By ED LENTZ

The public will soon be reminded that events affecting agriculture also may indirectly affect them.

Farmers were unable to plant many fields this year. Though the weather prevented crops from being planted, it did not slow down weeds.

Ragweed is one of these weeds that has grown quite well this year. Soon it will be pollinating, and for the 15 to 20% who suffer from hay fever, its pollen will cause runny noses, sneezing fits, and watery eyes.

Unless treated with allergy medication, those who suffer from hay fever will get no relief until a frost kills the pollen-shedding plants.

Don’t completely blame the farmers for ragweed. I can find ragweed growing in waste areas, construction sites, and unmowed areas in Findlay. It is one of the more common weeds in the area.

Ragweed plants account for most of the pollen that causes hay fever. There are two species found in our area: common ragweed (Ambrosia artemisiifolia L.) and giant ragweed (Ambrosia trifida L.), which can be distinguished by plant height and leaf shape when mature.

Common ragweed is a shorter and bushier plant than giant. It generally reaches a height of 3 to 4 feet. Its leaves are dissected, featherlike, but not compounded.

Giant ragweed, as its name suggests, can be a very large plant reaching heights of 12 feet. Its leaves are generally three-lobed (like a trident) and sometimes five-lobed. The leaves can be 8 inches across and 12 inches long.

Giant ragweed is more prevalent than common ragweed in our area. It also accounts for most of the hay fever pollen because of its prevalence and height (wind can carry it for miles).

Both species are summer annuals that are native to North America. They can emerge as early as late April and continue to emerge until temperatures get too warm for new seed germination.

Ragweeds produce separate male and female flowers on the same plant in late summer. The flowers are small and greenish in color.

The male flower stalks develop at the ends of the upper branches so pollen can easily be distributed by the wind. It has been estimated that one ragweed plant may produce one billion pollen grains.

The female flowers form in the axils of the upper leaves. A plant growing all season may produce 25,000 seeds.

Seeds may be distributed across the field by water erosion, birds, rodents, and human activity. They may remain viable in the soil for 25 years, but most only last three to five years.

Seeds will require a vernalization period (cold period that occurs during winter) before germinating the following spring. Germination will be triggered by optimum soil moisture and temperature. Seeds need to be near the surface to germinate.

Ragweeds are a major weed problem in farmers’ fields. They generally are easier to manage in corn than soybeans since they are a broadleaf weed and corn is a grass.

Farmers used to rely heavily on ALS inhibitor herbicides for effective control in soybean fields, particularly common ragweed. ALS-resistant ragweed populations had established in many places by the time Roundup Ready soybeans became available in 1996.

The use of glyphosate on Roundup Ready soybeans gave farmers a new herbicide that was effective on ragweeds. However, overuse of only glyphosate allowed resistant populations of ragweed to develop.

Today, farmers use herbicides with different modes of action, and pre- and post-application of herbicides to battle ragweeds and to prevent the increase of resistant populations.

Giant ragweed is much more difficult to control than common ragweed in soybeans. It emerges at different times of the year and requires the farmer to apply glyphosate earlier and possibly twice for adequate control.

This may explain why giant ragweed continues to be the second most common weed identified in our fall soybean weed survey in the county (marestail has historically been first).

General information may be found for common ragweed at the following site: http://www.illinoiswildflowers.info/weeds/plants/cm_ragweed.htm and giant ragweed at http://www.illinoiswildflowers.info/weeds/plants/giant_ragweed.htm.

Management practices to reduce giant ragweed may be found at https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/7/3461/files/2014/04/GWC-12-xgs6e7.pdf and https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/7/3461/files/2014/04/girwfactfinal-1e9rlem.pdf

Lentz is extension educator for agriculture and natural resources for the Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at lentz.38@osu.edu.

Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.

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