Pre and Post Crabgrass Killer Strategy

Because pre-emergent application dates are so rigidly fixed by the appearance of the first crabgrass seedlings, I have been running extensive tests on the advantages of combining pre- and post-emergent techniques for the ultimate crabgrass killer.

At first I thought a late spring application of a pre-emergent (even after the first seedlings appeared) would eliminate enough crabgrass to be worth while since it would control everything appearing later. Unfortunately, while this did give control of later seedlings, the spring crop was so enormous (about 75 per cent of the seed usually sprouts at that time) that the lawn looked as though 100 per cent of the current year's crop had survived.

My next move was to apply both post- and pre-emergent controls. When these materials went on together, however, injury to permanent grasses was often severe. Spacing the two treatments three weeks apart saved the turf but control from post-emergent crabgrass killer treatment was not always satisfactory because of low temperatures which often occur in spring.

Solution of this problem came with the introduction of a chemical called Super Sodar, an improvement on the older dry Sodar powder. It is not properly a Sodar product, since it does not contain disodium methyl arsonate but is a mixture of ammonium methyl arsonate and dioctyl methyl arsonate. It is, however, a very effective post-emergent crabgrass killer control and will work at lower temperatures than most chemicals in this class.

The program, then, is to apply calcium arsenate on vermiculite as early as possible in spring, even if crabgrass has germinated, and to follow this three weeks later with a spray of Liquid or Super Sodar (on some containers this may be listed as AMA). The ultimate crabgrass killer strategy.