ISSUE 12 JULY 22, 1999
SMALL GRAIN DISEASES
Wheat and barley diseases became much more evident this past
week. Heat and high humidities are
either favoring infection of some of the disease organisms, or are making some diseases more evident. I
am getting the greatest questions about the following three diseases:
Wheat leaf rust - Early planted fields of varieties such as
2375 or ACBarrie are showing high severities
of leaf rust on the flag leaves in many areas. Some other spring wheat varieties are also showing high levels
of leaf rust, while just a few have none to very little infection, in various research plots. Later planted crops
also are showing leaf rust symptoms. Where foliar fungicides were applied, flag leaves are still generally
very green, although it appears that a few rust pustules are starting to form on crops sprayed two to three
weeks previously. When evaluations of fungicide treatments and variety differences are in, and when the
combine dust settles, we should have some good information on performance of varieties and fungicides
against the prevalent races of wheat leaf rust. Only low levels of barley leaf rust have been observed.
Oat leaf rust is commonly observed now.
Yellow dwarf virus: Barley yellow dwarf is the name given to
a virus disease that attacks barley, wheats,
and oats. The symptoms of this virus disease in wheat have become very evident the past week in grain
that has recently headed - bright golden yellow flag leaves, yellowing from the flag leaf tip downward, with
a blotchy appearance, and tissues near the midrib of the leaf often staying green longer than the rest of the leaf.
The yellow dwarf virus is transmitted by common grain aphids, as
discussed several times already this year
under the plant pathology and entomology sections of NDSUs Crop and Pest Report. Aphid control has
been discussed in previous reports this year, and most fields will not warrant treatment now, especially if
virus symptoms are already evident. Symptoms dont become apparent until around 10-20 days after
the aphids have transmitted the virus. So detecting and controlling the aphids before theyve had a chance
to transmit the virus is tricky.
Losses from yellow dwarf depend on several factors, including the
variety, the time of infection, the
number of aphids, and environmental conditions. In tests in other states with artificially infected barley
plants, under a worst-case scenario, losses were 55% IF plants were inoculated in the seedling stage,
23% IF plants inoculated at tillering, and 19% IF plants were infected during jointing. Losses under
natural infection were much lower even under severe infections, more often closer to 15%. I
would estimate lower losses in ND, around 5% or less, in most spring wheat fields showing just some
yellow flag leaf tips.
Root Rot: With recent high temperatures, root rot symptoms
have made a nasty appearance in many
wheat and barley fields. Private consultants, agronomists, and extension area and county agents are reporting
as many as 10-15% of the plants with symptoms in some fields of wheat or durum, across much of the state.
Other fields also show the white plants scattered throughout the field, but actual percentage of affected plants
is much less. "Wet feet" early in the season precipitated infection by root rot fungi, and now we have the
visible expression of infection above ground, as plants cant translocate enough water to thirsty grain heads
through their rotted roots and crowns.
Infected plants have white heads, and the whole stem area, or the
lower stem and leaf areas are prematurely
white or tan. The crowns and roots of these plants are generally discolored brown to reddish-brown.
Management of root rot is through crop rotation, use of tolerant
varieties, and several seed treatment
products. NDSU evaluates their spring wheat varieties for tolerance to root rot, but only limited information
is attainable about the many other varieties currently available to ND producers.
With the weather we had this spring, all the management options
available may have not been enough to
stop root rot in some fields.
Other diseases: Fusarium head blight, or scab, is still on
everyones mind, and the disease certainly is
out there, but still is at low incidence(2-5%) in most fields surveyed. Later maturing grain in wet areas still
bears watching for scab development. Tan spot and Septoria are evident on the flag leaves of many wheat
crops, and severity depends on variety, growth stage, amount of moisture received, and fertility and fungicide
practices. Spores of the spot blotch fungus are also frequently being recovered from leaf spots on wheat and
barley. The spot blotch fungus is the same fungus that causes common root rot in wheat and barley, and the
fungus grows and sporulates more actively in warm conditions.
Extension Plant Pathologist
RUST ON DRY EDIBLE BEANS
Clark Helland, crop consultant in northeastern North Dakota, has
found rust on dry edible beans. This
report comes several weeks after a report of rust on small red beans 4 miles south of Plum Coulee, MB,
which is about 10 miles north of the border with Pembina County.
There have been numerous telephone calls asking if rust has been
observed yet. I believe that the major
factor impeding rust development is a major shift in the pinto varieties being grown in the state: 3 years ago
most of the varieties grown were susceptible, but now most of the varieties grown are resistant to the current
races of bean rust.
Commonly grown pinto varieties with resistance to the most prevalent
rust races include Chase, Maverick,
Remington and Winchester. Fields planted to susceptible pinto varieties, as well to pinks or small red beans,
should be monitored routinely for rust. If two pustules per leaf are found before the lower pods are striping
(have full sized beans), or if one or two "hot spots" develop in a field, a fungicide should be applied. Bravo
and maneb are registered for bean rust control. Bravo gives 7-10 days of protection and maneb gives 5-7
days of protection. Both are effective as protectant fungicides, but will not stop established infections. Tilt
has a section 18 emergency exemption in both North Dakota and Minnesota. Tilt is locally systemic, provides
14 days of protection and can kill infections up to four days old.
All varieties and classes should be monitored for rust. If rust
shows up at alarming levels in a variety
previously thought to be resistant, it may be necessary to assume that a new race is present and to take
appropriate action. Any such observations should be followed up by sampling. Samples should be placed
loosely in a paper envelope, allowed to air dry, then mailed to:
North Dakota State University
Fargo, ND 58105
Please include information on the variety and class grown, where
collected, and name and telephone
number of the person collecting the sample. This will help to track the development and prevalence of rust
races in the state.
ROOT ROT OF DRY BEANS
Telephone calls indicate that root rot is a problem for many dry
bean growers. Most of the problems
are in areas that have had excess moisture. Nothing can be done about the root rot, but some cultural
practices can help to reduce the effects. Cultivating, if possible, can help dry out the soil, preventing further
damage. Hilling up around the bases of bean plants can help promote the development of adventitious
roots, which develop above the rotted areas of the root and help to carry plants through to maturity.
Clark Helland, crop consultant in northeastern North Dakota, has
found rust on confection sunflower
in the Lakota and Edmore areas. This is a high temperature rust. It develops slowly during periods of cool
weather, but can develop explosively during periods of high temperatures. Following periods of high
temperatures, be alert for the rapid development of sunflower rust. Folicur is available under a section 18.
See Crop and Pest Report No. 3 for information on the use of Folicur and the timing of applications for
rust control on sunflower.
Extension Plant Pathologist
PLANT DIAGNOSTIC LAB REPORT
The most prevalent crop disease coming into the lab this week has
been Bacterial Brown Spot on
dry, edible beans. This is not surprising given the cooler, fairly wet weather across much of North
Dakota recently. There are three diseases involved in bacterial blight on dry beans. Two of those
disease are caused by Pseudomonas species of bacteria and one is caused by a Xanthomonas.
Common blight is the disease caused by Xanthomonas phaseoli, Halo blight is caused by
Pseudomonas phaseolicola, and Brown spot is caused by Pseudomonas syringae. Common
blight occurs when the temperatures are higher in the summer while Brown spot and Halo blight are
favored by cooler temperatures. Brown spot is generally more common in North Dakota. Cooler,
wet weather, such as we have had across much of North Dakota this season are very favorable for
disease development; and the storms that include hail and high winds are particularly conducive since
they can cause wounds in the plant that provide an entry point for the bacteria to get into the plant.
Brown spot is characterized by leaf lesions that are typically
circular, brown or necrotic, and may
be surrounded by a yellow or bright yellow halo. These lesions may fall out of the leaf, leaving a shot
hole appearance on the leaf. Leaf lesions are usually not water-soaked like many bacterial diseases,
but pod lesions from Brown spot may appear water-soaked initially. Pod lesions may also turn brown
or reddish and appear sunken, sometimes causing pods to twist or bend at the point of the lesion.
Bacterial blight in beans can be seed transmitted so using certified
seed will reduce disease potential
in the field. Applications of a bactericidal spray containing fixed copper may help to control spread of
the disease, however they are more of a protectant and have not proven very effective in North Dakota.
The only product labeled for bacterial blight on dry beans is Kocide 2000. The label suggests a protectant
application when plants are about six inches high and re-application every 7-14 days while disease pressure
remains high. However, if the weather should dry out and if the temperatures warm up, Brown spot should
be effectively shut down and not continue to be a problem. There is still time for plants to recover but losses
can be fairly severe with high infection levels.