ISSUE 12   July 29, 2009

NDSU IPM FIELD SURVEY UPDATE - JULY 29

NDSU IPM field scouts surveyed 118 wheat fields and 20 barley fields across the state for the week ending July 24th. Average growth stage over all wheat fields surveyed was "flowering complete" and for barley, average growth stage was "medium milk". Thus, the small grain crops are rapidly maturing in the state, and field scouts will start spending more time with the row crops in the IPM survey.

Wheat: Tan spot and/or Septoria blotch were observed in 85% of the surveyed fields, and average severity in surveyed fields was 9% of the leaf area covered by these two organisms. No leaf rust was observed in spring wheat this past week. Head scab was observed in 12 wheat fields, with an average field severity of 0.9%. Loose smut was observed in 22% of the surveyed wheat fields this past week, with an average % tillers showing loose smut at 4%.

Wheat streak mosaic virus (WSMV) symptoms were observed in 8.4% of the wheat fields surveyed, similar to the previous week. Barley yellow dwarf virus (BYDV) symptoms were very noticeable in crops this past week, with 23% of the surveyed wheat fields showing symptoms. Cereal grain aphids, the vector of BYDV, were observed in 44% of the surveyed fields, and there was an average of 13% of tillers showing aphids in these fields. It appears that this BYDV transmission by aphids has been fairly common this year. We do not have information on differences in variety susceptibility to BYDV or WSMV.

Bacterial leaf stripe symptoms were observed in 13.6% of the surveyed fields. Often, the head symptoms of black chaff also were evident. See previous Crop and Pest Reports for images of these diseases and others.

Barley: As in wheat, along with fungal leaf spot infections, symptoms of barley yellow dwarf virus were observed in some barley fields, with 35% of the 20 fields showing symptoms of this disease, a much higher level than the previous week. The first observations of head scab in barley were made this past week, with 2 of the 20 fields showing symptoms, and an average field severity of 10%. Loose smut was observed in 3 of the 20 barley fields surveyed, and % tillers showing the smut fungus ranged from 2 to 20%.

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

 

SUNFLOWER RUST UPDATE

Although sunflower rust was identified very early this year in localized parts of the state, it has developed slowly. Sunflower rust, like sunflowers, is slowed by cool temperatures. However, rust has not ‘gone away’, and as temperatures warm up, it is likely that more sunflower rust will become apparent. It is still very important to scout for the disease, particularly as summer warms up (we can hope). We have fungicides that do a very good job of managing the disease, but we need to stay in front of it.

Given our current growth stages, a fungicide application is likely economic once rust reaches the upper leaves. Optimum timing of the strobilurin fungicides (headline/quadris) is before rust is on the upper leaves or when disease severity is very low (up to 1 percent). In our three trials last year, 9 fl oz of the strobilurins were used. In one trial, Headline performed better than Quadris, but differences between the two products was not observed in the other two trials. Optimum timing for Tebuconazole (Folicur and generics) is about 3% severity on the upper leaves. A 4 fl oz rate of tebuconazole has been shown to be very effective in managing rust. If rust is found on the upper leaves with severity 1-2 percent, tebuconazole should be used. More detailed management information, photos, and severity diagrams can be found at the National Sunflower Association web site at www.sunflowernsa.com or in the July 2 issue of the Crop and Pest Report at http://www.ag.ndsu.nodak.edu/aginfo/entomology/ndsucpr/index.htm.

A note about scouting. Rust will form cinnamon brown pustules, whose spores can be easily rubbed off and leave a dusty streak on your thumb. You can not rub off the actual pustules; a small brown to yellow spot will remain where the pustule is. Although I don’t know of any other sunflower disease that resembles rust, some soil splash after heavy thunderstorms can resemble rust, and it does rubs off, like... dust. Be careful not to confuse the two.

 

SCOUT FOR DRY EDIBLE BEAN RUST

Last year, a new race of dry bean rust was identified in North Dakota, centered in Northern Traill County. The new race is capable of causing disease on 30 varieties that we tested. Although we didn’t test all varieties grown in our region, the safe assumption is that they are susceptible until shown otherwise.

Although we are actively scouting for dry bean rust, we haven’t found it yet. That being said, we will be out in numerous fields again this week. Whether I find rust or not, my recommendation is the same. Please scout your fields. Rust is favored by heavy dews and moderate temperatures, both of which we have had in abundance is some areas. Rust can be a very devastating disease, but is also a very manageable disease, if treated.

Rust can be identified by cinnamon-brown pustules on the leaves, frequently they have a yellow halo around them. The rust spores can be rubbed off with your thumb, and will leave a dusty streak of spores (Figure 1). The pustule can not be rubbed off.


Figure 1.
Rust

Several other diseases occur on soybeans, and can confuse rust identification including three bacterial diseases, bacterial pustule (Figure 2), common blight (Figure 3) and halo blight (Figure 4). Additionally, splashed soil after thunderstorms can resemble rust pustules, but if soil is rubbed off the leaf, no pustule will remain.


Figure 2.
Bacterial Pustule (Howard Schwartz)


Figure 3.
Common Blight (Howard Schwartz)


Figure 4.
Halo Blight (Howard Schwartz)

If rust is found, we have fungicides that are effective. Tebuconazole (Folicur and generics) has shown to be excellent management tools on rusts in many crops. A 4 fl oz rate is most likely sufficient. Additionally, tebuconazole has some kickback ability, and is usually the product of choice once you have rust at more than a trace level. The strobilurins (Headline and Quadris) are effective for rust management, but they should be thought of more as protectants. In sunflower rust trials last year, strobilurins did a good job of management at the 9 fl oz rate, if applied before rust reached a 2% severity level. As the beans mature, the threat of rust is less, fungicide applications made a stripping have not been found to be economic in the past (no damage was done at that point).

More detailed management information is available in my article in the spring 2009 issue of the Northarvest BeanGrower (vol 15. Issue 3, http://www.northarvestbean.org/html/magazine_archives.cfm#Spring%202009).

If rust is found in North Dakota, more information will be put into the next issue of the crop and pest report, ag alerts, etc...

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


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