Battling Weeds in the Lawn

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September is a time for the lawn. In my last article, I discussed overseeding and fertilizing the lawn, but weed control is another key to a healthy lawn. Some weeds in the lawn are often tolerated, but when the weed population begins to outweigh the turf population, management should be incorporated.

The Battle with Weeds

Plants are considered weeds because they are adaptive, aggressive and opportunistic. Weeds come into a lawn that is thin or bare. They are often found on the edges of our lawn or places where the grass doesn’t grow as well. Eventually they will work their way into the rest of our lawn. So overseeding a lawn may be the answer to reducing the weed population.

Growing turfgrass in the shade is not always possible. Even the shade mixes are not made to grow in high shade. Dense shade is not the growing condition for turfgrass and it often leads to weeds. In some cases, trees may be pruned to improve the sunlight getting to the turf, but be careful not to ruin the shape or health of a tree or shrub  just to get more sunlight to the turf. If the shade is too dense, a good alternative might be a shade tolerant groundcover or apply mulch where grass won’t grow.

Crabgrass

Crabgrass has been found in high populations this year, even in locations where crabgrass preventer was used. The University of Nebraska-Lincoln Turf department says the weather is to blame. Crabgrass germinates when soil temperatures reach 57-64 degrees at a one-inch depth, with the highest germination when soil temperatures increase to 73 degrees. Crabgrass will continue to germinate through the summer until soil temperatures reach 95 degrees. With the unusual weather we had this spring and summer, the largest amount of crabgrass germinated later than normal when the concentration of our original spring crabgrass pre-emergence herbicide was declining. This is why we saw so much more crabgrass later this summer than we usually do.

To help prevent this problem with later emerging crabgrass in the future, switch to longer lasting chemicals, such as prodiamine. You can also look to a second application of crabgrass preventer in mid-June to stop the germination of the late flush of crabgrass. There are also post-emergent herbicides to use for crabgrass, but I don’t recommend them this late in the season. Remember, crabgrass you are seeing now will die when the first frost hits. Also, it is difficult to kill a large crabgrass plant with a post-emergent herbicide.

Broadleaf Weed Control

As for when to treat for broadleaf weeds that do come into our lawns, fall is the best time to control them. In fall, perennial weeds are moving carbohydrates from the leaves into the roots for winter storage to help get them going again next spring. If you spray them in the fall, the herbicide will also be moved into the roots which makes the herbicide more effective. Also, the weather is more suitable for herbicide use than in the spring when Dicamba and 2,4-D have a potential to drift to non-target plants. Fall is also a great time to apply herbicides to kill the winter annual weeds such as Henbit either with a pre-emergent herbicide such as prodiamine (Barricade) or dithiopyr (Dimension) or with a post emergent after the henbit has germinated.

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Henbit along a sidewalk edge

The best time to apply herbicides in the fall is mid-late September and again in mid-late October. The second application helps to get better control on perennial weeds that may have been missed or were not fully killed. The second application also helps to ensure that winter annuals have germinated to help get control of those with a post-emergent herbicide. Products containing 2,4-D, carfentrazone, sulfentrazone, quinclorac, or triclopyr are all good for controlling perennial weeds in the lawn. Use caution around trees, shrubs, and landscape beds as these products can damage broadleaf plants but they will not harm our turf.

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Yard and Garden: May 18, 2018

Y&G Blog Photo, 2018

This is the Q&A for the Yard and Garden show for May 18, 2018. Yard and Garden Live is a call-in radio show I do on KUTT 99.5 FM from 10-11:30 am and it will run through August 3, 2018. It can also be found on kutt995.com for online listening. If you missed a show or just want to read through the questions, I have written them all in my blog and will continue to do so throughout the season.

Guest Host: Graham Herbst, Community Forester from the Nebraska Forest Service

1.The first caller of the show has moss growing on the soil of an area where he is trying to plant blueberries and asparagus. Is the moss an indicator of acidic soils? He has used a pH meter and it all reads at 7.0 pH. How can he get the right soil conditions for these plants?

A. Moss does like living in acidic soils, but it will grow in most any location that is moist and typically shady. To know for sure how the soil pH is, it would be most accurate to get a soil test completed. Do a separate test for each section of this garden to know what is best for the blueberry area and what is best for the asparagus patch. Understand that blueberries do not grow well in Nebraska due to our weather and our basic soils. The soil would need to be amended around the blueberries every year to ensure the acidic soil they prefer.

2. A caller sprayed the lawn with a weed killer with crabgrass control 10 days ago. Can he go back in now to apply a fertilizer with a weed killer in it?

A. Without knowing the ingredients in the crabgrass control and weed killer it is hard to tell, but it if there is a weed killer in both the crabgrass control and the fertilizer it would not be advised to use both. It would be best to go in with just a fertilizer now and avoid the weed control for now. It is recommended to wait at least 2 weeks between applications of herbicides.

3. This caller divided and transplanted hostas last year, they are not growing as large as they had been before they were divided. Should anything be done to help them grow larger?

A. Give them time to get over the transplant shock and to build their roots back up. You can fertilize them as well to help them grow healthier. A general fertilizer for perennials would be helpful, a 10-10-10 fertilizer would benefit.

He also wanted to know if it is too late to transplant lilies this year?

A. It would still be fine to transplant lilies this year. Just make sure on very hot days you keep the plants watered.

4. A caller has a native grass patch that now has volunteer plants of Siberian elms and cottonwoods. How can these tree saplings be controlled without harming the grass?

A. If they are small and the population isn’t too high, mechanical removal can be beneficial. They shouldn’t regrow from a sapling. He could also use 2,4-D or a product containing triclopyr as a stump treatment for the saplings to ensure no regrowth occurs.

5. This caller has boxwoods that turned brown over the winter months. What can be done about this?

A. This is likely due to winterkill. Evergreen plants still transpire through the winter, if that transpiration exceeds the amount of moisture the plant takes in through the winter, desiccation can occur. Prune out the brown areas. As long as there are still green leaves on some of the branches, it should grow back.

6. A gentleman has a wildflower prairie area that is getting grasses and weeds coming in. What should be done at the end of the season with this wildflower garden to help reduce the weeds?

A. Mowing the weeds at the end of the season will help reduce the seedheads of weeds. You can also continue to add new plants to compete with the weeds, taller weeds will be most effective. For more information, visit this NebGuide on Wildflowers for the Home Landscape.

Wildflower Collage

Wildflower Photos from the Nebraska Statewide Arboretum at: arboretum.unl.edu/wildflower-week

7. A caller received a black chokeberry with a collection of plants. What is that plant? How should it be grown?

A. This is a nice, multi-stemmed large shrub that can grow up to 3-6 feet tall. It is a great plant for full sun and it produces berries, also called aronia berries, that can be made into jams or jellies but it is typically not eaten raw. Here is an article from the UNL Community Environment website with more information on Chokeberries

8. Is it ok to transplant a lilac shrub now?

A. It would be better to wait to do in the fall rather than right now. The lilac could be cut back to no more than 1/2 the size of the plant before moving, to make it more manageable. Do not cut it back to the ground for a few years to allow the plant to work more on building roots than on growing.

9. This caller has a double weeping cherry tree that has developed a frost crack over the majority of the trunk and now it is not leafing out. What can be done to save the tree?

A. The lack of leaf development may not be due to the frost crack. If a callus has begun to form on the frost crack, that is a good sign. Once the frost crack has developed, there is nothing to do to fix it. The lack of leaves could be due to cold damage from the winter, but not necessarily the frost crack. Give the tree some time to see if it is just late coming out of this long, hard winter. Don’t fertilize it now, it can do more damage to fertilize an already stressed plant. Scratch the bark off on some of the smaller twigs, if it is green underneath, the plant is still alive, if it is brown, the plant is probably not going to survive.

10. How long does it take for a pear to start producing fruit? This caller has one that was planted in 2015 and has not yet bloomed more than just a couple of blooms.

A. It can take pear trees up to 10 years to start flowering and producing fruit, but the can begin this as early as year 3.

11. A caller has a snowball bush he would like to transplant. When is the best time to move this plant and how is it done?

A. Fall would be the best time for this. To be most successful with this transplant, dig up as much of the rootball as you can and only cut the plant back up to 1/2 the size that it is now. When replanting, dig a hole just as deep and twice as wide as the rootball and backfill with the existing soil from the new location.

12. The last caller of the day has a sawtooth oak that was planted last year. As soon as it was planted it dropped all the leaves but regrow them through the summer last year. Now, the tips of the branches seem to be dying back and the tree is suckering at the base. He mulched the tree in and he waters slowly for 10-15 minutes every 2 weeks or less. What is wrong with the tree and will it survive?

A. The water amount is sufficient, but more often would be beneficial to the tree. Water a newly planted tree for about 15 minutes once a week. This tree is likely facing some problems with transplant shock, but should be coming out of that. The oaks are slower to come out of dormancy this year. Give the tree a couple more weeks then prune out the tips that have not developed leaves while the rest of the tree has.