ISSUE 9 JULY 1, 1999
SMALL GRAIN DISEASE SURVEY UPDATE
The following information has been provided by the crop surveyors since the last issue of the Crop and Pest Report:
In the NC and NW regions, Brittany Sund has primarily found tan spot infections on the lower and mid-leaves of the crops. Most of the spring wheat crops in this area are still in the early tillering stage. A winter wheat field in Bottineau county had 17% of the flag leaf area infected with tan spot. Leaf rust has not been detected in this area of the state.
Tan spot also is the most common disease of wheat found by Amy Dukart in the SW and WC area of the state. Incidence levels are often high, but severities are still relatively low. For fields surveyed past the boot stage, some infections are now appearing on the flag leaf. Amy also has seen wheat leaf rust at very low levels in Hettinger, Stark, and Golden Valley counties. Spot blotch also has been observed in barley in Stark and Dunn counties. Two wheat fields in McKenzie county had 10% of the tillers showing loose smut infection.
In the Central and SC districts, Jerry Schneider has found tan spot to be the most commonly observed disease in wheat, but most levels remain low and infections are confined to the bottom or mid-leaves, except for one winter wheat field. Wheat leaf rust was commonly observed also, but severity levels remain low. Jerry also observed spot blotch infections in barley.
In the most eastern counties, Jerry Ries has commonly found tan
spot and leaf rust in wheat fields, but infections have been primarily confined
to middle and lower leaves, except in winter wheat. Growth stage of the crops in Cavalier
and Ramsey county were primarily in the tillering stage. Wheat leaf rust was observed in
Ramsey county on spring wheat in the two-five leaf stage. In Cass county, some fields
still have very high aphid populations. Loose smut in wheat is common and in
some fields, percent tillers infected is ranging from 2-3%.
No reports of Fusarium head blight (scab) have come in from surveyors or others yet. Symptoms of this disease become evident about a week to 10 days after flowering, if infection has occurred.
The latest wheat disease forecasting information provided on the
Internet by Dr. Len Francl, NDSU Dept. of Plant Pathology, indicates that favorable
infection periods for tan spot have occurred at most sites being monitored. Some
favorable infections periods have occurred for Septoria infections, as well, but
not at all sites. Detection of Fusarium spores has been minimal. June 28 was the
most recent date for checking of the spore samplers, and only two sites were positive for
detection, plus spore numbers were low. The two sites were in Minnesota, at Warren and
Stephen. This fungus requires wet conditions for the fruiting structures to mature and
develop spores, and this takes about a week for the process to complete once conditions
are favorable. Perhaps we will see more detections in the coming week, perhaps not.
Repeated heavy rain showers could be beating the spores back to the ground.
A number of inquiries about fungicide spraying have come in this past week to Area and County Extension Agents and to Dr. Art Lamey. I unfortunately was unavailable to field these calls, but greatly appreciate my colleagues responses. Wheat leaf rust is a concern, especially in more susceptible varieties, and there is always the concern about scab. Disease detection in advanced wheat crops has been common, but in most cases the diseases have not been severe. But many of the early seeded fields have very high yield potential and so interest in fungicide protection has been high, even at the low wheat prices.
In 1998, producers who sprayed with fungicides were very happy with the results, for the most part, and many realized yield responses of 20% or more. They provided control of their leaf diseases and the head scab. So far this year, the diseases have not progressed rapidly, even though they were detected early. The earliest seeded fields MAY not develop the severe symptoms we saw in some fields last year, but there is still a ways to go before grain fill is completed. With recent rains, there is the potential for inoculum to build up and be a threat, especially to later seeded crops.
We have better information on fungicides and application procedures, and better information on disease development this year. These tools are helping us work toward the goal of better decision making. Additional information gathered this year on the disease models and the fungicide research will bring us further towards this goal.
Extension Plant Pathologist
CERCOSPORA REPORTED ON SUGARBEET
Cercospora leafspot was observed last week on sugarbeet in Southern Minnesota, the Minn Dak district and the Moorhead factory district. This is about the same time as in 1998, and is only the second time that I have a record of Cercospora being found in June. In many years Cercospora does not appear until July 5-15. It looks like this will be another long spraying season.
Fungicide spraying is under way throughout most of the three factory districts where Cercospora has been found and spraying is beginning farther north, as well. Rain at the beginning of this week prevented ground spraying in some areas, raising questions whether extensive infection might occur before the crop was sprayed. Very little infection occurs below 60ºF, and the leaves must be wet for infection to occur. If extended periods (15+ hours) of wet foliage occur and the temperatures during this period are in the mid to high 60s, then infection potential has been high.
Eminent. Eminent use on sugarbeet was extensively
discussed in Crop and Pest Report No. 6. Eminent has up to 4 days of
"kickback" or post-infection activity. In other words, it can kill Cercospora up
to 4 days after infection has started. If significant infection periods have occurred less
than 4 days before a fungicide is applied, the use of Eminent will help to stop those
infections. Having said this, I must point out that use of Eminent to stop infections,
rather than prevent them, is contrary to resistance management strategies. Deliberate
delay in applications also can result in failure. It is very important that we use Eminent
judiciously, thus deriving maximum benefit from it.
Dr. Al Cattanach, General Agronomist for American Crystal, reported on Southern Minnesota Beet Sugar Company trials conducted by Mark Bredehoeft. Mark sprayed grass herbicides and oil as required with Eminent. The temperature was about 85 ºF when he sprayed. No injury was noted, even with a 2X rate of Eminent. Dr. Al Dexter, NDSU sugarbeet weed specialist, also has Eminent tank mix trials in progress.
Tin fungicides cannot be tank mixed with oils during hot weather as
leaf burn may occur; in some cases the burn may be severe. Mancozeb can be tank mixed with
In Crop and Pest Report No. 8, the potential of sunflower
downy mildew was discussed. Telephone calls since that report have confirmed that downy
mildew is showing up in many parts of the state. Keep in mind that the primary or systemic
infections can be serious if widespread, as most systemically infected plants die or if
they survive, do not produce seed. Secondary infections are favored by wet weather after
the primary infections have occurred. The secondary infections cause little or no yield
SUN SCALD ON BROAD-LEAVED CROPS
Several calls as well as samples have been received of dry beans and soybeans with yellowing between the main veins, or of tissues drying up and dying between the main veins. In some cases leaf margins or leaf tips also have died, and sometimes half or more of the leaf died. Usually these symptoms were observed on the older leaves. Newly emerging leaves looked normal. I have attributed this to a quick shift from cool cloudy conditions to hot and sunny conditions. In many cases wet soils limited root growth, so that the root system was not capable of coping with the stress of a sudden change to hot and sunny weather. Broad-leaved crops under stress run out of water first between the main veins, along the leaf margins and at the leaf tips. New growth should be normal and soon hide the damage to old foliage.
Extension Plant Pathologist
Aside from the steady stream of herbicide injury samples that continue to come into the lab, there are two other problems that seem to be fairly widespread. On crops, Pythium root rot has been found in soybeans, sunflowers, dry beans, sugarbeets, and wheat. The pathogen, Pythium ultimum and other species, is a water mold that requires free moisture to move in the soil. It can cause seedling blight or damping off in most plants. Disease development is favored by cool, wet conditions, which have been prevalent across much of North Dakota this year. Pythium root rot can be very destructive, causing poor emergence and potential yield reductions as well as reducing overall vigor and predisposing plants to other insect and disease problems. Seed treatments can provide some protection from Pythium root rot, but it is not complete protection.
On the horticultural side of things, there have been numerous calls and samples on apple and crabapple trees. Many of the trees show symptoms of, and we have confirmed, Apple scab. Not all the samples, however, are typically symptomatic of scab. It appears that there is more than one disease involved in the wide range of symptoms described. We have not been able to confirm it yet, but I believe the other problem is anthracnose. One of pathogens that causes anthracnose, Colletotrichum gloeosporioiedes, has a very wide host range, including apple and crabapple. Like the anthracnose on ash, anthracnose on apple species affects young, newly developing leaves first, and may affect fruit later. Disease development is favored by cool, wet weather. With the predominantly cool, wet conditions across much of North Dakota for most of the spring and early summer, it is not surprising that there is more of this disease this year. It is really too late to spray for anthracnose, but it is not too late to treat the apple scab (refer to the NDSU Crop and Pest Report, No. 7, pg.13).
Other samples in the Plant Diagnostic Lab: include herbicide injury on wheat, corn, dry beans, soybeans, sugarbeets, and trees; Pythium root rot on sunflower, lentil, dry beans, and soybeans; DED; several plant and insect identifications; Rhizosphaera and Pine needle scale on spruce; iron chlorosis on maple; WSMV and BYDV on wheat.