Onion Root Knot Nematode Management: How To Treat Root Knot Nematodes On Onions
Root Knot Nematode Of Onion Plants – Controlling Onion Root Knot Nematodes
Root knot nematode of onion is a pest that can drastically reduce the yield you get from your row of onions in any given year in the garden. They feed on the roots and cause plants to stunt and develop fewer, smaller bulbs. There are both chemical and non-chemical management practices you can use to reduce losses.
Signs of Root Knot Nematodes on Onions
Nematodes are microscopic roundworms that live in the soil, most of which do not damage plants. The root knot nematode is not one of those roundworms. It lives in the roots of a host plant, and there are four species that affect onions. They are able to infect onion roots when temperatures in the soil are over 41 degrees Fahrenheit (5 degrees Celsius).
Above the soil, what you’ll see in root knot nematode of onion infections is uneven growth and stunted plants. The necks of bulbs will be thicker and the bulbs themselves smaller. The plants will mature later during an infection. The leaves may also yellow.
Underground, the roots will develop galls, swollen and enlarged areas of the roots. Root growth will be stunted, and you’ll see shorter roots than is normal.
Onion Root Knot Nematode Management
Controlling onion root knot nematodes starts with prevention. There are no resistant onion varieties, but you can use plants or seeds that are clean and nematode free. This doesn’t, however, mean you won’t get an infestation because the nematodes may already be in your soil.
If you know that your soil is infested with this pest, you can use a pre-planting fungicide to fumigate the soil and reduce or eliminate root knot nematodes. This is generally considered to be an effective management strategy and is used in commercial onion growing.
To avoid fungicides, you can try crop rotation or cover crops. Rotate in crops that do not host root knot nematodes, like grains and corn, or grow them as cover between onion plants.
While using fungicide is the most effective way to manage onion root knot nematodes, using the non-chemical cultural practices of crop rotation and cover crops will reduce losses. These are worth trying if you don’t want to use chemicals in your garden.
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Onion Spacing: Tips and Tricks
Onions should be spaced 2 to 4 inches apart, with 12 to 18 inches between rows. Onion seeds can be sown close together, and thinned out once the seedlings have grown. Sets, or small immature onions, should be spaced like onion plants.
Green onions are the exception and can be planted one inch apart. It is a good idea to spread onions out around your garden instead of confining them to one spot. Onions can deter pests with their scent, so spreading them out can help protect your other veggies as well.
The way you space your onions depends on how you start them. Spacing for seeds is very different from spacing for onion sets or even more established onion plants.
If you are using one large container for your seeds, sprinkle them evenly over compost. Then cover the seeds with another, lighter layer of compost and water. This is one of the easiest ways to start onion seeds.
Instead of using a single container or pot, some gardeners choose to use a partitioned container. Individual cells keep the onion seedlings separate and lets you skip the sometimes tricky process of pulling apart seedlings that may have intertwined roots.
In a partitioned container, you should still plant at least a couple seeds in each cell in case one of the seeds doesn’t germinate. It is unlikely that you will have a 100 percent germination rate, and it would end up being a waste of space and time to find that half of the seeds in your cells have not germinated.
With seeds, remember to sow liberally. Once the seedlings have sprouted, you can pick and choose from the ones that are healthiest and have the best chance of producing a good crop.
Spacing for Onion Sets
Onion sets are small bulbs of immature onions. They are harvested specifically for the purpose of growing more onions. As they are a great deal bigger than seeds, they require more space.
As with seeds, you can use a partitioned container and plant one set per cell. This method makes for an extremely easy transplant once your sets have sprouted and developed some growth.
Sets are less difficult to separate than young plants grown from seed, so planting all of your sets in one large container or area won’t give you much difficulty when it comes time to transplant. You can also plant them directly into your garden.
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How to Plant and Grow Garlic (Allium Sativum)
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A close relative of the onion, garlic (Allium sativum) is an edible, bulbous plant that has been cultivated for several thousand years. It is more popular today than ever and, with over 600 sub-varieties available, there is ample room for gourmet garlic growers to carve out a niche. For the home gardener, it is quite easy to grow a year’s supply, and the leftover crop can be given away to friends and neighbors.
Varieties
The many sub-varieties of garlic fall into two basic categories: hardneck garlic (Allium sativum var. ophioscorodon), which includes the varieties porcelain garlic, rocambole garlic, and purple stripe garlic. The softneck garlic (Allium satvum var. sativum) varieties include artichoke garlic, silverskin garlic, and creole garlic.
Softneck varieties are best for warm climates, while hardneck is the garlic of choice for northern garlic growers. Softneck garlic stores and travels better than hardneck garlic. It also has a stronger flavor and generally speaking, produces larger cloves. If you want a milder garlic taste, try elephant garlic—which is actually more closely related to leeks than it is to true garlic.
Planting and Growing Tips
Garlic is planted either in the fall or the spring, depending on your climate. In the north, plant garlic in the fall. In warmer climates, it is best to plant garlic in early spring, though seed garlic must be chilled first to break it out of its dormant state. Garlic prefers loose loamy soil with plenty of organic matter.
- Separate the bulbs into individual cloves right before planting, leaving the papery layer around each clove. Choose larger cloves for planting and use the little ones for eating or preserving.
- Plant the cloves 2 inches deep if you plan to mulch and 3 to 4 inches deep if you do not plan to mulch.
- Be sure to plant each clove with the pointy tip facing up and the basal/root end facing down.
- Space the cloves 4 to 6 inches apart in rows spaced 18 to 24 inches apart. Commercial growers often plant the cloves and rows closer together; this leads to smaller bulbs but an overall higher yield in terms of garlic per square foot of garden.
Soil and Mulch
Soil should be kept evenly moist through the first part of the growing season, but allow the soil to go dry for two or three weeks before harvest time. If conditions are too wet near harvest time, mold may grow.
Mulching your garlic with straw, hay, swamp grass, reeds, or chopped leaves or plastic can be very helpful in some circumstances, though it is not recommended in wet climates. Mulch can protect against winter kill in cold climates, and in hot climates, It helps moderate soil temperatures and conserves soil moisture.
Good mulch can also help keep weeds in check. Weeds can easily outcompete young garlic plants, so be sure to keep the plot well-weeded.
Pests and Problems
Extreme temperatures can damage your garlic crop. Other problems include:
- White rot fungus: This disease, caused by the Sclerotium cepivorum fungus, is the most serious disease of garlic, and it can also strike all Allium crops, including onions. White rot-infected garlic plants can be identified by leaves that turn yellow and plants that wilt and die back partially. As the roots rot, infected plants uproot easily. This disease typically develops from the middle of the season up to harvest. Be sure you obtain cloves from certified disease-free stock because once a field has been infected with white-rot fungus, it can take decades for the infection to completely clear.
- Nematodes: These microscopic pests, Ditylenchus dipaci, are another chronic problem for garlic. These tiny worm-like creatures live inside the garlic plant itself, eating it as it reproduces. Nematodes do not need water to survive and they can live in the surrounding soil for several years. Nematode infestation can build up for several seasons without much damage, then strike and take out an entire crop. To control nematodes, make efforts to plant clean stock, inspect growing plants frequently, and remove any plants that look diseased.
- Onion thrips: Thrips are the most common insect to plague garlic. Thrips have rasping-sucking mouth parts that first damage the leaves then suck up the seeping plant fluid. Severe damage can cause the garlic plant to wilt and die. The wounds to the leaves may then create entry points for other diseases. To control thrips, keep areas free of moist, wet mulch that provides breeding areas, and trap the insects with sticky traps.
Harvesting
As it grows, hardneck garlic produces a curly green flower stalk called a scape. Garlic scapes should be harvested from the plant as it grows so that the garlic concentrates its energy into growing the bulb larger.
It’s time to harvest your garlic when 1/2 to 3/4 of the bottom leaves have died. This usually happens by mid- to late-summer—July and August for most areas. Harvest a test bulb or two to determine maturity. The garlic bulb should be well-wrapped but not split. To harvest garlic, loosen the soil with a shovel or fork and pull up plants by hand. Use caution, as garlic bruises easily.
Storage and Preservation
You can eat garlic fresh out of the ground, but if you want to store it for winter, you must cure it first. In warm sunny climates, garlic can be left in the field to dry, but it should be covered with leaves to prevent sunburn.
Place garlic in a dark place with good air circulation for 2 to 3 weeks after harvest to allow it to cure.
- For softneck garlic, you can braid ropes of bulbs and stems and hang them to dry.
- For hardneck garlic, trim stems to one inch above the bulb then place in a dark, well-ventilated place.
After curing, garlic will keep at for 6 to 12 months when stored in optimal conditions. Store garlic where it will have good air circulation, 65 to 70 percent humidity, and a temperature of 35 to 50 degrees Fahrenheit.
Propagation
Garlic is propagated by planting individual cloves separated from bulbs or by using bulbils—the tiny undivided bulbs found in the scapes of hardneck garlic. Propagating garlic using bulbils can be much more effective than planting cloves. If you are planting cloves, save 15 to 20 percent of your crop, making sure to use only truly disease-free bulbs for planting next season.
There are many more bulbils than cloves, making it easier to build up your planting stock, and since bulbils are above the ground, there is less chance of soil-borne diseases. Plant them just like you would cloves. If you are growing bulbils for seed, allow the garlic scape to grow—they are edible and delicious.
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Root Knot Nematode Control : Saving Carrots Affected By Root Knot Nematodes
Garden diseases are the bane of any gardener, especially when they threaten our food crops. Root knot nematodes in carrots are a major pathogen which also affects other food crops, such as onions and lettuce. Carrots affected by root knot nematodes display malformed, stubby, hairy roots. The carrots are still edible, but they are ugly and distorted with tough galls and thick skin. Additionally, root knot nematodes reduce yield. Root knot nematode control is possible through several corrective measures.
Carrot Root Knot Nematode Info?
If you have discovered your carrot patch is yielding stumpy, rough looking, forked roots, you probably have a root knot nematode infestation. This pathogen is common in root crops but also in celery and lettuce. Symptoms vary slightly by plant variety, but in all cases crop production is reduced and the food looks unsightly. Root knot nematodes in carrots are particularly prevalent in northern regions. The good news is that you can control the pathogen to a certain extent.
Nematodes are tiny roundworms not visible with the naked eye. It takes a soil sample to positively identify the pests. They live in soil and feed on plant cells through several developing stages. The second stage juveniles are the only mobile stage and enter the roots. Later stages and adults become larger as the carrot root enlarges.
Any stage of nematode feeds on cells by piercing it with a mouthpart called a stylet. Females will break through the root and deposit eggs, which form galls. These become woody, hard and nearly unpalatable. There are almost 90 different nematode species that are directly associated with carrot development.
Symptoms of Carrot Root Knot Nematodes
Recognizing parasitic nematodes in carrots is fairly obvious once you dig the roots up. On the surface of the soil, the foliage will be stubby and not well formed. Occasionally, it will also wilt. The roots will split and fork, looking like bizarre caricatures of possessed carrots. Some interesting forms appear but, overall, carrots affected by root knot nematodes will produce less edible roots, which are stunted and ugly.
In commercial growing, this represents less dollar yield and the roots collect more soil, requiring more extensive cleaning before the roots can be marketed. In the home garden, the less attractive roots can still be used, but some parts will be woody and preparation is more intense as opposed to the easily cleaned and peeled roots that are uninfected.
Root Knot Nematode Control
The most common treatments are crop rotation and allowing a field to lay fallow. Good sanitation practices such as cleaning machinery and tools is also useful. In some cases, solarization for 4 to 6 weeks can kill populations of some nematodes.
There are also several resistant crops that may be planted or a non-host plant can be installed. Such plants might be rye, fescue, corn, wheat, barley or sorghum. At this time, there are no resistant carrot varieties, but trials are underway and very soon these should be released.
There are a few soil fumigants that can be used up to 6 weeks before planting. They can be quite effective when used properly.
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How to Manage Pests
Pests in Gardens and Landscapes
Nematodes
In this Guideline:
Nematodes are microscopic, eel-like roundworms. The most troublesome species in the garden are those that live and feed within plant roots most of their lives and those that live freely in the soil and feed on plant roots.
Although California has many different species of root-feeding nematodes, the most damaging ones to gardens are the root knot nematodes, Meloidogyne species. Root knot nematodes attack a wide range of plants, including many common vegetables, fruit trees, and ornamentals. They are difficult to control, and they can spread easily from garden to garden in soil on tools and boots or on infested plants.
A number of other nematode species also can damage home garden and landscape plants including the ring nematode (Criconemoides xenoplax), root lesion nematodes (Pratylenchus species), the sugarbeet cyst nematode (Heterodera schachtii), the citrus nematode (Tylenchulus semipenetrans), the stem and bulb nematode (Ditylenchus dipsaci), and others. Tables 1, 2, and 3 list some common garden plant species and their nematode pests.
LIFE CYCLE
Plant-feeding nematodes go through 6 stages—an egg stage, 4 immature stages, and an adult stage. Many species can develop from egg to egg-laying adult in as little as 21 to 28 days during warm summer months. Immature stages and adult males are long, slender worms. Mature adult females of some species such as root knot nematode change to a swollen, pearlike shape, whereas females of other species such as lesion nematode remain slender worms. Nematodes are too small to be seen without a microscope.
It is believed the root knot nematode survives from season to season primarily as eggs in the soil. After the eggs hatch, the second-stage juveniles invade roots, usually at root tips, causing some of the root cells to enlarge where the nematodes feed and develop. The male nematodes eventually leave the roots, but the females remain embedded, laying their eggs into a jellylike mass that extends through the root surface and into the soil.
DAMAGE
Root knot nematodes usually cause distinctive swellings, called galls, on the roots of affected plants. Infestations of these nematodes are fairly easy to recognize; dig up a few plants with symptoms (see below), wash or gently tap the soil from the roots, and examine the roots for galls. The nematodes feed and develop within the galls, which can grow as large as 1 inch in diameter on some plants but usually are much smaller.
The formation of these galls damages the water- and nutrient-conducting abilities of the roots. Galls can crack or split open, especially on the roots of vegetable plants, allowing the entry of soil-borne, disease-causing microorganisms. Root knot nematode galls are true swellings and can’t be rubbed off the roots as can the beneficial, nitrogen-fixing nodules on the roots of legumes. Root knot nematodes can feed on the roots of grasses and certain legumes without causing galling.
Aboveground symptoms of a root knot nematode infestation include wilting during the hottest part of the day even with adequate soil moisture, loss of vigor, yellowing leaves, and other symptoms similar to a lack of water or nutrients. Infested vegetable plants grow more slowly than neighboring, healthy plants, beginning in early to midseason. Plants produce fewer and smaller leaves and fruits, and ones heavily infested early in the season can die. Damage is most serious in warm, irrigated, sandy soils.
Root injury from other nematode species can produce aboveground symptoms similar to those from root knot nematodes. However, the actual injury to the roots is more difficult to detect. Roots can be shortened or deformed with no other clues as to the source of the injury. You can confirm a nematode infestation by collecting soil and root samples and sending the material to a laboratory for positive identification of the infesting species.
Although nematodes can kill annual plants, they rarely kill woody plants. Nematode injury to woody plants usually is less obvious and often more difficult to diagnose. Infested fruit and nut trees can have reduced growth and yields. Woody landscape plants that are heavily infested can have reduced growth and branch tip dieback and can defoliate earlier than normal.
Detecting Nematodes in Soil Samples
| Host plant | Nematode(s) 1 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| albezia | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| alder | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| azalea | stunt | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| boxwood | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| cactus | root knot, cyst | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| catalpa | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| cedar | root knot, pinewood | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| euonymus | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| fir | dagger | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ginkgo | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| hibiscus | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| hydrangea | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| juniper | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| larch | pinewood | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| lilac | citrus | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| mulberry | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| oak | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| palm | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| pine | pinewood | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| pittosporum | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| poinsettia | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| rose | root knot, root lesion | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| spruce | pinewood | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| tamarisk | root knot | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Host plant | Nematode(s) 1 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Grapes and small fruits | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| grape | root knot 2 , root lesion, ring, citrus, dagger, stubby root | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| blackberry, raspberry | root lesion, dagger | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| strawberry | root knot, root lesion, foliar | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fruit and nut trees | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| almond | root knot 3 , root lesion, ring | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| apple | root knot, root lesion | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| apricot | root knot 4 , root lesion 4 , ring | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| avocado | root lesion | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| cherry | root lesion | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| citrus | root lesion, citrus | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| olive | root lesion, citrus | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| peach, nectarine | root knot 3 , root lesion, ring | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| pear | root lesion | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| plum, prune | root lesion, ring, pin | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| walnut | root knot, root lesion | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Host plant | Nematode(s) 1 | |||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Vegetables | ||||||||||||||||||||||||||
| beans | root knot 2 , root lesion | |||||||||||||||||||||||||
| beets | root knot, cyst | |||||||||||||||||||||||||
| carrots | root knot | |||||||||||||||||||||||||
| celery | root knot | |||||||||||||||||||||||||
| cole crops | root knot, cyst | |||||||||||||||||||||||||
| corn | root lesion | |||||||||||||||||||||||||
| cucumbers | root knot | |||||||||||||||||||||||||
| eggplant | root knot | |||||||||||||||||||||||||
| garlic | stem and bulb | |||||||||||||||||||||||||
| lettuce | root knot | |||||||||||||||||||||||||
| melons | root knot | |||||||||||||||||||||||||
| onions | stem and bulb | |||||||||||||||||||||||||
| peas | root knot, root lesion, cyst | |||||||||||||||||||||||||
| peppers | root knot | |||||||||||||||||||||||||
| potatoes (Irish) | root knot, root lesion | |||||||||||||||||||||||||
| potatoes (sweet) | root knot | |||||||||||||||||||||||||
| radish | root knot, cyst | |||||||||||||||||||||||||
| spinach | root knot, cyst | |||||||||||||||||||||||||
| squash | root knot | |||||||||||||||||||||||||
| tomatoes | root knot 3 | |||||||||||||||||||||||||
| turnips | root knot, cyst | |||||||||||||||||||||||||
| First winter | First summer | Second winter | Second summer | Third winter | Third summer | |
|---|---|---|---|---|---|---|
| Section A | fallow | fallow | fallow | plant summer-susceptible crop | plant winter/spring crop | plant summer-resistant crop |
| Section B | plant winter/spring crop | summer solarize | plant winter/spring crop | plant summer-susceptible crop | fallow | summer solarize |
| Section C | plant winter/spring crop | amend soil, plant summer-susceptible crop | fallow | fallow | fallow | fallow or plant summer-resistant crop |
