Whenever fields are cultivated, weed seeds and propagules of perennial species germinate and grow. Most have been produced in situ in weedy crops of the past, a fact that has given rise to the prediction embodied in the title of this chapter. In the context of this… Dormancy is a state of seeds and buds in which they are alive but not germinated. If all weed seeds were to germinate at one time, their seedlings could be destroyed. Dormancy allows storage of millions of weed seeds in soil and enables them to grow in flushes over years. In this context, the old gardeners saying “One year Seeding seven years weeding” is very appropriate. In fact, weed seeds have been found viable even after 20-80 years of burial in soil. After a 2-year break from K'gari, Eurong local David Anderson ponders the old adage of one year's seed, seven years of weed… with some trepidation!
One Year’s Seeds, Seven Years’ Weeds
Whenever fields are cultivated, weed seeds and propagules of perennial species germinate and grow. Most have been produced in situ in weedy crops of the past, a fact that has given rise to the prediction embodied in the title of this chapter. In the context of this book the term seed includes true seeds and the functional seeds (actually fruits) produced in the grasses and in several other plant families. Most perennial weeds produce seeds but may in addition reproduce asexually by means of bulbs, rhizomes, runners and other structures. Seed production by several species, including Dandelion (Taraxacum officinale) and Bramble (Rubus fruticosus) is essentially asexual because the seed is not always produced following sexual fusion, but instead generally contains diploid cells which are identical genetically with each other and with the parent. From the weed control point of view, such apomictic seeds are essentially similar to the homozygous ones produced by habitually self-pollinating species. In addition to increase by seed and vegetative means in situ, seeds are brought to the field as contaminants in crop seed, in soil, manure, straw or on farm machinery, in irrigation water and attached to animals; many seeds, especially those of the Compositae and of some trees, are windborne. Propagules arriving with the crop seed are in a specially advantageous position, often providing new introductions.
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One Year’s Seeds Seven Years Weeds
Dormancy is a state of seeds and buds in which they are alive but not germinated. If all weed seeds were to germinate at one time, their seedlings could be destroyed. Dormancy allows storage of millions of weed seeds in soil and enables them to grow in flushes over years. In this context, the old gardeners saying “One year Seeding seven years weeding” is very appropriate. In fact, weed seeds have been found viable even after 20-80 years of burial in soil.
1. Enforced dormancy – It is due to deep placement of weed seeds in soil during ploughing of the field. Weed seeds germinate readily when they are restored to top 3-5 cm. Enforced Dormancy is a non-specific character of seed. Cultivation encounters enforced dormancy by bringing the weeds to surface where they are exposed to light besides better aeration. High soil temperature and NO3 content of surface soil may further help in breaking seed dormancy.
2. Innate dormancy – It is a genetically controlled character and it is a feature of specific weed seeds, which fail to germinate even if they are present in the top 3–5 cm soil, and adequate soil moisture and temperature provided to them. The possible reasons are the presence of (i) hard seed coats e.g., Setaria, Ipomoea, Xanthiums pp. and (ii) immature embryos e.g., Polygonum. In certain weed seeds particularly of Xerophytic origin, presence of inhibitors is responsible for innate dormancy. It can be overcome with passage of time, or under the influence of some climatic pressure.
3. Induced dormancy – Induced dormancy results from some sudden physiological change in normally non-dormant weed seeds under the impact of marked rise in temperature and or CO2 content of soil, low O2 pressure, water logging etc. Wild oat (Avena fatua) seeds exhibit all three kinds of dormancy.
One Year’s Weed, Seven Years of Seed
That old adage about one year’s seeds, seven years of weeds? Does that mean the seven years of weeds promised or threatened by that adage are multiplied by each year of seeds?
I sincerely hope not. Seven years of weeds are bad enough. I’ve been off the island for over two years. I might be able to manage my patch around Eurong to control weeds for the next seven years. But 14 years? If I’m still around by then, I doubt I’ll be able to carry around a 15Kg knapsack of spray or bend over pulling weeds.
What planet was the poet Gerard Manley Hopkins on when he wrote about the beauty of Spring “when weeds in wheels shoot long and lovely and lush”?
Long and lush, I can understand, but “lovely”?
On my return to Eurong, I found plenty of the long and lush. There were fields of green after plenty of rain. Oh, and did I say “fields” of green? Well, carpets of green winter weeds of all descriptions: A variety of thistles, cobblers peg, dandelion, ragweed, Moss River burr, and blue billy goat weed.
There were, of course, the usual suspects growing unhindered in the places around Eurong I had been tackling for years – Guinea grass and coral creeper, Brazillian nightshade, basket asparagus, Easter cassia, mother of millions, morning glory, painted spurge and the odd beach almond seedling.
It wasn’t as if I didn’t have plenty of things to occupy my time after years of neglect. There was also a massive beach clean-up after the floods.
However, I spent several hours trudging around Eurong when time and the weather permitted, spraying weeds before a misstep and stumble caused a back injury which put me out of action. I eventually required surgical intervention.
What a great year 2022 was turning out to be.
Thank goodness for the FIDO groups who have kept up the fight against weeds in my absence.
During my recovery from surgery, I took one of their teams for a weed tour of “Residential Valley”. While they were weeding, I couldn’t help myself. I plucked a bag full of tiny mother of millions from an embankment in Jarvis Street by kneeling on the road, so I didn’t have to bend my back.
I have recovered enough now to carry a knapsack spray, bend at the knees, and even bend my back, enabling me to pull weeds again. I’m hoping to make a dent in the weed population while the sun is shining and as time permits.