This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
1. Allow no weeds to ripen seeds.
2. Kill while in the seedling stage if possible, for then the weeds die most easily and in the greatest numbers.
3. Induce autumn germination of the seeds of annuals by surface cultivation of fields after harvest. Many weeds are thus winter-killed before seeds can be produced. Following spring cultivation will rid the ground of a second crop of seedlings and leave the soil comparatively free of this class of plants.
4. Never plow under weeds bearing mature seeds. Burn them. For seeds of many weeds, particularly of some of the most troublesome annuals, have great vitality and may lie dormant in the soil for long periods, to germinate when brought to the surface by future cultivation. It is an old saying that "One year's seeding means seven years' weeding," but it may be much more than that. Mrs. Thaxter wrote that in her Island Garden she destroyed seedlings of Common Dodder every season for twenty years after the first seeding. Professor Beal's experiments demonstrated that the seeds of Charlock and Purslane will germinate after lying for thirty years in the soil, and it is said that the seeds of the Indian Mallow or Butterprint Weed have survived for more than fifty years, dormant but ready.
5. Thoroughly compost all stable manures that are known to contain the seeds of noxious weeds. Some few hard-coated seeds there may be which are able to survive the heat and ferment of the compost heap. Concerning this, the Iowa State Experiment Station, under the direction of Professor L. H. Pammel, has carried out a series of valuable experiments. Collections of various weed-seeds were made and placed in gauze bags in the heart of fermenting compost heaps for periods varying from five weeks to six months. The result proved that almost all seeds so treated were thoroughly rotted and their vitality was destroyed. The process is a costly one, in that the fermentation which kills the life-germs in the seeds also deprives the manure of some of its most useful properties, particularly of nitrogen, its most valuable constituent. But to sow weed-seeds broadcast, with a fertilizer to help them to grow, is still more expensive. One advantage of feeding hay from clean meadows and bedding the farm animals on straw from clean grain fields, is that stable manure may then be used as fast as it is produced, without loss of much of its fertilizing power from leaching and fermentation or expense from the necessary twice handling.
6. Sow clean seed; as near to perfectly clean as it is possible to make it. A thousand Clover seeds are but a small handful and will not suffice to plant a square rod of ground. If, then, the seeds of Dodder are but one to a thousand in a field of Clover, the crop is in danger of being ruined, and the land of being infested for a number of years with one of the worst of noxious weeds. Could the American farmer once be strongly convinced of the importance of this matter of sowing only the purest seed obtainable, the worst stronghold of the weed-army against which he fights would be conquered. All purchased seeds should be accepted only on a guaranty, and even then should be examined with care. It was undoubtedly by this agency that most of the foreign weeds which harass the land were brought to our shores and it is by this means that most of our home-grown pests are carried about and introduced in sections not before troubled by them. Only the best seed is good enough to plant, and the cheapest brand in the market is by far the most costly. The expense of preparing the land for a crop is equal, but the cost of its cultivation and care is much increased and the returns are greatly lessened where any considerable proportion of the seed sown produces worthless or aggressively pernicious plants.
7. Be on the watch for weeds new to the locality, and never trust to the harmlessness of such strangers. Had a few Dakota farmers been alive to the danger when the first Russian Thistles appeared in their flax-fields, the spread of that most pernicious plant might have been prevented, to the great advantage of large areas of the country. One of the services required by the State from each staff of Experiment Station workers is the identification of weed-seeds in samples of seeds submitted and the proportion of such impurities. Unknown plants may also be sent to the Stations for name and statement of qualities, and every farmer has the right of appeal to the Agricultural Department of his State for assistance in such matters.
8. Call in the aid of grazing animals, particularly sheep. Turning them into mutton and wool is a very profitable way of fighting weeds. In stubbles where a young and succulent growth of such plants usually springs up after harvest, and in old pastures where the more dainty neat cattle have selected the plants that they liked best and left the weeds to seed, sheep may be turned in and by their close cropping so shear down the leaf-growth as to cause many very undesirable plants to be root-smothered to death.
9. Practice rotation of crops. Continued growing of one crop not only exhausts the soil but serves to thoroughly infest it with the weeds that most commonly grow with that crop. Different plants take food from the soil in different amounts and proportions, and a proper rotation must be decided by conditions of soil and climate. It should be a systematic alternation on each field of the three general classes of field crops: grain crops, cultivated crops, and grass crops, including the clovers. The farmer whose scheme of rotation is mainly intent on the improvement of the land and not on his immediate profit, will, in the end, make the most money and have the least difficulty in suppressing the weeds. Any rotation should put much stress upon a cleansing crop, requiring such close care in cultivation as to allow no opportunity for weeds to grow. This has fully as important a place in the series as the crops grown solely for their money value, or as the manurial or feeding crop which is intended to return some of the lost fertility to the soil.
10. More wide-reaching and uniform laws, dealing with the control and eradication of weed plagues, should be in force. Many weeds are in the noxious class because they are so well equipped with the means of spreading their kind over large sections of the country. This quality increases the difficulty and expense of their extermination, and it should interest the entire community as well as the individual. If there are weed-laws already on the statute books, they should be made effective. If there are none, then persistent agitation for the enactment of such laws should be carried on by the persons who are most interested and who would be most benefited by their enforcement; namely, the farmers of the community.