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Chemical Control of Clubroot Disease of Brussels

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Chemical Control of Clubroot Disease of Brussels Chemical Control of Clubroot results from cooperative work between California Exten chemicals applied in setting water Clubroot, a soil-borne fungus disease, threatena industry. Control was achieved on 250 acres in ! grated three-phase research program carried ou controlled soil-borne fungus disease This research program and the results obtai Station and Extension Service of combining fo W. C. Snyder, 1. D. Leach, and R. H. Sciaroni instance, members of the University of Calif0 thology, Agricultural Engineering, and Vegetabl San Mateo County producers of cab- There is concern among Brussels co-ordinated effort toward development of an e bage, broccoli, and Brussels sprouts sprout growers in the central coastal ment, and adaptation of equipment to apply ch have incurred large financial losses-in counties of Santa Cruz, southern San sistant strain of seed. the past several years-because of the Mateo, Monterey, and San Luis Obispo, Paul F. Shaq clubroot disease of crucifer plants. because of the ease with which the dis- 1. Earl Coke, The clubroot disease caused by the ease is spread. soil-borne fungus - Plasmodiophora The clubroot fungus can persist in brassicae-has not been found in Cali- the soil for many years as resting spores. fornia, outside of San Francisco and San During favorable periods of tempera- resistance to cl u broot Mateo counties. ture, moisture, and soil conditions, the However, clubroot disease has been resting spore germinates and produces of breeding project ir known in Europe for more than a cen- a motile swarm spore. These motile tury and in the United States for many spores invade a plant through root hairs, years, where it is a major problem in young roots, or wounded tissue. Infec- certain areas, particularly in the Pacific tion may take place on seedlings in seed- Northwest. In 1938, the disease was beds or transplants in the field. Large, Development found-for the first time in California- swollen growths-clubs-develop in the of a strain of infecting large acreages of cabbage and root system as a result of root cell in- Brussels sprouts cauliflower in southern San Francisco vasion. These clubbed roots soon rot resistant to the County and northern San Mateo County and the root system is destroyed. As a fungus causing in the vicinity of Colma and Daly City. result of root infection, the tops of plants clubroot disease During 1945 and 1946, clubroot was wilt and droop. Wilting of the tops of was started be- introduced into the Half Moon Bay the plant is particularly noticeable on cause the use of area, probably on diseased transplants warm days. Early infection may cause chemical treat- brought in from near Colma. death of the plant before a crop is pro- ments at the time duced. Later infection generally leads to of transplanting A young Brussels sprout plant infected with reduced growth, lowered quality, and does not provide clubroot disease is at the left. A healthy plant is on the right. poor yields. a permanent so- The rotting and breaking down of in- lution for the fected clubs releases enormous numbers wroblem. of spores into the soil. A spectacular Applications of Roots of plants grown on soil L spread of the disease was observed in a HgCl,--mercuric left: resistant plant of the bad Brussels sprouts planting in Half Moon chloride - and Brussels sprouts; noh Bay, where only a few diseased plants PCNB - penta- were found in a 20-acre field one season chloronitrobenzene-have been spectac- and-two years later-almost the entire ularly successful in restraining the club- planting was infected. root organism sufficiently to permit the Because each spore is capable of in- growing of a good crop, but if accept- citing infection, the causal fungus can able lines of resistant sprouts could be be introduced easily into clean soil by bred, the problem could be solved with- diseased plants from infested seedbeds out the need for such treatments. The or fields; by the movement of soil by breeding program necessary for this ob- water or wind; on plants, farm equip- jective requires a number of years be- ment, hoofs of animals, and so forth. cause the plants must be bred for several Where infection has occurred, a 340- successive generations. The chemical 5-year rotation interval out of suscep- treatments therefore have great value in tible crucifer crops-such as broccoli, providing an immediate and effective cabbage, cauliflower, Brussels sprouts- stop-gap control. Furthermore, it is of has been of benefit but will not free the the utmost importance that the problem soil of fungus; it will only reduce the be attacked from both angles and that amount of the fungus. A satisfactory the work on both aspects be carefully crop might possibly be obtained after integrated. such a rotation. Work on the breeding of resistant Continued on page 10 Brussels sprouts was initiated in 1952, 8 CALIFORNI A AGRICULTURE, APRIL, 1955 ion Service and Experiment Station in San Mateo County California’s 4-5 million dollar Brussels sprouts liquid drop valve for transplanters UI Mateo County in 1954 as a result of an inte- under actual field conditions within the county. d are an example of the policy of the Experiment conserves chemicals and setting water ~s in an effort to solve county problems. In this aia Experiment Station departments of Plant Pa- Norman B. Akesson and Ralph R. Parks Crops joined with the Extension Service in a bnomical chemical control procedure, improve- Experiments in San Mateo County aicals and a breeding program to develop a re- showed that a metered amount of ,a mer- curic chloride solution applied-by Director of California Agricultural Experiment Station hand-to the roots of Brussels sprouts vector of California Agricultural Extension Service at the time of transplanting would con- trol the clubroot disease sufficiently for an economic crop return. A mechanical transplanter that would disease is goal meter the liquid carrying the chemical accurately and rapidly to the immediate Brussels sprouts vicinity of the plant root would conserve both chemical and water and make pos- sible large-scale treatment at a reason- able cost, but most mechanical trans- planters discharge a continuous stream would cause a drop in the flow because when various of water in the plant row. However, one of the wall thickness of the pipe. A 3/4” lines of sprouts type of machine in use does have a hose coupling--2%2“ ID-should be and related crops simple interrupted drop valve system. used to maintain the flow. of the cabbage Work was started with this machine to The drop valve assembly was con- species - Bras- develop a transplanter liquid drop valve structed with simple lumbing parts and sica oleracea - which would meter the setting water a minimum of we1cp ed joints. No ma- were tested for solution. A simulated transplanter with chining was necessary. resistance in a drop valve setup-using the simple Rapid flowout properly timed to the heavily infested gravity flow system-was made to pro- transplanter is the essential aim of the soil at Half Moon vide a maximum of one pint liquid drop system. This reduces the distance the Bay. One of the per second, which-when planting on material covers in the ground. For ex- lines of cabbage 36” intervals at about two miles per ample, at two miles per hour, if the valve tested remained hour-is equivalent to 7.5 gallons per is open 0.53 second--equivalent to 1.5 completely free minute flow. pints of material flow-approximately of the disease The source of gravity flow was a 55- 1.5’ of ground is covered, or on 3’ throughout the gallon barrel lying on its side at about plantings one half of the row length is season despite se- 30” above the valve. Thus when thk bar- wetted. At 0.38-second valve timing- vere damage to rel is full, the head is 51”-21” diame- 1.25 pints-about 1’ is wetted or only adjacent plant- ter-and when nearly empty, the head Continued on page 11 ings of susceptible lines. is 30‘’. Crosses were attempted between the The flow of liquid through a hose Transplanter with drop valve installed. resistant cabbage and the best available with the various couplings, adapters- strains of Brussels sprouts, and since from hose coupling to pipe-and valves these crops are interfertile, abundant is shown for three sizes of hose in the seed was produced. The resulting hybrid graph on page 11. The hose lengths -F,-generation was also grown under plotted are for 10’ plus the appropriate conditions of heavy infection in 1953 couplings to connect the hoses to ordi- and, like its cabbage parent, was found nary pipe fittings. The couplings are the to be completely free of clubroot symp- limiting orifice-smallest openings-in toms. This hybrid is intermediate be- the system. Hose coupling to pipe adap- tween the two parents in such vegetative ters-nipple type-and gate-type valves characteristics as height of stalk, devel- of the same ID-inside diameter-as the opment of axillary buds, and size and hose, have little or no further flow re- shape of leaf. stricting effect on the system. The table Having gained this evidence of domi- in the next column gives the ID sizes for nance of clubroot resistance, the F, hy- various components to be used with the brid was backcrossed to Brussels sprouts. hose size specified. Connecting a 3/4” ID These crosses were again successful in hose, for example, to a pipe by slipping Continued on next page the hose over a 1/”-ID 1%2’’-pipe CALIFORNIA AGRICULTURE, APRIL, 1955 9 CLUBROOT DISEASE Chemical Soil Treatment Control of Clubroot on Brussels Sprouts.
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