Davey Tree Flipbooks

36 PALMER AMARANTH (Amaranthus palmeri) PLANT DESCRIPTION Palmer amaranth, or careless weed, is a 3–5 foot tall broadleaf summer annual weed typically seen in summer with large spike flower heads. In the spring it can be seen as a seedling with a poinsettia-like appearance with evenly spaced leaf arrangement. The leaves are connected to the stem of the plant on leaf stalks that are longer than the leaf. LEAF: The leaf is spade or diamond shaped and has a smooth margin. STEM: There are no hairs on Palmer amaranth's stems or leaves. The uppermost branches and flowering spikes are long and can grow to lengths of 3 feet. FLOWER: Multiple branches and green flowering spikes are located on the upper portion of the plant. Flowering spikes resemble pipe cleaners; diameters can exceed the size of one's thumb. Palmer amaranth has both male and female plants; the flowers of the female plant have spine tips that are sharp when dry. SEED: In fall the female flowers enclose the small, brown, roundish seeds. Seeds fall below the parent plant. Individual plants produce up to one million seeds that can remain viable in the soil for up to 20 years. REPRODUCTION: Seeds function as the primary means of reproduction with most seeds dropping around the parent plant. They are often spread by mowing or agriculture equipment. WHY IT IS NOXIOUS: Palmer amaranth is a major threat to corn and soybean fields. It can outcompete young corn plants for light. Palmer amaranth can be toxic to livestock. SEASONAL IDENTIFICATION WHEN TO FIND: Palmer amaranth is most easily noticed in the early summer as it is flowering. Flowering spikes, similar to large green pipe cleaners, are easily spotted from a distance in low-growing crops. SPRING IDENTIFICATION = DIFFICULT Palmer amaranth germinates late in the season, usually in early summer. When seedlings emerge, leaves are oppositely arranged and resemble a poinsettia with an evenly-spaced leaf arrangement. SUMMER IDENTIFICATION = MODERATE The plant is characterized by tall, long, flowering spikes. A single plant has multiple upright flowering spikes that may sometimes droop at their upper ends. Female flowers start to develop spine tips. FALL IDENTIFICATION = EASY As the female plant develops its seeds late in the season, the long spikes become more brittle and have a sharp touch. Only at maturity will the female plant have this sharp touch. WINTER IDENTIFICATION = DIFFICULT This plant may only persist as a plant skeleton or seed into winter. SIMILAR-LOOKING SPECIES COMMON WATERHEMP (Amaranthus rudis) has a similar form but leaves are long and linear. The flowering spikes are shorter and skinnier. SMOOTH PIGWEED (Amaranthus hybridus) has similar leaves but has hairs on the leaf and stem surfaces. Flowering spikes are short, stout, and crowded at the top of the plant. REDROOT PIGWEED (Amaranthus retroflexus) has similar leaves but has hairs on the leaf and stem surfaces. Flowers form into a single, upright terminal cluster. LOW HIGH ohio distribution roadside distribution growth seeds ability to dominate difficulty of control WHERE TO FIND: Palmer amaranth is not prevalent in Ohio, but has been found in central Ohio. It has only been seen in agriculture fields but is capable of spreading into the right-of- way. Palmer amaranth is typically found in soybean fields in dry soil. If found in the right-of-way, it would most likely be from seeds spread from equipment use in nearby farm fields. CONTROL METHODS: MECHANICAL: Mow only in late summer to reduce seed production. Hand pull individual plants. CHEMICAL: Make directed applications to Palmer amaranth with selective herbicide in summer before flowering. Palmer amaranth has shown the ability to develop resistance to commonly used herbicides. Broadcast pre-emergent herbicide to soils before seeds germinate. CULTURAL: Plant tall fescue in early fall and allow to grow tall in summer. RECOMMENDATION SUMMARY: Palmer amaranth is a summer annual weed that can be resistant to commonly used herbicides. For best control results, make applications from midsummer to late summer before flowering. Palmer amaranth has shown an ability to develop resistance to glyphosate, ALS-inhibiting herbicides, and other agriculture herbi- cides. Monitor herbicide applications for effectiveness due to Palmer amaranth's ability to develop herbicide resistance. If a second application is necessary due to poor herbicide results, use alternate herbicides with different modes of action. If a large colony produces seed at the road edge, prevent future germination by making pre-emergent herbicide applications to soil in spring before seeds germinate. Mow only to reduce seed production in late summer. Hand pull to control individual plants, but be cautious not to distribute seeds to new locations if pulling plants that are past flowering period. Plant tall fescue in fall and allow to grow tall in summer to compete with Palmer amaranth. Failure to control Palmer amaranth will allow individual plants to produce up to one million seeds that can remain dormant in the soil for up to 20 years. summer annual RIVM LEVEL OF CONCERN

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