool enough the sap feeding beetles have gone dormant, typically starting in December. Earlier in the fall will stress the tree while it is storing energy for winter. Pruning any later than February will also run the risk of the wound not healing enough to protect the tree from Oak Wilt. If pruning the tree during the spring or summer is unavoidable, painting the wound with latex paint immediately will reduce the risk of attracting the beetles. They seek out trees that are leaking sap and can find a fresh wound in a half an hour.

Prevention is the best protection when it comes to Oak Wilt. Informed pruning and the removal of dead branches is healthy for the tree and will encourage more growth when done correctly. If you are not familiar with pruning, particularly for large branches, contact a certified tree service for assistance rather than risking an injury.

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Forages this Fall & Winter

Beth Ellen Doran, Beef Program Specialist

This has not been a normal year, and our feedstuffs are not “normal” feeds. Hence, there are some things to consider.

If you put up silage, feeding should be delayed until the product has gone through a complete fermentation. For corn silage, allow 3-4 weeks for it to ferment. Frosted sorghum or sorghum-sudangrass will increase in prussic acid content after a frost, but the prussic acid decreases dramatically during ensiling. Delay feeding it for 8 weeks after ensiling and test the silage for prussic acid level prior to feeding.

Before grazing cornstalks, check how much lodging occurred and the amount of corn remaining in the field. If a lot of corn is remaining, consider strip grazing the field or limiting the time that animals are allowed to graze daily. If limiting the time, provide a fair quality forage to the animals prior to the next day’s turnout. This will help avoid over-consumption of dropped ears when turned out to graze.

Due to the range in corn plant maturity and harvest moisture, this year’s corn may not be “normal.” Some of the corn may be lower in test weight, which leads to more handling breakage and fines. The corn should be monitored for the amount of fines and the ration adjusted if there is a significant amount of small, broken kernels. Fines are rapidly digested in the rumen and can lead to symptoms of acidosis, such as variable intakes, loose stools, bloat, founder and death.  

This year, I am recommending that all producers run a feed test to determine moisture and nutrient content. With an abnormal year and feedstuffs, a wet chemistry test may be more accurate than an NIR test. Also, check all feedstuffs, including cornstalk and hay bales, for the presence of mold and the potential for mycotoxin development.  But, be aware that the presence or absence of mold does not mean there are or aren’t mycotoxins. The best way to determine mycotoxins is with a mycotoxin test. Some mycotoxins inhibit performance; others can affect reproduction. And, remember that the “eye of the master” is still important, so, monitor animals closely.

More information on crop quality in 2019 may be found at:                                              

Upcoming Beef Meetings:

  • Nov. 21 – Beef Quality Assurance Training, 10:00 a.m. to noon, ISU Extension and Outreach – Woodbury County, Sioux City. Call 712-276-2157 by Nov. 19 to register. There is no cost to attend.
  • Dec. 10 – Beef Quality Assurance Transportation Certification, 1:00 to 4:00 p.m., Sioux Falls Regional Livestock, Worthing SD. Call 712-737-4230 to register. Major packers require certification by Jan. 1, 2020 for producers or custom transporters who deliver cattle directly to the plant. 
  • Jan. 14 – Feedlot Forum 2020, 8:30 a.m. to 3:15 p.m., Terrace View Event Center, Sioux Center. Focus is Cattle Marketing: Meeting Today’s Challenges and Expectations. Call 712-737-4230 by Jan. 9 to register. Cost is $25/person, which includes a meal and $10 beef certificate.

New Publications:

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Winterizing Your Ventilation System

Dave Stender, Swine Program Specialist

Now is the time of year to make sure our swine buildings and ventilation systems are set for winter.  Winter is the time when it is most challenging to ventilate a building correctly. The colder air brought in is heavier than the warm air inside a building and will drop rapidly on the pig living area if the ventilation is not working properly. The only way to avoid stressing pigs with cold air is to drop the air in an area where pigs are not living or to set the inlets to increase air velocity, so the cold air is shot out of the inlets fast enough to prevent it from dropping too fast. This air speed can be measured by how far the air travels over time, typically the measurement is feet per minute. Air speed at the inlet to minimize the dropping of cold air onto the pigs is about 800 to 1000 feet per minute. There is equipment available that can measure air speed at the inlet in a swine barn. 

Allowing air to drop is not a good idea for several reasons. Most importantly, cold air dropping on pigs will stress them and could lead to sickness. Dropping cold air will not mix well, resulting in warm stale air pockets not mixed with cold fresh air. Warm stale air will stress the pig as well, especially the respiratory system increasing the likelihood of respiratory disease. The third bad thing that happens is heavy cold air drops into the pit below the pigs, potentially forcing up the stale air from under the slats. This could also be harmful to the health of the pigs.  

Winter is a time when high air velocity at the inlets is most critical, but also the time when incoming air volume is very low, making it tough to achieve the inlet air speed (velocity) that we want (800 to 1000 feet per minute). Increasing the volume of air to reach the desired velocity is not a good idea either because bringing in extra cold air is expensive to heat and a waste of energy. It is critically important to prepare for winter. Fans need to operate at peak performance which means they should be clean. A dirty fan blade could cost you up to 40 percent efficiency. Dirty shutters cause the same efficiency problems. Make sure the discharge cones are in good repair. You need the cone to protect the fan operation on a windy day blowing at the fan. If fans have belts, make sure the belts are tight. And cover unused fans during the winter. Inlets should be in good working order, open uniformly and calibrated correctly for each fan stage.

Ventilation systems typically are negative pressure systems. The fan pulls a vacuum inside the building forcing air through the inlets (remember we want air speed at 800 to 1000 feet per minute). Any leaks in the shell of the building will short-circuit the fresh air, lowering the amount of air pulled through the inlets (this causes the problem of cold air dropping and not mixing). To solve this problem, the building should be air tight. Pumping ports should be sealed air-tight. Make sure there are no sags, gaps or holes in the curtains. Maintain at least 3-inch curtain overlap for a solid seal and make sure the end pockets are in good repair. The door seals should be maintained for minimum air flow through or under the door. 

Occasionally, ventilation workshops are offered or scheduled through ISU Extension and Outreach. The workshops provide more in-depth information regarding ventilation issues and management adjustments needed to keep pigs healthy using less energy cost. For more information on these, give me a call at 712-225-6196.

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Corn Ear Disease Issues (adapted from the Crop Disease Network Publication "Ear Rots," CPN-2001)

Joel DeJong, Field Agronomist

While walking through cornfields this fall before a lot of harvest began, I noted many ears with molds. Because we had wet and rather warm conditions before corn reached maturity, the most common disease I observed was Fusarium, but others were also present. After corn reaches maturity, farmers often allow the crop to dry down in the field to save on drying costs. However, the presence of ear rot diseases should influence harvest timing. The fungi that cause ear rot diseases can continue to grow, spread, and produce mycotoxins even after corn reaches maturity. The most common mycotoxins associated with ear rots are deoxynivalenol or DON (associated with Gibberella ear rot), fumonisins (associated with Fusarium ear rot), and aflatoxin (associated with Aspergillus ear rot). If you find ear rots during pre-harvest scouting, harvest the affected fields first and immediately dry the grain to levels that stop the fungus from growing and producing mycotoxins. More information about identifying ears rots is available in “Corn Disease Management: Ear Rots” (CPN-2001), available from the Crop Protection Network (

Drying corn quickly helps prevent fungi from infecting or further degrading previously infected grain. Wet grain degrades quickly in a harvest truck or grain bin and mycotoxin levels can increase, and the risk increases when temperatures are warm after harvest. However, if grain is stored at appropriately low moisture, evidence shows that mycotoxin levels will not increase. When grain is wet, mycotoxins can continue to accumulate. High-temperature drying stops mold growth and mycotoxin production. However, it will not reduce mycotoxins already present in the grain. Using high temperatures to quickly dry grain is preferable to using low heat to slowly dry grain. Be wary of using low-temperature, in-bin dryers for moldy corn, and be sure to meet proper ventilation requirements for storing dry corn. A good post-harvest drying target for storing grain is 15 to 15.5 percent moisture, which should be sufficient for short-term storage over the winter. Cooling the grain to below 55°F will slow the growth of fungi and inhibit insect activity. However, if you plan to store corn into the hottest months of summer, dry grain to less than 13 percent moisture. At this moisture level, mycotoxin-producing fungi are typically unable to grow.

Damaged corn kernels can cause airflow problems during storage. Ear rot diseases often damage kernels, causing them to break and be lightweight at harvest. If the ear rot fungi in your corn are species that produce mycotoxins, the risk of mycotoxin contamination in your grain will be high. Broken kernels and “fines” will accumulate in the center of the storage bin during filling unless the bin is equipped with a spreading device. This central core of fine material will hinder uniform air movement through the grain mass, which increases the risk that the grain will spoil. “Core” the bin to remove most of the broken kernels and fine material that accumulate there. If there are mycotoxins in the harvested grain, the majority of the mycotoxins can be detected in the broken kernels and fine material. Although costly, cleaning the grain before you store or sell it can greatly reduce the level of mycotoxin contamination. Although cleaning grain will reduce mycotoxin concentrations, the cleaned grain often still contains significant mycotoxin concentrations.

Regularly monitor your storage bins. Check for leaks in the structure and be on the lookout for condensation in the headspace. If condensed water drips on the grain surface, fungi may resume growing and this may lead to surface crusting. Inspect bins for sour, musty, earthy or putrid odors. These odors indicate a fungal problem — most likely due to high grain moisture from improper drying, leaks, or insect activity. If the grain gets wet, use a fan to increase airflow and reduce grain moisture, which can halt fungal growth. If mycotoxin-producing fungi begin to grow in high-moisture corn, the level of mycotoxins in your stored grain can increase.

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