If your plants look stunted and its leaves exhibit chlorosis and lack vigour, yet you’ve done everything right and you can’t figure out why, it’s time to check the roots of your plants. If the roots are knobbly and have galls, you have a case of root knot nematodes in your soil. I have experienced this on a few occasions, fortunately in my planters and not in-ground. Read on to find out how to control root knot nematodes organically.
What are they? These plant parasites are microscopic roundworms that damage plant roots and feed on its vascular system. This causes growths to form, affecting the plant’s capacity to absorb water and nutrients.
Shrubs, trees and herbaceous plants are susceptible to root knot nematodes. These include begonia, azalea, hibiscus, gloxinia, hydrangea, impatiens, cyclamen, coleus, some cacti, rose, and edible plants like tomato, capsicum, chilli, eggplant, rosella, okra, cucumber, pumpkin, melons, Malabar spinach, passionfruit, banana, pineapple, sweet potato among others.
What are your natural options? Here’s how to get rid of root knot nematodes organically, you can consider using a mix of methods to improve efficacy rates.
The American mountain ash (Sorbus americana) is a stunning ornamental tree known for its pretty white flowers, vibrant orange-red berries, and beautiful fall color. However, this favorite landscape tree can sometimes be plagued by tiny parasitic roundworms called nematodes. An infestation can lead to decline, dieback, and even death of your beloved mountain ash if left unchecked. Don’t despair! Here’s a comprehensive guide on identifying nematodes and effective methods to get rid of them, restoring health to your tree.
What are Nematodes?
Nematodes are microscopic unsegmented roundworms present naturally in most soils. While some species are beneficial, others become troublesome parasites of plant roots that feed on root tissue. Common pest species affecting mountain ash trees include:
- Root knot nematodes
- Root lesion nematodes
- Citrus nematodes
- Dagger nematodes
They enter young roots and multiply, causing cell damage that disrupts water and nutrient uptake. An infestation can quickly escalate, resulting in severely declined health. Learning to identify and control them is key for mountain ash care.
Signs of a Nematode Problem
Watch for these symptoms that indicate nematodes may be damaging your tree:
- Slowed growth
- Stunting and thin canopy
- Wilt, yellowing leaves, early fall color
- Dieback of branches
- Declining fruit/flower production
- Damaged feeder roots
If you suspect nematodes, have a soil test done to confirm since symptoms resemble other issues like drought stress. Finding and treating them early provides the best chance to save your tree.
How to Get Rid of Nematodes on Mountain Ash Trees
If nematodes are confirmed to be a problem take action right away! Here are effective methods to eliminate nematodes
Cultural Practices
Promoting vigorous growth helps trees better tolerate and withstand nematode damage
- Water thoroughly during dry periods
- Mulch around root zones
- Avoid excess fertilizer
- Manage other stresses and pests
Solarizing the Soil
Solarizing uses solar heat to kill nematodes and other soil pests.
- Mow, rake, and wet area around tree
- Cover soil tightly with clear plastic for 4-6 weeks in summer
- Trap heat to reach minimum 104°F temperature
Biological Control
Beneficial nematodes prey on pest nematodes.
- Obtain nematodes like Steinernema species
- Apply to soil according to product instructions
- Reapply as needed, especially after heavy watering
Chemical Control
Nematicide application may be warranted for heavy infestations.
- Active ingredients like oxamyl or fenamiphos
- Strictly follow label directions
- Use caution and minimize environmental impact
Resistant Rootstocks
Grafting susceptible Sorbus trees onto resistant rootstock prevents future nematode damage.
- Rootstocks like Sorbus alnifolia are nematode resistant
- Have grafting done by a professional
- Provides long-term protection as a preventive measure
Aftercare and Prevention
After treatment, continue care to help your mountain ash recover and protect its health:
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Allow time for roots to regrow and tree to regain vigor. Recovery takes 1-2 seasons.
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Address factors like compacted soil that encouraged nematodes initially.
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Repeat treatments to control any remaining or reintroduced nematodes.
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Plant resistant Sorbus species like European mountain ash in nematode prone areas.
With persistence using multiple control methods together, you can eliminate destructive nematodes and revive your declining American mountain ash. Be vigilant with followup care and prevention to ensure your tree thrives for years to come.
Add compost and organic matter
Good quality aerobic compost contains plenty of microbes. These include larger, predatory micro-organisms, including beneficial nematodes that can ingest root knot nematodes. By applying it directly as a top dressing or some prefer, compost tea, these microbes are introduced into the soil. Adding organic matter such as manure and leaves also encourages fungi, bacteria and naturally occurring good nematodes to inhabit soil.
In Singapore, you can get good quality compost from Soil Social, it is more pricey than other composts on the market, however it is aerobic and contains a high amount of beneficial microbes. I tried it and have seen improvements in my plants as soon as within a month. My stunted okra grew more lush and began fruiting more regularly.
You can also consider trying out this soil drench recommended by Jerry Coleby-Williams of Gardening Australia.
This method makes it very inhospitable for root knot nematodes, however it kills many organisms in the process, including pathogens, nematodes, weeds, and seeds. Soil solarisation involves laying clear (more effective) or black plastic sheets over wet soil for 4-6 weeks, therefore trapping heat and raising soil temperature. Nematodes are mobile, so this method will reduce numbers but it may not fully eradicate the population.
Grow biofumigant crops for root knot nematode control (Photo by
Brassicas such as Brassica rapa (field mustard) and Brassica juncea (mustard greens) have bio-fumigation properties and are effective at root knot nematode control when grown as a cover crop, however there are some other plants, like Tagetes patula (French marigolds), Tagetes erecta (Mexican Marigold) and oats, which are highly capable too.
How it works is it releases compounds to suppress pests and pathogens in the soil. It is effective when in its early flowering stages, plants are chopped or pulped and incorporated into the soil and watered. The soil needs to remain moist for a few weeks, and isocyanate gases are released by the plants as it breaks down.
Not all plants are susceptible to root knot nematodes. Through rotating the types of plants grown over two years or more, specifically incorporating plants that are not host plants, you can starve these nematodes. Root knot nematode resistant plants include corn, millet, grain sorghum, asparagus, and chrysanthemum and zinnia.
How to Sustainably Manage Parasitic Nematodes in the Garden
FAQ
What kills nematodes instantly?
How do you get rid of nematodes naturally?
What repels nematodes?
How do you get rid of ash tree worms?
Do mountain ash trees wilt?
Fungicidal sprays containing chlorothalonil or mancozeb can be used to protect healthy foliage. Identification: Root rot is a common problem in American mountain ash trees caused by various soil-borne pathogens. Symptoms include wilting, yellowing foliage, stunted growth, and dieback of branches.
Why do mountain ash trees need to be trimmed?
Proper trimming of mountain ash trees is crucial for their health, vitality, and visual appeal. Trimming promotes tree health by removing dead, diseased, or damaged branches and stimulating growth. It prevents hazards such as falling branches during storms and enhances flowering and fruit production.
How do you trim American mountain ash trees?
Before you start trimming your American Mountain Ash tree, make sure you have the right tools on hand: Pruning Shears: Ideal for cutting small branches up to 1 inch in diameter. Loppers: Use loppers for branches with a diameter of 1 to 2 inches. Pruning Saw: For larger branches that are too thick for pruning shears or loppers.
How to care for mountain ash trees?
Taking precautions, such as inspecting tools, wearing safety gear, pruning during the right season, and avoiding over-pruning, ensures safe and successful tree maintenance. When it comes to understanding mountain ash trees, it’s essential to grasp their unique characteristics and growth patterns to ensure optimal care.