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Turf and Bees: What's the buzz on pesticides in lawns?

By Ian Lane, Graduate Research Assistant

If you have been paying attention to the news lately, you know that bees have been making headlines. News outlets have done an amazing job of helping scientists sound the alarm on unsettling declines in bee pollinators. While we have good evidence for declines in honey bees and some of their cousins, the bumble bees, the cause of this decline is hard to pinpoint. Current thinking in the scientific community puts the decline down to a number of interacting factors, including reduction in stable food sources, introduction of bee diseases, and the irresponsible use of insecticides. While it's difficult to tease apart how these factors interact, we do have some good knowledge about how lawns fit into this theoretical framework.



Sam Bauer


Photo 1: White clover and dandelion can provide great early season forage for pollinators in lawns



Herbicides

Lawns are home to a number of weeds that are the bane of homeowners. While our gut reaction may be to reach for a herbicide, it's worth noting that many weeds actually can provide high quality forage for bees. Two of the most important lawn forage plants are the common dandelion (Taraxacum officinale) and Dutch white clover (Trifolium repens). Dandelions are one of the earliest, and often only, blooming flowers of spring. This early source of pollen and nectar is essential to overwintering honey bee colonies as they begin the process of raising new workers. White clover is another spring bloomer (though not as early) that provides highly nutritious pollen throughout the year. While the exact nature of bee's relationship with these flowers isn't widely studied, recent research at the University of Kentucky sought to characterize the types of bees visiting dandelions and clover. They found surprising diversity on white clover, including a number of at risk bumble bees (Larson et al. 2014). Similar preliminary research here at the University of Minnesota confirms many of their findings.

There may also be some solutions for homeowners looking to control weeds but leave clover in their lawn. One common herbicide known as 2,4-D is effective on many broadleaf weeds, but generally ineffective on clover. Small demonstration trials at the University of Minnesota confirm that 2,4-D has relatively low action on clover but is relatively effective against other weeds.

Insecticides

The another type of pesticide that can make a big impact on bees are insecticides . Much of the recent attention on pollinators has focused on a class of insecticides known as the neonicitinoids. Neonicitinoids are used in turf to help control a number of insect pests, most importantly grubs. They work by "dissolving" into the irrigation water or rain, which is then taken up by the plant and becomes part of the leaf and root tissue. This ensures that any insect munching on the tissues of your grass gets a lethal dose, and your lawn stays green. While bees would never have a reason to take a bite of your grass, your helpful lawn weeds are a different story. It turns out that not only do these insecticides move into plant leaves and roots, but the nectar and pollen of the flowering weeds as well.

Many studies have looked to see if neonicitinoids applied to lawns full of clover have negative effects on bumblebee colonies. The researchers in Kentucky do this by getting a colony of the commercially available common eastern bumble bee (Bombus impatiens), placing it on a patch of flowering clover that is treated with a neonicitinoid, then caging them so they are forced to forage on the treated clover. These experiments are always accompanied with a similar set-up but on a non-treated patch as a point of comparison. Here again the University of Kentucky has been leading the way with a study published in 2002 (Gels et al. 2002) that found if imidacloprid (a type of neonicitinoid) was applied to flowering turf without any post application irrigation that bumble bee colonies suffered worker weight loss, increased worker death, and sluggish behavior. However, if irrigation was applied directly following these imidacloprid applications, no negative responses were seen.

Similar responses were seen in a study investigating clothianidin, another type of neonicitinoid (Larson et al. 2013). Bumble bee colonies that were confined over patches of flowering clover, and that had the high label rates of clothianidin applied to the turf, saw dramatic effects on the number of workers, new queens, as well as total colony weight when compared to control colonies. The effects of irrigation were not part of this study, but when clover nectar from nearby sights that had been applied with clothianidin were sampled, they found high amounts of the neonicitinoid. This study's main aim was to compare clothianidin to a new chemistry of insecticides called anthranilic diamide (specifically chlorantraniliprole). This new class of chemical had seemingly no adverse effects on bumble bee colonies when compared to the controls. While there is more research to be done, this is a promising alternative to neonicitinoids for insect control in turf. You can currently purchase chlorantraniliprole for use on residential and commercial turf, and trade names include "Scott's Grubex" or Syngenta's "Acelepryn".

While urban landscapes and lawns are only one part of a very large system, they are nevertheless an important part of a vast majority of people's lives. Promoting animal diversity in urban landscapes, be it pollinator or other, helps improve important issues related to stormwater runoff (rain gardens and buffer strips) and urban agriculture (pollination and biocontrol services) and also enriches everyday life through learning opportunities and aesthetic value. Even the smallest effort, such as leaving some weedy flowers or choosing a safer insecticide, may make a difference.

Stay Informed

A new series on pollinators is being offered by the University of Minnesota Landscape Arboretum. "Pollinators: What you need to know and how to make a difference" is a 3-part series focusing on: 1) Plants and People, 2) Pesticides and Other Problems, and 3) Policies and Politics.

The Minnesota Turf and Grounds Foundation will be offering a 1-day session on Super Tuesday of the Northern Green Expo, January 13th, 2015. "Bee Aware: The importance of pollinators in the landscape" will feature expert presenters discussing real world issues surrounding pollinators, as well as practical strategies to promote them in the landscape. Stay tuned to www.mtgf.org as this program develops.

Works Referenced

Gels, J. A., D. W. Held, and D. A. Potter. 2002. Hazards of Insecticides to the Bumble Bees Bombus impatiens (Hymenoptera : Apidae ) Foraging on Flowering White Clover in Turf. J. Econ. Entomol. 95: 722-728.

Larson, J. L., A. J. Kesheimer, and D. A. Potter. 2014. Pollinator assemblages on dandelions and white clover in urban and suburban lawns. J. Insect Conserv. 18: 863-873

Larson, J. L., C. T. Redmond, and D. A. Potter. 2013. Assessing insecticide hazard to bumble bees foraging on flowering weeds in treated lawns. PLoS One. 8: e66375.

Dear Yard and Garden News Readers,

For those of you that are interested in learning more about lawn care and turfgrass science but have been unable to attend the School of Turfgrass Management in the past, we've developed a new offering for you, The 2014 Great Lakes School of Turfgrass Science. Much like the traditional turf school, this class was designed as a basic foundation of turfgrass science education for those that don't have a formal degree in turfgrass science or those looking for a refresher. Along with the traditional instructors from the University of Minnesota (Sam Bauer and Dr. Brian Horgan) and the University of Wisconsin-Madison (Dr. Doug Soldat, Dr. Paul Koch, and Dr. Chris Williamson), we've also added instructors from five other universities:

Dr. Dave Chalmers- South Dakota State
Dr. Kevin Frank- Michigan State
Dr. Dave Gardner- Ohio State
Dr. Aaron Patton- Purdue
Dr. Frank Rossi- Cornell University

This ten person team of instructors brings a whole new level of turfgrass science knowledge to this short course. Other features of the new format include:

- Fully online course; view session live on Wednesday nights from 6-8pm or watch the recordings

- Half the cost of the traditional School of Turfgrass Management

- Topics relevant to 21st Century Turfgrass Management

- The opportunity to take part from the comfort of your home or workplace

If you have any questions regarding this new school, please contact me at:

Sam Bauer
sjbauer@umn.edu
763-767-3518

Karl Foord, UMN Extension Educator

Photo 1: Canada thistle rosette in lawn.

Whenever I weed my gardens I always manage to find a number of Canada thistle plants, Cirsium arvense (L.) Scop. These are not the rosette seedlings that I see in my lawn which are fairly easily dealt with (photo 1). These are aerial shoots coming from established roots (photo 2). A mixed planting garden bed presents its own set of problems in dealing with this weed. Why is Canada thistle so persistent?

Missouri State University

Photo 2: Canada thistle underground root structure and aerial shoots.

Canada thistle is persistent for three reasons. Seed production, deep roots giving rise to stems, and root pieces that can regenerate plants.

Seed production per plant averages 1,500 seeds per plant but vigorous plants have been known to produce more than 5,000 seeds with viabilities greater than 20 years. So it will take persistence to reduce the seed load in the soil. Lesson 1: never let thistle go to seed. This will not remedy seeds coming in from an adjoining property, and seeds are reported to be able to travel a half mile in the wind.

Purdue University

Photo 3: Two years underground growth of Canada thistle from original one foot of root.

Canada thistle can reliably regenerate from half-inch long cut root pieces. Lesson 2: attempts to dig out the plant or chopping it up will likely not be successful and may only serve to propagate it.

Canada thistle is a perennial with a complex system of deep-seated roots that spread horizontally and give rise to aerial shoots (photo 2). The seedlings grow slowly at first producing a fibrous taproot which thickens and develops lateral roots in 7-9 weeks. Aerial shoots usually develop from buds on the branches of the horizontal system. The root system goes deep (6 - 10 ft.) and wide (> 10 ft. per year) with some 60% of roots existing at depths greater than 2 ft (photos 3 and 4).

Purdue University.

Photo 4: Extensive underground root systems of Canada thistle.

To eliminate Canada thistle one needs to prevent regrowth from the potentially extensive underground root system. The non-chemical approach involves strategies that persist until the starch reserves in the roots are exhausted. The chemical approach involves application of herbicides at the correct dosage avoiding damage to nearby plants.

Simply removing the aerial shoots can eventually exhaust the root reserves. One study showed that mowing the plants would eliminate the top growth similar to pulling the aerial shoots, but will not deplete the starch reserves unless it is repeated at 7-28 day intervals for up to 4 years. It is more likely that the thistle would win given this strategy.

If the plant can be isolated, it can be smothered with an impenetrable barrier like plastic or a landscape weed cloth. This would require clearing out the bed and dedicated time to starving the root system. The key problem here is isolating a plant with a creeping underground root system that could send up shoots in adjoining areas which would replenish the root system.

Photo 5: Canada thistle in sedum bed. A situation where a bedding plant could be isolated from spray on a Canada thistle.

If the chemical route is chosen, a non-selective herbicide like glyphosate (Roundup®), which has little or no soil residual, would be the chemical of choice. In some situations sensitive plants can be separated from the thistle and protected from spray with a physical barrier like plastic (photo 5). The plastic may be removed as soon as the spray dries.

Photo 6: Canada thistle in cotoneaster bed.

In other cases protecting sensitive plants is not possible such as a thistle nestled in a cotoneaster bed (photo 6). In this case one can apply material with a paint brush or spot spray taking care not to get spray material on the sensitive plant, and if you do wash it off immediately.

The goal is to kill the root system by getting as much chemical throughout the plant as possible. Use the lower of label recommendations as higher rates will kill the leaves and not get to the roots making the treatment ineffective. Make sure that the plants are not drought-stressed and that there is plenty of moisture. If the plants are stressed the chemical will not be effectively translocated throughout the root system. Be sure to read and follow all label directions carefully. It is highly likely that multiple applications may be needed to eradicate this weed.

Given the look of the below ground root systems it looks like the most we can hope for with Canada thistle is not elimination but rather a certain level of control.

Photos:
"Canada Thistle." Midwest Weeds, Missouri State.

"Control Practices for Canada Thistle."
Purdue University, Department of Botany and Plant Pathology.


Lawn Care Tips for October - Yes, Really, Lawn Care in October.

Bob Mugaas, UMN Extension Educator

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Photo 1: Healthy, vigorous late summer lawn.Bob Mugaas.

Even though much of the month of October can be one of the best times for grass growth and recovery, it's tempting to put away our thoughts, practices and equipment used to care for our lawns by the middle to end of September. The reason for this active period of growth is that the lawn grasses adapted to this area (e.g., Kentucky bluegrass, the fine fescues and perennial ryegrass) are best adapted to the cooler and usually moist conditions of spring and fall. See Picture 1. So, with that in mind, here are a few end-of-season lawn care practices that help support actively growing grass plants.

1. Mowing. So long as our grasses continue to grow, we should be continuing to mow as needed. With cooler temperatures and shorter days, mowing intervals usually become longer the later we go into the month. A common question at this time of year is "Should I cut my lawn shorter the last mowing of the year?" One reason to consider somewhat shorter mowing heights in the fall is the decreased (usually) incidence of snow mold come the following spring. Longer matted grass potentially creates more favorable habitat for the snowmold fungus to live and grow over winter. We see the results of that fungal growth the next spring when, as the snow melts and retreats from the lawn surface, the lawn appears covered with grayish or pinkish colored patches indicating the presence of snowmold.

However, reducing the height of a lawn should not be something reserved for only the last mowing. For example, if the lawn has been kept at about 2.5 - 3.0 inches during the growing season and the desire is to reduce that to two inches, then begin the process of gradually lowering that mowing height two to three mowings prior to your very last cutting. That will help the grass adjust to a lower height of cut more gradually instead of being scalped just before going into colder conditions; a more stressful condition for turfgrass. If the grass is still actively growing during October, you may need to mow somewhat more frequently in order to reach and then maintain the lower mowing height. This is because shorter heights of cut require more frequent mowing to establish and maintain them.

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Photo 2: Comparison of mowed (lower left) and unmowed (lower right) leaf covered lawn area. Bob Mugaas.

2. October is the month when leaves drop from our deciduous (leaf losing) trees. The spectacular fall colors of early October give way to leafless trees ready to face the winter months ahead. So, what to do with all of those leaves? A small amount (usually less than a couple of inches) of fall leaves can be left on the lawn surface and ground up with a rotary mower. Be sure to go over them several times such that the remaining leaf particles can more easily sift down into the lawn and soil surfaces. The lawn should look like it was raked when you are done. See Picture 2. If there are still piles of shredded leaves be sure to rake them off of the lawn surface and either compost them or use them as a mulch in other parts of the landscape. Leaves can also be removed from the lawn by picking them up using the mower's bagging attachment (if it has one) and redistributed as a mulch cover in another non-lawn part of the landscape or composted.

3. Early October is an excellent time to apply herbicides to perennial broadleaf weeds such as dandelions, creeping Charlie, clover, and plantain. See Picture 3. Where only a few weeds are present, hand removal can be just as effective as an herbicide. On the other hand, weed control products are now widely available in ready-to-use application containers. Hence, we can spot treat the specific weeds while introducing minimal amounts of herbicide to the environment. Where weeds are more numerous and scattered throughout the lawn, a broadcast application of an herbicide product can also be done. These can be applied either as a granular or liquid product. The products used should be weed control products only and not combined with a lawn fertilizer as this would not be a good time to be applying fertilizer. Always follow product label directions exactly - it's the law. Be sure the weeds (and lawn grasses) are actively growing at the time of application as the product's effectiveness will be much better than if weeds are growing under water stress. If necessary, water the area to be treated a day or two the planned application to help ensure their active growth.

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Photo 3: Common dandelion, a perennial weed effectively controlled with broadleaf herbicides in the fall. Bob Mugaas.

4. It hardly seems necessary or even appropriate to be talking about watering a lawn given the amount of rainfall and flooding issues experienced over the last few weeks. Nonetheless, should October turn dry and remain warm, lawn grasses will likely benefit from an additional watering or two before shutting down for the winter. In general, it's a good practice to not have lawn grasses go into winter conditions severely stressed due to lack of water. We don't need to follow the one inch per week at this time of year due to the cooler temperatures and shorter days. Both of those conditions slow the loss of water from the lawn and hence any watering required can be done at longer intervals. In other words, that same one inch of water per week, (including rainfall), during the summer months might be sufficient for two or even three weeks this time of year depending on weather conditions.

5. Finally, new suggestions for applying nitrogen fertilizers to Minnesota lawns no longer include a late October to early November application. In short, new research here at Minnesota and Wisconsin questions the usefulness of that nitrogen application due to the inefficiency with which it's taken up by the grass plant. Hence, the preferred late season fertilizer application time for Minnesota lawns is around Labor Day to the middle of September. Nitrogen absorption is much better at that time of year and it ensures adequate nitrogen nutrition for the grass plant going into a very active period of growth. For more information on this topic see the article in the August 1, Yard and Garden Newsletter.

Continuing through the fall with few important lawn care practices can help ensure a healthy lawn going into the winter months and a healthier lawn to begin the growing season next spring. Good Luck!

What's Up With That?!

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David C. Zlesak

Why do dandelions all look so similar? Other plants that reseed tend to result in individuals that have noticeable differences from each other. These differences among seedlings may be dramatic or subtle and can involve traits such as flower color, petal number, or plant habit. The answer is that dandelions primarily reproduce by apomixis. Apomixis is commonly defined as asexual reproduction through seeds. The embryos are genetically the same as the mother plant and are not the result of the union of two sex cells. Most plant and animal species rely on sexual reproduction to enhance genetic variability among individuals in populations. Variability can improve the chance that at least some individuals will have a competitive advantage when disease or other challenges come. Those individuals will hopefully survive and be able to reproduce in order to perpetuate the species. Dandelions, some turf grass species, and many citrus have a different strategy that uses apomixis. The best, well-adapted individuals clone or copy themselves through seed. A relatively small proportion of embryos are the product of sexual reproduction to support variability, while most are genetic copies of the well-adapted mother plant.

Photo 1: Bob Mugaas

Lawn Mushrooms

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Bob Mugaas, University of Minnesota Extension Educator

With some areas of the state receiving moderate to heavy amounts of rainfall over the past couple of weeks, mushrooms are beginning to randomly appear in lawnsTheir appearance often causes people to be concerned about the health of their lawn and whether or not a serious disease might be getting started.

It’s important to remember that mushrooms are the ‘fruiting bodies’ of fungi living in the soil and thatch. They are responsible for the production of microscopic spores that in turn help propagate the fungus. The vast majority of those fungi are not associated with any lawn disease causing organisms. It’s quite common for them to appear during periods of moist conditions resulting from either natural rainfall or excessive irrigation. Again, they are not necessarily indicative of any particular lawn problem. The fungi are living on decaying organic matter in the soil and/or thatch layers. This breakdown of organic matter results in at least some of the nutrients contained in that organic matter being released back to the soil. At that point the nutrients are available for continued plant growth or used by other microorganisms. If you find the mushrooms offensive, simply knock them over with a rake and remove them from the area.

Choose Weed Control Products Carefully

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Bob Mugaas, University of Minnesota Extension Educator

When trying to select the ‘right’ weed control product, consumers are often confronted with a bewildering array of possibilities at retail gardening outlets. This prompts the honest question of ‘Which one of these products should I choose?’ Likewise, this question can have a variety of responses depending on what weeds are being targeted. This could easily be the topic of several articles.

However, there is one word of caution that is worth noting. Nonselective weed killers, that is, those that will kill all green vegetation, should not be used to treat weeds in lawns and expect the lawn not to be damaged. The result will end up like pictured where all the plants that contacted the herbicide, including the lawn grasses are killed leaving small to large patches of brown dead grass. These will now need to be reseeded or resodded since none of the grasses in these areas will come back. The two most common ingredients in these types of herbicides are glyphosate (e.g., Round-up, Kleen-up, many others) and glufosinate – ammonium (e.g., Finale). These should not be used to treat weeds in lawn areas unless the desire is to kill both the existing grass and weeds such as might be done before installing a new lawn.

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