NDSU Crop and Pest Report
Plant Pathology


ISSUE 12   July 22, 2004

NDSU IPM CROP SURVEY, 7/12 TO 7/16 UPDATE

During the week of July 12-16, NDSU IPM field scouts surveyed wheat fields in flowering to soft dough stage of kernel development (see figure).

They also surveyed barley, primarily in the post-heading to early dough stages of development.

The NDSU field scouts found increasing levels of wheat leaf rust in their surveys. Nikki Zahradka, field scout in the northeast, found that incidences of plants infected with leaf rust were particularly high in Nelson county (see figure).

Severity of wheat leaf rust was primarily in the 1-15% range on the flag leaf.

Septoria and tan spot severity levels in wheat were generally below 15% severity on the flag leaf, except in the south central counties, where higher severities were observed. Leaf spot diseases remained at low levels in barley.

Fusarium head blight (scab) was observed

in 6 of the 61 wheat fields surveyed last week that were in milk to early dough stage of kernel development. These observations were made by NDSU scout Clara Presser in the south central area, and by Tammy Link in the south east. Severity of scab in wheat in these observations was low, ranging from 0.1 to 5%. In barley, two of the 38 post-heading fields scouted showed symptoms of scab, with severity less than 1%. One field was in the south central area and one in the north east.

On July 19, I observed low incidences (<1%) and severities of scab in susceptible cultivars of wheat in the Grand Forks county plots, and very low incidences of scab also were observed in the barley cultivars at this site. The NDSU Small Grains Disease Forecasting web site indicates continued high potential for scab infection and leaf diseases in most northern North Dakota counties where wheat or barley may still be in vulnerable growth stages.

Marcia McMullen
Extension Plant Pathologist
mmcmulle@ndsuext.nodak.edu

 

FUNGICIDES FOR DRY BEAN

Application of foliar fungicides to dry bean fields are sometimes needed to protect against three main diseases in North Dakota, white mold, bean rust, and anthracnose.

White mold. Three fungicides are registered on dry bean for white mold control. Topsin M (and generic formulations) can be applied once at 1.5 - 2 lb/A or as a split-application at 1 - 1.5 lb/A twice. If one application is made, the application should be made when 70 to 100% of the plants have at least one open blossom. If split-applications are made, the first application should be made when 10 to 30% of the plants have at least one open blossom, and the second application should be made 4 to 7 days later. Endura is a new fungicide available this year that has a use rate of 8 to 11 oz/A on dry bean. Endura should be applied at the beginning of bloom. A second application can be made at full bloom, if needed. Rovral can be applied to dry bean at 1.5 to 2 pt/A. Rovral should be applied at first bloom to when 10% of the plants have one open bloom. A second application can be made 5 to 7 days later or up to peak bloom, if needed.

Bean rust. Several fungicides are available that can provide protection against bean rust. In general, bean rust fungicides are only needed on rust-susceptible varieties. All of the bean rust fungicides should be applied as a protectant (before disease is present). Quadris and Amistar are stobilurin fungicides that contain the same active ingredient (azoxystrobin). Quadris has a use rate of 6.2 fl oz/A for rust control, and Amistar has a use rate of 2 oz/A for rust control. Headline is another strobilurin fungicide that contains the active ingredient pyraclostrobin. Headline has a use rate of 5.5 to 8 fl oz/A. Endura is also labelled for bean rust control, and has a use rate of 8 to 11 oz/A. Bravo and several other chlorothalonil products can be used for protection against rust. The use rates of the chlorothalonil products vary. Several products that contain the active ingredient maneb are also available for bean rust protection.

Anthracnose. Use of certified, disease-free seed will most likely prevent anthracnose outbreaks; however, foliar fungicides are available if needed. Quadris and Amistar have use rates of 6.2 to 15.4 fl oz/A and 2 to 5 oz/A, respectively for anthracnose control. Headline has a use rate of 5.5 to 8 fl oz/A. Topsin M (and generic formulations), Bravo (and other chlorothalonil products), and maneb products all can provide protection against anthracnose as well.

Carl Bradley
Extension Plant Pathologist
carl.bradley@ndsu.nodak.edu

 

FUSARIUM YELLOWS IN SUGARBEET

Fusarium yellows have been reported in some sugarbeet fields, particularly in the Moorhead factory district. Some varieties are more susceptible to fusarium yellows than others.

Fusarium yellows first appears on older leaves as yellowing between the larger veins. Later, younger leaves also become chlorotic, and the older yellow leaves become necrotic, die, but remain attached to the plant as they collapse around the crown. The outer surface of infected plants appear healthy. However, a cross-section of the root shows brown vascular discoloration that leads to rotting. Roots of infected plants have high respiration rates and do not store well in piles.

 

MANAGING CERCOSPORA LEAF SPOT

Cercospora leaf spot has been identified from leaf samples collected in the Moorhead factory district by Mr. John Prigge.

Cercospora leafspot develops rapidly in humid, warm and rainy weather. The Cercospora spores are produced at temperatures of 68-79E F and relative humidity (RH) of 90-100 %. Spore release is effected by rain and dew. Optimal spore germination and infection occurs when the temperature is 75-77° F and the RH is 100 % for at least 8 hours. Day temperature of 80-90° F and night temperatures above 60° F favor disease development. This means that current weather conditions are very favorable for disease development. As such, growers should follow the current fungicide recommendations to control Cercospora leaf spot.

Fields that have closed canopy and are close to shelterbelts or are along the river, or next to last year’s fields that had moderate to severe infection should be the first to receive fungicide applications. Usually, once Cercospora leaf spot is identified in a piling area, growers should be applying fungicides to protect their crop.

Growers have a good selection of fungicides for Cercospora leaf spot control. These fungicides include Eminent, Headline, Gem, Triphenyltin hydroxide (TPTH), Quadris, Topsin, and Mancozeb. Fungicides should be used at the recommended labeled rates, and effective fungicides from different chemical classes should be alternated.

Is it economical to apply fungicides for Cercospora leaf spot control? YOU BET! Studies conducted last year at Crookston Research and Outreach Center by Dr. Larry Smith, University of Minnesota, showed that Eminent followed by a mixture of Topsin and TPTH, then Headline resulted in returns of $1,092/acre; Eminent followed by TPTH then Headline resulted in returns of $1,092/acre; whereas the untreated check resulted in returns of $671/acre. It is economical and wise to use fungicides for controlling Cercospora leaf spot.

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


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