Australia
August 10, 2005
Leading
USA plant pathologists discuss some of the important plant
disorders being dealt with by growers, how they are being
managed, and the risk they may pose to the Australian cotton
industry.
TABLE OF
CONTENTS
 Introduction by David Kelly, CSD
Extension & Development Agronomist
In July of this year, a group of
plant pathologists, an extension officer and a member of ACGRA
conducted a study tour of a number of cotton growing regions in
the United States of America.
The trip funded, by the Cotton
Research and Development Corporation and Cotton Seed
Distributors focused on some of the important diseases and plant
disorders being dealt with by the USA cotton industry.
In this presentation
we hear from some leading researchers and extension personnel
talking about; nematodes in Arkansas, cotton root rot in Texas
and fusarium wilt in California. We asked these people about the
severity of these diseases, how they are being managed and
importantly their risk of being spread to Australia.
Nematodes
 Dr Terry Kirkpatrick,
Extension Plant Pathologist, University of Arkansas.
(Interviewed by Bill Tywrhitt, Auscott
Warren, ACGRA)
What is a nematode?
Nematodes are round worms. The ones
that parasitise plants are microscopic, and are all soil
dwelling. They can do quite a bit of damage in the United States
by parasitising roots of the plant. They don’t kill the plants
generally but they do reduce the productivity of the crop
considerably.
How many different types do you have
that effect cotton?
In Arkansas we have only two that we
consider to be economic. One of them is the root knot nematode
(Meloidogyne incognita). It’s the most widespread in the state.
It is found in every cotton producing area.
 We also have a relative newcomer, the
reniform nematode which is Rotylenchulus reniformis. In the
last twenty years it has increased in incidence tremendously in
eastern Arkansas where our cotton production area is located.
Will the soil type affect which
nematode you have?
They do, but cropping patterns and
crop history affect the nematodes probably to a greater degree.
Root knot has always been associated with the sandier soils and
tends to cause the most damage in these soil types.
Reniform nematode seems to prefer a
little more clay in the soil. Soils with 20 – 30% clay are where
the reniform nematode appears to be at its optimum.
What type of damage do they do and
what kind of yield losses can you expect?
You can anywhere from 10% up to 20 –
30% in spots. Root knot nematode is much more spotty in
distribution and so in a big field you may only have four or
five areas of the field that have a problem, but you can
sometimes get 40% yield loss in those spots.
 If Reniform has been in the field for
some time, it tends to be much more evenly distributed
throughout the field. That’s one of the subtleties of reniform,
because it is uniform; the whole crop looks the same. With root
knot you can see the bad spots. You can see stunted plants and
you can see that there is a decrease in productivity there. With
reniform, unless you eliminate the nematodes with a nematicide
or some other way, you are not going to know that you have a
problem because everything looks the same.
You mentioned nematicides, is that
current control measure?
In the United States, at least in our
area in Arkansas, nematicides are the primary mechanism of
controlling nematodes. We are limited on economically feasible
rotation crops so most growers just opt to try and control the
nematodes with a nematicide at the beginning of the season.
You have visited Australia, what
affect do you think nematodes would have on Australian
production?
I think if you had a nematode problem
in Australia it could be pretty damaging because you are limited
in your cotton acreage you are going to be growing, so you don’t
have a lot of room to manoeuvre. Just speculating, the soils
that I saw in Australia seem to be pretty heavy in terms of clay
content; too heavy for root knot to ever be much of a problem
but a lot of your soils look to me like they would be perfect
for reniform.
Continued on
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