ISSUE 12 July 23, 1998
DRY BEAN RUST UPDATE
Last week Cheryl Ruby reported that rust had been confirmed on dry beans. John Jones submitted a confirmation sample from Aneta in southeastern Nelson county. This week Brad Gaudry at Minto Flying Service reported that rust is common in the Minto area in eastern Walsh County, with it most prevalent on pink beans. This is not surprising, since currently available pink cultivars are all susceptible. Rust was especially common near shelter belts. In addition, Clark Helland has been seeing rust near Lakota in northwestern Nelson county and near Fordville in southcentral Walsh County.
Monitoring. All dry bean fields should be monitored for rust, with special emphasis along shelter belts, where the crops stays wet longer, as well as next to last years bean fields. Be sure to check in the canopy, as this is where the first rust may occur. Particular care should be taken to monitor cultivars with known rust susceptibility, but be sure to monitor all cultivars. This is important since there are now about 10 races of bean rust in North Dakota, and a new race might arise that could overcome currently resistant varieties. Monitor at least once a week and more often if recent night temperatures have been in the 60s and there has been at least 8 hours of dew.
Some of the newer dry bean cultivars, including some new pinto cultivars, have good resistance to current rust races. Many navy cultivars have good resistance to current races, as do most cranberry, black and dark red kidney cultivars. Cultivar rust reactions are given in the back of NDSU Extension Circular A-654, North Dakota Dry Bean Performance Testing 1997. If alarming levels of rust appear on any cultivars listed as rust resistant please contact Art Lamey (tel. 701-231-7056; FAX 701-231-7851, e-mail email@example.com) and collect samples so that Dr. Venette can make a race determination. Collect leaf samples, place them loosely in a paper envelope and allow the leaves to dry in a cool dry place. Then mail the envelope to Art Lamey, Walster Hall, Room 306, NDSU, Fargo, ND 58105-5012. Please enclose a note with information on the variety and where collected, and include your name and telephone number.
Fungicides. A fungicide is needed if there is an average of two pustules per leaf and the first pods still have not developed to full size. In the case of pinto cultivars, once the lower pods begin striping, no fungicide is needed. If a few hot spots develop with moderate to heavy rust, apply a fungicide immediately even if there is a field average of fewer than 2 pustules per leaf. Prompt action is needed to prevent rust from spreading from these hot spots.
Chlorothalonil (Bravo, Echo, Evade, Terranil) and maneb are protectant fungicides that provide good rust control if applied when there are only a few infections in the field. Tilt is a systemic fungicide; it has up to 4 days of post infection activity, but will not stop infections that have been present for more than 4 days. Thus, Tilt is most effective when used as a protectant. Also, using Tilt as a protectant reduces the danger that the rust fungus may develop resistance to Tilt. Recommended spray intervals are: maneb, 5-7 days; chlorothalonil, 7-10 days; Tilt 14 days. Regardless of the fungicide used, it is important to apply early before rust populations are high. Once populations are high, control is very difficult.
Chlorothalonil cannot be applied within 14 days of harvest, Tilt within 28 days and maneb within 30 days. Since it is not economic to apply after lower pods of pintos begin striping, these harvest restrictions are consistent with economic control practices.
Timely action is important. If no rust has been found in an area, it is all right to wait until rust has been detected before spraying. However, if rust is present and becoming severe in the area, it is time to spray all susceptible fields in the area, even those in which rust has not been detected. Failure to do so may result in a field being bombarded with spores from a nearby field; in such a case first detection of rust may be too late for effective control.
Extension Plant Pathologist
SCAB (FUSARIUM HEAD BLIGHT) UPDATE
Spring wheat/durum: Scab levels have increased this past week. Infections are now readily apparent in recently flowered hard red spring wheats and durums in Bottineau and Ward counties, as observed by field scout Shane Crawford, working out of the Minot REC. Some fields in this area are showing very high incidences, but still relatively low severities.
Surveys of rapidly maturing crops in Cass, Sargent, Ransom, Richland, McIntosh, Dickey, Foster, and LaMoure counties indicate that field severities of scab averaged between 3-5%, with one field in Dickey county having a field severity of 8%.
As field scouts Sarah Gehler and Carrie Buttke moved northward, higher severities of scab were detected, with field severities ranging from 5-18% in Griggs, Benson, Ramsey, Walsh, Traill, Pembina, and Cavalier counties. The most severe infections were seen in the NE area, and in these counties, highest average incidence recorded was 50%, and highest head severity was 37%. These fields may have additional development of scab, until hard dough stage is reached. Fields in some of these counties were already being swathed on July 21.
Barley: Recent surveys of barley in Cass and Benson counties by Jeremy Pederson, Extension barley technician, indicated that incidences of scab in Cass averaged about 40% and head severities ranged between 5-8%, while in Benson, incidences averaged 30%and head severities from 2-5%, giving field severities from less than 1% to 3.2%. Thus, yield losses in these fields will not be high, but the levels of infection will very likely be high enough to increase vomitoxin (DON) above the 0.5 ppm level required by some malting and brewing companies.
In NE counties, barley scab levels are higher, with incidences from 60-75%, and head severities from 4 to 14%, giving field severities up to 10%. Jeremy will survey barley field in NC counties next week.
Fungicides: Preliminary evaluations of fungicide plots over the past week have indicated reductions in scab at levels similar to or better than last year, but final evaluations and summaries of data will not be possible until after harvest. The systemic fungicides should have activity in the plant for 2 to 3 weeks; following this 14-21 day period, prolonged high dew points and high humidities may have allowed some additional development of scab and leaf diseases.
Wheat leaf rust is abundant in most spring wheat fields surveyed in counties in the SE, SC, EC, C, and NE districts. As we move further westward or to fields near the Red River, then leaf rust is much less abundant. Severities of wheat leaf rust range from 0-80% in surveyed fields. In an irrigated spring wheat variety trial at Carrington, AC Barrie had close to 100% severity of leaf rust on the flag leaf. The good news is that one of the replicates in this trial had been sprayed with a systemic fungicide at flowering, and the flag leaves of AC Barrie were still relatively green where the fungicide had been sprayed. Although AC Barrie has good tolerance to scab, the leaf rust potential on this variety indicates the need for a fungicide if it is to be grown in counties which appear to be along the "rust pathway".
A trace amount of barley leaf rust has been seen occasionally in barley fields in Benson and Cavalier counties.
LEAF SPOT DISEASES
Tan spot and Septoria species are abundant on flag leaves of spring wheats now. Severities on the flag leaves range from less than 1% to almost 100%, depending on location, variety, and crop maturity. A combination of fungal leaf spots and wheat leaf rust are going to cause some economic yield losses and lower test weights in many fields, especially if they were not sprayed with fungicides.
In barley, net blotch and Septoria blotch are the most common leaf diseases being observed, with a range of severities, depending on crop maturity and location. Leaf diseases observed in barley overall have not been as severe as seen in wheats. Use of fungicides in some barley fields has significantly reduced leaf disease severities.
The NDSU Extension Circular on Ergot has recently been revised by Charles Stoltenow, NDSU Extension Veterinarian, and Marcia McMullen, NDSU Extension Plant Pathologist. The Ergot Circular is available through county extension offices or through the NDSU Agriculture Distribution Center in Morrill Hall, NDSU. The circular # is PP-551 and the publication date is June, 1998.
Ergot infections recently were observed in Cass Co. by Bob Stack, NDSU Plant Pathologist, in barley and in brome grass. Since a lot of hay is being cut now, producers should be checking for the black ergot sclerotia in the grass heads prior to cutting. Ergot can cause significant problems in animals fed ergoty grain or hay.
Extension Plant Pathologist
PLANT DIAGNOSTIC LAB REPORT
Weve seen some sunflower samples infected with Downey mildew this past week. This disease is caused by a water mold fungus called Plasmopora halstedii. Yield losses due to this disease are dependent upon weather conditions favorable to disease development. Seed borne infection is rare since seed from infected plants is often not viable. Infection can occur as a damping off (death of preemerging seedlings) or as a seedling blight (death of postemerged seedlings). Systemic infections of downey mildew on sunflowers occur as the result of an infection of the roots. These infected plants are stunted and leaves may be puckered and chlorotic. If weather conditions are favorable for disease development, cool and wet, sporulation can occur usually on the underside of the leaves. This will appear as a white fuzzy growth that is the production of a dense layer of asexual spores of the fungus. Rainsplash and wind can spread these spores within a field causing secondary infections. Depending on the race of the fungus and the sunflower cultivar, a more localized infection may occur. These secondary infections can continue to occur as long as the climate is favorable for disease development, but studies show that they do not decrease yields or produce an economic loss. Primary, root infection is most injurious at the seedling stage but may occur later in the growing season, resulting in a taproot gall and possible drought intolerance as the only symptom.
Studies show that there are many races of P. halstedii capable of infecting sunflower. Cultivars of sunflower exhibit different levels resistance and susceptibility to specific races of the fungus. Currently, the fungicide metalaxyl as a seed treatment has given good control of the disease and economic losses are minimal. The past 2 years of fairly wet soil conditions in some of the sunflower growing regions and what appears to be a higher incidence of disease suggest the possibility of resistance within the population of downey mildew fungi to the metalaxy seed treatment. The USDA sunflower pathologist at NDSU is currently conducting studies to determine if the incidence of disease is really an issue of fungicide resistance or more likely the result of environmental conditions. More information will be available at the end of this growing season.
The number of tree samples with symptoms suggestive of canker diseases is increasing. There are several species of fungi that can cause canker diseases on trees and these are often listed as the ultimate cause of death of a tree. Because of the general hardiness and sheer size of most trees, death occurs over a long period of time and is usually the result of a number of factors, such as disease(s), insects, and environmental conditions. The severe winter of a two years ago, a mild winter last year and the extremes, both flooding and drought, experienced around the state have contributed to increased stress which predisposes a tree to canker disease infection. The symptom of a canker disease is wilting, yellowing or fairly immediate browning of branches or limbs within a tree canopy. At the end of the cankered branch that is yellowing or browning, the stem will be discolored and or sunken, where the tissue is dead. Managing these disease is generally universal for all canker fungi, remove the dead material. Unlike pruning out fireblighted plant tissue, it is not necessary to disinfect cutting tools between cuts. Fungi are not transmitted in the same manner as the bacterium that causes fireblight. It is necessary to remove the infected tissue only with a canker disease.