Fall Lawn Do’s and Don’ts
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Lawns in southeastern North Carolina are suited to warm season turf grasses including St. Augustine, Zoysia, Bermuda and centipede. Caring for warm season lawns is very different from caring for turf grasses grown in cooler climates. As soil and air temperatures cool and warm season lawns get ready to transition into the dormant winter season, there are some important things that should be done, and others that should not, to keep lawns healthy.
Do NOT Fertilize!
Grasses should only be fertilized with nitrogen when they are actively growing. For warm season grasses this is during the spring and summer, not fall or winter. Fertilizing warm season lawns in fall or winter wastes fertilizer, encourages weed growth, and can intensify disease problems like large patch. In the cooler parts of NC and the United States, cool season grasses such as fescue and Kentucky bluegrass are grown. Opposite to warm season grasses, cool season grasses grow during the fall and early spring, and require fertilization at these times. Commercials and ads about fertilizing lawns with high nitrogen fertilizers in fall are referring to cool season grasses only.
If soil test results have shown potassium (aka potash) to be deficient in your soil, early fall is a good time to apply a potassium fertilizer such as muriate of potash (0-0-60) or potassium sulfate (0-0-50) . To make a difference, these fertilizers need to be applied at least six weeks before the first expected frost. The first frost generally occurs the first week of November for inland areas in our region and mid to late November for coastal areas, so for most gardeners it is too late to apply potassium this fall. If you have not soil tested in the past three years, do so this fall. Be sure to submit samples before mid November to avoid the new peak season fee ($4 per sample). Learn more: //pender.ces.ncsu.edu/2013/08/how-soil-testing-can-help-you/
Do NOT Water!
Warm season lawns should not be irrigated after early September unless soils become excessively dry. Fall is the time when warm season lawns are shutting down for winter. Continuing to irrigate lawns during fall can increase winter cold injury and encourage disease problems. The only exception would be if we were experiencing a fall drought. While soils in our area did become dry in September, the soaking rainfall of this past week has restored soil moisture levels so irrigation systems can be turned off.
Do NOT over seed
Many people would prefer a green lawn year-round. One way to accomplish this is to over seed dormant warm season lawns with ryegrass. The problem with this is that for most lawns, over seeding with ryegrass is detrimental to the lawn’s long term health. The only type of turf that can withstand this type of treatment every year is Bermuda. Over seeding is especially harmful to less vigorous turf grasses like centipede and St. Augustine.
DO Treat for Large Patch and Fire Ants
If your lawn was diagnosed with large patch this past spring, fall is the best time to treat to prevent this disease from being a problem again next year. Treating areas infected with large patch is most effective when fungicides are applied after soil temperatures fall below 70 degrees, even if symptoms are not obvious. Current soil temperatures in our area are in the upper 60’s. You can monitor soil temperature on the NC Climate Office website, http://www.nc-climate.ncsu.edu/map/?table=daily (select Soil Temperature from the drop down menu in the upper right corner).
The most effective fungicides available to homeowners for treating large patch are products containing the active ingredient Azoxystobin (Heritage G) or Propiconazole (Bayer Advanced Fungus Control for Lawns). One fungicide application will control minor cases of large patch, but two to three applications on a 4 to 6 week interval as long as soil temperatures are between 40°F and 70°F may be needed to control severe cases.
Large patch is favored by excessive nitrogen in the fall and spring, poor soil drainage, over-irrigation, excessive thatch accumulations, and low mowing heights. Centipede grass and seashore paspalum are most susceptible to large patch, followed by zoysia grass, and then St. Augustine grass. Bermuda grass, rarely affected by large patch, recovers very quickly when the disease does occur.
Fall is also the most effective time to control fire ants with baits. Make sure to apply fresh baits on a day rain is not predicted. Learn more from this Pender Gardener article: //pender.ces.ncsu.edu/2013/06/treating-for-fire-ants/ and this free Extension webinar: https://learn.extension.org/events/837
DO Control Weeds
Just as there are warm and cool season grasses, there are also warm and cool season weeds. Cool season weeds come up in the fall, live through winter, then flower and die in the spring. Most cool season weeds are annuals, coming up each year from seed, but a few are perennials. Cool season perennial weeds come back year after year from roots that persist in the soil. Two of the most troublesome, Florida betony and wild onion, have started sprouting in yards over the past few weeks.
Like most perennial weeds, it is very difficult to control Florida betony or wild onion by digging them up. Repeated mowing can weaken these weeds but will not kill them. The only way to really get rid of most perennial weeds is to spray them with herbicides, but one application will not do the job. Instead it takes repeated sprays over a couple of seasons. To begin controlling Florida betony or wild onion in your lawn, spray them now and again in February.
Which herbicide to use depends on your lawn type. In zoysia and Bermuda lawns, wild onion and Florida betony can be controlled with herbicides containing a combination of the active ingredients 2,4-D, mecoprop and dicamba. Brand names for these products include Weed-B-Gone, Lesco Three Way, and Speed Zone Southern. These herbicides will also control many of the common cool season annual weeds that are coming up in lawns now, including chickweed, cudweed, and spurweed.
Centipede and St. Augustine lawns are sensitive to 2,4-D. In these lawns instead apply Image, active ingredient Imazaquin, to control wild onions, and atrazine to control Florida betony. Atrazine is sold as Purge II, Image for Centipede and St. Augustine, and HiYield Atrazine. In addition to controlling Florida betony, atrazine will also control many cool season annuals weeds. NOTE: Read the label before applying any pesticide. Most products containing atrazine should not be applied more than twice a year and should not be applied to soils with a pH over 7.0.
Weed Control Without Synthetic Chemicals
There are a few organic herbicides available but most will not selectively control weeds in lawns. Most organic herbicides contain vinegar, plant oils, or soaps as their active ingredient. They work by burning plant tissue they come in contact with, and are most effective when sprayed directly on small weeds that have recently sprouted. These products damage all plants they come in contact with. Corn gluten has been promoted as a natural pre-emergent herbicide but few studies have proven this product to be effective. In addition, corn gluten contains relatively high levels of nitrogen, which have the effect of fertilizing weeds.
A new herbicide containing a form of iron (Fe HDTA) as the active ingredient has recently become available. Brand names include Bayer Advanced Natria Lawn Weed Control and Ortho Elementals Lawn Weed Killer. These products kill only broad leaf weeds (clover, chickweed, henbit, etc) and do not damage turf grasses. Like all herbicides, they are most effective on small, actively growing weeds.
For the long term, the most effective way to control weeds in turf is to nurture a healthy, dense lawn by following correct cultural practices. These include mowing at the correct height, having any insect or disease problems correctly diagnosed before treating, sending soil samples to the NC Department of Agriculture to determine your nutrient or lime needs, and following turf care recommendations for your lawn type available on the NCSU TurfFiles website, http://www.turffiles.ncsu.edu (click on the Maintenance Calendar tab).
Please note: Brand names are included in this article as a convenience to the reader and do not imply endorsement by NC State University nor discrimination against similar products or services not mentioned.
- Soil Testing: //pender.ces.ncsu.edu/2013/08/how-soil-testing-can-help-you/
- What You Can Learn From a Pesticide Label: //pender.ces.ncsu.edu/2013/03/what-you-can-learn-from-a-pesticide-label/
- Centipede Lawn Problems: //pender.ces.ncsu.edu/2012/04/centipede-lawn-problems-2/