Crop weeds are weeds that grow amongst crops.
Despite the potential for some crop weeds to be used as a food source, many can also prove harmful to crops, both directly and indirectly. Crop weeds can inhibit the growth of crops, contaminate harvested crops and often spread rapidly. They can also host crop pests such as aphids, fungal rots and viruses. [1] [2] Cost increases and yield losses occur as a result. Striga , one of the main cereal crop weeds in Sub-Saharan Africa, commonly causes yield losses of 40–100% and accounts for around $7 billion in losses annually. Around 100 million hectares of land in Sub-Saharan Africa are affected by striga. [3] Barnyard grass has been identified as a culprit in global rice yield losses and certain species have been known to mimic rice. [4]
Examples of crop weeds include chickweed, barnyard grass, dandelion, striga and Japanese knotweed . [5] A less commonly known crop weed is Abelmoschus ficulneus.
A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize. Edible grains from other plant families, such as buckwheat and quinoa, are pseudocereals. Most cereals are annuals, producing one crop from each planting, though rice is sometimes grown as a perennial. Winter varieties are hardy enough to be planted in the autumn, becoming dormant in the winter, and harvested in spring or early summer; spring varieties are planted in spring and harvested in late summer. The term cereal is derived from the name of the Roman goddess of grain crops and fertility, Ceres.
Rice is a cereal grain and in its domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species Oryza sativa —or, much less commonly, Oryza glaberrima. Asian rice was domesticated in China some 13,500 to 8,200 years ago; African rice was domesticated in Africa about 3,000 years ago. Rice has become commonplace in many cultures worldwide; in 2021, 787 million tons were produced, placing it fourth after sugarcane, maize, and wheat. Only some 8% of rice is traded internationally. China, India, and Indonesia are the largest consumers of rice. A substantial amount of the rice produced in developing nations is lost after harvest through factors such as poor transport and storage. Rice yields can be reduced by pests including insects, rodents, and birds, as well as by weeds, and by diseases such as rice blast. Traditional rice polycultures such as rice-duck farming, and modern integrated pest management seek to control damage from pests in a sustainable way.
Millets are a highly varied group of small-seeded grasses, widely grown around the world as cereal crops or grains for fodder and human food. Most millets belong to the tribe Paniceae.
Finger millet is an annual herbaceous plant widely grown as a cereal crop in the arid and semiarid areas in Africa and Asia. It is a tetraploid and self-pollinating species probably evolved from its wild relative Eleusine africana.
Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. This practice reduces the reliance of crops on one set of nutrients, pest and weed pressure, along with the probability of developing resistant pests and weeds.
Cenchrus purpureus, synonym Pennisetum purpureum, also known as Napier grass, elephant grass or Uganda grass, is a species of perennial tropical grass native to African grasslands. It has low water and nutrient requirements, and therefore can make use of otherwise uncultivated lands.
Echinochloa is a very widespread genus of plants in the grass family and tribe Paniceae. Some of the species are known by the common names barnyard grass or cockspur grass.
Striga, commonly known as witchweed, is a genus of parasitic plants that occur naturally in parts of Africa, Asia, and Australia. It is currently classified in the family Orobanchaceae, although older classifications place it in the Scrophulariaceae. Some species are serious pathogens of cereal crops, with the greatest effects being in savanna agriculture in Africa. It also causes considerable crop losses in other regions, including other tropical and subtropical crops in its native range and in the Americas. The generic name derives from Latin strī̆ga, "witch".
Cyperus rotundus is a species of sedge (Cyperaceae) native to Africa, southern and central Europe, and southern Asia. The word cyperus derives from the Greek κύπερος, kyperos, and rotundus is from Latin, meaning "round". The earliest attested form of the word cyperus is the Mycenaean Greek 𐀓𐀞𐀫, ku-pa-ro, written in Linear B syllabic script.
Push–pull technology is an intercropping strategy for controlling agricultural pests by using repellent "push" plants and trap "pull" plants. For example, cereal crops like maize or sorghum are often infested by stem borers. Grasses planted around the perimeter of the crop attract and trap the pests, whereas other plants, like Desmodium, planted between the rows of maize, repel the pests and control the parasitic plant Striga. Push–pull technology was developed at the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya in collaboration with Rothamsted Research, UK. and national partners. This technology has been taught to smallholder farmers through collaborations with universities, NGOs and national research organizations.
Paspalum scrobiculatum, commonly called kodo millet or koda millet, is an annual grain that is grown primarily in Nepal and also in India, Philippines, Indonesia, Vietnam, Thailand, and in West Africa from where it originated. It is grown as a minor crop in most of these areas, with the exception of the Deccan plateau in India where it is grown as a major food source. It is a very hardy crop that is drought tolerant and can survive on marginal soils where other crops may not survive, and can supply 450–900 kg of grain per hectare. Kodo millet has large potential to provide nourishing food to subsistence farmers in Africa and elsewhere.
A weed is a plant considered undesirable in a particular situation, growing where it conflicts with human preferences, needs, or goals. Plants with characteristics that make them hazardous, aesthetically unappealing, difficult to control in managed environments, or otherwise unwanted in farm land, orchards, gardens, lawns, parks, recreational spaces, residential and industrial areas, may all be considered weeds. The concept of weeds is particularly significant in agriculture, where the presence of weeds in fields used to grow crops may cause major losses in yields. Invasive species, plants introduced to an environment where their presence negatively impacts the overall functioning and biodiversity of the ecosystem, may also sometimes be considered weeds.
Cleome gynandra is a species of Cleome that is used as a leaf vegetable. It is known by many common names including Shona cabbage, African cabbage, spiderwisp, cat's whiskers, and stinkweed. It is an annual wildflower native to Africa but has become widespread in many tropical and sub-tropical parts of the world.
Striga hermonthica, commonly known as purple witchweed or giant witchweed, is a hemiparasitic plant that belongs to the family Orobanchaceae. It is devastating to major crops such as sorghum and rice. In sub-Saharan Africa, apart from sorghum and rice, it also infests maize, pearl millet, and sugar cane.
Large scale rice production in the state of Arkansas became a significant industry in the late 19th/early 20th century with its wide scale propagation within the state by entrepreneur W.H. Fuller around 1896. Arkansas has historically been the largest rice producer in the entire United States, and accounted for nearly 45% of U.S. rice production in 2001, as well as just less than half of the total number of acres of rice harvested nationwide. Much of Arkansas' rice is grown in the east-central portion of the state, where it requires nearly three times more the amount of irrigation water than the average eleven inches the region receives during the growing season. In the areas of lowest precipitation, or where weedy red rice is a significant problem, farmers follow a three year, three phase "old rotation" of rice-soybean-soybean. However, most Arkansas rice producers follow a two year, two phase crop rotation of rice following soybeans.
Rhamphicarpa fistulosa is a flowering plant species in the family Orobanchaceae - and the genus Rhamphicarpa. The plant is pale-green but can turn reddish towards maturity. It has needle-like leaves and white flowers with long corolla tubes. The flowers only open after sunset and are supposedly pollinated by night moths. The plant has a broad distribution in Africa and can also be found in New Guinea and northern Australia.
Digitaria eriantha, commonly known as digitgrass or Pangola-grass, is a grass grown in tropical and subtropical climates. It grows relatively well in various soils, but grows especially well in moist soils. It is tolerant to droughts, water lodging, suppresses weeds and grows relatively quickly after grazing. This grass demonstrates great potential for farmers in Africa in subtropical and tropical climates, mostly for livestock feed.
There are numerous effects of climate change on agriculture, many of which are making it harder for agricultural activities to provide global food security. Rising temperatures and changing weather patterns often result in lower crop yields due to water scarcity caused by drought, heat waves and flooding. These effects of climate change can also increase the risk of several regions suffering simultaneous crop failures. Currently this risk is regarded as rare but if these simultaneous crop failures did happen they would have significant consequences for the global food supply. Many pests and plant diseases are also expected to either become more prevalent or to spread to new regions. The world's livestock are also expected to be affected by many of the same issues, from greater heat stress to animal feed shortfalls and the spread of parasites and vector-borne diseases.
Sorghum is an important staple crop for more than 500 million people in sub-Saharan Africa and South Asia, including many people in Nepal. In statistics collected from 1992 to 1994 about general millet, Nepal had an area of 0.21 million ha, with a yield rate of 1.14 (t/ha), and produced around 0.24 million tons of sorghum. The entirety of the crop is highly valued, with both the grain and the stem being utilized. The Terai region of Nepal tends to be more tropical which is ideal for the growth of sorghum. It tolerates hot climates better than maize or soybeans. For subsistence farmers, like those in Nepal, fertilizers are not necessary and the crop is frequently harvested by hand.
Jonathan Gressel is an Israeli agricultural scientist and Professor Emeritus at the Weizmann Institute of Science in Rehovot, Israel. Gressel is a "strong proponent of using modern genetic techniques to improve agriculture" especially in third world and developing countries such as Africa. In 2010, Gressel received Israel's highest civilian award, the Israel Prize, for his work in agriculture.