PUBLISHED IN FEBRUARY, MARCH, APRIL, A U G U ST AND SEPTEMBER BY O. M. SCOTT 8c S O NS CO. MARYSVILLE, OHIO Fifteenth Year Number 71 CHEMICAL WARFARE ON CRABGRASS THE CASE against Crabgrass was pre- sented in the previous issue of L A WN C A R E, Number 7 0. There it was pointed out that as desirable grasses take a sum- mer rest, Crabgrass is apt to slip in, incon- spicuously at first but with such vim and vigor that it is soon a real problem. for If its presence. Even in early August a severe infesta- tion of Crabgrass may go unrecognized. Every lawn should be carefully examined now found and attacked at once there is still time to keep it from producing seed to propagate its kind another year. If not removed or chemically controlled now the two ugly stages of Crabgrass will soon be in evi- dence. The first when the heads mature to purplish or reddish brown color and the second when frost kills the plants leaving unsightly patches of brown. An early start is the best control for Crabgrass. But those who hand pick the seedling plants in the two leaf stage or follow the prescribed raking and mowing program ( L A WN C A RE N O. 7 0, p. 3) should continue this into August because new plants may still be sprouting. is serious, drastic If there has been no control and the infestation treatment with the rake and mower is necessary to prevent wholesale seeding. A special Crab- grass rake or a stronger iron rake with flat teeth may be employed to lift up the pros- trate stems and runners so a closely set mower will cut them ofi. The clippings should be caught and destroyed. Repeat the treatment in an opposite direction in order to remove all the seeding stems. Follow up each week with the same treatment as long as seeding continues. The use of certain chemicals may offer an easier method of control. Even these will not work magic and the results with any weed killing chemicals will be modi- fied by the various factors described on page 4 of L A WN C A RE N O. 70. However, there are sufficient reports of success to make one of the following chemicals worth trying on Crabgrass and other weeds. Chlorates—The use of Sodium Chlorate has been described frequently in L A WN C A R E. Its sale is greatly restricted because of the war. Another form of Chlorate available for weed control is ATLACIDE, made by the Chipman Chemical Com- pany of Bound Brook, New Jersey. Sodium Chlorate presents a fire hazard. By itself it is not inflammable but any- thing burnable that becomes saturated with a Sodium Chlorate solution will easily ignite from friction when dry. Thus it is better to wear rubber boots when working with it and to keep it off cloth- i ng ( S ee L A WN C A RE N O. 2 ). Arsenicals—Various compounds of arse- nic are toxic to weeds. These include Sodium Arsenite and Arsenic Acid. They are generally available through drug stores or chemical supply houses. It is not neces- sary to use chemically pure grades. All arsenic compounds are poisonous (includ- ing Lead Arsenate) so they should be handled carefully. U s i ng A r s e n i c a ls a nd C h l o r a t es There are two types of treatment: first, selective control by which the weeds may be destroyed or weakened without perma- nent injury to the grass, and second, a complete surface destruction of all vege- C O P Y R I G HT BY O. M. S C O TT & S O NS C O. tation, a clean-up treatment that rids the lawn of both weeds and grass so the ground can be scratched up for seeding. Selective control of Crabgrass is not possible unless started in the very early summer while the plants are small and vulnerable. August is usually too late to inaugurate selective chemical treatment. In late summer Crabgrass growth is so heavy that a stronger chemical treatment is required even though it will also scorch the good grasses and possibly destroy their roots, too. However, this need not be of great concern because by mid-August a heavy stand of Crabgrass will have pretty well smothered all good grasses anyway and the plants are easily replaced in fall seeding. Where turf is so badly infested with Crabgrass and other weeds that there is little else, a renovation program such as the following may be carried out. Timing—First treatment between Au- gust 15 and September 1, second treatment about ten days after the first. Wet Spray Materials—Mix 4 oz. Sodium Arsenite with 16 oz. Sodium Chlorate or 24 oz. Atlacide and then stir into suffi- cient water to spray on 1000 square feet of lawn. The amount of water needed will depend upon the kind of sprayer to be used and will vary between one and two gallons to the 1000 square feet. It is advisable to experiment with the sprayer first. Measure off a section of 1000 square feet (40 ft. x 25 ft.). Then put clear water in the sprayer to see how much is needed to go over the area. Mix the chemical with double this amount of water so the area can be gone over in two directions, thus insuring that all vegetation is coated with the spray. First Application—The soil should be thoroughly moist before treatment. Cut the lawn closely and catch or rake up the clippings. Then apply the spray or dry mixture. A chemical solution can be put on with a sprinkling can but at least twice as much solution will be needed. Unless a heavy rain washes ofi the chemical, the vegetation will turn brown in a few days. Second Application—In about ten days, rake off the dead matted material. Loosen the soil with rake or hoe, apply Turf Builder at 10 pounds per 1000 square feet, then seed. Later the same day repeat the previous application of chemical in that way insuring destruction of the weeds. The chemicals will not harm the seed but would injure young grass if delayed until after germination. the Scott Spreader. With DRY METHOD—Instead of spraying, these chemicals can be applied by mixing them with a dry carrier such as screened soil or sand and then broadcasting by hand or through a fertilizer spreader such as the dry method it is necessary to use twice as much chemical because less sticks to the foliage than in spraying. The bulk needed will be 3 or 4 gallons per 1000 square feet. Two separate treatments should be made the same as by spraying. C o n t r ol S e e d i ng Chemical treatments do not always turn out perfectly and sometimes it is difficult to find the reason why. A heavy rain may wash the chemical off the leaves before the plants absorb it. The mixture may not have been strong enough or coverage not complete. But generally a careful series of treatments will have the two-fold effect of stopping the seeding of Crabgrass and destroying other weeds. is needed The fact that Crabgrass is a summer annual plant bears repeating. Cultural or chemical control to prevent seeding. It is not necessary to kill the roots since they will naturally die in the fall. Prevention of seeding this year is the way to check Crabgrass next year. This is accomplished by raking and mow- ing, by applying chemicals or by burning off with flame torches as described on page 4 of L A WN CARE N O. 7 0. $ These L A WN CARE bulletins have been published continuously since 1928. Sepa- rate issues may be had for the asking. Complete sets of back issues with index are available at a nominal price to cover binding and mailing.