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Published May 11, 2008, 12:00 AM

Will's Windmill column: Corn needs heat units to emerge

Corn requires about 100 growing degrees days (GDDs) to emerge .

By: Will Yliniemi, DL-Online

Corn requires about 100 growing degrees days (GDDs) to emerge (but emergence requirements can vary from 90 to150 GDDs). To determine daily GDD accumulation, calculate the average daily temperature (high plus low) divided by 2 and subtract the base temperature, which is 50 degrees Fahrenheit for corn.

If the daily low temperature is above 50 degrees, and the high is 86 or less, then this calculation is performed using actual temperatures, but if the low temperature is less than 50 degrees, use 50 degrees as the low in the formula. Similarly, if the high is above 86 degrees, use 86 degrees in the formula.

If it takes a corn hybrid 100 GDDs to emerge, and daily high and low temperatures average 70 and 50 degrees following planting, 10 GDDs accumulate per day, and corn should emerge in about 10 days (100 GDDs to emerge/10 GDDs per day = 10 days). However, if daily high and low temperatures are cooler, averaging 60 and 45 degrees after planting, 5 GDDs accumulate per day, and it may take nearly three weeks (100 GDDs to emerge/5 GDDs per day = 20 days) for corn to emerge.

Seedling emergence is dependent on soil temperature and air temperature. Also, keep in mind that estimates of emergence based on GDDs are approximate and can be influenced by various factors including residue cover, tillage, and soil organic matter (soil “color”) and moisture content.

Corn emergence can be slowed by inadequate soil moisture. Moreover, dry soil conditions can cause uneven emergence in some fields that may impact yield if emergence delays exceed 1.5-2 weeks. We have observed this problem in some cornfields, when weather turned dry after an early spring wet period.

Crops vary widely with regard to the minimum moisture content required for emergence. For corn, the minimum moisture content at which the radicle (first root) emerges is 30 percent of the seed dry weight. In contrast, for soybean, the reported minimum moisture content required for germination is 50 percent. However, since a soybean seed generally weighs only 2/3 or less the weight of a corn seed, a soybean seed requires less water to germinate.

Remember, you need those heat units to get that corn crop out of the ground. Warm days and nights will get that crop growing.

Invasive weeds: A growing problem

Many weeds have pretty flowers, but they are becoming a growing pain in our communities, and their looks certainly can be deceiving. These invasive weeds crowd out native plants, harm animal and human habitats and can increase erosion.

To many people, invasive weeds are simply beautiful wildflowers, such as Purple Loosestrife, Canada Thistle, Common Tansy, Crown Vetch, Wild Parsnip, Spotted knapweed, and Leafy Spurge. But when allowed to escape and spread into wild lands, private or public property, these plants can cause serious ecological and economic damage.

These weeds and others take over important habitat areas for wildlife, devastating shelter and forage while reducing the diversity and quantity of native plants. When weeds do not hold and protect the soil the way native plants do, erosion increases, causing sediment in streams and lakes, which can hurt fish populations and water quality.

Weeds also reduce land values, causing damaging economic impacts to local communities. For example, weeds have a profound effect on agricultural operations because they can reduce production of forage and crops, or cause harm to livestock or humans.

Invasive weeds are a problem from coast to coast in the United States, ranging from invasions such as kudzu, an aggressive Asian vine in the Southeast, to spotted knapweed, Canada thistle and wild parsnip, which are tough, rapidly invading plant competitors in Becker and Hubbard counties.

It is time for an all out attack on these invading plant menaces. The first thing that we need do is to increase awareness, by informing officials and citizens on how to recognize the threat, as well as gaining the ability to identify the invading weed species. It is not enough to just identify the problem weed species, but we must act to take measures to control these invasive plants.

It must be a multi-faceted approach between state, county, township and private entities. The Becker County SWCD and County Weed inspector are in the process of building a partnership to attack this problem of invasive weed species. If you have patches of any of the above mentioned problem weeds on your farmland, your county and township roads, gravel pits, or other areas in your neighborhood; contact your agricultural inspector and start the process of working out a plan of control.

Your Becker County Agricultural Inspector can be contacted at 1-218-846-7360, and your Hubbard County Agricultural Inspector can be reached at 1-218-732-4270.

For more information on growing degree days (GDDs) and crop emergence or other crop production informatio, or general questions about how to control certain weed species, please contact me, Will Yliniemi, Hubbard/Becker County Extension educator, at 1-218-732-3391, 1-218-846-7328 or by cell at 1-218-252-1042, or by e-mail at ylini003@umn.edu.

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