A great time to talk about weeds


Warmer weather means things are greening up, but if you look close, some things are also starting to die. This is a great time to talk about weeds because there are times we think we may have issues but maybe not. A couple weeks ago, I saw fields and gardens that were covered in a pinkish/purple flowered plant and some folks get concerned. This plant is actually purple deadnettle and is considered a weed but not all weeds are the same. This one is actually a winter annual plant, which means it germinated last fall, has already set seeds and is now dying. There are several weeds like this. I often get questions on how to control weeds but identifying the plant and understanding the biology is very important. In this case when I get questions on how to control this plant, I tell them now to plan for the future. The plant is now dying, the time to control was last fall for winter annual plants.

As we start thinking about working outside and around the farm, don’t forget now is the time to begin management of problem weeds. One we see a lot of across the area is poison hemlock. This dangerous invasive non-native weed can send the uninformed to the hospital. All parts of the plant are poisonous: the leaves, stems, seeds, and roots. However, the toxins must be ingested or enter our body through our eyes, nasal passages, or cuts in our skin to induce poisoning. The toxins do not cause skin rashes or blistering. Poison hemlock stems are hairless, light green to bluish-green, and covered with obvious purplish blotches. The purplish-blotched stems are first evident as the rosettes begin to bolt and become even more obvious on mature plants. Mowing poison hemlock just after plants begin to bolt but before they bloom can be highly effective although mowers may pass over the low-growing first-year rosettes. However, equipment operators should approach mowing large poison hemlock infestations with caution. Non-selective herbicides with the active ingredient glyphosate are effective but can also eliminate plants that compete with poison hemlock. Grasses are effective competitors against poison hemlock and a range of selective post-emergent herbicides can be used that will preserve grasses but kill the poison hemlock. These include triclopyr and products that contain a combination of 2,4-D, dicamba and others. Poison hemlock is currently in the growth stages in southern Ohio that are susceptible to early-season management options. Be sure to act soon as these problem weeds.

Then we have our wonderful summer annual weeds like foxtail and crabgrass. These tend to be problems in our lawns. If they are objectionable for you, we must prevent seeds from germinating by using a preemergent herbicide. The problem is this is the time of the year that seeds start germinating so it could be just the right time to prevent them starting. If you still wanted to try, do it as soon as possible. If these weeds do cause you a problem, they will die sometime into summer.

Then we have our perennial weeds and dandelion is the classic example. They can be controlled by digging them up – the more of the root you get, the better the chance of killing the plant, or you can use a labeled herbicide. Keep in mind that flowering will be largely done in a few weeks and not be much of an issue the rest of the season, but now is the time to control this plant either way as it finishes flowering.

Finally, the toughest of them all are the complex perennials – ones that reproduce by more than seeds. We have plants like our ground ivy or creeping Charlie that also spreads by stolons above the ground and Canadian thistle that spreads by underground rhizomes. These take a lot of effort to control. The bottom line for effective control of any weed is to know the plant, how it grows, what are the best control options for you, and controlling the weed at the right time. Call me any time if you have specific questions.

It is time to start planting in our gardens. As we prepare our garden for this year, keep a few things in mind. First, recall where crops were planted last year then rotate this year’s crop to a new location. This will reduce disease pressure on your plants. Avoid the temptation to work up the soil if it is too damp. It is ready to till when you can grab a clump of soil and it crumbles in your hand. Prior to the last tillage of the soil, consider adding a low nitrogen fertilizer. A 6-24-24 or 5-20-20 fertilizer works best. Avoid fertilizers that have a higher first number (nitrogen) than the last two numbers (phosphorus and potassium). Too much nitrogen will make the plant grow fast but not set fruit. The exceptions are leafy vegetables and corn which need more nitrogen.

All of these and more educational opportunities can be found on the brown.osu.edu website or our blog page – u.osu.edu/browncounty. As always, I look forward to working with you more, feel free to reach out by stopping by the office, calling, or sending me an email at 937-378-6716 or [email protected]. I am happy to help in all your agriculture, natural resources, and community development needs.

CFAES provides research and related educational programs to clientele a nondiscriminatory basis. For more information, visit cfaesdiversity.osu.edu. For an accessible format of this publication, visit cfaes.osu.edu/accessibility.

Trevor Corboy is the Agriculture & Natural Resources and Community Development Extension Educator at OSU Extension Brown County.

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