The Complete Guide to Landscape Design, Renovation, and Maintenance
by Cass Turnbull

HERBICIDES: Tales of Hope and Tales of Horror

In the following section on herbicides, I often use trade names as well as the chemical names. I have done this to simplify presentation. No endorsement of brands is implied or given.

Tales of Hope
While working for the Seattle Parks Department, I took care of an urban park sandwiched between the freeway and a porno theater. It had become so overgrown and nasty it deserved not the name of Park. This park had perhaps fifteen years of grass, morning glory, horsetail, fireweed and--you name it--growing unchecked on sun-baked clay soil. The shrubs were suffering Zable laurels, rhododendrons, a row of great, ten-foot, double-file viburnums and some beaten and baked trees. During one group project we dug up and pulled out the weeds, found scores of wine bottles, litter and syringes left by prior users of the park, and had to dodge rats as we went. Then we sprinkled dichlobenil (Casoron) ____ granules and covered it over with bark mulch. In addition, the antique water system was repaired and revived and the area fertilized. It stayed neat and tidy that entire year--and with a modicum of regular hand weeding, with water and fertilizing, it became a pleasant place to sit and eat lunch. Casoron lasts in the soil for about six months, preventing new seeds from growing and preventing tiny bits of roots (like morning glory) from re-emerging.

Another tale of hope. The second year of working as a private gardener, I had occasion to estimate the cost of restoring a landscape that was being overcome with weeds. Others had tried and failed. Most discouraging was the grass coming up through the vinca ground cover. Vinca, or periwinkle, grows as a mat of criss-crossing threadlike strands. The grass, its stalks protected by the groundcover and its roots entwined with the vinca's, was tough to thoroughly weed out by hand. I vividly recall hours of weeding in the rain, the strands of vinca cutting at my cold, sore hands, and with a rematch scheduled for next month. I estimated a day and a half a month to keep this yard looking good--for the first year, anyway.
Then I heard about sethoxydin (brand name Poast ____) a new chemical that kills just grass. Spray it over non-grass plants (those listed on the label), it would kill just the grass. Expensive as it was, I decided to give it a try. In the spring as the new shoots of grass, as thick as turf, emerged among the vinca, I applied the new herbicide. I came back next month to find little, if any, grass with which to continue the fight. Maintenance dropped to one-half day a month immediately. Poast does not kill all species of grasses or grass gone to seed. Still it is a powerful weapon.

Another: A rockery overgrown with morning glory, grass, vetch, dandelions and others, defied hand weeding because the roots were too tightly crammed under and protected by the rocks. With our weedeater we mowed down the grass to encourage soft, tender new re-growth. Then as it grew back we sprayed the whole area with glyphosate (Roundup). We let it bake in for a week or two, pulled off the dead yellow tops and replanted. Glyphosate (the active ingredient in Roundup and Rodeo) is used as a contact spray. This means it kills what it touches. The treated weeds translocate (move) the chemical throughout the plant to roots, stems and fruit. It interferes with biological-chemical processes specific to plants. According to a June, 1986, registration standard, the Environmental Protection Agency considers glyphosate to be relatively non-toxic to most non-plant forms of life. According to the same report, glyphosate shows little tendency to "bio-accumulate." Data indicate that it does not cause mutagenic (mutations), teratogenic (birth defects) or reproductive effects.

Roundup binds tightly and quickly to the clay particles in soils. It is not, therefore, available to poison adjacent plants or leach through the soil to the watertable. It decomposes by microbial activity in about two weeks. The soil is then ready to replant with desirable ornamentals. Many otherwise organic gardeners will, on occasion, resort to Roundup for these reasons. Since Roundup does not "poison" the soil, remaining weed seeds will germinate.

Be sure to spray Roundup on young, healthy, growing weeds. It doesn't work on old, dusty grass and weeds. Dirt inactivates it. Roundup is good for the un-pullable dandelion in the sidewalk crack. However, it does not kill horsetail, clovers, and it has a tough time penetrating the waxy leaves of ivy and holly. Oddly enough, creeping jenny is unaffected as well. It is still a very powerful tool for the gardener. Be sure to spray only target plants.

Some nastier chemicals exist for other weeds. For moderate success on horsetail, Amitrol-T,___(1) For false bamboo, also called Japanese knotweed (Polygonum cuspidatum), dicamba. Dicamba can also be used on bamboo (or Roundup can be used instead). Dicamba is known to move through the soil and kill roots of nearby desirable shrubs. It is very soluble. Its residues are persistent (two months to a year). Be careful not to contaminate ground water and don't use it when rain is likely.

Other tales of hope include the lawn herbicides, which if used correctly (that is to say, applied at the appropriate time and carefully following all label directions, sprayed on a shaggy lawn area and not washed off for two days by the irrigation system or mowed off) will eliminate broadleaf weeds from your lawn (moss and annual grasses have to be dealt with separately).

I once saw a fearless gardener spray the steep slope just adjacent to a new area with "Trimec___" a potent lawn-type formulation of chemicals. This treacherously steep slope was a maintenance nightmare of blackberry vines that shot up to obscure the view of the city which park users expected to see from the bench above. Each year we were forced to use hand tools and screaming brush blades, at great risk to life and limb, to clear the bank. The Trimec curled and killed the young vines in a matter of days, leaving tall grass to stabilize the slope and look nice for the public.

Tales of Horror
Tales of hope always come with tales of horror. Once a ballfield attendant applied Casoron to the freshly weeded dirt area of the baseball field. A rainstorm followed, washing the granules onto the grass and down onto the neighbor's lawn. The resulting dead grass and the affected dirt beneath had to be replaced by the city at taxpayer expense.

In another old city park, several beds that once contained beautiful old rhododendrons now lie empty. A maintenance laborer who was sent out to apply Casoron to the freshly weeded bed, tripled the rate of application to make sure the weeds stayed down. This circumstance in combination with the fact that rhododendrons (as well as pines) are somewhat more susceptible to damage by Casoron than other plants, caused them to die.

Casoron, when properly used, can be a useful tool. More often than not it is abused by homeowners and landscapers. Usually excessive application rates just stunt the plants, causing tell-tale yellowing at the edges of the leaves. One sees it everywhere.

Another tale of horror. A lady determined to rid herself of morning glory, including the vines covering her rhodies, sprayed them with Roundup--killing both vine and shrub. Roundup is non-selective--it kills whatever it touches.

And another: A fully mature and particularly beautiful maple in a yard next to a prominent viewpoint overlooking the city simply failed to leaf out one year. Indeed, it was dead. Overuse of lawn weed killer was the cause. The ingredients in lawn herbicides work on all broadleaves, be they dandelions or trees, leaving only the grass unaffected. Since most of a tree's roots are in the top eighteen inches of the soil, and they extend far beyond the dripline, trees are far more susceptible to chemical damage than one might suppose.

The potential dangers of all pesticides (herbicides and insecticides are both pesticides) are assessed in several ways. Scientists evaluate the relative toxicity (how much does it take to kill 50 percent of the test animals), whether it collects in the food chain, whether it degrades quickly or slowly, how it degrades (digested by microbes? decomposed by light?), whether it is likely to move through the soil to adjacent plants or to the water table, whether it causes particular kinds of physical damage to the test animals (e.g., cancer, birth defects, kidney failure, etc.) with either a single exposure or through repeated exposures.

Sometimes a particular pesticide will pose a serious threat to some non-target species. For example, dogs are especially sensitive to 2,4-D, a common ingredient in many lawn herbicide formulations, and geese and other birds have died browsing on lawns treated for cranefly with incorrect application of diazinon.

You should exercise caution with all pesticides and herbicides. The fact that home and garden chemicals appear on the shelves and are registered with the Environmental Protection Agency (EPA) does not mean that the EPA guarantees their safety. In 1983, of the 600-odd chemicals in common pesticide formulae, only four had successfully submitted all the test results required to indicate relative safety to humans and the environment. At that time the EPA estimated that it would take twenty more years to fill the data gaps.

Many test results are based only on analysis of the "active ingredient." The majority of a bag or bottle of herbicide is made up of "inert ingredients," which are sometimes other chemicals. Chemical combinations are unpredictable, and two chemicals which alone may be relatively non-toxic can be dangerous when combined. No testing is done on these combinations. The term "inert" can be misleading. In 1986, sample testing of registered pesticides turned up "inerts" which were themselves pesticides. An EPA staffer discovered DDT--outlawed since 1972--listed as an inert ingredient in some registered pesticides.(2) A secondary ingredient (POEA) found in some glyphosate formulations is three times as toxic as glyphosate itself.

There are several tales of horror concerning the validity of test results submitted to the EPA by chemical companies, and about loopholes which enable a manufacturer to sell pesticides before all the required tests have been completed (i.e., conditional registration).

So, don't assume that any pesticide, or any chemical for that matter, is safe. We simply do not know. Treat them with a healthy respect, but not paranoia.

If you choose to wage chemical warfare with either herbicides or insecticides, you need to adhere religiously to several common sense rules and procedures, whether or not they are comfortable or convenient.

Using Chemical Weapons Safely
First, do your homework. Unlike other do-it-yourself projects do not read the instructions only when all else fails. Plan to spend some time reading and understanding the label. Bring it inside, sit down, use good light, perhaps take notes on mixing instructions. Take your time. The label is a legal document. If you spray pesticides other than according to label directions, you are breaking the law. Anything and everything on the label is there for a very good reason. They don't make up application restrictions just to be on the safe side. Label instructions are serious business. Home and garden pesticides can be as much of an ecological or health danger when abused as any of the so-called industrial chemicals.

Suited up for chemical warfare. To use chemicals responsibly you must dress correctly, whether or not you find it comfortable or convenient.

If you do your own spraying, use two well-marked (nail polish works well) spray tanks, one for "bugs" one for "weeds," it will help you avoid a serious, serious mix-up. Think about it. Keep all chemicals in well-marked (original) containers. Never, ever, ever store chemicals in old food or drink containers. Keep all such materials locked or shut up in a safe place--like a garage cupboard, and include with them all mixing paraphernalia like measuring spoons or cups--which should also be well-marked and used for that purpose only. Do not use aluminum gear and avoid storing chemicals in spray tanks--they can be very corrosive.

Wear protective clothing, rubber gloves--solid ones, not just kitchen types, but not ones with cloth linings which may absorb pesticide particles. Safety glasses and a cloth face mask are in order. This is especially true when mixing, and pouring materials, and cleaning equipment--which is when most accidents occur, usually involving higher volumes and concentrations of chemicals. This may seem obvious, but people easily forget to "suit-up" when mixing or will absent-mindedly take off their safety glasses just before opening the pressurized lid to the tank. Your eyes, nose and mouth absorb fumes and particles most readily. This is followed by the palms of your hands, soles of your feet and your forehead. So a hat may be a wise addition.

Mix small amounts so that you run out on the job. It's unacceptable to return to the spigot with a tank of unused material. Spray it all out in the yard. Don't dump it next to your spigot and never, ever, ever pour excess chemicals down drains, toilets, or sewers. Are you crazy? Do you want to eat it in your clam chowder?

After you are through, wash your gear and your clothes and yourself--right away.

Don't ever, ever mix two chemicals together if it's not allowed in the instructions. It could be a very big mistake. Don't ever, ever, ever, ever use some "extra for good measure." Know what plants you're spraying and/or what pests or weeds are the target. Be sensitive to conditions that affect your spray. On very hot days liquid pesticides will vaporize into a fine mist and can drift quite far. Be sensitive to even small breezes. Big droplets from the spray nozzle will not drift as far as fine mists. With herbicides, keep that nozzle close to the plant--not waving around up high, as is commonly shown in TV ads. Buy a shaker for your granular herbicides to ensure even coverage and so you don't get it all over yourself and down in your sweaty rubber gloves. Be sensitive to the presence of pets, wildlife, children, pregnant women, waterways (even if they just look like that old ditch), and to foraging bees.

My own policy is that chemical intervention should be considered an option only when it is absurd to employ cultural methods (hand weeding, mulch, etc.). Sometimes chemicals are used during an initial cleanup. Avoid using herbicides for regular, basic shrub bed maintenance. I guarantee that truly responsible use of herbicides is at least as time consuming, physically demanding (the discomfort factor alone), and expensive as mechanical control. Additionally, it is brainracking and the potential for disaster (P.for D.) is, needless to say, considerably greater. In the vast majority of situations, weed control using hand-to-hand combat is equally as effective as chemical warfare. There are specific weeds and certain situations which may be considered exceptions, but exceptions they are. Pesticides should be the weapon of last resort.

There are dozens of more commonly used herbicides that are available to homeowners. I've just told tales of hope and horror about ones I have dealt with or will use as last resort. The tales of horror are worse for many other chemicals, especially soil "sterilants" (I don't want anything to grow there ever!). Herbicides are tools to use, not abuse.

Think of hand weeding as a game, not a chore. Once everything is cleaned up, mulched and under control, weeding is not time consuming or arduous--it just needs to be done regularly. It helps me to sing the weed song--to the Kenny Rogers tune "The Gambler." It goes

"You gotta know when to hoe 'em
Know when to pull 'em
Know when to walk away
Know when to run"

Forward to Fertilizers and Organics

Back to Weeds: Hand-to-Hand Combat