Seasoned landscape professionals have learned to recognize and control some of the usual suspects when it comes to annual fall weeds. But it\u2019s important to keep an eye out for new offenders and disease-weakened grass. Weather patterns and overall lawn stress are driving the quantity and type of weeds to look out for this fall.<\/p>\n
Crabgrass is the mid-Atlantic region\u2019s primary weed, notes Pete Landschoot, University of Pennsylvania professor of turfgrass science.<\/p>\n
\u201cIt dies after the first hard frost, but it\u2019s very noticeable into September and early October,\u201d he says.<\/p>\n
Other weeds in this region include ground ivy and wild violet. Dandelion and clover are not difficult to control, but do make return appearances, notes Landschoot.<\/p>\n
Perennial grassy weeds can be troublesome. Nimblewill dies off in the fall, but not before it begins to take over lawns, he adds.<\/p>\n
Creeping bentgrass and rough bentgrass also are problematic.<\/p>\n
In the Pacific Northwest, annual bluegrass and moss present problems, notes Alec Kowalewski, associate professor, turfgrass specialist at Oregon State University\u2019s Department of Agriculture.<\/p>\n
With its lack of cooler temperatures found elsewhere, landscaping in Florida means \u201cin the fall, we\u2019ll still be battling those summer annual weeds species,\u201d says Chris Marble, an assistant professor of landscape and weed management in the University of Florida environmental horticulture department. \u201cCommon (weeds) include the spurge species, Florida pusley, artillery weed and many others. There are also perennial species, including nutsedges and torpedo grass.\u201d<\/p>\n
Cool season weeds that might be problematic in north Florida where the season is more typical of the rest of the country include chickweed, annual bluegrass and Henbit weed.<\/p>\n
\u201cAnnual bluegrass and moss will germinate and establish in the fall, growing vigorously through the wet and cool winter months,\u201d says Kowalewski. \u201cAnnual bluegrass will produce seed heads in the spring and often turn yellow and die in the summer months. Moss has a similar life cycle, growing prolifically in the cool weather but entering dormancy in the summer months.\u201d<\/p>\n
Weeds give off telltale signs and represent turf management issues that require mitigation, such as frequent mowing, irrigation and fertilization.<\/p>\n
As the season wraps up, those practices will provide a dense lawn preventing encroachment of crabgrass, a summer annual and a good example of a spring-establishing weed, says Kowalewski. Adding pre-emergence herbicide applied in the spring months can help prevent that.<\/p>\n
Marble regards weeds as secondary invaders symbolizing other underlying problems.<\/p>\n
\u201cTurfgrass is competitive with a lot of the weeds, but when something comes in during the fall like large patch disease, that weakens the turf and allows weeds to grow,\u201d says Kowalewski. \u201cOftentimes, we see the weeds come in when the biggest issue is probably irrigation.\u201d<\/p>\n
\u201cA lot of weed species can be prone to those areas where there is a lot of over-irrigation,\u201d he says. \u201cThey like wet areas and can also stress the turfgrass. Improper mowing height or frequency can also lead to weeds becoming a problem.\u201d<\/p>\n
Watering frequency and mowing height depend on the grass species and time of year, Marble notes. For example, St. Augustine grass might need to be mowed every week.<\/p>\n
Not many people irrigate their lawns in the mid-Atlantic region, \u201cbut occasionally we run into a severe drought. The lawn gets thin and large patches die. Guess what comes back first? Weeds,\u201d says Landschoot.<\/p>\n
In the Northwest, mowing the lawn at least once weekly between 2 to 3 inches also helps.<\/p>\n
\u201cReturn the grass clippings with mulching blades to return valuable nutrients to stimulate future turf growth,\u201d Kowalewski says, adding that lower heights upon the canopy allow space for weed growth.<\/p>\n
Landschoot says homeowners don\u2019t fertilize often enough.<\/p>\n
\u201cThey\u2019ll do it once every two or three years and then the lawn thins out,\u201d he says. \u201cAnytime you have space available and sunlight, weeds can start to grow.\u201d<\/p>\n
Kowalewski recommends Northwestbased contractors fertilize four to six times yearly, applying 1 pound of nitrogen per 1,000 square feet per application, totaling 4 to 6 pounds of nitrogen per 1,000 square feet annually.<\/p>\n
Fertilizing in the fall and spring avoids summer and winter month applications during extreme temperatures, Kowalewski adds.<\/p>\n
Those using synthetic fertilizer should look for a bag containing a high concentration of nitrogen and low concentration of phosphorus such as: 25-5-10 (25% nitrogen, 5% phosphorus pentoxide, 10% potassium oxide).<\/p>\n
\u201cOrganic fertilizer can also be used. However, these products have low levels of nutrient, 3-3-3 for example,\u201d says Kowalewski. \u201cHigh application rates will be required to reach the nitrogen rates required for vigorous turf growth.\u201d<\/p>\n
\u201cIrrigate three to four times per week from Labor Day to Memorial Day,\u201d he adds. Apply \u00bc inch of water per application, totaling between \u00be and 1 inch weekly.<\/p>\n
With dandelion and clover flowering in spring, herbicides should be applied to these weeds in the fall months when the plant is sending nutrients to the roots to prepare for overwintering, says Kowalewski.<\/p>\n
\u201cActive ingredients that control these weeds include 2,4-D (2,4-Dichlorophenoxyacetic acid) for dandelion and triclopyr for clover,\u201d he adds.<\/p>\n
In using chemical applications, \u201cidentify those most problematic species in the landscape and choose an option that\u2019s going to control that top species so you\u2019re not indiscriminately applying herbicides when they might not be effective on the weed species you\u2019re targeting,\u201d says Marble.<\/p>\n
Applying pre-emergence herbicides in the fall helps prevent the germination of weeds like annual bluegrass. Ethofumesate can be applied for post-emergence management of annual bluegrass, notes Kowalewski.<\/p>\n
\u201cMoss is controlled well with carfentrazone and fatty acid soap,\u201d he adds. \u201cControl is best when application is coupled with dethatching to physically remove the moss from the turfgrass.\u201d<\/p>\n
Up to 2\u00bd months of crabgrass control is achieved with pre-emergence herbicides that include pendimethalin, says Landschoot, adding it\u2019s best done in the spring before the crabgrass emerges and when timed with forsythia bloom.<\/p>\n
The long residual of most pre-emergence products in the soil won\u2019t prevent germination, but it will prevent emergence, with the root of the germinating seed taking up the herbicide, says Landschoot.<\/p>\n
Herbicides addressing crabgrass can also contain prodiamine, says Marble.<\/p>\n
\u201cFor something like Doveweed \u2014 problematic in the summer and early fall in Florida \u2014 those herbicides aren\u2019t going to be as effective,\u201d Marble notes.<\/p>\n
\u201cUse something like indaziflam or dimethenamid. In planting beds, use flumioxazin to control that particular species more effectively.\u201d<\/p>\n
Proper turf management practices lead to great success, notes Marble.<\/p>\n
\u201cWhen you\u2019re using herbicides, it\u2019s important to follow an integrated program. No herbicide is going to work if those other practices aren\u2019t in place first,\u201d he adds. \u201cCombining herbicides with other strategies will offer the best success, cost less money, be the most environmentally friendly and give the best results.\u201d<\/p>\n
Target annual bluegrass, chickweed and Florida pellitory weed in late season and early spring, says Marble.<\/p>\n
\u201cCrabgrass is the big one in the spring,\u201d he notes.<\/p>\n
\u201cWe can be challenged in Florida, especially because with all of our warm season turf grasses like St. Augustine, the most commonly used turf grass in Florida, we don\u2019t have any way to selectively control crabgrass in it. With pre-emergence herbicides, we can prevent it from becoming a problem in the first place.\u201d<\/p>\n
Landschoot says he doesn\u2019t recommend herbicide use late in the season.<\/p>\n
\u201cEarly spring is a time to get on the crabgrass and put down pre-emergence herbicides for crabgrass control, other annual grasses and other annual broadleaf weeds. Mid-fall is the best time to control ground ivy and wild violet. Apply broadleaf herbicides after the first hard frost, which in my area is sometime around mid-October.\u201d<\/p>\n
\u201cThese are perennial weeds,\u201d says Landschoot. \u201cThe leaves will die off, but the crowns will be alive over the winter and produce new leaves the following spring after the first frost.<\/p>\n
\u201cAt the time the plant is moving sugars back into the crown region, it\u2019ll also be more efficient in taking up the herbicide,\u201d he says.<\/p>\n
Fall is a good time to do weed control in general, says Landschoot.<\/p>\n
\u201cIf you time it with the frost, that\u2019s even better,\u201d he adds. \u201cIf you can\u2019t do anything in the fall, you always have the spring to follow up next year.\u201d<\/p>\n
The major issues in turf management of weeds are soils, shade and fertility, notes Landschoot.<\/p>\n
\u201cI always tell people, to get it down to the basic level,\u201d Landschoot says of turf management practices. \u201cChoose good quality seed for the lawn from the start. Get a soil test before doing any kind of renovation or a new establishment work. If the pH is off, the fertilizer is not going to be very efficient.\u201d<\/p>\n
In the case of acidic soil, the soil test can indicate how much nutrients, lime and phosphorus potassium are needed, he adds.<\/p>\n
\u201cAs far as the nitrogen goes, there are general guidelines for the different species of grasses used in our region,\u201d says Landschoot. Kentucky bluegrass can call for two or three applications, but something like a tall fescue may only need one or two applications per year.<\/p>\n
There are a lot of clay soils in the region, says Landschoot, adding that working a good quality compost into the soil can increase the organic matter and help retain moisture as well as provide better soil structure.<\/p>\n
And while a small amount of shade is fine, lawns don\u2019t do well in heavy shade, and while one won\u2019t find crabgrass in such lawns, \u201cyou will see a lot of other shade-tolerant weeds coming into those lawns,\u201d he adds. \u201cUnless you\u2019re willing to take down a tree or really prune it up, I suggest putting in ground covers, because heavy shade and grasses just don\u2019t mix.\u201d<\/p>\n
Landschoot doesn\u2019t believe there are many highly effective options for organic weed control. His studies of gluten meal, for example, show 50% control in contrast to 90% and higher with chemicals. For pre-emergence effects, they\u2019re not strong and unless applied at the right time, they will not yield good control, he adds.<\/p>\n
Some iron-based compounds like iron sulfate are used in areas where broadleaf herbicides are not utilized which burns back the foliage, he says, adding it doesn\u2019t do much to kill the crowns of the plant.<\/p>\n
For planting beds, plant oils like caprylic acid and vinegar-based caprylic acid products are good options, says Marble.<\/p>\n
\u201cA lot of municipalities have banned glyphosate, so people are looking for organic or certified options,\u201d he points out, adding plant oils won\u2019t be as effective on perennial species and are all contact action.<\/p>\n
\u201cThey\u2019re not systemic and might require more frequent applications, but they can be used as part of a good integrated weed management program with good success.\u201d<\/p>\n
Kowalewski notes the best weed prevention and control method in turfgrass management is mowing, fertilization and irrigation.<\/p>\n
\u201cWe call these the primary cultural practices because you should be spending more time and money on these cultural practices than the rest,\u201d he adds. \u201cA weedy lawn is an indication that someone is not properly implementing these three things.\u201d<\/p>\n
Beat fall weeds with strong maintenance practices and proper chemical applications.<\/p>\n","protected":false},"author":15,"featured_media":3801,"parent":0,"template":"","main-categories":[28],"class_list":["post-3796","features","type-features","status-publish","has-post-thumbnail","hentry","main-categories-landscape"],"yoast_head":"\n