NDSU Crop and Pest Report
Plant Pathology


ISSUE 9  June 27, 2002

 

DRY BEAN RUST & SECTION 18 FOR TILT

Dry bean rust, caused by the fungus Uromyces appendiculatus, can be a serious disease on susceptible dry bean varieties in favorable weather conditions. The disease can easily be detected by checking leaves for the presence of pustules containing rusty_colored masses of spores (See photo). The use of a resistant variety, such as Maverick, is a very good way to manage the disease. However, with the shortage of dry bean seed this spring, some growers may be planting susceptible varieties that they are not familiar with. Most pinto and navy bean varieties are moderately resistant (MR) to resistant (R); however, there are a few that range from susceptible (S) to moderately susceptible (MS). All cranberry, black, dark red kidney, and white kidney bean varieties that were tested by NDSU in 2001 are MR to R, but most of the small red, pink, and light red kidney beans are S. Below is a condensed list of varieties that rated as being S to MS. This information was obtained from the North Dakota Dry Bean Performance Testing 2001 Report (A_654) available from the NDSU Extension Service.

Varieties rated as S to MS for rust:

Class Variety
Pinto AC Pintoba
Arapaho
Aztec
Fargo
GTS 900
Hatton
Othello
Pintium
Topaz
Navy Voyager
Small Red AC Earl's Red
Garnet
NW559
NW63
UI-239
UI-259
Pink Alberta Pink
Flamingo
Rosalee
UI-537
Viva
Lt. Red Kidney California Early
Sacramento
Great Northern UI 59
US 1140

Rust pustles on dry bean leaves

Rust pustles on dry bean leaves

A section 18 emergency exemption has been granted for the use of Tilt fungicide (propiconazole, Syngenta) on dry beans for control of rust. It may be applied up to 3 times at 4 fl. oz/acre each time. No more than 12 fl. oz/acre can be applied in a growing season. Application should begin at the first appearance of disease and continue on a 14-day schedule. Susceptible varieties should be monitored very closely for the presence of the disease.

Carl Bradley
Extension Plant Pathologist

cbradley@ndsuext.nodak.edu

 

WHEAT LEAF RUST COMMON ACROSS STATE

Wheat leaf rust is being observed in most locations of the state, both on spring wheat and winter wheat. Leaf rust was observed by IPM field scouts in the southwest, southeast and south central portions of the state this week; on 4-5 leaf ‘Ingot’ spring wheat in Wells County, by Greg Endres, Extension Area Agronomist at Carrington; on winter wheat variety plots at Minot, by Kent McKay, Extension Area Agronomist at Minot; and on most spring wheat varieties in plots near Devils Lake and on the third leaf of 6 ˝ leaf ‘Ingot’ spring wheat at Tulna, by Terry Gregoire, Extension Area Agronomist at Devils Lake. Additional reports of leaf rust have come in from consultants and a Manitoba agronomist. The level of infection is still low in these observations, but the disease is not hard to find.

Durum cultivars have a slow rusting reaction and generally are not severely impacted by leaf rust. Late seeded crops of susceptible spring wheat varieties will be at most risk of potential damage from leaf rust. Response of spring wheat varieties to the prevalent races of leaf rust in recent years is given in the following table:

Reactions of Some Common Spring Wheat Cultivars
to Prevalent Leaf Rust Races

Susceptible or Moderately Suscep.

Resistant or Moderately Resistant

Grandin

Argent

Alsen

Reeder

2375

Dandy

Amidon

Ivan

AcBarrie

Walworth

Kulm

Aurora

Ingot

McVey

Hamer

Mercury

2398

Ember

Trenton

Intrepid

Russ

Parshall

Verde

Norpro

Forge

Reeder

Keene

Conan

HJ98

Hagar

Oxen

Keystone

Ernest

Butte86

McKenzie

Knudsen

Scholar

Nora

Prodigy

Stoa

 

FAVORABLE CONDITIONS FOR SMALL GRAIN DISEASES

Additional heavy rains and/or frequent thunder-showers have made environmental conditions favorable for infection of leaf and head diseases of wheat. Field scouts, extension agronomists, and extension county agents report tan spot infections are common in many wheat fields. Conditions are also favorable for infection by the Fusarium head blight (scab) fungus in some areas.

On June 25, the NDSU Small Grain Disease Forecasting web page indicated that a high risk for infection by the scab fungus existed in portions of Cass, Walsh and Pembina counties in North Dakota and in neighboring counties in MN, (Figure below; dark (red) areas on eastern edge of ND and into MN. This risk map will change on a daily basis, depending on temperatures and humidities.

Risk map

Above map for June 25=6 found at flowering growth stage information at any NDAWN site AND at the link to Model 1 at:

http://www.ag.ndsu.nodak.edu/cropdisease/cropdisease.htm

Also, recent samplings for spores of the Fusarium head blight fungus have detected high to extremely high spore counts in the past week at the NDAWN sites of Prosper, ND and Sabin, MN, sites within the high risk areas indicated above. Many growers in these areas also have crops in the heading to flowering stage. Growers in these areas need to assess their crop condition, yield potential, growth stage, and susceptibility of their variety, and then make a fungicide decision.

Risks of scab will change as humidity and temperatures change. High temperatures of 90+ will reduce the risk. Also, the areas of risk indicated on the map are general, based on NDAWN site data, and individual fields within in any area may have greater or lesser risk, depending on local conditions.

Marcia McMullen
Extension Plant Pathologist

 

QUADRIS MIXED WITH HERBICIDES IS PHYTOTOXIC TO SUGARBEET

Rhizoctonia solani causes damping-off of seedlings, root rot and crown rot. This fungus infects seedlings and plants in dry and wet conditions and is active at temperatures of 68-86EF. Rhizoctonia crown rot is favored when infected soils is thrown into crown of plants during cultivation.

Quadris may be used as a banded application before infection occurs to control Rhizoctonia. However, Quadris should not be applied in a mixture with the micro-rates of herbicides since this would result in severe burning of the sugarbeet leaves. Quadris should be applied alone.

Mohamed Khan
Extension Sugarbeet Specialist
mkhan@ndsuext.nodak.edu

 

CERCOSPORA LEAF SPOT IN SUGARBEET

Cercospora leaf spot is the most damaging foliar disease of sugarbeet resulting in lower tonnage, reduced sucrose content, poor storageability, and increased impurities resulting in higher processing costs. The fungus Cercospora beticola causes Cercospora leaf spot. The most common source of the Cercospora fungus is infected sugarbeet debris in the field. The fungus is spread mainly by wind and water. Cercospora leaf spot develops rapidly in warm, humid and rainy weather. The Cercospora spores are produced at temperatures of 68-79E F and relative humidities (RH) of 90-100 %. Spore release is effected by rain and dew. Optimal spore germination and infection occurs when the temperature is 75-77E F and the RH is 100 % for at least 8 hours. Day temperatures of 80-90E F and night temperatures above 60E F favor disease development. Leaf spot symptoms may occur about 5-7 days after infection. Cercospora infection produces circular spots about 1/8 inch in diameter with ash gray centers and dark brown or reddish-purple borders. Individual spots may coalesce and kill entire leaves, particularly on susceptible varieties. In humid conditions, the spots may become gray and velvety with the production of spores. These spores further spread the disease, especially within fields, resulting in many infection cycles during the growing season.

As such, it is important to have early control of Cercospora leaf spot. An integrated approach is recommended for controlling Cercospora leaf spot. This includes cultural practices such as burying infected tops by tillage, planting approved varieties in fields with a minimum rotation interval of three years, selecting fields as far away as possible from the previous year’s infected field, and the timely and proper use of recommended fungicides. Eminent 125 SL (tetraconazole), which was very effective at controlling Cercospora leaf spot in field trials, was approved (Section 18 label) for use on sugarbeet at 13 fluid ounces product per acre at a recommended 14-day interval in alternation with a fungicide from a different class. Alternate Eminent 125 SL with other registered compounds such as triphenyl tin hydroxide (TPTH), Gem, and mixtures of Topsin M with TPTH or Penncozeb (Mancozeb) in order to delay the development of resistance to these products.

Points to note:

Mohamed Khan
Extension Sugarbeet Specialist
mkhan@ndsuext.nodak.edu


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