How To Control Crab Grass And Other Lawn Weeds

No matter how much care you take to exclude weeds from the lawn, they remain a constant threat to every plot of mowed turf. While a weed-free sod is possible, it is probable only with constant attention. Before we go into that, let me call your attention to an excellent guide to the common lawn weeds—the accompanying set of weed drawings, plus descriptions and best controls.

I have never been able to obtain an accurate figure on the number of home lawns in the United States but, by combining several estimates from different sources, a reasonable figure seems to be somewhere around 30,000,000. Equally certain is that if this is a true figure, at least 20,000,000 of these lawns are invaded every year by crab grass. Sufferers from this pest will be willing to say this figure is too low and swear that at least nine out of ten lawns harbor crab grass.

In addition to this true grass weed, there are many broad-leaved weeds that are well-nigh universal. The development of chemical controls has decreased the menace of plantain, dandelion and similar lawn enemies, yet these are still rated as major problems by many.

No single year's treatment will eliminate weeds forever. You must be prepared to do unending battle to keep your bit of sod from being taken over by these aggressive, vigorous, healthy invaders, all of which, if not restrained, can and will overcome the good grass plants in your lawn.

Some of the most spectacular advances made in lawn culture have been made in the field of weed control. The introduction of 2,4-D was a milestone. This chemical (like others that followed) is a selective herbicide: it is formulated so that it can be applied to a general area of vegetation but will act on only certain kinds of plants. Thus, where weeding on hands and knees was once a part of the summer scene, today a ten-year-old boy can walk across a home lawn and, in a matter of half an hour, wipe out weeds without harming the good grasses, as though he had a magic wand.

ANNUAL BLUEGRASS (Pao annua)

Short, light green grass sometimes spreading to form large patches in lawn. Reproduces by seed no matter how short it is cut. Seed heads may be only ¼ inch high. Often dies out in summer, and grows in late summer from seed.

CONTROL: Calcium arsenate in late fall or early spring.

I recall spraying my first crab grass with sodium arsenite, a chemical that was supposed to be a good control for this weed, and one of the earliest selective weed killers. Every blade of permanent grass turned dull brown and died, but the arsenical poison seemed to spur the crab grass into even more vigorous new growth.

The next few lines may come as a shock to some of my friends, many of whom look upon me as a rabid advocate of chemical weed control. I am convinced that the final answer to eliminating undesirable plants from turf is not to kill them with any type of spray but to produce a biologically superior community of grass plants which can resist invasion. That is merely a fancy way of saying that the grass in a lawn ought to be vigorous enough to take care of itself.

LACK MEDIC or yellow trefoil (Medicago lupulina)

Annual, of clover family, spread by seeds. Stems slender, hairy and creeping, 1 to 3 feet long. Leaves with three leaflets closely resemble white clover. Flowers bright yellow in oblong, dense heads. It thrives in a close clipped lawn, and is difficult to eradicate.

CONTROL: Dust with 2,4,5-TP whenever in active growth.

Chemicals Are A Crutch

But we must keep in mind that weeds are tough. Rigorous methods are needed to knock them out. The real role of chemicals is not to fully control these pests and relieve us of all responsibility for clean turf. They do help us gain the upper hand, but their real purpose is not so much to kill the weeds as it is to create a more favorable environment for grass. As long as we lean on the crutch of chemical help we will not produce the type of turf that will stand on its own and fight back.

Our aim should be to develop a sod so dense that weeds can find no room in it, so healthy that disease cannot weaken it and so persistent in its growth that there are no long periods during which the lawn lies open to invasion. This is the ideal toward which we must work. Admittedly, weeds are not enemies that give up lightly. From time to time, we will still have to touch up the lawn with a chemical control to down some persistent pest. New species of weeds will invade our lawns. In the end, however, our main reliance must be on strong, healthy grass.

CHICKWEED, COMMON (Stellaria media)

Annual or winter annual. Creeping stems turn up at tips and root at joints. Numerous small leaves cover the ground like a green mat. Leaves opposite, not more than % inch in length, pointed. Flowers small and white. Low creeping habit makes mowing difficult.

CONTROL: Apply 2,4,5-TP in late fall or early spring. Summer control less effective.

Crab Grass—Lucifer's Gut To Lawns

Crab grass is perhaps the best example of why chemical control alone will not answer the weed problem once and for all. Here is a weed which seems to have been invented by the devil to plague the home gardener, for certainly it is diabolically adapted to survive in the cultivated turf.

In the wild, it is seldom a serious problem. Nowhere in open fields is it able to compete with the more vigorous, taller growing grass species. Seeds that fall into a thick bluegrass sod are destined to lie dormant forever. Because crab grass seed must have direct sunshine before it can sprout, it is able to survive only at the edges of fields or in open places where poor soil prevents luxurious growth of good grasses.

When it is able to invade a mowed lawn, however, it becomes a demon, running over the surface like a green tidal wave, engulfing the permanent grasses and robbing them of light, food and water.

CHICKWEED, MOUSE-EARED (Cerastium vulgatum)

Perennial, spread by seeds and creeping stems. Stems prostrate or erect, to 4 inches high. Leaves and stems covered with fine sticky hairs. Leaves small and opposite. Small white flowers in loose cluster.

CONTROL: Apply 2,4,5-TP in late fall or early spring. Summer control less effective.

Crab grass  (Digitaria sanguinalis)  is a true annual grass  that sprouts, matures and sets seed the same year; it is killed by frost.

Crab Grass Seed Lives On

The adaptation of this pestiferous weed to survival in the mowed lawn begins with its long-lived seed. Perhaps no species which plagues the gardener has seed with the viability of crab grass. In tests, this seed has been buried for as long as forty years, yet it retained vitality and grew when dug up and exposed to light. I had an experience in 1955, which indicates that it has an even longer life span.

In the spring of that year, we had to lay a new water line to the street to replace one which, from its appearance, must have been laid when the house was first built in 1868. The house had been remodeled in 1900, so when we dug into an old brick carriage drive a couple of feet below the surface, we assumed that it must have been laid in 1868 and covered in 1900. Underneath the brick drive we uncovered a rich mine of deep black prairie soil which, if our deductions were correct, must not have seen the light of day for eighty-seven years. At the very least it had been out of sight for fifty-five years. There was no chance for the buried soil to be contaminated with freshly ripened crab grass seed at that season of the year. And yet, when watered, the old soil produced a bountiful crop of crab grass.

CLOVER, LAWN (Trifolium repens)

White Dutch clover is another common name. True 3-part clover leaf, spreading stems. Old plants tend to become woody. Foliage slippery. White flowers disfigure lawns. Often, winter kills. Sometimes included in old-fashioned lawn mixtures.

CONTROL: 2,4,5-TP when in active growth.

Crab grass seed has another survival trick, a method of burying itself much deeper into the soil than might at first seem possible.

CRAB GRASS (Water Grass, Finger Grass, Digitaria sanguinalis)

Tender annual spread by seed and stems which root at joints. May be erect or prostrate. Leaves and stems sometimes hairy, wiry. Seed stalk produces 3 to many "fingers" maturing in late summer after seed of cultivated grass is harvested. Seed may remain dormant in soil for many years.

CONTROL: Calcium arsenate as pre-emergence control; Sodar for mature plants.

The seed is very light and seems incapable of penetrating to any depth. A cubic foot of it, by the way, weighs about a pound.

Remember how your lawn soil surface develops deep cracks during dry weather in summer? Watch these cracks during the time when crab grass seed is ripening. You will see that it can easily drop into the openings and fall all the way to the bottom. These cracks are often 10 to 12 inches deep, which puts the seed substantially under the surface. When fall rains come, they wash soil into the cracks, filling them and burying the seed. Apparently, it would take a miracle to bring the seed to the surface again, short of digging it out with a spade.

Here is where the lightness of the seed goes to work. The surrounding soil, being heavier, forces the seed slowly upward. Each winter, frost action under the seed gives it a tiny prod upward. A year, two years, or ten years later it arrives at the surface.

DANDELION (Taraxacum officinale)

Perennial, reproduction by seeds and new shoots from a fleshy tap root. Leaves are deeply cut and lobed and form a rosette. Flowers yellow on a solitary stem which are followed by fluffy balls.

CONTROL: 2,4-D at temperatures above 70 degrees.

Rise For Shine

Here another mechanism of adaptation takes over. If the seed were to sprout when it had to compete with the vigorous, dense growth of spring turf, it would be choked out before it could become an effective plant. Some mechanism in the seed, however, prevents this from happening. Before it can sprout, it must be touched by direct sunshine. Many seeds require daylight for germination, as does Kentucky bluegrass, but of the seeds I have studied, crab grass alone demands direct sun. This means that it can only break its rest when the turf thins out and the competing permanent grasses are weakened. The summer dormancy of common Kentucky blue-grass, for example, gives crab grass just the opportunity it needs, particularly if the owner, in a misguided effort to revive the browning turf, begins to water. This supplies the seed with the one other missing element it needs—adequate moisture.

GOOSE GRASS or Silver Crab Grass (Eleusine indica)

Sometimes called Wire Grass or Crab Grass. Annual, branching at base, erect or prostrate. Stems, smooth, flattened, 1 to 3 feet. Upper leaf blades smooth, lower with a few hairs on edges, light green. Seed stalks have 2 to 10 fingers.

CONTROL: Sodar: Several applications may be needed.

Crab grass, then, is a weed protected against extinction by a series of mechanisms which enable it to survive where it is least welcome—in the home lawn. Since the seed—once deposited in an area—is practically always present, any chance of permanent control by chemical means is obviously small. A single crab grass plant is capable of ripening thousands of seeds, so on an average lawn the total amount of seed produced in a single year is frightening. Worse yet, because of the seed's survival mechanism, each year sees an additional store of viable seed added to that already in the soil. Repeat that population and that seed production for a few years and the proportions of the problem are staggering.

A common illusion among beginning lawn-makers, not to mention many old-time gardeners, is that seed dealers and garden centers deliberately sell lawn mixtures contaminated with crab grass seed. If the people do not think the adulteration was made deliberately, they at least are sure that the good seed was carelessly cleaned and that crab grass actually does come in packages.

GROUND IVY or Gill-over-the-ground, Creeping Charlie (Nepeta lederacca)

Perennial, spreading by seed and creeping stems which root at joints. Many erect flowering branches. Leaves numerous, scalloped, round or kidney-shaped with slender stems. Flowers purplish in small clusters at the base of the leaves.

CONTROL: Stubborn, but a mixture of Potassium cyanate and 2,4,5-T will keep in check.

No Crab Grass For Sale

I am glad to be able to put in a word for the beleaguered dealer. The chance of getting crab grass seed into lawn mixtures is about as great as that of having tulips and daffodils burst into full bloom in a Chicago garden on the Fourth of July. In addition, no seedsman in his right mind would deliberately add this weed seed to packages of fine turf grass seed. His pocketbook would dictate the folly of such action because he would have to pay at least $5.00 a pound for crab grass seed. I know, because I have tried to buy some for experimental purposes. I finally had to fall back on high school boys, whose wages cost me more than $5.00 a pound for the seed they stripped by hand. They didn't get rich, by the way, since about the most a boy could gather was a pound a day if he worked hard.

What the accusing lawn-maker overlooks is that we are dealing with two entirely different seasons of seed ripening, and two entirely different levels of growth. Even where crab grass does exist in pastures from which the seed of Common Kentucky bluegrass is harvested, this operation is over when crab grass is barely out of the ground. The crab grass has no chance to ripen seed. Even if, by some oddity, crab grass seed did ripen at the same time, it could not be picked up (at its height of not over 12 inches) by the mechanical bluegrass seed strippers that work 24 inches or more above the ground.

HEAL-ALL or self-heal (Prunella vulgaris)

Perennial, spread by seeds, underground roots and stems rooting at joints. In lawn it may produce seed when 2 inches high, elsewhere grows to a foot. Leaves smooth or slightly hairy, smooth edged or with shallow scallops. Flowers small, whitish to purple in dense spikes at top of stem and base of leaves.

CONTROL: 2,4,5-T not much better than hand weeding.

Even the package used for regular grass seed would prevent such a wretched mixture. A pound of crab grass seed would fill about a cubic foot; it is at least three times as bulky as lawn-seed mixtures.

For all these reasons, we must look to our own soil, not to the seedsman's package, for the source of our trouble.

Pre-Emergence Seed Killers

Fortunately, a new discovery of science, utilizing an old chemical, has given us a powerful weapon against crab-grass seed germination. Now on the market are several trademarked brands of a special grade of calcium arsenate which can kill 100 per cent of the seedlings as they burst the seed coat. These materials, logically, are called pre-emergence killers.

Here, at long last, is the remedy which has been sought for many years. As can be clearly seen, an attack on the seed itself is the logical way to control crab grass. But this new chemical must be used with care, according to package directions, for it not only destroys crab-grass seed but all others, too. The new calcium arsenate treatment does not attack the seed itself, but the emerging seedling as it breaks the seed coat.
The discovery of this chemical came about as the result of attempts to improve a chemical control for crab grass which goes back at least thirty years. I recall that in 1928 I applied arsenate of lead —IS pounds to 1,000 square feet—as a crab-grass control. That particular application worked like a charm. Not a blade of crab grass appeared, and, except for a slight yellowing of the Common Kentucky bluegrass (which disappeared after an application of mixed fertilizer), there was no sign of injury to the permanent lawn. This chemical has been used spasmodically by turf experts for years, but was not considered the answer to crab-grass infestations because of its erratic action. Today, we know that the effectiveness of lead arsenate is dependent upon the phosphorus content of the soil; that is, the amount of soluble and available phosphorus in the soil. The germinating crab-grass seedling needs phosphorus for growth. Arsenic has certain similarities to phosphorus: they occupy similar positions in the plant cell. If the soil is low in available phosphorus, the seedling absorbs the highly toxic arsenate instead and is killed before it can begin to grow.

Arsenic does not affect the seed: I have actually immersed crab-grass seed in solutions of both lead and calcium arsenate, then washed these off and the seed germinated normally. Since arsenate is only effective when the seedling is breaking through the seed coat, it is important to have the chemical present in the soil at that moment.

One thing that is difficult to explain is why the chemical is so lethal at that time but, later in summer, when the same spots are re-seeded with permanent grasses, these grow normally. This seems to be related to the fact that at the time crab-grass seed begins to germinate—in mid- to late spring in northern regions—the soil bacteria have not been working on the insoluble phosphorus, so this element is short. Later, the soil warms up and phosphorus is more available. Too, we know that annual plants are more sensitive than perennials to arsenate; why, no one knows.

Efficient Killer

Ordinary calcium arsenate 70 per cent—the old-time cotton spray —will work better than lead arsenate, but a special 85 per cent grade is even better. The latter contains about 4 per cent quick-soluble arsenic, which seems to make the difference. Even a year later, the 85 per cent grade is more active, again without any particular known reason. The important thing is that an 85 per cent grade, applied before the early crocuses have faded, will give 100 per cent control of crab grass that year and the following year. No qualifications—just 100 per cent control.

Commercial preparations are available in two forms. One is pelleted—pressed into grains. While this is easy to handle, it introduces one problem. The pellets are likely to remain intact without dissolving rapidly. Sometimes the crab-grass seed germinates before this happens, so the kill is not good. Another fault is that birds are likely to pick up the pellets.

My preference is for an 85 per cent grade of calcium arsenate adsorbed on vermiculite. This is wetted as soon as it touches moist soil, and cannot be picked up by birds when so dissolved. Calcium arsenate is more quickly toxic to earthworms than lead arsenate. As a result the worms are not as likely to crawl to the surface before they die. If the soil is waterlogged so that the worms are within an inch of the surface, they may crawl out before they die and are then a menace to birds, particularly robins. Watch for and pick up any dead or dying worms.

HENBIT (Lamium amplexicaule)

Annual or biennial. Stems square spreading, with erect branches frequently rooting at lower joints. Leaves opposite, slightly hairy, rounded with scalloped edges. Purplish flowers mostly at base of upper leaves. A vicious weed seeding almost the year around.

CONTROL: 2,4-D, above 70°,

Later Control

Once crab-grass seed has germinated, at least after the plant has passed through the two-leaf stage, it can no longer be killed by this chemical. Fortunately, a more active yet less toxic arsenical preparation—Sodar—will quickly destroy the seedling once it has emerged from the seed coat. The crab-grass plant remains sensitive to Sodar through the rest of its life. As it ages, however, more and more chemical is needed to kill it.

KNOTWEED, PROSTRATE (Polygonum aviculare)

Annual spread only by seeds. Stems may grow 2 feet slender, prostrate, jointed, forming a dense mat. Leaves small and narrow, bluish green, alternate. Flowers small and inconspicuous, white or pinkish, in clusters at base of leaves. Seed maintains vitality many years.

CONTROL: Calcium arsenate lead arsenate applied before March 1st.

Sodar is the most satisfactory chemical for summer control, except that it must be used with care on lawns containing bent grass. Bents seem to be quite sensitive to it. For this reason, most owners of bent lawns prefer to use a PMAS product (phenyl mercuric acetate stabilized). This chemical is also an excellent fungicide, and, in addition to killing off crab grass, controls many of the diseases to which bents are subject.
 
Sodar is also an excellent control for goose grass, sometimes called silver crab, and confused with true crab grass. It will also kill out common chickweed, although, by the time Sodar is ordinarily applied to lawns, this weed has set seed and is on its way out. Sodar also controls knotweed, but for this purpose must be sprayed on the turf during thaws in March. Actually, calcium arsenate also controls this winter annual; the treatment must be made in March.

MONEYWORT (Lysimachia nummularia)

Also called Creeping Charlie and Creeping Jenny. Perennial reproduced by seeds and creeping stems that root at the joints. Leaves opposite, rounded and smooth. The yellow flowers are borne at the base of the leaves.

CONTROL: 2,4-D, above 70".

Lethal Trio

Sodar can be applied in three forms, all of which are quite generally available. The original is a dry salt which can be dissolved in water. It is probably the cheapest form and quite effective. The second is a liquid. This is made with an ammonia carrier, which penetrates the crab-grass leaf very quickly and produces a rapid kill. The third form is dry, on vermiculite. One of the best of these dry formulations also contains 2,4-D, so that, in one application, both crab grass and broad-leaved weeds are destroyed. This is the easiest form to apply, since it can be put on with an ordinary fertilizer spreader. It costs somewhat more than either the dry salt or liquid forms.

Nimble Will

A serious problem in some lawns is Nimble Will, Muhlenbergia. This is an annual grass with a leaf that goes off sharply from the sheath. It is aggressive and will fill in practically any bare spot where it finds room, in sun or shade. This distinguishes it from crab grass, which thrives only in direct sunshine. The two are often confused, but once the difference is seen, they are easy to tell apart. Sodar, while not a complete control, will check Nimble Will. Tearing it out with a sharp rake is perhaps the best control.*

PIGWEED, PROSTRATE (Amaranthus blitoides)

Annual reproduced by seeds. Stems smooth, reddish, spreading flat over the ground from a central tap root and erect at the tips. Leaves small, alternate, wider at the top. Flowers greenish in small dense clusters at the base of the leaf stalks.

CONTROL: 2,4-D, above 70°.

*Experimentally, Endothal has given excellent results in some tests on Nimble Will, but exact dosages have not been worked out. Desperate victims of this pest may want to run their own tests.

Quack Grass

The only other grassy weed likely to give trouble is quack grass. In a tight, hard clay this can be a terrible pest, as it seems to like having its roots packed in soil. In lighter sands, merely mowing it at regular lawn height will kill it out in a year or two. It is quite persistent in heavy soil. Usually, three to four years of mowing will not kill it. No selective weed killer will destroy it without harming the permanent grasses as well.
 
Where the infestation is severe and the owner is desperate, quack grass can be killed with Dalapon but this will also kill the desirable grasses. Fortunately, Dalapon is water-soluble and can be washed out of the soil as soon as it has done its work. Kill is not rapid: the grass will turn yellow after three to four weeks. When this happens, set a sprinkler so it will cover the treated area. Turn it on and apply 2 inches of water, after which the soil is safe to re-seed.

PLANTAIN, COMMON or broad-leaved plantain (Plantago major)

Perennial, reproducing by seeds and new shoots from the roots. Leaves broad, rounded with prominent reins, attached by thick stalks at the base of the plant. Flowers borne in a dense, slender cylinder-like blunt spike.

CONTROL: 2,4-D, above 70°,

Broad-Leaved Weeds

Dandelion, plantain and other broad-leaved weeds are easily destroyed with 2,4-D, but modern practice calls for stepping up the action by using a product that also contains 2,4,5-T. For best kill, air temperatures should be 70 degrees or above. To avoid injury to nearby roses, tomatoes and other sensitive plants, watch out for two things. First, be careful of drift. If the spray is applied at high pres-sure through a very small nozzle, it will break up into very fine droplets, which are so light that they may drift hundreds of feet even on a light breeze. Cotton plants have been killed over a mile away by such herbicide drift. Roses and tomatoes are very sensitive and are usually the first to show injury.

PLANTAIN, BUCKHORN rib grass (Plantago lanceolata)

Perennial, reproduced, by seeds and roots. Leaves long, narrow ribbed on the upper surface, clustered at the base of the plant. The flower stems are slender, leaflets and topped with a club shaped head.

CONTROL: 2,4-D.

The answer to drift is to spray on a calm day and use low pressure and a nozzle with a large hole. This combination will produce a spray with a large drop, which falls immediately and "breaks" on the leaf.

Volatile Hazard

Volatility or vaporization is the second hazard that must be avoided. Even where a coarse breaking spray is used and no drift occurs, vaporization can still cause trouble if the wrong kind of 2,4-D is used. The high-volatile esters (compound ethers) which are the worst offenders are going off the market, but I still see them on dealers' shelves, usually carry-over stock. These high volatile ester forms of 2,4-D have such a low boiling point that a warm sunny day will turn them into gas. The gas will drift even farther than a misty spray.

PURSLANE or pursley (Portulaca oleracea)

Annual, spread by seed. Stems prostrate, branching extensively from a tap root and forming a dense mat. Leaves alternate and in clusters at branch ends wedge shaped, thick and succulent. Flowers small, at base of leaves. Each plant produces hundreds of seeds.

CONTROL: 2,4-D.

The various salts of 2,4-D do not vaporize, but may still cause trouble if they drift. I do not like them because they are not as deadly to weeds as the ester forms. If rain falls within eight hours of the time they are applied, a new spray will have to be put on. With an ester, even if rain falls half an hour later, the weed will be killed.

The answer is to use a low-volatile ester of 2,4-D and 2,4,5-T. Any product which is made with such a low-volatile ester will state the fact on the label. If it does not, better check before buying. The butyl and betoxyethanol esters are commonly used forms. These have such a high boiling point that the amount of vapor they can give off at temperatures under 100 degrees is very small. I have even placed cans containing solutions of these chemicals on the ground under tomato plants—a very severe test—without signs of vapor injury.

QUACK GRASS or couch grass (Agropyron repens)

A perennial spread by seed and white runners deep underground. Each joint of which can produce a new plant. Cultivation may spread runners, increasing infestation 1 to 3 feet tall. Leaves thin and flat, smooth on upper, hairy on lower surface.

CONTROL : Cannot be killed selectively. Dalapon will destroy, but also kills desirable grasses.

SPEEDWELL, COMMON (Veronica officinalis)

Perennial, reproducing by seeds and creeping stems. Flowering stalks are erect with leaves mostly opposite. Leaves % to 1 inch long, hairy on both sides, and finely toothed. Flowers small, pale blue or white, marked with dark blue or violet lines.

CONTROL: Endothal. Same chemical also controls V. filiformis.

SPEEDWELL, CREEPING (Veronica serpylifolia)

Perennial, reproduced by seeds and creeping stems, which root at joints forming dense mats. Flowering stalk erect. Rounded leaves on creeping stem are opposite; narrow leaves on flowering stalk are alternate. Flowers pale blue or white striped with darker blue. CONTROL: Endothal.

Chickweeds, An Increasing Menace

With 2,4-D effective against most broad-leaved weeds, and with Sodar as a remedy for crab grass that can at least clean out the current crop, duckweeds have been growing more and more annoying as lawn weeds. Note that I write in the plural. There are two distinct chickweed species—common and mouse-ear—which are badly confused.

The most irritating, and the most difficult to kill, is the annual common chickweed, Stellaria media. This is a lettuce-green creeping plant with oval leaves, pointed at the ends, and white starry flowers in early spring. Plants appear as soon as the snow melts and they bloom a few days later.

Actually, they have been growing and sometimes even flowering, all winter: this is what is known as a winter annual. The fall before, late in October, the seed sprouted and produced a tiny seedling. Every time the temperature went above freezing during winter thaws, that seedling grew a little and, by spring, it was mature.

SPURGE, PROSTRATE or milk purslane (Euphorbia maculata)

Annual, spread by seeds. The plant lies flat and sends stems in all directions to form a dense mat. The reddish stems contain a milky juice. Leaves opposite, numerous and small with a reddish-brown spot on the surface.

CONTROL: 2,4,5-TP.

YARROW (Achillea millefolium)

Perennial, spread by seeds and runners. Plants persist in lawns as clusters of fem-like leaves. Stem 1 to 2 feet, erect and hairy, branching near top. Leaves alternate, covered with fine hairs which give a grayish-green cast. Tiny white or pinkish flowers form a flat topped cluster. Very rank odor.

CONTROL: 2,4-D, above 70°.

Several chemicals can be used against it. Kuron (2,4-TP) seems to do an excellent job, but only if applied in cool weather. It is likely to injure turf if applied at temperatures above SO degrees.

Good Control

I have had excellent results with an old, old chemical which few people have had any success with on duckweed—2,4-D, mixed with 2,4,5-T. If sprayed on in spring, it is practically worthless. It will knock off the leaves, but not hurt the rest of the plant. If, however, the 2,4-D is used in late fall, after soil temperatures are down in the 40's but before the soil freezes, it will give pretty close to 100 per cent kill. The reason is simple. Ordinarily, these chemicals are eaten and digested by soil bacteria. When the bacteria are active, the chemicals will disappear out of a soil in three weeks. When the bacteria are not working, 2,4-D does not leach out of aay soil which contains some clay and humus, and so it remains toxic to common chickweed all winter long. By spring, every plant usually is dead.

During warm spells in winter, common chickweed will be bright green against the dead grass of the lawn. If the temperature goes much above 42 degrees, the plants can be sprayed with Sodar, which will kill them.

The use of calcium arsenate as a control for crab grass will also eliminate common chickweed, provided this chemical is put on in fall. Like crab grass, the chickweed seedling absorbs arsenic in lieu of phosphorus and is killed.

Where mature chickweed plants are to be killed, potassium cy-anate is perhaps the most effective product to use, with Sodar as a second best. Either chemical should be used at the strength recommended for mature crab grass.

The Mouse-Ear Kind

The other form of chickweed, called mouse-ear (Cerastium vul-gatum), looks quite a bit like the annual variety, until examined closely. Then you will see that the leaf is shaped like a mouse ear, without a point. To add to the mouse ear metaphor, the leaf has tiny hairs along the edge which can be seen when it is held up against the light.

The leaf color varies somewhat, but when both common and mouse-ear chickweed occur in the same lawn (they often do), the former usually shows up as light lettuce green, while the latter is more of a pine-green shade. Mouse-ear chickweed is a true perennial, but grows rather vigorously early in spring. If it cannot be killed with the usual 2,4-D and 2,4,5-T combination, then a straight 2,4,5-T brush killer should get it. The one difficulty is in finding a warm enough day to kill it early in spring. Air temperatures should be above 70 degrees.

The Latest And Best

Now, however, it seems that obsolescence has descended on all of the foregoing chemical "controls" for both kinds of chickweed.

There is a new chemical you can use, the result of three years of research. This most lethal enemy of both mouse-ear and common chickweed is 2,4,5-TP (Kuron), or, technically, 2-(2,4,5-trichloro-phenoxy) proprionic acid. It is applied either in late fall or early spring to areas where chickweed has occurred in the past. Where summer control is used, the methods previously recommended are still valid, but since both of these species ripen and drop their seeds before warm weather comes, summer control is not too effective.

Follow-Up Chores

When you are using weed killers you should be ready with a mixture of seed that matches the rest of the lawn—plus some light black loam (vermiculite can be substituted if the loam cannot be had)— to sprinkle over bare spots as soon as possible after treatment.

In warm weather, this means three weeks after 2,4-D-type killers have been applied. The limitations of Dalapon have already been discussed. Sodar can be washed out so readily that an ordinary sprinkling will prepare any soil for re-seeding. The same is true of potassium cyanate.

Phenyl mercuric acetate in a soil containing a reasonable amount of organic matter (as a good lawn soil should) is likely to be fairly persistent. I have seen injury a week or two after application. Washing with water does some good.

Kuron, if used for control of common chickweed, is somewhat more persistent than 2,4-D.

Calcium and lead arsenate are, of course, extremely persistent, but usually cause yellowing of mature grasses but only during the spring immediately after application. A feeding with a complete fertilizer will overcome this tendency.

All of which brings us to a point that has been made before, but deserves final re-emphasis: We are not merely trying to get revenge on the lawn pests that annoy us. Killing the weeds is necessary, but only half of the job. The real objective of our efforts is to remove the weeds as competitors of the desirable grasses, and quickly to reestablish a healthy lawn.

Chips Off The Chapter

Like a bad hangover, crab grass in the lawn is the butt of many jokes—but they are only funny if you don't have the headache. If it is true that "A weed is only a plant out of place," then crab grass is the king of weeds, for where is its proper place?

But, and with thanks again to turf scientists, the weedy grasses and the broad-leaved weeds can be reduced to the status of an annoyance. Chemicals do the trick, although you should not lean on them all the time. The ideal combination is a chemical attack followed by increased emphasis on good lawn-building practices.

NOTE.—The line drawings in this chapter were taken from the "Wall Chart of Lawn Weeds" published by Vaughan's Seed Co., Chicago 6, Illinois.

Are You Ready To Move Onto The Next Lesson? Click Here….