TOMATO-SEEDLING DAMPING-OFF.

New Zealand Journal of Agriculture, Volume 54, Issue 6, 21 June 1937, Page 321

TOMATO-SEEDLING DAMPING-OFF.

CONTROL BY SEED DUSTING.

E. E. Chamberlain

and R. M. Brien, Plant Diseases Division, Plant Research

Bureau, Department of Scientific and Industrial Research.

In a previous paper (Brien and Chamberlain, 1936) on the control of tomato-seedling damping-off, it was pointed out that the organisms responsible were soil fungi, and that control of the disease could be secured only by soil treatments. If a suitable therapeutant is applied to the surface of the seed before sowing, the soil in its immediate vicinity is disinfected,' and protection is given to the young seedlings during the period they are susceptible to attack. Therapeutants are most conveniently applied to the seed in- the form of dusts. Experiments described herein were undertaken to test the efficiency of this method and to determine which dusts gave the best control. Review of Literature. Experiments carried out by Godbout (1930) with “ Bayer dip dust,” “ Semesan,” and nickel sulphide as seed dusts, showed that “ Bayer dip dust ” and “ Semesan ” gave satisfactory control of damping-off (Pythium de Baryanum), on muskmelon, cucumber, radish, cabbage, and brussels sprouts. Horsfall (1932 A in a series of experiments on the control of tomato-seedling damping-off (Pythium ultimum) used red copper oxide, copper carbonate, and copper sulphate. He found that red copper oxide was more effective than copper carbonate for both pre- and post-emergent phases of the disease, but was less satisfactory than copper-sulphate dust for the pre-emerg ent phase. The same writer (Horsfall, 19328) showed that monohydrated copper sulphate was more effective than copper carbonate in protecting tomato-seedlings against both phases of damping-off. Anhydrous copper sulphate was shown to be equally efficient, but Horsfall did not recommend it for general practice because of its high cost.

Experimental Method.

The experiments - were carried out in the glasshouse using a soilmixture of clay loam and silt in seed-boxes 18 in. by 12 in. by gin. Seven to ten days prior to sowing, the soil, either untreated or steamdisinfected, was inoculated with cultures of Pythium ultimum grown on potato dextrose agar. Seed was shaken with the dust for five minutes in a glass vessel, the excess being then screened off. The seed was sown at the rate of either oz. or 500 seeds per box. Following the appearance of damping-off, counts of infected plants were taken daily. Final counts of the healthy plants left in the boxes were taken four to five, weeks after sowing, by which time they had advanced beyond the damping-off stage. The following dust materials were tested : —■ (1) “ Ceresan U.T. 1875.” — This proprietary organic mercury dust contains, as its active constituent, mercury-phenyl-acetate. (2) “ Agrosan ’’—Another proprietary organic mercury dust, of which the active constituent is mercury-tolyl-acetate. (3) Monohydrated Copper Sulphate. — A dust prepared- by heating crystalline copper sulphate at 105° C. The crystals break down to a fine pale blue powder. It is unstable when exposed to air, and must therefore be stored in an airtight glass or earthenware container. (4) Copper Carbonate. — For the purpose was used a high-grade basic copper carbonate having a copper content of 50 per cent, to 54 per cent., and a particle size less than 10 microns. (5) Red Copper Oxide {Cuprous Oxide). — This is not a standardized material, the commercial article being of variable purity. It is unstable in the presence of air. (6) Copper Oxychloride. — A proprietary product marketed under the name of “ Smutol ” was used. It has a copper content of 54 per cent., and particles averaging 5 microns in diameter. (7) “ R.D. 7312.” — An organic mercury dust the active constituent of which is ethyl-mercury-phosphate. This dust is still in the experimental stage, and has not been placed on the market. “ Ceresan,” “ Agrosan G.,” copper carbonate, and copper oxychloride are all available in New Zealand. Experiment I. “ Ceresan,” monohydrated copper sulphate, red copper oxide, copper carbonate, and copper oxychloride were used. The . soil was inoculated on 13th August, 1935, and on the sth September was sown with

Sutton’s Best of All tomato-seed at the rate of oz. per box. The seed gave a germination test of 99 per cent, in ten days. Results are given in Table I :

Experiments 11, 111, and IV. In these were used the seed dusts “ Ceresan,” “ Agrosan G.,” copper carbonate, and “ R.D. 7312.” The soil was inoculated on the 6th July, 1936, and sown on the 29th July with Sutton’s Best of All tomatoseed, which gave a laboratory germination test of 99 per cent, in ten days. The seed was sown at the rate of 500 per box. In experiment II seed was sown in steam-disinfected soil which had been subsequently inoculated with the damping-off fungus. Soil used in experiment 111 was untreated and inoculated with P. ultimum. Soil for experiment IV was untreated and. uninoculated. Results are given in Tables 11, 111, and. IV :

Experiment V. “ Ceresan/’ “ Agrosan G.,” copper carbonate, and “ R.D. 7312 ” were again used. Untreated soil was inoculated on the Bth September, 1936, with P. ultimum, and the tomato-seed sown on the 29th September, at . the rate of 500 per box. The seed was of the same variety as used in the other experiments. Results are given in Table V: —

Discussion of Results. ' AU dusts tested gave seedlings a decided protection against dampingoff caused by P. ultimum, but none gave complete control. Damping-off was more difficult to control in soil which had been steam-disinfected before being inoculated with the damping-off fungus. Results reported in our previous paper showed that this applied also with soil treatments. The results of experiment IV showed that the farm soil used for these experiments was naturally infected with P. ultimum and illustrates the wide distribution of the fungus. (1) “ Ceresan U.T. 1875.” — Although it failed to give good control in steam-disinfected soil inoculated with P. ultimum, this dust gave consistently good results in the other four experiments (see Figs. 1 and 2). It caused slight delay in germination in one experiment. (2) “ Agrosan G.” This dust gave fairly good results in the two tests made. It was less efficacious than “ Ceresan ”or copper carbonate. No delay in germination resulted from its use. (3) Monohydrated Copper — Promising results were secured in the one test made. It controlled damping-off slightly better than did either Ceresan ”or copper carbonate, and caused no delay in germination. . (4) Copper Carbonate. Consistent results were secured in all tests (Fig. 2). In one experiment it gave better control than “ Ceresan,” but in the other four it proved slightly less efficacious. Slight delay in germination occurred in two of the experiments. (5) Red Copper Oxide. — In the one test it gave promising results, being slightly more efficacious than “ Ceresan,” copper carbonate, or monohydrated copper sulphate (see Fig. 1). (6) Copper Oxychloride in the one test proved slightly less efficient than “ Ceresan,” copper carbonate,, monohydrated copper sulphate, or red copper oxide. (7) “ R.D. 7312.” — the three experiments this dust gave consistently good control of damping-off, but caused severe injury to the seedlings (see Fig. 3).

Recommendations. None of the dust materials gave complete control of damping-off. Sufficiently good results were obtained, however, to warrant their use by growers who have not the facilities for treating their soil. Organic mercury dusts such as “ Ceresan ” or “ Agrosan G.,” or high-grade copper

carbonate are recommended under such conditions. They do not take the place of soil treatments, so that, where practicable, growers are recommended to disinfect seed-box soils by the practices outlined in our previous paper. ~ - - . Summary. (1) Results are given of experiments with various seed dusts for the control of -tomato-seedling damping-off (Pythium ultimum). .. . (2) Damping-off was . more severe and more difficult to control in soil which had been steam-disinfected prior to the addition of cultures of P. ultimum.

(3) None of the dusts tested completely eliminated the disease. Several, however, gave a high percentage of control. (4) It is suggested that growers who have not the facilities for soil disinfection, may combat damping-off by using such seed dusts as Ceresan,” “ Agrosan G.,” or copper carbonate. .' Literature cited., . ' • Brien, R. M., and Chamberlain, E. E. (1936) : N.Z. Jour. Agric., Vol. 52, pp. 257-267. - : . Godbout, F. L. (1930) : Proceedings Canadian Phytopath. Soc., 1929, pp. 47-54. Horsfall, F. G. (1932 A : New York (Geneva) Agr. Expt. Stat.' Bull., 615, 26 pp. Horsfall, F. G. (19328) : New York (Geneva) Agr. Expt. Stat. Bull., 198, 34 pp.

* Untreated seed was sown in steam-disinfected soil, the average germination per box being taken as representing complete germination and used as a basis on which to calculate the percentage of damping-off occurring in the seed-dust treatments. The same method of calculation was used in Experiments 11, 111, and IV. .

* The percentage damping-off was calculated on the assumption that the seed was capable of giving 100 per cent, germination.

Seed Dust employed. Number of Plants emerged. Percentage of Plants damped-off. Average Percentage of Plants dampedoff. Remarks on Germination. Preemergent. Postemergent. . - > Preemergent. Postemergent. Untreated seed .. Monohydrated copper sulphate “ Ceresan ” Copper carbonate .. Copper oxychloride Red copper oxide . . Box A = 258 Box B = 198 Box A = 440 Box B = 402 Box A = 454 Box B = 449 Box A =; 463 Box B = 408 Box A = 407 Box B = 441 Box A = 405 Box B = 428 44 58 6 14 3 4 • 1 ■ 12 13 5 13 8 28 22 9 .11 13 9 12 20 15 15 9 . 5 J 7 6 { 2I { J 23 } 24 } - Slight delay. Slight delay. J ■ 76 . = 20 ’21 C 23 f 2 4 r 18 Slight delay. Slight delay. *S t e a m - disinfected soil Box A = 469 Box B = 463 0 - 0 0 0 } 0 Slight delay.

Table I. —Results of Experiment I: Seed sown in Untreated Soil inoculated with Pythium ultimum.

i Percentage of Plants Seed Dust employed. Number of • Plants emerged. ■Percentage of Plants damped-off. Average Percentage of Plants Pre-damped-emergent. off. d-off. Remarks on Post-Germination. Preemergent. emergent. Average Percentage of Plants Post- dampedemergent. off. Remarks on Germination. Untreated seed ... “ Ceresan ” Copper carbonate .. “ R.D. 7312 ” Box A = 83 Box B = 64 Box A = 318 Box B — 326 Box A = 413 Box B — 442 Box A = 385 Box B = 367 83 87 36 34 17 11 22 26 11 7 14 17 • 25 24 8 6 } 94 ■ ’ 94 } 51 } 39. r 31 Slight delay. Much delay. Steam - disinfected soil not inoculated Box A = 500 Box B = 492 0 0 0 0 r 0 .

Table II. —Results of Experiment II: Seed sown in Steam-disinfected Soil inoculated with Pythium ultimum.

Seed Dust employed. Number of Plants emerged. Percentage of Plants damped-off. Average ■ Percentage of Plants . Pre-damped-emergen t. off. of Plants sd-off. Remarks on - Post-Germination. Postemergent. Average Percentage of Plants . Pre-damped-emergent. off. Remarks on Germination. Untreated seed Box A = 185 63 15 67 Box B = 300 4° 16 J “ Ceresan ”, Box A = 481 3 3 Box B = 485 2 2 J 5 “ Agrosan G.” Box A = 394 21 3 V 18 Box B = 451 9 3 J Copper carbonate .. Box A = 480 3 IO 16 Box B = .453 9 9 / “ R D. 7312 ” .. Box A = 185 Box B = 300 Box A = 481 Box B = 485 Box A = 394 Box B = 451 Box A = 480 Box B = 453 Box A = 450 Box B = 458 63 4° 3 2 21 9 3 9 9 8 15 16 3 2 3 3 IO 9 3 2 67 { 5 } 18 } 16 bDelayed. Steam - disinfected Box A = 500 0 0 soil not inoculated Box A = 500 Box B = 492 0 0 0 0 } 0 J

Table III. —Results of Experiment III: Seed sown in Untreated Soil inoculated with Pythium ultimum.

Seed Dust employed. Number of Plants emerged. Percentage of Plants damped-off. Average Percentage of Plants dampedoff. Remarks on Germination. . Preemergent. Postemergent. Untreated seed Box A = 337 32 18 4 Box B = 423 15 13 1 39 “ Ceresan ” Box A = 487 2 7 1 IO Box B — 466 6 4 / 10 Copper carbonate . . Box A = 464 6 4 1 13 Box B = 472 5 IO J " R.D. 7312 ” Box A = 462 Box B = 477 7 4 1 2 7 9 Delayed. Steam - disinfected Box A = 500 0 0 I 0 soil not inoculated Box B = 492 0 0 r 0

Table IV. -Results of Experiment IV: Seed sown in Farm Soil naturally infected with Pythium ultimum.

Seed Dust employed. Number of Plants v emerged. Percentage of Plants damped-off. *Average Percentage of Plants dampedoff. Remarks on Germination. Preem ergent. Postemergent. Untreated seed Box A = 236 53 14 > 69 - Box B = 205 59 12 “ Ceresan ” Box A — 483 4 . I Box B = 476 4 I ■J 5 r 5 • • • “ Agrosan G.” Box A = 463 7 2 r 14 Box B = 434 13 5 J Copper carbonate . . Box A = 455 9 ■ 3 h- . Box B = 462 8 '2 J “ R.D. 7312 ” .. Box A = 430 Box B = 450 14 IO 1 } 14 ■ Much delayed.

Table V.—Results of Experiment V: Seed sown in Untreated Soil inoculated with Pythium ultimum.