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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Crabgrass

crabgrass, Joseph Berger, Bugwood

Crabgrass photo, courtesy of Joseph Berger, Bugwood.org

This time of the year is always full of activities to do outside. It is a great time to get outside in the comfortable weather. Lawncare is always at the top of our spring outdoor ‘to do’ list, and crabgrass is number one on the concerns.

Crabgrass Basics

Crabgrass is a summer annual grassy weed that takes advantage of thin areas in our lawns to become established. As a summer annual weed, crabgrass germinates in the spring and, if not controlled, new plants continue to germinate throughout the summer. Each plant grows for one summer, then dies with the first hard frost in the fall. New crabgrass that you see in your lawn each year is from seed that was set the previous year by the crabgrass growing before.

Crabgrass is a problem in our lawns. Each plant will compete with our desirable grass species. Once crabgrass gets into a lawn, it will compete with our grass for water, sunlight and growing space. Plants produce a large amount of seed that will germinate the following year, creating an ongoing problem on your lawn.

Prevention

Crabgrass is difficult to eradicate once it becomes established, so it is better to prevent this weed from becoming established in the first place. Crabgrass preemergent herbicides are used to inhibit the growth of young seedlings, destroying them before they can emerge from the soil. Which is why many people prefer to use a preemergent herbicide to control the crabgrass in their lawn.

Preemergent herbicides should be applied before crabgrass has started to germinate, which happens when soil temperature has reached 55-60 degrees F, measured at 4-inch soil depth, for at least four days. This is not based on a date range, because soil temperatures differ from year to year. It is based on the weather conditions for that year. We have reached that point now this year.

It is not beneficial to apply the preemergent too early in the year. Once applied products begin to degrade and breakdown. If your application is made too early, before crabgrass germination has started, you are wasting your product and monty because you will have a shortened period of control once crabgrass does start germination.

Plan on making two applications of preemergent to give season-long crabgrass control. Purchase enough product in spring for two applications; garden centers often run out of preemergent products by the end of spring so it could be hard to find later in summer. Each product has a slightly different length of residual action, so follow the product’s label directions on when the second application should be made.

Controlling Existing Plants

Post-emergent herbicides can be used to control crabgrass that has emerged in your lawn. Products containing Mesotrione, commonly found in the product called Tenacity, works as both a pre- and post- emergent herbicide on grasses and broadleaf weeds. It can also be used at seeding if you have a history of crabgrass problems and need to overseed.

The other commonly used post-emergent herbicide for controlling crabgrass would be products that contain Quinclorac, commonly found in the product called Drive.

If crabgrass does appear in your lawn, you can reduce future problems by keeping plants mowed short enough that they don’t produce seedheads. Then at least there won’t be additional seed in the soil to increase your problem next year.

What is wrong with my lawn?

What's Wrong With My Lawn blog post

This year has been extremely humid and warm. We have seen a summer full of warm temperatures during the day that cool down in the nighttime to the dew point, which has been causing a high number of turf diseases. We are also now experiencing a great deal of crabgrass and other summer annual weeds in our lawns. These are things that decrease the overall appearance of our lawns but they are not long lasting this late in the summer.

Brown patch is a fungal turf disease showing up in our lawns right now. This disease often shows up in lawns that were overwatered or were fertilized heavily in the summer months as brown patches in an otherwise green lawn. Upon closer investigation, you may notice that the leaves may have long tan-colored spots that are surrounded by a dark brown margin. You can avoid this disease by avoiding over-irrigation and over-fertilization of the lawn.

Summer Patch at Christenson Field, P Hay

Summer Patch on a baseball Field, Photo by Paul Hay, Nebraska Extension Educator in Gage County.

Summer patch is also showing up in our lawns right now. This fungal disease also leaves brown patches in your lawn, but usually they are in a circular pattern with an area of green turfgrass in the center, like a frog-eye appearance. The leaves do not have a distinct marking on them but the roots will be brown. The best control for summer patch is to follow fertilization and watering requirements to reduce the stress to your lawn.

The diseases that we see in our lawns this time of the year are mostly environmental. You can help to reduce the incidence of these diseases if you take good care of your lawn. Keeping the lawn mowed at 2-3 inches high, correct fertility, and correct watering, will help keep your turf healthy and able to compete with these diseases. Fungicides can be used, but they need to be applied as a preventative and are not usually necessary in home lawns. Home lawns can tolerate a low level of damage without the need for fungicides. If this is a problem that is seen in the same location of your lawn year after year, you may need to use a fungicide, but that should be used in the spring or in the summer as the first signs begin to appear in your lawn. At this time of the year, fungicides will not fix the damage that is already seen in the lawn this year. So in the late summer and fall, fungicides are not recommended.

crabgrass, Joseph Berger, Bugwood

Photo of Crabgrass by Joseph Berger, Bugwood.org

Crabgrass and other summer annual grasses are also becoming more problematic now. In addition to the maturation of plants that germinated earlier in summer, incidence has also increased from recent rains and warm weather that allowed more seed to germinate where a sufficient herbicide barrier is not still present, especially in full sun or thin turfgrass canopies. Control is not necessary this time of the year because the crabgrass present in your lawn now, will die with the first fall frost in a few weeks. It is the best environmentally and economically for you to use a pre-emergent herbicide next spring.

Lawn fertilization should occur with the holidays: Arbor Day, Memorial Day, Labor Day, and Halloween. Applications for Labor Day can be done anytime now. Apply 1 pound of Nitrogen per 1,000 square feet on your lawn. Once the temperatures cool down, you can begin using 2,4-D products to combat broadleaf weeds such as dandelions, clover, and henbit. The fall is the best time to treat for the perennial weeds so that the chemical is taken into the roots with the nutrients the weeds have in their leaves that they store in their roots over the winter months. For henbit, it is best to treat this in the fall as well to kill it before it sets seed next spring.

Spring Lawncare

Spring Lawncare, blog post

April is finally here, which means spring should be bringing in warmer weather. April is a good time to get out and start working in the lawn and garden to prepare our yards. To help ensure that you have the best lawn on the block, here are few tips to improve your lawn this spring.

April is a great time to overseed your lawn. If you had some spots that were flooded out last spring, now is a great time to get some new seed planted. The beginning part of April is best for seeding lawns, but it can be done until the end of the month. Frequent, light irrigation is necessary to keep newly seeded lawns moist. It may be necessary to water twice a day to keep it from drying out and dying. Straw mulch can be applied to keep the seedbed moist, but it is not necessary and can bring problems with weed seed that is often a contaminant of straw. Do not apply any pesticides to newly seeded lawn until you have completed 2-3 mowings. Also, do not try to overseed right before or right after applying crabgrass preventer as this chemical will prevent the germination of your desired grasses as well.

We often face difficulties with weeds in our lawns. The key to weed management is to keep your lawn healthy to avoid weed infestations and to identify the weed before chemical controls are used. Many of our herbicides are specific to either a grass weed or a broadleaf weed and won’t work on the other weed type. Also, you need to know the weed to know the lifecycle for when the best time is to manage that weed with a chemical. As I stated in my previous news column, henbit is a winter annual and should only be chemically controlled in the lawn in the fall, the spring is too late.

crabgrass, Joseph Berger, Bugwood

Crabgrass Photo By: Joseph Berger, Bugwood.org

Crabgrass pre-emergent herbicides need to be applied before crabgrass germinates, which is when the soil temperature is 55-60 degrees Fahrenheit. This typically occurs toward the end of April. Applying this chemical too soon may cause the chemical to stop working earlier in the season when crabgrass may still be germinating. In this case an additional application may be necessary later in the spring, so it is best to wait until the correct time to only have to apply this one time per season. Broadleaf weeds, such as dandelions, clover, and ground ivy should be controlled in the fall for best control but can be managed in the spring with 2,4-D products.

Fertilizing turf can be done up to 4 times per growing season. Apply fertilizers at a rate of 1 pound of nitrogen per 1,000 square feet for each application. A good trick for remembering when to apply fertilizers is to fertilize with the holidays: Arbor Day, Memorial Day, Labor Day, and Halloween.

Mower Collage

We are now getting to the time of year when we will have to start mowing our lawns. Prepare your lawn mower for the season before you start mowing. Start by sharpening the blades. Dull mowing blades can cause tearing to occur on the grass blades rather than a smooth cut. These tears can lead to more insect and disease problems. Change the oil in your lawn mower, if you didn’t do that in the fall. Check your spark plugs and tire pressure. Finally, make sure you clean under the deck for any grass that may still be stuck under there from last season. You can start mowing as soon as the grass starts growing. Remember to mow at a height of 2.5-3.5 inches and only cut off 1/3 of the grass blade each time you mow.

Fall Insects & Weeds

fall landscapeWith fall coming right around the corner, many things are going on in our landscapes. There are many weed species creeping their way through our trees and lawns. We are also having a great deal of problems with many nuisance insect pests in our trees. The following are the horticultural pests I have had the most calls on over the past couple of weeks that I feel the majority of the public is trying to deal with.

2015-07-30 17.00.35We are seeing wild cucumber covering up trees in our windbreaks. This weed is very similar to cucumber vine that you grow in your vegetable garden and it grows up and over our trees, especially through windbreaks. If left on the tree, most often the tree will survive, but in some cases, this vine can smother the tree from sunlight and cause death. It is very easily pulled and can be treated with general herbicides, such as 2,4-D, but only as a stump treatment or carefully painted on the leaves.

Another problem that many people are facing this year is the issue with high populations of crabgrass in lawns. With all of the spring rains we had this year, many weeds are taking over our lawns. Crabgrass is a warm season annual so it germinates early in the spring and dies with the first frost of the year. What is in your yard now, does not need to be controlled as it will die in the next couple of weeks. Just remember to apply a crabgrass pre-emergent herbicide in the spring next year.

Damage from Twig Girdler

Damage from Twig Girdler

I have had numerous calls lately on small branches on the ground all around large trees. This is most likely due to a couple of beetle insects, the twig girdler or the twig pruner. These are two very similar insects that cause similar damage to trees. These insects will chew small branches of trees causing them to fall out of the tree on windy days. The twig pruner causes branches to have a jagged edge where it tears from the tree after the inside is chewed. Twig girdler causes branches to have a very smooth cut on the outside of the branch, like it was pruned off with a pair of pruning shears. Both of these insects cause minimal damage, it is mainly an aesthetic nuisance to the tree. Chemical treatments are not necessary or recommended for treating twig girdler or twig pruner.

Fall Webworm photo by G. Keith Douce, University of Georgia, Bugwood.org

Fall Webworm photo by G. Keith Douce, University of Georgia, Bugwood.org

One thing that we all see as we drive around Nebraska right now, is fall webworm. Fall webworm is the immature form of a medium-sized white moth. The caterpillars form webbing at the ends of branches of many deciduous trees in the fall. This webbing entangles and kills the leaves within it, and causes no further harm to the tree. They are not necessary to control with chemicals and it is not effective to get chemicals through the webbing. If they are not wanted in your tree, for aesthetic reasons, they can be pulled out with a broom and put into a burn barrel (where permitted) or a bucket of soapy water.

Yard and Garden: June 26, 2015

Yard and Garden Green Logo

This is the Q&A for the Yard and Garden show for June 26, 2015. 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 July 31, 2015. 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: Sarah Browning from Nebraska Extension in Lancaster County

1. A caller has a pine tree with needles that are turning brown at the bottom of the tree. What would cause this?

A: There are a couple of common fungal diseases on pine trees, needle blight and tip blight. Both of these diseases will start from the base of the tree and move upward. Depending on the species of tree, it could also be pine wilt, but this disease progresses rapidly, causing death in only a few months. There are fungicides to be used for needle and tip blight, but they are best used in May and June. Neither of these fungal diseases should kill the tree in one growing season. This publication from the Nebraska Forest Service, Diseases of Evergreen Trees, shows pictures of both diseases and pine wilt and goes over treatment methods.

2. This caller has tomatoes that have black specks on the leaves which eventually turn yellow and die, but there are no specks on the tomatoes themselves. She was also curious why it makes a difference to water from below rather than above?

A: This would be a fungal disease called black speck or black spot. It is best controlled through good sanitation practices such as watering from below the plant, removing infected leaves as they are first seen on the plant, removing plants in the fall after the growing season, avoid crowding plants, rotating plants each year in the garden, etc. There is a great NebGuide on Leaf and Fruit Diseases of Tomatoes that will be helpful with many of our tomatoes this year with all of the rains as we are seeing many more leaf diseases. Watering from below the plant helps reduce spores splashing from plant to plant and from the soil to the plant. Watering from below also helps to keep the leaves dry throughout the day and into the night to reduce leaf wetness and humidity in the plant which is conducive to disease development.

3. A caller has a bur oak that is 15 feet tall with leaves that are curled under. What would cause that?

A: This could be herbicide damage from a 2,4-D product. It could also be from aphids or lacebugs. To determine if it is due to insect feeding, look on the underside of the leaves for tiny, green bugs, lace-like bugs, or frass. If it is aphids, they can be controlled with many general insecticides. Lacebugs rarely warrant insecticides as their damage is minimal to the tree. If it is herbicide drift, the tree should grow out of it, depending on severity of damage.

Bagworm

Bagworm

4. Is it time to spray for bagworms yet?

A: They have not yet begun to emerge in Southeast Nebraska. They are behind in their development this year due to the cool spring. They should be emerging in the next week or two. Ensure that the immature bagworms are active on your tree before treating to get best control from your pesticide.

5. Another caller wanted to know if it is illegal to use rainwater in Nebraska?

A: No, Nebraska does not have a law to prohibit the catching and use of rainwater, as some other states do. Rainwater is a good use of extra water to avoid so much runoff and contamination to the water supply. Be careful to not use rainwater on vegetable crops to avoid contamination from non-potable water.

6. This caller has a Kentucky coffeetree that was planted in the right-of-way by the city within the last 2 years. The bottom of the tree has leaves and new growth, but the top of the tree does not. Will it survive?

A: This tree probably is having troubles with establishment or may have been planted incorrectly. Due to this, the top of the tree is not receiving water and nutrients from the roots. It can be pruned back to the growth with possible success. Be sure to watch for a new leader to develop or you may have to start a new one to help it grow taller as the central leader will be pruned off of the tree.

Photo by Howard F. Schwartz, Colorado State University, Bugwood.org

Yellow Nutsedge Photo by Howard F. Schwartz, Colorado State University, Bugwood.org

7. How can nutsedge be controlled in lawns?

A: A product that is specific for use on sedges can be used in the lawn with no harm to the turfgrass. The most commonly used product for yellow nutsedge is Sedgehammer, it should be applied multiple times throughout the growing season, as new plants come up. It is better to spray with Sedgehammer early in the life of the new plant to reduce nutlet production and reduce the size of the plant.

8. A caller wondered when the best time is to prune an oak tree?

A: It is not advisable to prune oak trees during the summer months to avoid chances of getting oak wilt in the tree. The best time to prune oaks, and many of our deciduous trees, would be in the dormant season, such as November.

9. A caller has a fescue lawn that is getting yellow in spots. What would be the cause of that?

A: This year we have faced many days of cool, wet, cloudy weather which is favorable to many turfgrass diseases. This sounds like it is either brown patch or dollar spot disease. Brown patch has tan colored lesions on the leaf blades that have a dark margin around the tan spot. Dollar spot would just be tan spots in the lawn that are typically half-dollar sized but you can see many dollar spots coalesce into one larger spot. As the weather dries out and warms up, the fungus should fade in the lawn, or you can use fungicides in the lawn if necessary.

10. A caller has bindweed in the lawn. What can be done to control it?

A: A herbicide that is just for broadleaf weeds will work on the bindweed and not harm the lawn. Triclopyr is a great choice to use. This is commonly found in brush killer, poison ivy killer, and clover killer in the stores. Make sure that the temperature on the day of application is below 85 degrees Fahrenheit to reduce the risk of harm to non-target plants.

11. A lady has cucumbers that are flowering with no fruits developing. What would cause that?

A: Cucumbers have both male and female flowers on the same plant. Early in the season you may see development in only male flowers with no female flowers to produce no fruit. The female flowers will have a tiny cucumber structure at the base of the flower. This also could be due to low pollinator presence in the garden. Rainy days and hot days discourage pollinators. Give the plants more time, they should begin to produce female flowers and fruits soon. Hand-pollination may also be necessary if it is due to low pollinator presence. To hand-pollinate, take a Q-tip and touch the pollen of all of the flowers.

12. A caller has a clematis plant that is dying back, causing all of the leaves to turn brown.

A: Clematis commonly gets a fungal root and crown rot. If this plant was in a location where water sat this year with all of the heavy rains, it may have caused this fungal disease to occur. Cut the plant back to the ground and see if it will grow back, if not, you will need to replant.

13. This caller has Iris plants that have completed their blooming period for the year. Can these be cut back now?

A: No, all spring blooming plants need to be left, without being cut off, for the remainder of the summer until their foliage turns brown in the fall. This allows the plants to make sugar throughout the summer months to have a starting supply for early spring blooming next year. The flower stalks can be removed after the flowers are done.

14. A caller has patches of clover in the lawn. What can be done for management for the clover?

A: The best time for treatment of clover is in the fall with a Triclopyr or 2,4-D product. At this point, the temperatures are too high for herbicide control without possible harm to non-target plants. Both of these products can turn into a gas and move to non-target plants if temperatures are above 80-85 degrees Fahrenheit, the 2,4-D can volatilize for up to 72 hours. Be sure to mow the clover prior to herbicide treatment to mow off the flower blooms and cause less harm to bees.

15. A caller has grass planted in late March and added more seed later in the spring. She used a starter fertilizer and covered the areas with straw, and now there are brown spots appearing in the lawn. What would be causing that?

A: Brown patch disease is common on young seedlings of tall fescue. Look for irregular shaped tan spots with a dark margin to know if it is brown patch. Bayleton is a good fungicide that may still be effective on this lawn. Also, remove the excess straw to reduce disease problems.

16. That same caller has crabgrass coming up around her trees. Can she use roundup to control it?

A: Roundup can be used around the base of trees with minimal damage to the trees. A better option would be to use a post-emergent crabgrass herbicide such as Dimension or Fusilade.

17. A caller wanted to know if it was allowable to use Grass-B-Gone in their sweetcorn?

A: No. Grass-B-Gone kills all types of grasses, including sweetcorn. Also, Grass-B-Gone is not labeled for use in a vegetable garden.

18. A gentleman has mock orange and bridal wreath spirea. When can these plants be pruned?

A: Both of these plants have just finished blooming for the year so they can be pruned now. Remove no more than 1/4 of the plant in a growing season. This can be done by removing the largest canes at the base of the plant. If it is too tall, you can remove 1/4 of the height, if it is a 4 foot tall shrub you can prune it back to 3 feet tall.

19. A caller wanted to know what to do for management of dandelions in their lawn?

A: Dandelions are best controlled in the fall with a 2,4-D product.