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‘Most Wanted’ List

Saturday, December 1, 2018
filed under: Disease

By Sam Markell, Bob Harveson and Febina Mathew*
#1: Phomopsis Stem Canker
Deadly fugitive that has resurfaced in the last decade.
       Last Spotted:  Phomopsis stem canker has ravaged Northwest Minnesota and Eastern North Dakota in recent years and has stolen yield as far south as the High Plains.
       Description:  Phomopsis stem canker appears as a large (often greater than 6 inches) and brown stem lesions, always centered on a petiole. The stem becomes hollow underneath the lesion, is easily punctured with thumb pressure and frequently results in lodging. 
       Commonly Known Hangouts: The fugitive will survive the winter on sunflower residue but may also survive on weed hosts.  The fugitive flourishes in wet weather, but can still cause infections with average rainfall. An aggressive attack by this fugitive early in the season will devastate a crop.
       Apprehension in 2019:  Difficult.  Consult your seed company for a hybrid less susceptible to the disease. Strobilurin fungicides (FRAC 11: such as Headline, Quadris, etc.) applied in early reproductive growth stages have shown some promise, but are not guaranteed to slow this fugitive down.
#2: White Mold
Deadly fugitive that attacks sunflower in three different ways.
       Last Spotted: Most common in the Dakotas and Minnesota.  Also spotted in High Plains.
       Description:  The fugitive can attack the base of the stem (causing wilt), the middle of the stem (stem rot) or the sunflower head (head rot).  Plants under attack express a water soaked lesions that become tan, enlarges and eventually shreds.  The fugitive often leaves evidence behind in form of hard black sclerotia and fluffy white fungal growth. 
       Commonly Known Hangouts:  The fugitive attacks other broadleaf crops (soybean, dry bean, canola, potatoes, etc.) and survives as sclerotia for many years, lying dormant until it re-emerges with a vengeance.  You’re likely to find the fugitive in locales with wet soils, cool daytime temperatures (60s-70s F) periods of wetness (rain, frequent heavy dews, lush canopies).
       Apprehension in 2019:  Difficult.  A long crop rotation (four years) and a less-susceptible hybrid may slow this fugitive down. In the High Plains, growers can also reduce irrigation late in season as a deterrent.
#3: Rust
Fugitive attacks sunflower throughout the Plains but is most likely to steal yield from confections.
       Last Spotted: Texas to Manitoba. 
       Description:  Dusty cinnamon-brown pustules that harden and turn black at the end of the season.
       Commonly Known Hangouts: The fugitive frequents locales with free moisture (dew and fog).
       Apprehension in 2019: Likely. Selection of a hybrid with resistance may help prevent rust. If spotted, multiple fungicides are effective — but only if applied early in an epidemic. 
       Do not take your eyes off the crop if the fugitive is in the neighborhood in 2019.  This fugitive is notorious for fast and clandestine attacks. 
#4: Downy Mildew
Fugitive steals yield one sunflower plant at a time.
       Last Spotted:  North Dakota and Minnesota.
       Description:  Plants may die after emergence. Survivors are severely stunted, have chlorotic leaves with white fluffy growth and horizontal heads.  Fugitive steals 100% of yield from plants when they are attacked early.
       Commonly Known Hangouts:  Fugitive survives in soil for many years and attacks seedlings when fields are cool and wet after planting.  Seedlings most likely attacked in low spots.
       Apprehension in 2019:  Likely.  Selection of a hybrid resistant to downy mildew may thwart the fugitive.  Efficacy of Oxathiapiprolin, the new fungicide seed treatment from Corteva (Lumisena) and Syngenta (Plenaris), is significantly greater than other labeled products to battle fugitive.
#5: Rhizopus Head Rot
Fugitive kicks you when you’re down.
       Last Spotted: Fugitive commonly spotted in Southern and Central High Plains with occasional raids into the Dakotas. 
       Description:  Wounded heads have soft lesions that enlarge and rot.  Fugitive leaves evidence behind inside heads that it attacked: fluffy gray mold with black specks.
       Commonly Known Hangouts: Fugitive attacks heads that are already wounded by hail, birds or insects. Most likely to attack wounded heads in hot temperatures.
       Apprehension in 2019:  Difficult.  Attack is directly related to wounding, which is impossible to prevent. Efficacy of fungicides and genetic resistance are uncertain.
Before apprehending any of the suspects with fungicides, please consult the most up-to-date information on efficacy and timing, and remember to read and follow the labels.
*Sam Markell is extension plant pathologist with North Dakota State University. Bob Harveson is plant pathologist at the University of Nebraska’s Panhandle Research & Extension Center.  Febina Mathew is plant pathologist with South Dakota State University.
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