CEREAL RUST BULLETIN
Report No. 5
May 21, 1997
Issued by:
Cereal Rust Laboratory, Agricultural Research Service,
U.S. Dept. of Agriculture
University of Minnesota, St. Paul, MN 55108
(612) 625-6299 FAX (612) 649-5054
markh@puccini.crl.umn.edu
http://www.umn.edu/rustlab/
rust survey mail list: cereal-rust-survey@coafes.umn.edu
€ Wheat leaf rust is more severe than usual in Texas with some
indication that new races may be attacking previously resistant
cultivars.
€ Although wheat stem rust overwintered in Louisiana, it was not
found in Texas until early May, where it is too late for it to
cause significant damage.
By the second week in May, winter wheat harvest had started from
southern Georgia across southern Texas to southern California.
Much of the crop in the central plains is a few days behind normal
maturity for this date, but with more warm dry weather, the crop
should develop at near normal rate. The cold weather in the
spring grain-growing area delayed planting and crop emergence
behind average for this date. Spring grain planting will be 2-3
weeks later than normal near the Red River of the North .
Wheat stem rust
The first report of stem rust in Texas was in early May in
varietal plots in central Texas. As reported in the previous
bulletin, stem rust overwintered in Louisiana, and is locally
severe in at least one field in northeast Louisiana. In mid-May,
traces of stem rust were found in plots in both southern and
northeast Louisiana. Wheat in the Mississippi Valley will be most
at risk from the northward spread of stem rust from Louisiana this
year.
Wheat leaf rust
By harvest time in south Texas, wheat leaf rust was more severe
than normal. By the second week in May, leaf rust was severe in
plots in central Texas. Most commercial cultivars in Texas are
showing susceptible reactions to leaf rust this year, which
suggests that there may be new races in the area. Reports
indicate that resistance of the cultivars Big Dawg, Longhorn and
Tomahawk is still holding up fairly well. By testing leaf rust
collections at the Cereal Rust Lab, we should be able to determine
what new races, if any, developed in Texas this year. The
earliest collections have turned out to be races that have
occurred in previous years.
Leaf rust was found on flag leaves of wheat in the southern tier
of counties of Kansas (excluding the far southwest) early in May.
By mid-May, leaf rust severity on flag leaves in south central
Kansas was as high as 40% in some fields of susceptible winter
wheat cultivars. In plots in the same area, severities on the
flag leaves ranged from 0 to 60%. In mid-May, leaf rust was also
found on flag leaves throughout central and northern Kansas, but
in those areas there was little rust on the lower leaves. The
lack of rust on lower leaves indicates that the flag leaf
infections came from spore showers from outside the region. From
the timing of the infection, it appears that Texas was the most
likely source of the spores. Leaf rust that overwintered on lower
leaves of wheat in southern Kansas was slow to develop due to
the cooler than normal night temperatures. In southern Kansas,
the rust was late in moving to the flag leaves from which it could
be spread farther north by wind. Leaf rust can now be found
throughout Kansas (Fig. 1). Wheat in the west and south central
areas of the state is under moisture stress. Overall, leaf
rust is developing more slowly than expected, but recent warm
temperatures and more moisture will result in faster increase of
rust, so significant damage may still occur.
In southern Arkansas during early May, leaf rust development on
flag leaves was severe in many late-planted fields of susceptible
cultivars. Cultivars most affected were Wakefield, Hazen,
Jackson, Coker 9803, Hickory and Pioneer 2580. While the leaf
rust epidemic in southern Arkansas was too late to cause major
damage on the whole wheat crop, this is the most significant rust
problem in several years in the state and will cause damage in
late-maturing fields.
In mid-May, in the coastal plain of South Carolina, wheat leaf
rust caused premature senescence of the state¹s predominant
cultivar (Coker 9835). No preliminary estimates of yield losses
to leaf rust are available yet for South Carolina.
Leaf rust was severe in the San Joaquin Valley of California by
mid-May, but because of the advanced crop development, losses are
not expected to be significant.
The leaf rust races identified so far in the 1997 survey (Table 1)
were also found in previous surveys. Race MBRL, the most commonly
identified race this year, was also the most common race the last
four years.
Table 1. Wheat leaf rust races identified through May 16, 1997
_______________________________________________________________
Number of isolates per state
Prt
code Virulence formula1 AL AR GA LA TX
_______________________________________________________________
MBBL 1,3,10 1
MBRL 1,3,3ka,10,11,30 3 6 2 3
MCBL 1,3,10,26 1
MFBL 1,3,10,24,26 3
TBBL 1,2a,2c,3,10 1
TDBL 1,2a,2c,3,10,24 2 6
TDRL 1,2a,2c,3,3ka,10,11,24,30 2
TFCL 1,2a,2c,3,10,24,26,30 1
TLGG 1,2a,2c,3,9,11,18 2
_______________________________________________________________
Number of isolates 3 12 4 2 12
Number of collections 2 6 2 1 8
_______________________________________________________________
1 Single gene resistances evaluated: Lr 1, 2a, 2c, 3, 3ka, 9, 10,
11, 16, 17, 18, 24, 26, 30.
Wheat stripe rust
In mid-May in Arkansas, south of I-40, stripe rust was still
active in many wheat fields because of the cool temperatures.
Fungicides were sprayed in some fields to control the rust.
Wheat stripe rust was increasing in central Washington in mid-May
on hard red winter and club wheats. Little rain has fallen in the
last two weeks so rust infection periods have decreased.
Oat stem rust
During the second week in May, oat stem rust was increasing
rapidly in varietal plots in College Station, Texas. Severe oat
stem rust was found in varietal plots and fields throughout
central and northeastern Louisiana by mid-May.
In early May, oat stem rust was found in plots in the Sacramento
Valley of California.
From collections made in south Texas in late March, the common
race NA-27 was identified.
Oat crown rust
Throughout the southern U.S., crown rust has continued to increase
on oats and is now as severe as in any of the last 3 years.
Inoculum from the south is likely to have an impact on crown rust
increase farther north.
Crown rust pycnia appeared on buckthorns in St. Paul on May 19.
The infections apparently came from basidiospores released from
germinating teliospores on infected straw during rains on May 7-8.
Buckthorn bushes are the alternate host for crown rust and
generally provide the initial spores for crown rust infections of
the northern oat crop. Aeciospores, which can infect oats, will
likely begin to be produced on the infected buckthorn leaves
within 1 to 2 weeks.
Barley stem rust
As of May 20, no barley stem rust has been reported in the U.S.
this year. Limited amounts of barley are grown commercially in
the southern states. Stem rust on barley rarely occurs in this
area.
Barley leaf rust
There have been no new reports of barley leaf rust since the April
22 bulletin.
Stripe rust on barley
There have been no new reports of barley stripe rust since the
last bulletin.
Rye rusts
Rye leaf rust was found in a nursery in Plains, Georgia on May 13.
Forty-percent leaf rust severities were observed on winter rye in
fields in north central Oklahoma on May 19. As of May 20, no rye
stem rust has been reported in the U.S.
Cereal Rust Bulletin #6 is tentatively scheduled for June 3.
Special Note: CRL web page and mail problem
The Cereal Rust Lab web page is moving; please update your
bookmarks. The new url is: http://www.crl.umn.edu/
We apologize for the difficulty that some of you have had in
getting messages to us and in some cases receiving messages from
us. Many of the messages were delayed by a glitch in the campus
computer system. We believe the problem is now fixed.