CONTROL OF ROOT-KNOT. 51 



about 5 feet, so as to retain the solution. One part of conixnercial 

 formaldehyde (about 40 per cent strength) was mixed with 100 parts 

 of water. About 25 gallons were applied to each tree — i. e., about 3 

 gallons to the square yard. In some cases water was applied after- 

 wards to cause the solution to penetrate deeper; in other cases no 

 water was added. A few of the older leaves turned yellow and 

 dropped off a day or two after the treatment, but no further injury 

 was noticeable. In two weeks the nematode root galls, containing 

 living nematodes, were found to be almost as numerous as ever, 

 although a good many of the galls on the roots nearest the surface 

 were found to contain dead nematodes. These and other experi- 

 ments lead the \\Titer to believe that where the soil is rather deep and 

 the liquids applied can drain through instead of remaining in the 

 immediate vicinity of the roots this formaldehyde treatment is not 

 likely to prove very effective. 



Calcium carhid. — The use of calcium carbid was also recom- 

 mended by Gandara.^ His instructions were to mix 4 parts of it 

 with 1,000 parts of water. After letting it stand half an hour this 

 milky solution is to be injected into the soil in five holes per square 

 meter, 10 grams to a hole. Through lack of other trees suitable to 

 test it on, papaya trees were also used in testing this method. A 

 modification was also made in that about an ounce of the calcium 

 carbid, without previous treatment with water, was placed in the 

 bottom of 8-inch holes, which were promptly plugged with earth, 

 about eight or ten holes being made to the square yard. Afterwards 

 the soil was thoroughly watered. In this case a strong odor of acety- 

 lene was noticeable for two days. No damage was done to the trees 

 and the nematodes in the galls were not killed by either treatment. 



Other chemicals. — Various other chemicals recommended have the 

 disadvantage that they are poisonous to living plants or too expen- 

 sive. It is still possible, however, that some easily volatilizing liquid 

 may be found whose vapors while fatal to the nematodes will not 

 seriously injure the plants harboring them. Of those already men- 

 tioned carbon bisulphid has many desirable qualities ; but its poison- 

 ous effect on vegetation is against it. It is possible that by applying 

 it only during the dormant season of the plant and carefully regulat- 

 ing the quantity applied it may prove as effective as it is claimed by 

 some investigators to be against phylloxera in the vine. The WTiter's 

 experiments were mainly carried on at Miami, Fla., where there is 

 no dormant season; hence this point could not be well determined. 

 It is also conceivable that after a period of dry weather the chemical 

 might be less harmful, as the trees would then be in a less actively 



1 G&ndara. 1906. 

 217 



