June 16, 2008

OBSERVATIONS FROM LAST WEEK

Not a lot new to report from Golden Valley County this week. I have had a report of Black Leaf Spot in Alfalfa.

The management of black leaf spot is best obtained by harvesting as early as the budding stage to reduce leaf loss.

For more information please give me a call.

NDSU CROP MANAGEMENT FIELD SCHOOL AT CARRINGTON

As a reminder, a crop management field school will be offered Thursday, June 19, from 9 a.m. to 4:30 p.m. at the

NDSU Carrington Research Extension Center. For further details and preregistration information, contact the

Carrington center at (701) 652-2951 or go to http://www.ag.ndsu.nodak.edu/carringt/. A completed preregistration

form and $50 fee is requested by June 16 ($75 after June 16).

GET READY TO SCOUT FOR CEREAL APHIDS
Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

Cereal aphids have been reported in South Dakota on winter wheat. These aphids will be migrating into North

Dakota soon. The greenbug, English grain aphid and bird cherry oat aphid are the principal species that cause

problems in North Dakota small grains. These aphids transmit the disease barley yellow dwarf virus (yellowing from

the tip of the flag leaf – see photograph). When aphid populations are high, the disease can spread quickly through

small grain fields. At greatest risk are later-planted fields, which attract migrating aphids that are moving from more mature fields.
Descriptions:
Greenbug - pale green with dark stripe down back.
Bird Cherry Oat Aphid - olive green, brownish patch at bases of cornicles.
English Grain Aphid - bright green with long black cornicles.
When to Scout: For wheat, field scouting should begin at stem elongation and continue up to the heading stage.
Thresholds for Small Grain Aphids: English Grain, Bird Cherry Oat, Greenbug
To protect small grains from yield loss due to aphid feeding, three different treatment thresholds are available:
- 85% of stems with at least one aphid present prior to complete heading.
- 12-15 aphids per stem prior to complete heading
- 100 aphid days prior to complete heading (=0.6 bu/acre yield loss)
Barley yellow dwarf virus
If you averaged 10 aphids per stem and had 12 days to reach heading, you would have 120 aphid days (10 aphids x 12 days).

This is above the 100 aphid day threshold and an insecticide should be applied to prevent yield loss. On the other hand,

if you averaged only one aphid per stem and had 12 days to reach heading, you would only have 12 aphids days

(1 aphid x 12 days). Thus, no control action would be necessary.
Susceptible Crop Growth Stage:
Crop growth stage also affects its susceptibility to aphids. Vegetative to boot stages are the most susceptible

stages to aphid feeding and subsequent yield loss. For example, in the 4-6 leaf stage, injury caused by aphids is

stunting, decreased number of kernels per head, and decreased kernel weight. In the boot stage, only kernel size and

kernel weight are affected by aphid feeding (not number of kernels per head). By heading, only kernel weight is affected.

After flowering, small grains are less susceptible and producers are discouraged from spraying.
Natural Controls:
Lady beetles, aphid lions, syrphid fly, and parasitic wasps play a major role in reducing aphid populations. When

natural enemies are present in large numbers, and the crop is well developed, farmers are discouraged from spraying fields.

COOL WEATHER FURTHER DELAYS CORN
DEVELOPMENT
Joel Ransom
Extension Agronomist for Cereal Crops
Joel.ransom@ndsu.edu

That the weather this spring is cool is not news, but now that we are six weeks into the corn growing season the 

magnitude of the lag in corn development is becoming a concern. Based on a May 1st planting date, we are now 

running between 80 and 143 corn growing degree days (GDDs) behind the long term average, depending on the 

region of the state (see following table). Since GDDs typically accumulate at the rate of 13 per day in early
June, this means that we are currently about six to seven calendar days behind normal corn development.
Furthermore, this means that corn is 1.0 to 1.5 leaves behind normal (about 85 GDDs are required for each new leaf 

that develops). It is still early in the season and there is certainly potential for crops to catch up if temperatures 

during the remainder of the season are above normal. Nevertheless, if temperatures remain normal, the current delay 

in crop development will translate into wetter grain at harvest. From research we conducted last year, we found that 

a deficit of 80 GDD at harvest could translate into about 2% more moisture in the grain for an adapted hybrid if fall 

temperatures are normal and harvest is planned for before November 1st.
Accumulated corn growing degree days (AGDDs) for selected locations in North Dakota for the period 1 May to
10 June, departures from normal for the same period, and typical daily GDDs for early June (data from NDAWN

http://ndawn.ndsu.nodak.edu/).

Ascochyta Blight of Chickpea. Ascochyta blight, caused by the fungal pathogen Ascochyta rabiei, is the most significant disease on chickpeas (also called garbonzo beans) in North Dakota. In 2005, the Ascochyta blight pathogen became resistant to the QoI class of fungicides (FRAC group 11, also called strobilurins), which include Headline® and Quadris®. Fungicide resistance to these products reduces management options for the disease in chickpeas. A new extension publication discussing Ascochyta blight of chickpea is now available. Included are numerous pictures and discussions of biology and management techniques. The publication is available online at: www.ag.ndsu.edu/pubs/plantsci/smgrains/pp1362.pdf,and is currently being printed. Printed copies should be available at the time of Pulse Days this summer.

Blackleg of Canola. Blackleg is a serious disease of canola in North Dakota. Recently, new pathogenicity groups (PG’s) have been identified in the state, which may challenge some of the resistance currently used in hybrids in the future. A publication of the same name was originally authored by Dr. Art Lamey in the mid 1990’s. This new publication incorporates some of the original information from Dr. Lamey, and includes new information about PG groups, disease prevalence and management, and numerous new photos of symptoms.  This publication is available at: http://www.ag.ndsu.edu/pubs/plantsci/crops/pp1367.pdf, and is currently in print. Printed copies should be available at Canola Days this summer.

Rust Diseases of Wheat. Three rust diseases have the ability to infect wheat in North Dakota. Leaf rust currently is the most important of the three, but stem rust has been problematic in the past, and stripe rust may appear in cool summers. This publication (PP-1361) is a revision of PP-589 Wheat Leaf Rust, most recently revised in 2002, but the three major wheat rusts are included in the new publication with symptoms, life cycle, and management discussed. This publication is available at: www.ag.ndsu.edu/pubs/plantsci/smgrains/pp1361.pdf.   It also is currently being printed and will be available through the NDSU County Extension offices and through the NDSU Ag. Communication’s Distribution Center.

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