Selective Control of Weeds Explained

IN August GOLFDOM I discussed the pros and cons of ammonium sulphate as a weed-control agent, while the importance of proper fertilization and management of turf were stressed in the September number from the weed control angle. While it is vital that the greenkeeper be thoroughly versed in both the theory and practice of the above phases of turf maintenance, nevertheless, in themselves, they do not furnish him with ammunition adequate for a winning battle with the weed problem. It would appear that I can wind up this series of three articles on weed control in no better manner than by supplying him with a few soft-nosed cannon balls. Weeds and the fine turf grasses are all plants, obvious as it may sound. Consequently if you have a turf in which both are present, and wish to eradicate the former by chemical means, it is good business to watch your step. Don't get too rough in your tactics or you will succeed in eradicating not only the weeds, but the grass as well. To succeed in the quick e l i m i n a t i o n of weeds by chemical means, you m u s t use what is technically termed a selective agent. You might, in ordinary parlance, refer to it as having a discriminating action, if we can attribute such a quality to such an inanimate material as a chemical. Iron sulphate, for instance, has been k n o w n for years as a w e e d control agent. Theoretically, at least, you can spray a mixed turf of weeds and grass with this compound and the weeds will die while the grass will be unharmed. Theoretically this may be true, but in actual practice the compound is tricky and uncertain. You never know what the ultimate result will be, and often the grass is killed. Greenkeepers are afraid of it, and justly so. Consequently it has never had much vogue in turf maintenance circles. The compound lacks discrimination, or, in other words, it is not foolproof. Selective Control Agent Arsenate of lead, on the other hand, from the standpoint of its use on turf, is a striking example of a successful selective control agent in that it is rich, juicy meat for the majority of fine turf grasses and poison to the majority of weeds. In order to explain this fact, suppose we consider briefly the chain of chemical events which occur when arsenate of lead is mixed with the soil in which a mixed stand of fine grass and weeds are growing. When arsenate of lead is added to soil it is acted upon chemically by the soil solution or, in plain language, the soil moisture. This soil solution or soil moisture is not just simply water, as a great many people think. Rather, it is water in which are dissolved a great many things, such as phosphates, nitrates, sulphates, potash salts, etc. It is f rom this soil solution that the plant obtains a porL E A C H W A N T S T O H E A R F R O M B E R M U D A GRASS T E R R I T O R Y