Ecological Weed Management Field Day Focuses on Cover Crops and Perennial Weeds
Posted: September 15, 2009
Weed scientist Matt Ryan identifies velvetleaf at the Ecological Weed Management field day. (Photo by Liesel Dreisbach-Williams)
The first step to weed control is identification
The goal is to learn the biology of the weeds that cause you problems and then exploit their weaknesses in order to make weed management a small part of your overall management effort. If you correctly identify barnyardgrass, which can produce 300,000 seeds on just one plant, or common purslane, whose seed can remain viable in the soil for up to 20 years, you will know to keep these weeds from flowering and adding to the seed bank.
What is a ligule?
At a June field day in Northampton County, weed scientist Matthew Ryan explained how we can use plant parts like a ligule, auricles, leaf number and shape, leaf and stem hairs to distinguish between weeds. The differences can be subtle. Many of us thought we knew a weed until we worked our way through the key and checked it with Matt to find some right and some new answers.
Now I know what weed it is – How do I control it?
Ryan focused on one difficult to control group - perennial grasses. Certain perennial grasses such as johnsongrass and quackgrass spread not only by seed but also by underground storage structures called rhizomes. Because these grasses have a ready supply of stored sugars, they grow vigorously and compete strongly with spring planted crops. If you have an infestation it can spread quickly. Management requires an integrated approach including prevention and tillage, grazing or mowing followed by a competitive crop to keep rhizome buds from flourishing. “Repeated, shallow, tillage” is the key emphasized by Ryan. The first tillage will actually stimulate rhizomes to activate new buds. Second, third and fourth tillage cycles, before the grass has more than three leaves, will starve the rhizomes and expose them to the harsh drying action of the sun. A recent study found that while a significant number of quackgrass rhizomes can be killed in the first year of management, at least two years of tillage are required to completely eradicate it.
Diversify your strategy
Growing cover crops in hard to manage fields can help reduce weed populations. “If your goal is to manage weeds you need to pick a highly competitive cover crop, such as rye and seed it at high rates,” said sustainable agriculture educator Tianna DuPont. At Reeder Farms the field day participants observed 10 cover crops, some planted in combinations. Spring planted oats and triticale both put on 3 to 4 tons per acre of dry matter. Small grains and combinations of small grains with legumes competed better with weeds than legumes alone. Though in this wet spring, weeds were far from scarce.