Among the many different kinds of organisms known to cause plant diseases, nematodes or eelworms are the least known to gardeners.
They are, nevertheless, important disease-producers, and are frequently the cause of stunted growth, leaf might, and, occasionally, even death of many economic crops, trees, shrubs, and ornamentals.
Small Size of Nematodes
One reason why they are not recognized more generally is their small size. Many of the parasitic nematodes are only 1/125” inch long.
Moreover, the damage they cause often resembles that produced by other organisms.
In addition, some eelworms attack below-ground parts, particularly roots, and the infestation is not discernible unless the plants are lifted, and the soil is washed away.
At this time of year, damage to hardy chrysanthemums by the foliar nematode is especially pronounced.
The blighted leaves along the lower part of the stem and the yellow ones with V-shaped dead areas along the upper stem are characteristic of this nematode.
Although it is too late in the season to control this pest, the severe damage so plainly evident now may spur gardeners to resolve to adopt the proper preventive measures early in the 1954 growing season.
Preventing of Infections
Suggestions on how to prevent infections will be presented later.
Other species of nematodes attack ferns, begonias, and gloxinias, causing a complete collapse of leaf tissues.
Others attack bulbous crops like narcissus, while others cause severe distortion of stems and leaves of phlox, sweet, and hydrangea.
Perhaps most common and destructive are those kinds which attack roots. Of these, the root-knot nematodes are the most prevalent in this country.
They enter the roots of hundreds of different plants and cause knots or galls, which usually spell death to the distal portions of the roots beyond the swollen area.
Such damage interferes with the normal water and mineral absorption, resulting in weak, yellow, or stunted growth of the above-ground parts.
Knotting of Root for Nematodes
In the North, root-knot nematodes are most prevalent in the roots of roses, gardenias, tomatoes, cucumbers, and other plants grown under glass.
In the South, they occur commonly in the roots of trees, shrubs, and ornamentals growing outdoors.
Primarily hot-weather parasites are favored by short, mild winters, long hot summers, and light sandy soils.
Meadow Nematodes: Roof-Infesting Group
Finally, a root-infesting group known as meadow nematodes has recently become rather widely prevalent and destructive to the roots of trees, shrubs, and ornamentals along the Eastern Seaboard.
Boxwood, pin oak, iris, and peony are among the more susceptible plants.
Meadow nematodes cause lesions on some roots and decay in others bin no galls. Repeated attacks result in a stunted, shortened, and less efficient root system.
The control measure to adopt depends on the species of nematode involved, the crop affected, and the planting size.
Control measures for leaf-infesting species may vary anywhere from keeping water off the leaves to dipping pot-grown plants in hot water.
Apply a highly poisonous chemical to the soil or even spray the leaves with a chemical at periodic intervals throughout the growing season.
The hot water dip is effective on potted begonias or individual begonia leaves to be used for propagation.
Soaking of Plants
A 5-minute soaking of these plant parts at a 110° temperature will destroy the nematodes within the leaves without seriously affecting the plant.
Sodium selenate no longer available was sold under the trade name P-40. It was applied to soil in which chrysanthemums were growing and absorbed by the plants killing any leaf nematodes.
Highly Poisonous Chemical
Soils treated with this highly poisonous chemical cannot be used later to grow food crops because the edible parts may absorb some of the poison.
Commercial growers control the mum nematode by spraying chrysanthemum plants every ten days with Parathion or Systox.
These chemicals are organic phosphates, which are extremely dangerous, and consequently, I do not recommend that amateur growers use them.
Some researchers may soon find that Malathon, a close relative of these chemicals, which is much safer to use, will give control of leaf-infesting nematodes.
Soil-infesting nematodes can be eliminated by various means. Heating soil to 180° will give complete control.
Years ago when heat treatments were not feasible, good control was achieved by using any one of several excellent fumigants:
- DD Mixture
- Dowfume N
- Dowfume W-40
- Fuml-Soil Capsules
- Soil-Fume Caps
These were purchased in drums, cans, or capsules, depending on the amount of soil treated.
Some can be used to treat the soil near growing plants; others cannot. The manufacturer supplied details on precautions to observe and the proper application method.
Mixing Calcium Cyanamid Into Infested Soil
In the Southeast, many growers mix calcium cyanamid into infested soil.
Better crops result both from the consequent reduction of the nematode population and the fertilizing and liming effects of this chemical.
Effect of Presoaking Dormant Plant
For several years. now I have been studying the effect of presoaking dormant plant parts such as seeds, roots, bulbs, and corms in a nutrient solution before planting.
My latest tests completed a few months ago had to do with tulips and narcissus bulbs.
Last fall, I soaked hundreds of Marjorie Bowen tulips and King Alfred daffodils for an hour in a fertilizer nutrient solution.
Tulips thus treated produced more and stronger roots immediately after being planted, and emerged earlier this spring with more vigorous foliage and better flowers than tulips that were soaked in just plain water.
The differences between treated and untreated narcissus were not as striking, although several people who observed the results thought.
The Rapidgro-treated daffodils had larger, more deeply yellow flowers and more vigorous foliage than untreated ones.
Recently introduced into this country is Fertosan torn post accelerator.
According to the introducer, Fertosan is an entirely new product that reduces vegetable matter to rich, humus-laden manure in five to six weeks.
The process does not require turning the pile, nor does the compost heat up, killing the beneficial bacteria in the humus.
Streptomycin: Controlling of Plant Diseases
Streptomycin, the antibiotic so well known in medicine, may yet find its way into gardens as a control for plant diseases.
Research workers in the U. S. Department of Agriculture secured excellent control of the halo-blight disease of beans by spraying the plants with streptomycin sulfate.
The cost of controlling this disease was quite high because the purified material was used. Perhaps someday, using crude or sub-clinical grades of this antibiotic will bring it within the budget range of farmers and gardeners.
Russell C. Mott of the Department of Floriculture at Cornell University reports that cattleya orchids watered daily throughout the year were larger and produced more pseudo bulbs and flowers than those watered less frequently.
The tests were conducted on young Cattleya labiate, and amesiana plants. Tests are being continued with this variety, as well as with others.
44659 by P. P. Pirone