Report on the Agricultural Experiment Stations, 1952 Page: 58

58 REPORT ON EXPERIMENT STATIONS, 1952
The Mississippi station was able to control damping-off in Chinaasters
by steam pasteurization of the medium at 100 F. for 1 hour and
by treatment with Dowfume MC-2 at 1 pound per 121/2 cubic feet
It also developed an improved method of inoculating China-asters
with the aster wilt organism, which will enable growers as well as
researchers to test quickly and accurately the susceptibility of any
variety to aster wilt.
Tree Diseases
The Illinois station estimates that 65 percent of the 10 billion feet
of merchantable timber in the State is oak. More than 100,000 board
feet of merchantable timber have been killed by the oak wilt disease.
In the summer of 1951, trees containing 50,000 board feet of timber
showed the disease for the first time. Observations show that trees
in the red oak group get the disease more rapidly than white oaks;
that the disease kills red oaks much more rapidly than white oaks;
that within a species the largest and most valuable trees are most likely
to be attacked; and that the damage is not localized but is distributed
quite uniformly over the 1,600-acre area and in adjacent woodlands.
This potentially serious disease is receiving attention by many of
the State stations. Laboratory investigations by the West Virginia
station have shown that quick identification of the oak wilt fungus
may be made in liquid media or on a special agar medium low in
sugar and containing phenylalanine as the only nitrogen source. Early
diagnosis of the causal fungus by this method should help to prevent
the disease from spreading.
The rates of movement of liquid in the vessels of healthy and
diseased northern pin oak were determined by the Wisconsin station
with solutions of radioactive rubidium. This chemical moved upward
approximately 1 foot per minute in healthy trees, as well as in
inoculated trees, prior to symptom development. However, movement
was reduced abruptly by 90 percent and 99 percent at the time of
incipient and severe wilt, respectively. These results indicate that
vessel plugging results when the host is infected and that such obstruction
may limit the available water supply, causing a shortage
which may help to bring on leaf symptoms.
During the past year, the Missouri station (coop. USDA) found
that tanoak, bush chinquapin, European chestnut, and two Asiatic
oak species were susceptible to the oak wilt fungus in greenhouse inoculation
tests. The progression of symptom development appeared
to be similar in all species. A great many chemicals have been tried
by the Iowa station in an attempt to control oak wilt. Some of the
chemicals retarded the disease sufficiently to warrant further investigations.
The mode of action of these chemicals in controlling this
fungus suggests that they are able to neutralize the toxin produced
by the fungus.
RESEARCH ON USEFUL AND DESTRUCTIVE INSECTS
Recent reports have emphasized the significance of using modern
methods for insect control. The introduction of the newer insecticides
and acaricides (mite-killing chemicals) represents a definite step
ahead in scientific farming. Many of these insect controls grew out