GROWING MEDIA
Critters Down Under: Root-Knot Nematodes
Tuesday, May 7, 2019 | Troy Buechel
Nematodes are microscopic round worms that are not visible to the human eye and are the most abundant members of the animal kingdom on Earth. There are over 25,000 known species that can be found around the world in the Arctic, deserts and deep in the ocean, but most dwell in outdoor soils. Many of these species feed on bacteria, fungi, algae, other nematodes, or insect larvae. In fact, Steinernema feltiae is a common nematode that is used to control fungus gnats and western flower thrips larvae in soils or growing media.
Although many nematodes are beneficial, there are some species that are herbivores and are therefore plant parasites that feed on plant roots, leaves or stems. Some nematodes are host-specific and feed off a small number of plant species, while most have a wide host range. Although it is highly unusual to find parasitic nematodes in professional growing media, they can be accidentally introduced. The focus of this article is to discuss the most common parasitic nematodes, root-knot nematodes.
Although many nematodes are beneficial, there are some species that are herbivores and are therefore plant parasites that feed on plant roots, leaves or stems. Some nematodes are host-specific and feed off a small number of plant species, while most have a wide host range. Although it is highly unusual to find parasitic nematodes in professional growing media, they can be accidentally introduced. The focus of this article is to discuss the most common parasitic nematodes, root-knot nematodes.
Northern Root-Knot Nematodes
The most common root-knot nematode is the northern root-knot nematode, Meloidogyne spp. It infects hundreds of types of perennials (daylilies, hostas, etc.) and vegetables (carrots, celery, parsnips, peppers, tomatoes, etc.) grown in fields in the United States and Canada. They can also infect some grass species, which may not exhibit the classic symptom of “knots” (from which their name comes from) or galls on the roots (see below).
“Root-knot nematode as seen through a microscope. Source: https://www.thriftyfun.com”
Root-Knot Nematode Lifecycle
The life cycle of root-knot nematodes starts when eggs are laid by females. Nematodes molt four times, with the first molt occurring within the egg. After hatching, the emerging juveniles move through water films on the soil particles, looking to enter and infect plant roots, usually near the root tip. The root-knot nematode inserts its stylet (piercing mouthpart) into the root cell, where it extracts nutrient-rich fluids. Chemicals emitted by the root-knot nematode cause surrounding cells to swell. Since root-knot nematodes use the same feeding site for most of their lifecycle, the swelling cells around the nematode form a “knot” or gall, enveloping the root-knot nematode. Juveniles will molt three more times before becoming adults.
Adult male root-knot nematodes can move within the root, while females enlarge and eventually deposit 200-400 eggs, either outside the root or within the gall, surrounded by a gelatinous, protective material. These eggs can either hatch if environmental conditions are favourable, or the eggs can persist in the soil to infect a future crop. Depending on soil temperatures, the life cycle of the root-knot nematode takes approximately 4 to 8 weeks to complete. Ideal soil temperatures for root-knot nematodes are 70-80 °F (21-27 °C).
Adult male root-knot nematodes can move within the root, while females enlarge and eventually deposit 200-400 eggs, either outside the root or within the gall, surrounded by a gelatinous, protective material. These eggs can either hatch if environmental conditions are favourable, or the eggs can persist in the soil to infect a future crop. Depending on soil temperatures, the life cycle of the root-knot nematode takes approximately 4 to 8 weeks to complete. Ideal soil temperatures for root-knot nematodes are 70-80 °F (21-27 °C).
Root-knot nematodes caused swelling and round galls on the roots of this daylily. Source: http://www.the-greenexpert.com”
Plant Symptoms
The most obvious symptoms appear on the roots as galls. Galls are hardened tissue that is part of the root. It can appear as individual small round growths on roots or, if infestation is heavy, many infected spots coalesce into enlarged gnarled roots. Galls can be confused with nodules formed by nitrogen-fixing bacteria in legumes (beans, peas, etc.). Nodules easily rub off the roots, whereas galls do not.
Since root-knot nematodes are stealing plant nutrients and water, the plant appears to have symptoms of a poor functioning root system. This can include chlorosis or off-coloured foliage from nutrient deficiencies, stunting, early wilting in hot conditions, and reduction of fruit / vegetable yield. The stress and damage caused by root-knot nematodes often make plants more susceptible to root rot pathogens. Symptoms are more pronounced if root-knot nematode populations are high. At low populations, plant damage is almost negligible, and if damage occurs, it is towards the end of the crop cycle when the soil is warm and root-knot nematodes had more time to develop larger populations.
Since root-knot nematodes are stealing plant nutrients and water, the plant appears to have symptoms of a poor functioning root system. This can include chlorosis or off-coloured foliage from nutrient deficiencies, stunting, early wilting in hot conditions, and reduction of fruit / vegetable yield. The stress and damage caused by root-knot nematodes often make plants more susceptible to root rot pathogens. Symptoms are more pronounced if root-knot nematode populations are high. At low populations, plant damage is almost negligible, and if damage occurs, it is towards the end of the crop cycle when the soil is warm and root-knot nematodes had more time to develop larger populations.
Link to Growing Media
Growing media are generally not the source of pathogenic nematodes. However, if transplanting infected bare-root perennials such as hostas or daylilies into a container filled with growing medium, nematodes from the bare-root perennial will invade and continue to infect the newly forming roots of these plants. Root-knot nematodes can be introduced into growing media from contaminated outdoor soil, where root-knot nematodes are more common. Peanuts are often infected with root-knot nematodes, so using poorly composted peanut hulls as a growing medium amendment can introduce them.
Control
Root-knot nematodes are close to impossible to eradicate from outdoor soil or after they are introduced into the growing medium. Containerized plants that are infected should be discarded. There are nematicides and biological controls that provide moderate success. Hot water dips have been used with good success with bare-root plants, but it can cause damage in emerging foliage. Another successful procedure is to root prune bare-root perennials as root galls and root-knot nematodes tend to be in the middle or tips of the roots, where they can be pruned off.
For field crops, chemical and biological controls are moderately effective. Resistant plants, especially grasses and other monocots, could be grown for a season, which will cause root-knot nematodes to starve, reducing populations. Incorporating composts or other biologically diverse soil amendments can provide microorganisms that compete with nematodes, or at least release plant nutrients to maintain better health and help plants withstand root-knot nematode infections. Soil flooding, in which the soil is under water for numerous 2- or 3-week cycles, can drown nematodes, while repeated tilling helps by bringing nematodes up from the soil depths to the surface where the sun and wind can dry them out and kill them.
For field crops, chemical and biological controls are moderately effective. Resistant plants, especially grasses and other monocots, could be grown for a season, which will cause root-knot nematodes to starve, reducing populations. Incorporating composts or other biologically diverse soil amendments can provide microorganisms that compete with nematodes, or at least release plant nutrients to maintain better health and help plants withstand root-knot nematode infections. Soil flooding, in which the soil is under water for numerous 2- or 3-week cycles, can drown nematodes, while repeated tilling helps by bringing nematodes up from the soil depths to the surface where the sun and wind can dry them out and kill them.
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In this regard, several of the soils and growing media we offer are certified by the OMRI (Organic Materials Review Institute), an international nonprofit organization whose mission is to support the growth and confidence of the global organic community through experts and independent reviews.
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Premier Tech Horticulture received a tribute for its valuable contribution to research and responsible management of peatlands. This renewed support reflects the Premier Tech Horticulture's dedication to Laval University's research in sustainable development since 1992.
Some 15 years after its first large-scale peat bog restoration project, the company still continues its efforts, and this, all over Canada. Since it cares about making knowledge progress, Premier Tech Horticulture always devotes a part of its peat bogs to various research projects. Those efforts, combined with the experience acquired over the years, allow Premier Tech Horticulture to offer products with a small ecological footprint.
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Why Use Sphagnum Peat Moss?Sphagnum peat moss has been used for many years for horticulture purposes for its ability to hold large amounts of air and water, making it ideal as a component of propagation media. This is because sphagnum peat moss possesses interconnected cells with thin lignified walls and large cavities that are built-up and prevent the sphagnum cells from collapsing when they dry out. This characteristic provides a capillary system for sphagnum peat moss to absorb and transport water easily. As the water evaporates, these cells and cavities fill with air. As a component of growing media, developing plant root systems can easily access oxygen and water. Combined with the proper ratio of aggregates, limestone and other ingredients, peat-based media are perfect for seed starting, rooting of cuttings and young plants development.
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Publications"Restoration Research" : http://www.peatmoss.com/blog/environment/restoration-research/
"Peatland Restoration Guide" : http://www.peatmoss.com/blog/environment/peatland-restoration-guide/
"Peat Moss: still the best value" : http://www.peatmoss.com/blog/using-peat-moss/professional-horticulturalists/professional-horticulturalists-peat-moss-still-the-best-value/
"What is Peat Moss?" : http://tourbehorticole.com/en/peat/index.php
"Peat Harvesting" : http://tourbehorticole.com/en/responsible-production/harvesting.php
Premier Tech Horticulture has grown around one of the most abundant natural resources in Canada, sphagnum peat moss. Over the years, our company has leveraged its expertise to create a wide assortment of natural products intended for home gardeners, professional horticulture and large-scale grain and vegetable crops.
For Premier Tech, manufacturing products that are safe for the environment is of the greatest importance, and as such, the respect, protection and responsible management of raw materials constitutes a priority. We aim to improve overall productivity levels in a spirit of sustainable development, by means of completely natural active ingredients.
In this regard, several of the soils and growing media we offer are certified by the OMRI (Organic Materials Review Institute), an international nonprofit organization whose mission is to support the growth and confidence of the global organic community through experts and independent reviews.
GROWING WITH RESPECT FOR THE RESOURCE
For many years, sustainable peatland management and the protection of ecosystems such as its sphagnum peat moss harvesting sites have been firm commitments at Premier Tech Horticulture. To preserve the vitality of those areas for many generations still, Premier Tech Horticulture actively participates in the restoration of peat bogs. Even when knowledge was limited regarding the sustainability of resources, Premier Tech Horticulture promoted university research in that field.
Premier Tech Horticulture received a tribute for its valuable contribution to research and responsible management of peatlands. This renewed support reflects the Premier Tech Horticulture's dedication to Laval University's research in sustainable development since 1992.
Some 15 years after its first large-scale peat bog restoration project, the company still continues its efforts, and this, all over Canada. Since it cares about making knowledge progress, Premier Tech Horticulture always devotes a part of its peat bogs to various research projects. Those efforts, combined with the experience acquired over the years, allow Premier Tech Horticulture to offer products with a small ecological footprint.
PEAT MOSS
Why Use Sphagnum Peat Moss?Sphagnum peat moss has been used for many years for horticulture purposes for its ability to hold large amounts of air and water, making it ideal as a component of propagation media. This is because sphagnum peat moss possesses interconnected cells with thin lignified walls and large cavities that are built-up and prevent the sphagnum cells from collapsing when they dry out. This characteristic provides a capillary system for sphagnum peat moss to absorb and transport water easily. As the water evaporates, these cells and cavities fill with air. As a component of growing media, developing plant root systems can easily access oxygen and water. Combined with the proper ratio of aggregates, limestone and other ingredients, peat-based media are perfect for seed starting, rooting of cuttings and young plants development.
THE INDUSTRY’S MOST CONSISTENT AND UNIQUE METHOD OF PEAT MOSS SELECTION
For many years now, Premier Tech Horticulture has used a very unique approach to peat moss gradation and selection. Over the years, it has assured a consistency in the final product that is usually very difficult to achieve in the industry. Premier Tech Horticulture is very proud to provide growers with products offering predictability in results.
Publications"Restoration Research" : http://www.peatmoss.com/blog/environment/restoration-research/
"Peatland Restoration Guide" : http://www.peatmoss.com/blog/environment/peatland-restoration-guide/
"Peat Moss: still the best value" : http://www.peatmoss.com/blog/using-peat-moss/professional-horticulturalists/professional-horticulturalists-peat-moss-still-the-best-value/
"What is Peat Moss?" : http://tourbehorticole.com/en/peat/index.php
"Peat Harvesting" : http://tourbehorticole.com/en/responsible-production/harvesting.php