Agricultural Science Digest
Vol. 12, Nov. - Dec., 1968 PURDUE UNIVERSITY

CRAZY TOP OF CORN

The appearance of crazy top of corn was
relatively widespread in Indiana and some ad-
jacent states during 1968, occurring in plant-
ings made in late April and early May. There
was a direct correlation between the high in-
cidence of the disease and the increased pre-
cipitation during most of'May.

In fields where no drainage problem exists
under normal rainfall, the excess rain satur-
ated the soil for extended periods and created
conditions favorable for infection.

Because crazy top occurred in fields
where it had not been seen for five to ten
years, it is possible that inoculum, in the
form of oospores in the soil, may be able to
survive for relatively long periods.

The increased occurrence of crazy top
provided plant pathologists a chance to ob-
serve the following symptoms of the disease:
excessive tillering;
rolling and twisting of whorl leaves;
excessive dwarfing with narrow strap-
like leaves;
phyllody of the tassel.
Some variation in symptoms was seen
among different plantings, and this may be
correlated with the time of infection of the
young seedling. For the first time, differ-
ences in susceptibility were observed among
corn genotypes.

A study was also made of seed transmis-
sion of the pathogen. It seemed likely that
kernels harvested from diseased plants could
give rise to infected seedlings.

The greenhouse-grown plants displayed
similar symptoms to those seen in the field
except for the absence of phyllody in the
tassel. Plants grown in the greenhouse from
seed harvested from diseased plants in the
field showed the following:
shortening of internodes with result-
ing dwarfing;
elongation of ear shank and flag leaves;
leafy termination without inflorescence;
buckling of whorl leaves due to failure
to unfurl;
rugose striations in whorl leaves.

Journal paper 3595, A.J. Ullstrup and
M.H. Sun, Department of Botany and Plant
Pathology.

CONTROL OF RUST

Spearmint rust is often damaging to
plantings of Scotch and common spearmint.
It can cause losses in production of the es-
sential oils by leaf damage and premature
defoliation.

In 1967 and 1968 plant pathologists ex-
perimented to see if spearmint rust could be
controlled when transplants were used.
Crated transplants were dipped in the fungi-
cide dichlone (Phygon) immediately after
coming from the field. The transplants were
then set in another field.

The incidence of rust infection was sig-
nificantly lower in those treated. In Spring
1968, the plot established from treated
transplants (1967) showed a greater number
and more uniform plants than the plot from
untreated plants. This advantage disappear-
ed after two or three weeks, but suggested
better winter survival and vigor in the fol-
lowing growing season when rust was con-
trolled.	

Because of the risk of severe
loss from spearmint rust when	 transplants are used 

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