ISSUE 7   June 26, 2008

SOYBEAN RUST/APHID SCOUTING BEGINS NEXT WEEK

Beginning next week (June 30th –July 4th) monitoring for soybean rust and soybean aphid will begin. Monitoring is done by scouting ‘sentinel plots’, which are small areas in soybean fields. Sentinel plots are scouted once a week for soybean rust and soybean aphid, and any other diseases or insects that may appear. Twenty sentinel plots are scattered throughout Richland, Cass, Traill, Grand Forks, Walsh, Barnes, Ransom, Sargent, La Moure, and Dickey counties. Each sentinel plot will be visited once each week until the beans are mature. All information collected is available will be available at the website www.sbrusa.net.

The monitoring effort is part of a national program to track the movement of the soybean rust as it moves across the country. Soybean rust can only survive the winter in warm climates, which in the United States means along the gulf coast. As the growing season progresses, the disease moves northward on winds from the south. Last year soybean rust was found as far north as Iowa and Ontario (Canada), although the disease was found to late in the season to cause much damage. It is too early to tell how far north soybean rust will go this year. Currently the disease is active in Texas, Louisiana, Florida, and Alabama. For information about soybean aphid see Jan Knodel’s article in the Entomology section.

 

PEA DISEASE SURVEY

Last week, my research specialist and I scouted 23 pea fields from Sheridan County to Williams County. The majority of pea fields looked pretty healthy. However, we took ten plants were taken from each field and evaluated the roots for disease. Root rotting pathogens were recovered from about half the fields. The primary pathogens were Fusarium (rot or wilt) and Ascochyta (foot rot) species. Although there is not much one can do to manage root rots during the growing season, we recommend that people take note of potential problems (poor stand, wilted spots in field). Some root rot pathogens can persist in the soil for several years, so management decisions like rotation and seed treatment may be influenced by what happens this year. Next week we will make another trip around the state to scout for more pea diseases.

Sam Markell
Extension Plant Pathologist
samuel.markell@ndsu.edu

 

NDSU IPM SMALL GRAIN SURVEY RESULTS - JUNE 24

The NDSU IPM field scouts surveyed 165 wheat fields and 24 barley fields last week. Of the wheat fields, 37 were winter wheat, and the rest spring wheat or durum.

Wheat growth stages map

In wheat, tan spot fungal leaf disease was by far the most common disease, with severity higher in winter wheat crops or where wheat was planted into wheat stubble. In barley, about 1/3 of the surveyed fields were showing fungal leaf spot infections.

Wheat leaf rust was found in one additional spring wheat field, in Ransom County, last week, but by June 24th, three-fourths of the spring wheat fields in Cass County had trace levels of leaf rust. Greg Endres, area extension specialist in Carrington, reported seeing low levels of leaf rust on June 23rd in a number of varieties of winter wheat in field plots at Ellendale, ND.

 

DISEASE FORECASTING INFORMATION

On June 24th, the NDSU disease forecasting model for small grains (http://www.ndsu.edu/scabforecast/)

indicated only about a third of the NDAWN weather stations had favorable weather for leaf disease infection. NDAWN stations showing risk were those that had rainfall during the past 3-5 days. Head scab risk on June 24th was low for all NDAWN sites. However, the occurrence of scattered thunderstorms across the state this week may change disease risk at any site at any time, so continued monitoring of the disease forecasting site and the crop is necessary throughout the heading and flowering stages. Most spring wheat fields are not yet flowering, a key time for fungicide decisions and application. Some barley fields are fast approaching full head emergence.

Marcia McMullen
NDSU Extension Plant Pathologist
marcia.mcmullen@ndsu.edu

 

OPTIMAL GROWTH STAGE TIMING FOR FUNGICIDE APPLICATION TO SMALL GRAINS FOR SCAB MANAGEMENT

Timing in wheat

The optimum growth stage for applying fungicide for scab control in wheat, the Feekes 10.51 stage, is the same for all classes of wheat (winter, spring and durum). The Feekes growth staging system is used as it describes development from spike emergence to grain-filling in more detail than other systems (see table). Applying fungicide during early flowering helps protect against the fungus infection when it can do the greatest damage. The length of time from head emergence to the beginning of flowering is temperature dependent, but usually takes about three days. Experience has shown that it is better to apply fungicide too early rather than too late, so the beginning of heading is a good indication of when to get serious about spraying for scab in wheat.

Feekes scale: start of heading to early grain fill

Scale

Description

10.1

First spikelet of head just visible

10.2

One-fourth of head emerged

10.3

One-half of head emerged

10.4

Three-fourths of head emerged

10.5

Head emergence complete

10.51

Beginning of flowering (for wheat)

10.5.2

Half of florets have flowered

10.5.3

Flowering complete

10.5.4

Kernel watery ripe

The center spike in the following durum photo is at the ideal stage for applying fungicide in wheat. The spike on the left has emerged from the boot, but has not yet started to flower (note that there are no visible anthers extruded from the glumes). The spike on the right is past the optimum stage. Note that the anthers are bleached and dried, unlike the turgid, yellow anthers in the center spike.

Durum

Timing in barley

Flowering in barley begins just before head emergence, so barley florets are not overly susceptible to scab infection. Although scab infections do not generally impact yield greatly, the fungus is able to infect the glumes and produce DON (vomitoxin), which impacts the value of the grain in the market. The optimum stage for applying fungicides to protect the glumes of barley from infection is when the spike is fully emerged from the boot (Feekes 10.5).

Barley

In the barley photo, the plant second from the right is at the optimum stage for spraying. The plant on the far right is beyond the optimum stage. With barley, the appearance of the first spikelet from the boot, like the first plant on the left in the photo above, is a good indication that the best stage for spraying is only a few days away.

Joel Ransom
Extension Agronomist
joel.ransom@ndsu.edu

Marcia McMullen
Extension Plant Pathologist
marcia.mcmullen@ndsu.edu


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