138 



THE AGRICCJLTURAL NEWS. 



Apeil 27, 1912. 



INSECT NOTES. 



EEL WORMS, OR NEMATODES. 

 PAHT I. 



In previous numbers of the Agricultural Xews, eel worms 

 Slave been discussed from the points of view of the amount 

 <if injury which these minute worms inflict on crops and other 

 -cultivated plants, methods of control, methods of spread, and 

 'means to be adopted for the detection of this pest in sugar- 

 'Cane fields. The following references to these notes may be 

 given: Vol. Ill, p. 2S3: Vol. VI, p. 123; Vol. VIII, pp. 138, 

 280, 327; Vol. IX, p. 314. 



At the present time, much interest is being shown in the 

 subject of eel worms in different parts of the world, since it 

 is now realized that many crops are being seriously injured, 

 and much loss is resulting, from the attacks of these minute 

 •worms. 



The summary is reproduced here that is given in Bulletin 

 2v^o. 217 of the Bureau of Plant Industry of the United 

 States Department of Agriculture, entitled Boot Knot and its 

 Oontrol: — 



(1) the disease known ns root knot, characterized by 

 enlargements of the roots, and often leading to the death of 

 the plant affected, is caused by a nematode (Ilcttrodera 

 radicicola (Greet) Mull.). This was probaVily originally native 

 in the tropics (of the Old World!) but has spread into nearly 

 every part of both temperate zones. 



(2) The plants recorded as more or less subject to attack 

 number almost 480 species and varieties, including nearly 

 all the larger families of flowering plants. Probably many 

 more are actually susceptible, but have not yet been reported 

 as hosts. Most of the important field and garden crops and 

 ornamental plants are more or less subject to root knot. 



(3) The life-cycle of this nematode, from egg to egg, may 

 take place in four weeks, or longer, depending upon the temp- 

 erature of the soil. The larval stage is that in which entry 

 into the host takes place. It then becomes motionless and soon 

 enlarges and undergoes a sort of metamorphosis, the males 

 eventually recovering the original worm shape, while the 

 females become pear- or flask-shaped and very much enlarged 

 in their transverse dimensions. Each female lays -jOO or 

 more eggs. The winter is passed probably most frequently 

 in the larval stage in the soil, but in the case of galls of 

 perennial roots the nematodes may overwinter in these in 

 a more advanced stage, even as practically mature and perhaps 

 already fertilized females. 



(4) For the rapid multiplication of the root knot nema- 

 tode the following conditions are necessary: (a) A certain 

 degree of warmth of the soil. Thus in southern Florida 

 this nematode is active the year round, in part of South 

 Carolina the active season is from April 20 or .May I to the 

 middle or end of October, while farther north the period is 

 still shorter, (b) Loose-textured soil. Only sandy or at 

 least light soil is favourable to its spread, (c) Moisture. 

 The drying out of the .soil is frequently fatal to the nematode, 

 and in any case prevents it from doing aiiy harm. Appar- 

 ently the moister the soil, as long as it is well supplied with 

 air, the more favourable it is to the nematode's development. 

 However, wet soil, that is soil in which the air spaces 

 are filled with water, is at length fatal to the neraatod-e. 

 (d) Food supply. The larvae are able to exist in the soil for 

 more than one year, but apparently not for two years, with- 

 out the presence of living plants into which to enter. They 

 are apparently unable to develop beyond the larval stage 

 unless they enter a suitable host plant. 



(5) The nematode is distributed in several ways: (a) The 

 larvae move through the soil by their own motion, but the 

 distance traversed thus is probably not more than <> 

 feet or so a season (b) They are carried from field to 

 field in earth clinging to implements, the hoofs of 

 animals, the shoes of labourer.s, wagon wheels, etc. (c) They 

 are conveyed in tlie soil; that is washed from one field 

 to another by heavy rains, a very common mode of 

 distribution of this pest, (d) It is possible that heavy 

 winds may carry larvae or eggs with the soil blown 

 from one field to another, but probably most would be 

 so dried out in the process that this is not much to be 

 feared, (e) They are introduced into new places in the roots 

 or in the dirt adhering to the roots of nursery stock, in 

 rooted cuttings, potted plants, etc., especially those of the 

 peach, grape, fig, mulberry, potato and ginseng; also dirt in 

 which some seeds are packed, (f) They are sometimes 

 brought to a field in manure, if the manure pile has stood on 

 infested soil. 



(6) The following methods of control in greenhouses and 

 .seed beds may be used: (a) Tlie most efficient method of con- 

 trol is the use of live steam at fairly high [rressure. The 

 steam is forced through a system of perforated pipes laid at 

 the bottom of the bed or bench, (b) The old, infested soil 

 may be entirely removed and the benches thoroughly cleaned 

 out. The non-infected soil may be put in its place. This 

 method IS not advisable in regions where the nematode occurs 

 out of doors in the vicinity, (c) Infected soil, when it is 

 desired to save it and steaming is impracticable, may be 

 freed by allowing it to lie through the winter in a place 

 where it will be exposed to alternate freezing and thawing, 

 and especially to drying, (d) Soil containing perennial plants 

 can be nearly, if not quite, freed from nematodes by the u.se 

 of an abundance of a solution of formaldehyde ( 1 part of 

 commercial formaldehyde to 100 parts of water). 'I'his solu- 

 tion is fatal to many plants and can be used only with great 

 caution. 



(7) For the control of the nematode in the field where 

 the land is occupied by perennial crops no entirely satisfac- 

 tory chemical application can be recommended. Places where 

 trees are to be reset should be freed from nematodes bj- the 

 use of carbon bisulphide at a rate of 3 or 4 oz. per square yard, 

 placed in about nine holes per square yard, these holes being 

 about 6 to 12 inches deep and to be filled with soil as soon as 

 the chemical is placed in them. Carbon bisulphide cannot be 

 used with safety around living trees. Flooding the land seems 

 to be unsatisfactory, as flooding long enough to kill the nema- 

 todes is usually fatal to trees. High fertilization and con- 

 stant cultivation to induce growth often so help the trees 

 that they are able, us it seem.s, to outgrow the trouble, the 

 roots either penetrating to levels where the nematodes are 

 less abundant or being formed faster than the galls can be 

 produced. Avoid growing susceptible cover crops, like the 

 ordinary non-resistant varieties of cowpeas, for example, for 

 these multiply the nematodes in the soil manifold. In pre- 

 paring the land for setting out a perennial crop the soil 

 should be freed from nematodes by the use of the methods 

 suggested below. 



(8) For land infested with nematodes and not bearing 

 a perennial crop, the following methods may be recommended: 

 (a) Keeping the land free from vegetation of all kinds for two 

 years. This is the most effective method, but it is not prac- 

 ticable in many cases, (b) Planting the land to nf'U-suscep- 

 tible crops for at least two (perhaps better three) years, using 

 in the winter small grains, such as wheat, rye or oats, and in 

 the summer the velvet bean, Florida beggarweed, the iron 

 cowpea, or even ground nuts, .scrupulously destroying all 



