Most annual and perennial weeds reproduce from seed, but many perennials also reproduce vegetatively. Examples of vegetative reproductive parts of weeds include stolens, rhizomes, roots, tubers, bulbs, and nutlets. Bermudagrass has stolens, which are above ground horizontal stems. Quackgrass spreads by rhizomes, which are underground horizontal stems. Canada thistle, milkweed, hemp dogbane, horsenettle, and bindweed species have a deep complex root system with distinct vertical and horizontal roots. Wild bean has tubers. Nutsedge has nutlets that can live dormant in the soil for several years. Perennial weeds are much more difficult to control than annual weeds.
Weeds cause serious crop losses every year by reducing yield, quality and earliness of grain, forage, vegetable and fruit crops. Perennial weeds include any weed that lives for more than two years. Common perennial grass weeds in the mid-Atlantic region include quackgrass, Johnsongrass, Bermudagrass, and wirestem muhly. Common herbaceous perennial broadleaf weeds in the mid-Atlantic region include Canada thistle, milkweed, hemp dogbane, hedge and field bindweed,Canadagoldenrod, white heath aster, and horsenettle. Common woody broadleaf perennials include Virginia creeper, poison ivy, creeping dewberry and other brambles, multiflora rose, greenbriar, and mulberry tree seedlings. Yellow nutsedge and purple nutsedge are two perennial sedges commonly found in the region.
Primary and secondary tillage are effective control methods for annual weeds, but annual plowing and disking or field cultivating prior to planting often only spreads perennials by breaking roots, rhizomes, and stolens, and dragging pieces to uninfested parts of the field, or to other fields. Perennial weed control requires a significantly higher degree of commitment. The grower must make perennial weed control a high priority task. They must recognize that success will require more time, cost more money, and may affect a field’s crop rotation sequence to be effective.
Perennial weeds can be controlled by carbohydrate starvation. Perennials emerge in the spring by relying on carbohydrates stored in roots, rhizomes, stolens, tubers, bulbs or nutlets. Control measures should start when the carbohydrate reserves in the weed are at their lowest. This is often after the weed has used stored reserves to overwinter and emerge in the spring. Beginning when the weed shoot(s) break the soil surface, carbohydrate flow continues from the root toward the shoots for an additional 7 to 10 days to establish a leaf canopy. Between 10 and 14 days is a transition period. Within 14 days of emergence, the weed moves carbohydrates from the leaves back down into the root.
STARVATION OF PERENNIAL WEEDS IS ACCOMPLISHED BY NEVER ALLOWING THE WEED TO MOVE CARBOHYDRATES DOWN INTO THE ROOTS. This can be accomplished by tilling (or close mowing of tall upright weeds) every 7 to 10 days until they cease to attempt to emerge. It is critical that NO timing be missed or be late! One single missed tillage can negate all the effort expended up to that point. EXPECT TO CONTINUE THE EFFORT FOR 4 TO 6 MONTHS! Success may require more time if the effort was not started when carbohydrate reserves in the weed were low at the start of the process.
Typically, a field is fallowed and shallowly tilled on a weekly schedule for one growing season to eliminate a perennial weed problem. Begin with the first sign of the emergence of the weed in the spring. Maintain a seven (7) day tillage schedule. This time schedule provides about a three to seven day cushion in the event of a wet period when the field can not be tilled. The schedule MUST be maintained and must be a high priority for the grower.. One, single missed tillage can negate all the effort expended up to that point. Advance the schedule when wet weather is anticipated rather than suffer a delay. The reason for missing the timing is not important. Preventing ANY carbohydrate from moving from the leaves back into the root is critical for success until the weed is dead.
A field need not be fallowed for the year, provided the grower maintains a seven day cultivation and hoeing schedule. The weekly tillage cannot be stopped when the crop becomes established. The weekly tillage and hand hoeing must be continued until the weed is dead.