Report on the Agricultural Experiment Stations, 1950 Page: 69
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RESEARCH ON PLANT DISEASES AND THEIR CONTROL 69
Sweetpotato diseases
Extensive experiments conducted at the California station on
fusarium wilt or stem rot of sweetpotatoes showed that wounds
involving the water-conducting elements of the plant were necessary
for infection. The fungus that causes this disease enters
only through freshly cut stems, roots, or fresh leaf scars, but
not through uninjured stems or roots, root eruption wounds,
stomata (skin pores), or the callus of a healed basal wound.
Sweetpotato sprouts in plant beds in southern New Jersey
for a number of years have shown a brown decay which in severe
cases prevents emergence and in mild cases results in twisted
sprouts. Sprout decay has caused total failure in about one-fifth
of the beds and about 80 percent have shown typical injury. The
cause of the trouble remains obscure although it is evidently associated
with the soil. Broadcasting as much as 1 ton of superphosphate
per acre resulted in a nearly perfect stand. Use of
1,000 pounds also resulted in excellent stands although the height
was not uniform.
The Louisiana station is studying the virus-induced internal
cork disease which is causing much concern in the South. Records
taken over 3 years on samples of sweetpotatoes grown from
stocks exhibiting ring-spotting of the leaves and from stocks
showing "corky" roots indicated strongly that the agent that
causes cork is distinct from that causing leaf-ring-spot or that
possibly a combination of two separate viruses may occur. Certain
clonal lines showing leaf spot were grown for 3 years without
showing cork symptoms in the roots.
Improved cottonseed treatments
Poor seed germination and seedling blights have been lessened
by the development of more effective methods of seed treatment.
The North Carolina station reported highly successful results
with a chlorinated zinc phenol compound which is less troublesome
to operators than certain other standard materials and,
as proved by South Carolina tests, of little danger to animals
fed with treated seed. It is estimated that this treatment makes
it possible to use 10 to 15 pounds less of seed per acre planted
than formerly practiced. Greenhouse and field experiments conducted
for 3 years by the North Carolina station failed to show
any clear evidence of significant growth stimulation from hormones
used as seed treatments. The Arkansas station has proved
that, under some conditions, expensive thinning (chopping) of
cotton can be discontinued by planting treated seed, 5 to 8 per
foot, with proper machinery. Seed treatment probably added
22 million dollars in 1 year to the value of the Arkansas cotton
crop. Oklahoma station tests have shown that seed treatment
almost eliminates bacterial cotton blight in the seedling stage.
Tobacco diseases
No important tobacco-growing area exists in the United States
where growers are free from large losses caused by various types
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United States. Office of Experiment Stations. Report on the Agricultural Experiment Stations, 1950, book, January 1951; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc5992/m1/71/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.