By: Elaine Roddy, Vegetable Crop Specialist, OMAFRA, Ridgetown
From OMAFRA’s ONvegetables.com
The website, Ontario CropIPM, contains the full range of pest management information from many vegetable crops, including asparagus. Many users do not realize that it is also home to weed galleries, herbicide injury information and critical weed control period information. The following three problem weeds for asparagus are excerpts from the weeds and herbicides section of Ontario CropIPM. Continue scrolling for the best control options for each of the problem weeds.
Eastern Black Nightshade (Solanum ptycanthum Dun.)
Eastern Black Nightshade is often mistaken for pigweed seedlings. Eastern black nightshade is distinguished from other weeds as it is an annual plant that has thin, oval to diamond shaped leaves, small umbels of white flowers on the side of stems and black berries when mature. Eastern black nightshade is an annual reproducing only by seed.
The hypocotyl (stem below cotyledon) is hairy and can be green or maroon. The cotyledon leaves are oval, smooth and green on the upper surface, maroon on lower surface. The leaves are alternate (1 leaf per node), oval or diamond shaped and pale green, soft and nearly translucent. Young pigweed leaves can be distinguished by a shallow notch at the tip.
The stems are erect, 5-100 cm (2-40 in.) high, very branched in the upper part of the stem and mostly hairless. Eastern black nightshade flowers from June until late autumn. The flowers are small and usually grouped together in a small umbel of 2 to 5 flowers. The petals are white and may or may not be tinged with purple. They resemble potato flowers but are smaller (9-15mm) in diameter. The fruits are black berries that are first green and contain many flat seeds. The berries are reputed to be poisonous
Best control options: Chateau, simazine (trade names Simazine, Princept Nine-T and Simadex) and Callisto are the top rated asparagus herbicides for nightshade control.
Field Bindweed (Convolvulus arvensis L.)
Field bindweed is a perennial reproducing by seed and by a persistent, extensively spreading underground root system.
The cotyledon leaves are opposite, round and notched at the end. The leaves are Leaves are alternate (1 per node) with short or long stalks. They are commonly arrowhead-shaped with 2 basal lobes and smooth margins. Occasionally they are long and narrow, or broader and nearly round except for the 2 basal lobes.
The stems are slender and smooth or very finely hairy. They are usually twining or curling; they lay prostrate on the ground or grow up any nearby object.
Field bindweed flowers from mid-June until autumn. The flowers form on long stalks from axils of leaves, always with a pair of small, narrow, green bracts on the flower stalk some distance below the flower. The flowers have 5 small green sepals and a white to pinkish funnel-shaped corolla 2-2.5 cm in diameter when fully opened
The seedpods are roundish, about 5mm long containing 1 to 4 seeds each of which is about 3mm long, pear-shaped and 3-angled with 1 side rounded and with tiny grayish bumps
Best control options: controlling field or hedge bindweed is a challenge, because of its extensive, perennial root system. Because bindweed grows in patches, a systemic herbicide with glyphosate (eg. Roundup) can be effectively used as a spot spray. The key is to wait until bindweed shows first bloom (bud to full bloom), and use a 2% solution (2L Roundup in 100L water). Established patches usually take at least two applications in subsequent years for complete control.
Horsetail (Equisetum arvense L.)
Horsetail is a perennial plant. It never has flowers or seeds but reproduces by spores and by aggressive horizontal underground stems (rhizomes). The rhizomes are dark brown or blackish, spread out for long distances and are often 1 m below the ground surface. It is an intense competitor and can severely suppress crops and other plants.
In early spring the shoots are ashy-gray to light brown, unbranched, hollow, jointed stems. Each node (joint) is surrounded by a toothed sheath. The tip of stem ends in a brownish, spore-producing cone. After the cones have shed their spores (early May) these light brown stems wither and die down. At the same time, the second type of shoot emerges from the ground. These shoots have green, slender, erect, hollow stems. They are leafless but have whorls of 6 to 8 branches at nearly every node. Each branch may branch again with whorls of smaller branches.
Best control option: Sandea is labelled for horsetail suppression. Use maximum labelled rates for best results. A non-ionic surfactant or crop oil concentrate should be used with post-harvest applications. Contact with asparagus fern may cause temporary yellowing. Crop injury will be minimized and weeds will be controlled more effectively when applications are made with drop nozzles to direct the spray below the fern to allow for more complete coverage of target weeds.
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