Issue # 4, June 27, 2000

• Fungicide Decisions and Timing for Small Grains
• White Mold Concerns for Row Crops and Canola
• Be Aware of Herbicide Injury on Yellow Soybeans

FUNGICIDE DECISIONS AND TIMING FOR SMALL GRAINS

    Last week's rains certainly may change the story of possible disease problems in Griggs County. A week to 10 days is necessary for disease infections to become evident in small grains, once environmental conditions trigger fungal sporulation and spread. Diligent scouting will be necessary now and during the next few weeks to determine disease threat.
    Small grain producers MUST assess the condition of their crops before making a fungicide decision.
1) A waterlogged field with long standing water has a high potential for root rot and crown death. Such a field is not a good candidate for protecting against leaf and head diseases.
2) Crops flattened by wind, heavy rain, or hail may not recover enough to warrant fungicide treatment. Wait a few days to assess how the crop recovers. NDSU does not have data on the effect of fungicides on severely lodged grains.
3) Crops in the early heading and flowering stages will be the best candidates for fungicide protection. Winter wheat crops that have already flowered and are in kernel development may be beyond the need for fungicide application.
    Spring wheat crops with high yield potential and at the early flowering stage have the highest potential to benefit from fungicide treatment. Head scab is a looming threat, because the saturated soils are going to favor spore production along with high humidities and dew points necessary for disease development.
    NDSU fungicide research has consistently shown that the optimum timing of fungicide application for Fusarium head scab control is at early flowering for spring wheat and durum, and at early full head emergence for barley. These stages equal Feekes 10.51 for wheat and durum, and Feekes 10.5 for barley (barley flowers while head in boot). Early flowering means that 10-25% of the main stems are flowering, while tillers have not started yet.
    These fungicide timings also have given excellent control of tan spot, Septoria leaf blotch, and leaf rust. Our leaf disease pressure so far hasn't warranted a fungicide application at boot stage, but this could change in the next 10 days.  NDSU Extension Service circular AE-1148 'Application of fungicides for suppression of Fusarium head blight (scab)' should be consulted to aid in effectively applying fungicides. A summary of the recommendations include the following:

• For ground application, angle spray toward grain heads, using forward and backward mounted XR8001 nozzles or nozzles that have a two-directional spray, such as Twinjet nozzles.
• When using XR flat fan tips, use 40 psi with 9-10 gpa, and 90 psi with 18 gpa.
• Increase spray volume for durum and barley to improve head coverage and disease control.
• Use a good adjuvant.
• Use dew as additional water.
• When using aerial application, spray in evening or early morning to capture dew as extra water volume, and use a small droplet size.
• Base your decision on yield potential (40 bu. or greater), crop price, disease presence, recent weather, and forecast for upcoming weather. Also, NDSU has a disease forecasting system for scab and leaf disease on the internet at http://www.ag.ndsu.nodak.edu/cropdisease/.

WHITE MOLD CONCERNS FOR ROW CROPS AND CANOLA

    Recent rains, along with the heavy infestation of sunflower head rot last fall, may be the perfect conditions for the dispersal of sclerotinia spores. Critical infections stages for susceptible crops are as follows.

Sunflower: This crop can be infected by more than one method. The most common infection is sclerotinia stalk rot. This is when the sunflower root comes into contact with a sclerotinia fruiting bodies. Symptoms usually begin to show up at flowering. This is when the plant begins to wilt and the base of the plant will have a bleached appearance. Shortly after wilting the plant cannot support itself and break over. Infections usually appear in spots and can spread by root grafting.
    The second method of infection is mid-stalk rot. This is similar to stalk rot, only the infection takes place by spore that land on an injury or other type of wound on the stalk. Again infection sites will take on a bleached appearance and later cause the plant to break off.
    The third method of infection is head rot. This was very serious in 1999. This is caused by spore dispersal during flowering. The spores will infect the flowers and slowing begin to consume the head causing the heads to shatter and have a stringy appearance.
    As of now, nothing is cleared for control or prevention of white mold in sunflower. Our only defense is the dry weather.

Canola: There is only one infection period in canola. This is during flowering and sclerotinia spores are present. They will infect dead or dying blossoms then penetrate the stalk and cause the plants to have bleached branches that will not produce any seed. These infections are very noticeable and can cause yield losses in accordance with the percent of infection. There are two fungicides that have labeled for prevention, Quadris and Ridomil (section 18).

Quadris: apply at 10 to 25% bloom (about 3-7 days after flowers are detected). Rate=9.2 to 15.4 fl oz/acre (9.2 fl oz/acre is suggested at a cost of about $21-22/acre plus application costs).

Ronilan: apply at 20 to 50% bloom (about 4-8 days after flowering begins). Rate=10.6 to 16 oz/acre (suggested rate is 12 oz/acre at a cost of about $16/acre plus application costs). Consult labels for details before use.

Soybeans: Infections occur during flowering and are more severe when soybeans are solid seeded verses rows. Usually, white mold has not been a major concern in soybeans, but as more beans are solid seeded, we are seeing more problems.

Drybeans: Infections occur during flowering and are usually more severe in pinto beans than navy beans. Rain events 10 days prior to flowering provide ideal conditions for possible white mold infection. Most common fungicides used are Benlate or Topsin. Both products have shown good control and yield increases. There is some work being done in the counties of Griggs, Steele and Traill, using liquid calcium as a carrier. There has been some good results, but at this time the jury is still out. Under heavy disease pressure, the full fungicide rate is still recomended.

BE AWARE OF HERBICIDE INJURY ON YELLOW SOYBEANS

    Recent research at NDSU has shown that soybeans that are chlorodic or under excess moisture conditions, are more likely to be injured when sprayed with herbicides. The question arises, are we going to cause more damage with the herbicide or by not controlling weeds. In 1998 and 1999, Dave Franzen did some studies in four locations to determine what type of injury each herbicide had on soybeans under moisture or salt stress. Each herbicide had some injury with some of the burndown products such as Cobra and Blazer tended to hurt the beans a little more. When determining whether to wait for the plants to recover will depend on weed pressure. High weed pressure can cause high yield losses but also could also help protect the soybeans from receiving high doses of product. In conclusion, we must look at all the conditions and crop potential. Drowned out spots will not recover so then evaluate the remaining stand. Under high chlorosis conditions, be prepared for some damage. But if the weed pressure is high, treating will probably be a better alternative than waiting for recovery. To get further information on this study, go to the following web site: http://www.ag.ndsu.nodak.edu/aginfo/entomology/ndsucpr/Years/2000/June/1st/soils_1june00.htm#HERBICIDES.

Please Contact Our Office For Additional Information
E-mail: griggs@ndsuext.nodak.edu
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