Tag: purslane

In August, I wrote about nutsedges, weeds with three methods of reproducion; in July, Pigweeds (amaranths), warm weather annuals that put out seeds in a “Big Bang” as Chuck Mohler describes in Manage Weeds on Your Farm. In June, I wrote about docks, tap-rooted stationary perennials that are best tackled early in life; in May, galinsoga, a warm weather annual that dribbles out seeds from a young age.

This month is the turn of late summer weeds, the ones that only really get going after a long period of warm or hot weather. Here I will feature Purslane, Velvetleaf, Flower of an hour, Horsenettle, Fall panicum and Johnsongrass,

Identifying Late Summer Weeds

Virginia Tech has a very good weed ID site and links to similar sites in some other states.

Also see Manage Weeds on Your Farm; and A Virtual Tour of Major Weed Plant Families by Mark Schonbeck for eOrganic.

Principles of Sustainable Weed Management in Organic Cropping Systems, by Mark Schonbeck, 2011.

Some Species of Late Summer Weeds

Purslane

Common purslane (Portulaca oleracea) is an edible, succulent, drought-tolerant summer annual weed which grows in sprawling mats and can compete severely with young or low-growing crops. The succulent stems and leaves store water enabling the plants to surviving drought. It grows during the hottest time of year, with seed germination occurring when the soil temperature exceeds 77°F (25°C) with an optimal temperature of 86°F (30°C).

Common purslane has red fleshy stems with over 90% water content, succulent shiny oval leaves and tiny yellow flowers. It produces tiny (1mm), black, shiny, oval seeds that can remain viable in the soil for 20-40 years! Plants can produce viable seeds as soon as three weeks after emergence, with each plant capable of producing over 200,000 seeds. These traits, combined with its worldwide distribution (over 40 ecotypes,) make it the world’s ninth worst weed.

Common purslane can become a major weed in over 50 crops, especially lettuce, tomato and pepper, and in row crops such as cotton and sugar beet. It is also a common weed in lawns and flower beds.

It is hard to control by hoeing, as whole plants and pieces re-root easily, if left lying on the soil. It is best hand-pulled and removed, or laid on top of dry mulch.

There are some domesticated varieties of purslane grown as a salad green. The common type is completely edible. But if keeping plants as a food crop, be warned not to let them go to seed! (New Zealand spinach is a succulent crop plant with similar seeding issues.)

Common purslane has many beneficial attributes. It is used widely for food for people and livestock. The leaves and stems can be eaten as salad, boiled or pickled. Purslane has a salty, slightly acidic taste some find similar to spinach.

It is a rich source of omega-3 fatty acids, (which support heart health), beta-carotene, (a precursor of vitamin A), and vitamin C, and antioxidants.

It has medicinal value for its anti-inflammatory and diuretic properties, and can soothe the skin and treat wounds.

It has also been shown to be an effective remediating plant to desalinate high-salt soils.

The origin of this weed is unknown, but it may have originated in northern Africa or western Asia. It was present in America in pre-Columbian times and in Italy during the Roman Age, where two sub-species were discovered during archaeological excavations.

Information and photo from Nature’s Weedy Gift? By Rakesh Chandran, WVU. (Not organic)

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Velvetleaf Abutilon theophrasti.

AKA buttonweed and piemaker. This is a summer annual growing up to 7′ (2.1m) tall. The large hairy heart-shaped leaves can be up to 6″ (15cm) long, beautiful to the eye, but foul-smelling if crushed. The hairiness of the stems and leaves starts from emergence, with the seedlings having one round cotyledon and one heart shaped leaf. The yellow-gold flowers grow on short branches from the alternate leaf axils. They have 5 petals and are 0.5-1 inch (1-2.5cm) in diameter. Seed pods are round, slightly hairy, and can resemble shortened okra pods. The tap roots can grow quite large.

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Flower of an hour Hibiscus trionum.

Aka rose mallow, Venice mallow, Shoo-fly, Bladder ketmia and modesty. On our farm, this weed shows up most often in the watermelon patch. It takes the same kind of conditions as watermelon in terms of temperature and days to maturity. The leaves and sprawling growth habit of this weed even somewhat resemble watermelon plants.

The 5-petalled flowers are white or pale yellow with a purple throat, and grow from the leaf axils. The five sepals form a bladder with green veins. The fruits, if you let them happen, are round, hairy capsules

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Horsenettle Solanum carolinense.

These thorny perennial nightshades are not particularly tall, but their extensive thick white rhizomes contribute to a high success rate in taking over spaces. The white star-shaped flowers are typical nightshade types (compare with potatoes and tomatoes), and the fruits are yellow globes containing 40-70 flat round orangish seeds.

They emerge in May here and do best in dry sandy soils, and in perennial or long-term crops. No-till practices encourage this weed.

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Fall panicgrass Panicum dicotomiflorum aka FALL PANICUM, Western witchgrass.

A tall summer annual grass, reaching heights of 4 ft (1.2m). The stems are often angled at the nodes, creating in ‘zig-zag’ growth habit. The seedhead is a large (16″/40cm), fanning panicle. Each spikelet produces only one seed.

Fall panicum tends to grow in cultivated areas and disrupted areas. The fibrous roots can be hard to pull, and then hard to dry out to prevent re-rooting.

Seedlings of green foxtail are similar to fall panicum in that they both have hairy ligules and lack hairs on leaf sheaths and blades.  The margins of green foxtail sheaths have hairs, unlike those of fall panicum.

Fall panicum emerges later than the foxtails and this can provide the crop a head start.

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JOHNSONGRASS Sorghum halepense,

This is a very large perennial clumping grass with roots like small bamboo. It can grow to a height of 6-7ft (2-2.3m). The large, loose, red-brown panicle flower heads appear May-August. It can spread via the rhizomes or the seeds. It does not tolerate repeated close mowing (Aha! The Achilles tendon!). It is especially a pest in perennial crops and no-till or reduced-till systems.

 

See UC IPM Weed Gallery

 

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12 Steps for Tackling Late Summer Weeds

Mark Schonbeck has a lot of good info on the eOrganic site. His Principles of Sustainable Weed Management in Organic Cropping Systems, lists 12 steps for tackling weeds on organic farms, set out using the Biointensive IPM method (starting with least widely harmful strategies, and only if needed moving to the more specific control methods).

Here I have customized the steps as I see them applying to late summer weeds:

Pre-season Planning

Step 1 – Know your weeds, be sure you recognize them. Extension agents can help.

Step 2 – Plan cropping systems to minimize opportunities for late summer weeds. Include early and late cool season vegetables in rotation and vigorous summer cover crops (I love sorghum-sudangrass!) Use buckwheat or soy for short summer gaps between crops.

Step 3 –Choose row spacing based on the cultivation equipment you plan to use.

Preventive (Cultural) Practices

Step 4 – Design your crop rotation with food crops that mature at different times of year following each other.

Step 5 – Grow vigorous, competitive crops. Adjust row and in-row spacings to help the crop canopy close sooner, but don’t overcrowd your crops, as this reduces total yield, and can encourage fungal diseases. Potatoes, sweet potatoes, melons, winter squash and pumpkins all cover the ground, leaving little space for weeds. Over-winter crops like garlic and potato onions, get harvested when the late summer weeds might be starting to germinate. Be sure to sow a cover crop after allium harvests, leaving no opportunity for late summer weeds. Use drip irrigation to water only the rows of crops, not the weeds in between.

Step 6 – Put the weeds out of work – grow cover crops. This point has already been mentioned in the earlier steps.

Step 7 – Manage the weed seedbank – minimize “deposits” and maximize “withdrawals.” Mow before weeds set seed. Pull purslane, horsenettle (carefully); hoe flower of an hour and velvet leaf before they get and tough; till (repeatedly as needed) to kill the grass weeds.

Control Tactics

Step 8 – Knock the weeds out at critical times. See Manage Weeds on Your Farm.

If possible, follow multiple tilling with solarization while the weather is still hot. Organic mulches will not stop Johnsongrass or horsenettle. Solarize with clear or green polyethylene for several summer weeks. In the Southeast, clear IR plastic works best for solarizing, and heats down to a depth of 4″ (10 cm).

Step 9 – Use biological processes to enhance weed control. Not sure how to apply that idea for late summer weeds.

Step 10 – Bring existing weeds under control before planting weed-sensitive crops.

Enhancing and Fine-Tuning the Weed Management Strategy

Step 11 – Observe your weeds, and adapt practices accordingly. Make a weed logbook. Keep notes and photos of your weed management decisions and results, and avoid making the same mistake two years running.

Step 12 – Experiment and keep up with new developments in organic weed management. There are some mycorrhizal fungi that benefit most food crops, but are mildly parasitic to purslane.

Secondary Troublesome Weeds in September in Central Virginia

Bermuda Grass; Green Carpetweed; Japanese stiltgrass (Virginia Tech Weed ID site)