Opinions differ as to what plants are lawn weeds. The golf course superintendent will tolerate nothing but bent grasses in his putting greens, while most homeowners accept any permanent bluegrass, fescue, or bent.
Moreover, some regard white clover as a desirable component of turf and find in its vigorous, spreading nature a valuable ally in combating less desirable weeds.
No home-owner, however, will tolerate crabgrass if he can eradicate it; nor will he permit a host of broad-leaved species to grow in his lawn.
The golf-course superintendent knows that the presence, in abundance, of certain weeds in established turf is an indication that something is wrong either with the soil or his maintenance practices.
The homeowner, too, should realize that permanent eradication of weeds entails not only the removal of the present crop by hand-weeding or chemicals but also adopting a definite maintenance program to build up a turf that will withstand future invasions.
Seeding New Lawn
It is also important to know that many weed species grow in newly-seeded lawns but will die after a few clippings.
Examples are lamb’s-quarters, Chenopodium album; milkweed; ragweed; witch-grass; Agropyron repel’ (not crabgrass); (oxtails, and most of the mustard family.
Too often, the homeowner, having noted these weeds in profusion in his new lawn, will dig it over and re-seed at great expense, when in fact, the weeds would have disappeared as mowing got underway.
Before seeding a new lawn, several courses are open that will minimize future infestations of the worst weeds.
a. Restrict the seeding to the period August 20 — September 20.
b. Treat the soil chemically. Cultivate it periodically before seeding.
c. Obtain weed-free topsoil.
d. Grow a smother crop.
e. Use a high-quality seed mixture of permanent grasses. Too high a quantity of temporary nurse grasses will result in a weedy lawn when the nurse grasses die.
By seeding from August 20 to September 20, the seedling grass will establish turf in the cool Autumn months when a few obnoxious weeds are germinating.
Weeds appearing in the autumn are mostly those species that die after the lawn has been mowed a few times.
Late summer seeding is far and away the best method of obtaining a weed-free turf to start, and if at all possible, one should wait to seed then.
Chemical Treatments When Seeding
When seeding in other seasons, chemical treatments of the soil are sometimes effective; but these chemicals will also kill the grass seed unless a period of three to six weeks is allowed to elapse after treatment and before seeding.
For this purpose, 2-4-D is used at one and a half to two times the rate given on the container for eradicating weeds in established lawns, or calcium cyanamide is applied at 2.5 pounds per 1,000 square feet.
These chemicals can be applied dry and should be raked into the top inch of the soil.
Unless there is heavy rain, the area should be watered heavily at least four times before seeding.
Although chemical treatments may kill most or all of the weed seeds, it is not always effective; the young turf is still vulnerable to invasions from other areas.
Reduce Weed Seeds Before Seeding
A third means of reducing weed seeds before seeding: but one that takes time, is to cultivate the topsoil after it is in place every three weeks for about nine weeks. This, however, exposes the soil to wind and water erosion.
Of course, if one can obtain weed-free topsoil in the first place, he is assured of partial success. Soils from fields where hoed crops have been grown for the last few years or soil from recently-cleared land are usually comparatively weed-free.
If one does not know the source, the only way of telling whether weed seeds are present is to obtain representative samples; keep them moist and under favorable growing conditions; then observe the quantity and type of weeds that grow.
Growing cover or smothering crops will reduce weed content. Buckwheat sown at two pounds per 1,000 square feet in May or June, and turned under in mid-August, provides effective use of a smother crop before September seeding.
Removing Weeds
When weeds appear in established turf, we can assist desirable grasses in their competition by hand-weeding or chemical applications.
If there are only a few weeds, the former method is recommended; if one does 15 minutes to half an hour’s work a week on the weeds, the job need not become laborious.
In manually removing weeds with long taproots, such as dandelions, or those with bulb-like bases or corms, such as bulbous buttercup, it is crucial to get out most of the taproot or base; otherwise, the weeds will grow again.
There are several good hand tools on the market.
If large quantities of weeds are present, we should resort to the use of chemical herbicides. The well-known herbicide 2,4-D kills many broad-leaved weeds but does not injure the grasses.
The best times to apply 2,4-D are about two weeks after either spring fertilizing (if the grass is then growing vigorously) or after Fall fertilizing, though it can be applied safely and effectively at other times.
2,4-D can be applied as a dust or in solution as a spray. There are innumerable formulations on the market. In using them, observe the following precautions:
a. Follow directions on the container as to rate and dilution.
b. Do not let the herbicide, either in dust or spray form, come in contact with other plant materials. Very small amounts will kill annuals and perennials and will defoliate and sometimes kill shrubs and even trees.
c. After using a sprayer for 2,4-D, use it after that only for lawn purposes because it is very difficult to clean it out.
d. Do not use 2,4-D on lawns containing a large percentage of bent grasses unless small-scale tests have shown that it will not damage the bent grass in your lawn.
e. Do not use 2,4-D on young grass until at least two months after germination or on lawns where recently seeded patches.
Killing Young Crabgrass
Besides killing broad-leaved weeds, 2,4-D will also kill very young crabgrass plants; but when this weed is older, other chemicals are needed.
Two such useful chemicals are phenyl mercuric acetate and potassium cyanate.
Both sell under several trade names. Manufacturers’ directions should again be followed closely and, to be on the safe side, the home-owner should try a preliminary test on a small portion of his lawn.
This gives him a chance to judge the effectiveness of time material and the damage it might do to his desirable grasses. It also acquaints him with the technique of application.
Most Effective Crabgrass Killer
A third chemical, Sodium Arsenite, is a most effective crabgrass killer; it will also kill chickweed and other weeds.
Because of its poisonous nature and the damage it can do to the lawn if not properly handled, it is limited to those lawn owners who exercise the most painstaking care in its use.
The insecticide chlordane is also a crabgrass killer, but experiments are not yet completed.
An ounce of prevention is worth several pounds of cure in dealing with crabgrass. For example, its growth is encouraged by-such faulty maintenance practices, such as light, daily sprinkling, mowing too close, and neglecting spring fertilizing.
Raising the ‘might of cut to 3″ or 4″ inches’ from June 1 to the end of Summer will greatly reduce the crabgrass content of a lawn. If clipped at this height, the lawn will not look very neat.
This treatment is recommended for those homeowners who have tried other means of crabgrass control without success.
If crabgrass has once gained a foothold in time lawn and is seeding, it is best to clip the grass at the usual height of one and a half inches.
Before every fourth clipping, if a chemical crabgrass killer is not being used, rake the lawn to make the seed heads stand upright.
Then mow with the machine set to cut as close as possible and with a catcher on to remove the seed heads. This practice also makes the lawn look mature and presentable.
Crabgrass Species
There are two separate species of crabgrass. These are the large, hairy kind, Digilaria sanguinalis, and the small, smooth form, Digilaria ischemia.
Their prevention and cure are the same. Silver crabgrass or goose grass, Eleusine indica is an entirely different plant.
There is no satisfactory control for it other than hand-weeding, although it is encouraged by the same faulty maintenance practices as are large and small crab grasses.
Moss Problem
Moss provides yet another problem. Its presence often shows that fertilizing and liming have been completely neglected.
Spring and late summer fertilizing with an autumn liming will frequently remove it, and desirable grasses will return without seeding.
Sometimes mosses result from poor drainage, compaction, or too much shade. The condition must then be removed, the moss raked out, and the area re-seeded.
Many weeds will die after one application of 2,4-D, but a second dose two weeks after the first is sometimes necessary, and even a third in stubborn ease.
The following is a partial list of lawn weeds that can be eradicated easily with 2,4-D:
- Dandelion, Taraxacum officinale
- False dandelion, Hypochaeris radicata
- Carpenter weed, Prunella vulgaris
- Lawn pennywort, Hydrocotyle rotundifolia
- Ground ivy, Nepeta hederacea
- Broad-leaved plantain, Plantago major
- Buckhorn plantain, Plantago lanceolata
- Creeping Charlie, Lysimachia nummularia
- Sheep sorrel or sour grass, Rumex acetosella
- Cinquefoils, Potentilla species
- Buttercups, Ranunculus species
Killing Chickweed
Common chickweed, Steliaria media, and mouse-ear chickweed, Cerastium vulgatum, are difficult to eradicate with 2,4-D. Sometimes, but not always, applications in October will remove them.
Spot-treating each patch with a solution of 2,4-D liquid with water (about 10 parts of water to one of 2,4-D) is much more effective.
A few drops of the solution are placed on the center of each patch. Care must be taken not to splash this strong solution onto the grass.
The writer has made time to follow observations in dealing with large turf areas such as golf courses and playgrounds.
a. In late September or early October, when the ground is soft following heavy rain, the chickweeds can be easily raked out of turf with an iron rake. By seeding the bare patches with vigorous, quick-germinating grass, such as Astoria colonial bent, this grass will cover the patch before the weeds return.
b. Sour grass and cinquefoil will usually disappear without resorting to 2,4-1) after fertilizing the lawn in spring and again in late summer.
c. Knotweeds, Polygonum species, will not always respond to 2,4-D. However, when the plants are very young in April, even a light application of 2,4-D will kill them.
d. Yarrow, Achillea millefolium, seldom responds to 2,4-D. Yet, this small, fern-like weed is not objectionable on turf, and in wet Summers, it will die out.
e. Purslane, Portulaca oleracea, can be eradicated by continued raking of plants before mowing to make them stand upright.
Homeowners who do not like white clover will not find 2.4-D very effective. A spray of 2,45-T will kill a lot of clovers. Endothal, a new chemical, gives fair results.
Chemicals will remove the immediate crop of weeds, as also well as hand-weeding. But a turf will not be free of weeds for long without Spring and Fall fertilizing and clipping at 1 1/2″ inches.
44659 by Geoffrey S. Cornish