Weed populations give you an indication of your soil IF you know how to interpret them. Jay McCaman’s Weeds and Why They Grow and Charles Walters, Jr’s Weeds, Control Without Poisons are worth your review. Weeds and Why They Grow provides an excellent coverage of over 600 specific weeds and the field conditions they prefer. When seen as indicators of field conditions – too much potash or magnesium or insufficient calcium – the grower can make decisions other than rescue chemical control. My neighbor had some dolomite lime delivered and was waiting to spread it. “Why dolomite” I asked him. “That’s what the fertilizer test recommended” he replied. The next year we looked at his new weed pressures. I showed him Jay’s book and each weed was related to magnesium!
In the late 1980’s a PA strawberry grower planted oats in the fall (oats help make phosphorus available to the next years crop) which were then winter killed. After tillage he then planted strawberries and applied 2 gal/A liquid calcium and blackstrap molasses to hopefully suppress weed germination. No herbicides were applied or mechanical cultivation was performed throughout the summer however periodic applications of lesser amounts of calcium & molasses were applied. A picture three months later clearly showed weed germination in the section without the calcium and molasses program. That fall he again planted oats which were again winter killed.
A 1988 test plot near Ossian, IA with corn planted on an old alfalfa field showed excellent weed control also using the calcium/molasses program.
Insects, like weeds, also have a purpose. We believe they represent Nature’s cleanup crew. Their purpose is to consume low brix, low nutrient density foodstuffs while leaving that with high brix and high nutrient density to us. Depending on the fertility of the crop insects will eat the crop or the weeds as in these pictures. Philip Callahan, retired USDA scientist from USDA Insect Attractant and Behavior Laboratory at Gainesville, Fl showed conclusively that insect antenna tune in to specific wavelength frequencies which they either ignore or seek out. Change that frequency via conventional fertility and management practices and what originally sounded like I’m Here now turns into HEY MAN, COME AND EAT ME!
Biological growers find pressures from both weeds and insects greatly diminish as their transition continues.