ISSUE 7 June 15, 2000
MONITORING FOR DRY BEAN RUST
Dry bean rust often begins to show up around the end of June or
early July. Monitoring for rust should begin soon, with emphasis on susceptible varieties.
All pinks and most small reds are susceptible. Some light red kidneys also are
susceptible. Most older pintos are susceptible, but many new varieties are resistant to
rust races currently present in North Dakota. Rust resistant pintos include Apache, Burke,
Buster, Chase, Elizabeth, Focus, Frontier, Kodiak, Maverick, Montrose, Remington, UI-320
and Winchester. These varieties have been released within the past few years, and
represent an exciting
advance in pinto variety improvement.
Rust races are constantly changing and the number of races present in North Dakota has increased in recent years. This underscores the need to monitor not only fields of susceptible varieties, but all varieties. Susceptible varieties should be sprayed with a rust fungicide once there are 2-3 pustules per leaf and the pods are not yet striping. If there are one or two "hot spots" in a field, it should be sprayed. If rust is present in other fields in an area and the crop is in the flat pod stage or earlier, it should be sprayed. If rust begins to build up in a variety that is supposed to be resistant, a fungicide might be required. I would also recommend sampling rust in that field and submitting it for race determination (see next article for details).
Bravo and maneb are registered for 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, provide 14 days of protection and can kill infections up to four days old.
RUST SAMPLING IN DRY BEANS
Pat Gross at NDSU has been actively identifying races of dry bean rust. The number of races present in North Dakota has been increasing and it is essential to determine what races are present. This could provide an early warning system if races develop that can attack currently resistant varieties. I would encourage crop consultants, agribusiness personnel and growers to collect samples of rust and submit them for identification.
Collect rust samples, place them loosely in a paper envelope and allow them to air dry. Then mail them to:
Department of Plant Pathology
North Dakota State University
Fargo, ND 58105
Please include information on the variety and class grown, where collected, and name and telephone number (or e-mail address) of the person collecting the sample.
Extension Plant Pathologist
SMALL GRAIN DISEASE SURVEY UPDATE
Highlights: Wheat leaf rust was detected in spring wheat during the past week. Aphid counts are increasing in some areas. Grasshopper numbers are increasing slightly in the southwest and northwest. Tan spot is the most common wheat disease now. Specifics from each area of the state follow:
South Central and Central counties: Additional detections of wheat leaf rust were made since the last Crop and Pest Report. Jerry Schneider found trace amounts of leaf rust in hard red spring wheat fields in LaMoure, Barnes and Wells counties the week of June 5-9. We dont know the variety identity of these spring wheat fields, but remember that 2375 and AcBarrie were among the hardest hit by leaf rust in 1999.
Jerry found tan spot to be the most common disease detected in spring wheats in the south central and central counties, but levels are still very low and on the bottom leaves. He found only two fields with aphid infestations, with 2% of the tillers with 1 or more aphids.
Southwest counties: Amy Dukart found tan spot to be the most common wheat disease in most fields, but generally confined to the bottom leaves. Tan spot is most severe where wheat was planted into wheat stubble. She also detected WSMV in a field in Slope county and BYDV in a field in Bowman county. She is detecting increased grasshopper activity, plus some leafhopper and aphid activity in her area, as well. Leafhopper counts were around 1-2 leaf hoppers per square foot in field margins. Aphid numbers ranged from 0-10% of tillers in a field showing at least one aphid.
Northeast and Southeast: Matthew Gregoire found tan spot to be the most common disease observed in wheat this past week, in counties from Richland and Sargent northward to Pembina county. Percent tillers infected and severities remain at low levels in most fields, although in winter wheat infections were common on middle leaves and a few were visible on the flag leaf, as well. Low levels of net blotch or spot blotch also were found in some barley fields.
Aphid detections increased over the past week. Several spring wheat fields in Pembina, county had 20% of the tillers showing at least one grain aphid, and 0-20% of tillers with at least one aphid were observed in Ransom, Cass, Sargent and Griggs counties. Matthew also picked up a few bird cherry oat aphids in southeast counties.
Mike Peel, Extension Agronomist from Fargo, found trace amounts of leaf rust in his winter wheat plots in Ransom county.
Northcentral and Northwest counties: Wheat crops in the northcentral and northwest region are in the 1/1/2 leaf stage to tillering stage. In Bottineau, Renville and Rolette counties, Holly Semler found tan spot incidence to range from 14-21% of plants infected and severities were 2-5% on lower leaves. She also found some Septoria spotting on these young plants. No insect problems were found in these counties.
Laura Neal detected tan spot and root rot in wheat in Ward and McLean counties. Tan spot severities were 15% on mid-leaves in one field. She also detected 2-3 grasshoppers per square yard in the field margins of two fields in McLean Co. In McKenzie county, Allison Marsland found wheat in the early tillering stages to have tan spot, with severities on bottom leaves ranging from 5-9%. She also found 1-3 grasshoppers/sq. yard in field margins in McKenzie Co.
DISEASE FORECASTING SYSTEM
As described in last weeks Crop and Pest Report, the wheat disease forecasting system provided by Dr. Len Francl, NDSU Plant Pathologist, now includes information about favorable infection periods for leaf rust. For example, according to the disease forecasting web site:
Favorable infection periods for leaf rust did occur at several NDAWN sites on June 11. As instructions for the disease forecasting model indicate, "in order for the forecasting model to work as intended, the disease-causing agent must be present. Thus, each field first must be scouted for the presence of leaf diseases". When disease is present and multiple favorable infection periods occur, as indicated by the disease forecasting model, then a fungicide may be warranted. The forecasting model also tells if favorable infection periods occurred for tan spot and Septoria (Stagonospora) blotch.
Extension Plant Pathologist
ROOT ROT PROBLEMS OF SUGARBEET
Sugarbeet plants that are in warm, wet soils may be affected by
Aphanomyces root rot. Aphanomyces is most common in southern Minnesota and the Southern
areas of the Red River Valley. This disease can be devastating in the seedling stage, and
can also cause serious root rot later in the season. Infected plants turn a sickly yellow
green and tend to wilt in the afternoons of
hot and sunny days. Some plants may die; those that survive usually have stunted and feeder roots and are unproductive.
Aphanomyces can be managed by using tolerant varieties that are not as severely affected as susceptible varieties; using Tachigaren pelleted seeds; planting early; keeping the soil dry by cultivation and enhanced drainage; effective weed control; and avoid spreading of contaminated soil from infected fields to disease free fields.
American Crystal shareholders can have their soil
indexed for this disease. Fortunately, most growers planted early and
most sugarbeet fields were not warm and wet during the sugarbeet seedling stage. As such,
we have not had an acute phase of Aphanomyces. However, now that the soils are warming up,
and with the blessing of some showers, we need to ensure there is
proper field drainage to protect plants from the chronic stage of Aphanomyces.
Most of our sugarbeet fields in North Dakota (except for a few dry areas in Grafton and Drayton) and Minnesota are looking good to excellent. The early indications are that we are going to have another good sugarbeet crop, once we take care of Cercospora leaf spot!
Extension Sugarbeet Specialist
PLANT PEST DIAGNOSTIC LAB
Problems recorded in the lab include: Ash (anthracnose, ash male flower gall mite, ash bark beetles, lecanium scale); flax (probable frost injury); sugarbeet (Rhizoctonia and Pythium root rot, probable, unidentified nutrient deficiency); honey locust (honey locust pod gall midge); elm (leaf scorch); soybean (Phytophthora, Rhizoctonia, Pythium root rot); alfalfa (spring black stem, alfalfa stem weevil, alfalfa blotch leafminer); spruce (dieback due to wet soils); Roundup injury on corn, wheat, and barley; and growth regulator herbicide injury on sugarbeet, basswood, linden, ash, apple, and Austree.