Pre-emergents versus post-emergents<\/h2>\n
Weed control products fall into two major categories: pre-emergents, the primary tool for preventing weeds from coming up in the first place; and post-emergents, which zap them once they pop their ugly little heads up.<\/p>\n
The season with pre-emergent treatments, mainly to keep the crabgrass from germinating. \u201cIt\u2019s important to put it down before the second or third week of May before it gets warm enough for the seeds to germinate. It also helps keep out some of the summer annuals and broadleaf weeds as well,\u201d Samson says.<\/p>\n When to apply herbicide depends on your climate zone. \u201cIn warmer markets, you\u2019d have to put down the crabgrass pre-emergents twice a year, but in our market, once a year is usually enough,\u201d Samson continues. \u201cAnd then the rest of the year we\u2019ll blanket a lawn with the post-emergent products, to take care of dandelions, ground ivy and white clover. Throughout the summer we might see summer annuals like oxalis or speedwell popping up. They\u2019ll usually be in isolated pockets, so we can get by with spot-spraying them. Once we get into fall we like to blanket the lawn again with a post-emergent to get the weeds that pop up again, like thistle.\u201d<\/p>\n Whoever came up with the old saying, \u201cWhen all else fails, read the directions,\u201d could have been thinking about herbicides. Samson says, \u201cThe label is your roadmap to proper application and mixing techniques. It\u2019ll tell you how many ounces you put in per gallons of water and tell you just how to mix it, and when the outside temperature might be too hot to put it down.\u201d<\/p>\n Brian Thompson, marketing manager, turf, professional and specialty solutions for herbicide manufacturer BASF Corp.<\/a>, Florham Park, New Jersey, agrees. \u201cYou need to really read those labels to gain the best value of these products and the best efficacy.\u201d<\/p>\n He says that a lot of herbicides, such as BASF\u2019s Drive XLR8 or Pylex products, have label language that instructs the user to mix it with an adjuvant such as methylated seed oil that helps the herbicide get into the plant and makes it more effective.<\/p>\n These chemicals aren\u2019t all that forgiving, so precision is required. When a herbicide isn\u2019t applied the way the label specifies, in the proper amount, at the right time and at the right outdoor temperature, grass can be damaged.<\/p>\n \u201cIn the southern climates, you have some grasses that you really have to be careful with, for example, St. Augustine grass \u2014 my understanding is that it\u2019s very sensitive to weed control chemicals,\u201d says Samson. \u201cIn the north our grasses are less susceptible, but you still have to be careful \u2014 you could hurt them if you apply this stuff on a day that\u2019s 95 degrees or even 90 degrees, put it down too heavily or mix it wrong.\u201d<\/p>\n Pre-emergents often come in granular form while post-emergents are usually liquid. This has to do with the way the weeds absorb them. Pre-emergents are absorbed through the roots, which lends itself to a granular approach, while post-emergent products use the leaves as their entry points, which is why they are usually in liquid form.<\/p>\n Many lawn care professionals use a combo fertilizer\/pre-emergent herbicide product early in the season which is almost always granular.<\/p>\n It seems a bit counterintuitive to be distributing something that feeds plant growth \u2014 fertilizer \u2014 at the same time as we\u2019re setting out an agent that retards it \u2014 herbicide. Aren\u2019t we fertilizing the weeds along with the grass? Not really, says Samson. \u201cYou can simultaneously get rid of weeds and stimulate the growth of grass. Because of the selectivity of the herbicides, there is no negative impact on the weed control. It still works.\u201d<\/p>\n Will Jellicorse, owner of Tennessee Turfgrass LLC, Knoxville, Tennessee, doesn\u2019t use fertilizer\/herbicide combo products. \u201cI like to spray my herbicide separately \u2014 that way I know exactly where it\u2019s going. I\u2019m not worried about flinging fertilizer in a bed or out in the road or down a drain, somewhere it doesn\u2019t belong.\u201d<\/p>\n Preventing weeds in landscape beds is a different game than preventing them in turf. That\u2019s where landscape fabric comes in.<\/p>\n Some landscapers don\u2019t like using landscape fabric, saying that it suffocates the soil and kills the beneficial bacteria that lives in it. They may be thinking of older products that weren\u2019t much different than plastic trash bags.<\/p>\n \u201cWhen I first went into the landscape business, black plastic sheeting was being used,\u201d says Larry DeWitt, CEO of Sikeston, Missouri-based DeWitt Co. \u201cThe soil couldn\u2019t breathe, just as you couldn\u2019t if you tied a plastic bag around your head.\u201d<\/p>\n What was needed was a permeable fabric that lets water, air and sunlight through, and today we have it from DeWitt and other manufacturers.<\/p>\n Landscape fabrics today are light-years ahead of that old black plastic. Today, they\u2019re made of polyethylene and come in different forms for different uses: biodegradable, woven, nonwoven spunbonded and nonwoven point-bonded.<\/p>\n Even so, there are advantages and disadvantages to using landscape fabric. It holds moisture in very effectively, but also tends to restrict the movement of earthworms and other beneficial soil mixers, and soil can become compacted beneath it. And weeds can still poke through the barrier after a while.<\/p>\n Still, landscape fabric is a great tool to have in your arsenal for keeping weeds out of beds and planters or slowing them down.<\/p>\n<\/div>\n When we\u2019re talking weed prevention, one of the major targets \u2014 and a hardened one at that \u2014 is crabgrass. Many landscape pros believe crabgrass is something that you have to treat preventatively, with pre-emergents, or else, as they say in New York, \u201cfahgeddaboudit.\u201d<\/p>\n \u201cThat\u2019s not correct,\u201d says Ron Freeman, owner of Arbor Pro Plant Care Experts<\/a>, a lawn care and weed control business in Rochester, New Hampshire. \u201cYou can put down a pre-emergent and a lot of times crabgrass will still come up. It\u2019s actually easier to spray it and kill it after it comes up.\u201d<\/p>\n Samson agrees with the general consensus that it\u2019s best to tackle crabgrass pre-emergently. \u201cPost-emergents are only effective on crabgrass in the first couple stages of maturity, at the seedling or young plant stage. Once it matures it\u2019s very tough to control even with a post-emergent.\u201d<\/p>\n \u201cThe sentiment that crabgrass must be treated pre-emergently may come from its physiological uniqueness,\u201d says Thompson. \u201cVery young and very old crabgrass is easy to control. But for some reason, when it\u2019s between the two- and four-tiller (leaf) stages, it metabolizes the herbicide in a way that makes the herbicide less effective. That\u2019s why post-emergents applied at that stage often don\u2019t work.\u201d<\/p>\n Thompson says using a combination of quinclorac and topramezone will nullify that metabolic process. \u201cThose two chemistries together create a synergism, like a one-plus-one-equals-three effect.\u201d<\/p>\n What is it about crabgrass that makes it such a tough opponent? Samson blames its aggressive root structure and the way it leafs out. \u201cIt tends to kill the grass around it or out-compete it for nutrients and sunlight. That\u2019s why it\u2019s really best to use the pre-emergents on it. If you do get crabgrass later in the season, you can use post-emergents, but it\u2019s difficult to control at that point.\u201d<\/p>\n Cultivation practices can help prevent weeds too. The right amount of irrigation helps keep grass healthy. Freeman says that the mere fact you\u2019re irrigating at all can discourage crabgrass. \u201cThe dirt stays cooler, and the cooler the dirt, the better the lawn,\u201d as crabgrass needs hot soil to emerge.<\/p>\n Water management is critical, says Jellicorse, who recommends watering deeply and infrequently, every two to three days, \u201cespecially this time of year, when it\u2019s hot and humid \u2014 you don\u2019t want to overwater. Fescue will tell you when it\u2019s under drought stress. You\u2019ll see it start turning a purplish-gray color. But that\u2019s fine, you can let it stress out a little bit.\u201d<\/p>\n \u201cCutting high is very important for weed control,\u201d says Samson. \u201cA cutting height of 3 inches or higher is very helpful for keeping weeds out. The longer the grass is allowed to be, the deeper its roots can go.\u201d<\/p>\n \u201cIt\u2019s important to keep the mower blades sharp too, because you get a cleaner cut,\u201d says Jellicorse. \u201cThe grass leaves heal faster, which helps keep them strong.\u201d<\/p>\n An inconvenient truth about weeds is that they\u2019ll eventually develop a resistance to any herbicides we hit them with.<\/p>\n \u201cWithin any population of weeds there will always be a small subset of individual plants with a genetic mutation or some other mechanism that allows them to survive an herbicidal attack,\u201d says James Brosnan, Ph.D., associate professor of plant sciences at the University of Tennessee, Knoxville, and the leader of its new Weed Diagnostics Center. He also serves as an advisor to several turf management organizations.<\/p>\n Brosnan has done a lot of research on herbicide resistance. \u201cIf the same measures are implemented over time, you\u2019re selecting the same subset of the population. Eventually, that builds to the point where your control measures are no longer effective as there are now more resistant plants than susceptible ones in the landscape.\u201d<\/p>\n \u201cThe resistance problem has really grown in turf,\u201d adds Brosnan. \u201cThe USDA calls it an epidemic, especially in bluegrass. They\u2019ve funded a $5.2 million project to tackle it in all turfgrass systems \u2014 golf courses, sod farms, residential and commercial lawns, and athletic fields.\u201d<\/p>\n But he cautions, the answer to resistance will not come exclusively from a jug. \u201cIt\u2019ll be more of an integrated approach where we\u2019re trying to optimize the growing environment. We can do some things agronomically to make conditions more favorable for the turfgrass and less favorable for the weeds.\u201d<\/p>\n One of those agronomic things is remembering that every herbicide has a certain mode of action, the biological system it attacks in a weed in order to kill it. Using a different herbicide with a different mode of action every year helps avoid the resistance\/adaptation problem.<\/p>\n But it can be tough to remember which chemical acts as a cellular mitosis inhibitor, a photosynthesis inhibitor or what have you. \u201cThere\u2019s an easy way to keep track of this \u2014 just look at the group number on the label,\u201d says Brosnan. \u201cThat number correlates to what that herbicide\u2019s mode of action is.\u201d<\/p>\n Jellicorse is one of Brosnan\u2019s former students at UT. He must have paid attention in class because he says, \u201cI\u2019m a big fan of rotating my herbicides. To avoid creating resistance, I never use the same thing over and over.\u201d<\/p>\n There\u2019s no magic bullet when it comes to weed prevention. The best method is to maintain a strong, healthy lawn with nice thick grass that doesn\u2019t give weeds any weaknesses to exploit. By building a healthy lawn, you\u2019re building a defensive wall that\u2019s high enough to keep weeds out. Good luck with your battle plans!<\/p>\n Weed prevention can seem like a losing battle, but with the right tools and strategies, we can increase our odds against these nasty little invaders.<\/p>\n","protected":false},"author":28,"featured_media":5175,"parent":0,"template":"","main-categories":[28],"class_list":["post-4170","features","type-features","status-publish","has-post-thumbnail","hentry","main-categories-landscape"],"yoast_head":"\n![\"weed](\"https:\/\/innovativepixel.com\/IGIN\/wp-content\/uploads\/2019\/07\/waging-war-on-weeds-2.jpg\")
Lush Lawn<\/a>, a company that specializes in lawn care, tree care and weed and pest control services at five locations in Michigan, uses both methods. \u201cI\u2019d say it\u2019s about 50\/50,\u201d says Aaron Samson, founder and CEO. \u201cIt\u2019s important to do a mixture of both pre and post.\u201d<\/p>\nRead that label!<\/h2>\n
Product formulations<\/h2>\n
Protecting bedding plants with landscape fabric<\/h3>\n
Tackling crabgrass<\/h2>\n
![\"weed](\"https:\/\/innovativepixel.com\/IGIN\/wp-content\/uploads\/2019\/07\/waging-war-on-weeds-3.jpg\")
Irrigation and mowing<\/h2>\n
Resistance and adaptation<\/h2>\n
This article originally appeared in Irrigation & Green Industry magazine.<\/em><\/h6>\n
Mary Williams-Villano<\/strong><\/a> is a contributing editor to Irrigation & Green Industry and can be reached at pouncerspy@gmail.com<\/a>.<\/em><\/h6>\n","protected":false},"excerpt":{"rendered":"