Why is Rhizoctonia increasing? Favorable weather Susceptible crops sown in rotations - Crops affect populations of R. solani in soil Management Rhizoc

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1 RHIZOCTONIA FORUM: EPIDEMIOLOGY AND ROTATION CROPS Carol Windels University of Minnesota NW Research & Outreach Center Crookston, Minnesota Moderator: Gary Franc

2 Why is Rhizoctonia increasing? Favorable weather Susceptible crops sown in rotations - Crops affect populations of R. solani in soil Management Rhizoctonia on sugarbeet - Rotation crops & other cultural practices - Plant resistance - Fungicides

3 Background: : Rhizoctonia solani Common soil fungus worldwide Infects wide range of plants Field crops, weeds, vegetables, ornamentals Temperature: F; ideal = F Soil moisture: variable; ideal = moist - wet

4 Background: : Rhizoctonia solani Common soil fungus worldwide Infects wide range of plants Field crops, weeds, vegetables, ornamentals Temperature: F; ideal = F Soil moisture: variable; ideal = moist - wet Survives In diseased plants (mycelium & sclerotia) Colonizes plant debris Primarily in 0- to 6-inch depth

5 R. solani a complex species Composed of different populations Anastomosis Groups = AG Sugarbeet seed rot and damping-off: AG: 2-1, 2-2, 2, 4, 5 Rhizoctonia i crown & root rot (RCRR) AG-4 AG-2-2 2IV&AG IIIB (intraspecific ifi groups) AG IIIB 95 0 F, AG 2-22 IV does not

6 Rhizoctonia solani AG ISGs known to attack crops grown in MN & ND Crop R. solani R. solani AG 2-2 IV AG 2-2 IIIB Sugarbeet Soybean Edible beans Corn - + Spring wheat = nonhost ++ = moderately aggressive + = slightly aggressive +++ = severely aggressive

7 Red River Valley acres sown: 1995 to 2007 FROM: USDA Agricultural Statistics Service

8 Crops grown before 2007 sugarbeet in SMBSC Corn S. corn Soybean Mix Peas Less than 1% each of: alfalfa, navy bean, potato, set aside, small grain

9 Prevalence of R. solani AG 2-2 ISGs in RRV & So. MN ~ 970 isolates of R. solani AG 2-2 collected from infected sugarbeet: Red River Valley (465) Traditional small grain rotation Shift to corn/soybean last 10 yr So. Minnesota (504) Sugar beet rotated with corn/soybean since % 7% AG 2-2 IV AG 2-2 IIIB Intermediate 66%

10 Prevalence of ISG in the RRV by previous crop 6% 7% 17% 39% Wheat (227) 77% 54% AG 2-2 IV Edible bean (76) AG 2-2 IIIB Corn? (6) Intermediate 6% 13% Soybean (49) Potato (16) 81%

11 Prevalence of ISG in So. MN by previous crop AG 2-2 IV AG 2-2 IIIB 6% Intermediate t 25% Corn (301) Soybean (36) Wheat? 69% Edible bean (16) Unknown (133)

12 Crops rotated with sugarbeet in various regions of USA Michigan (Steve Poindexter): Soybean, dry bean, corn Wyoming (Gary Franc): Dry bean, barley Montana (Gary Franc): Dry bean, barley, spring wheat, corn Idaho (Carl (Carl Strausbaugh): Winter wheat,,p potato, corn, hay, alfalfa

13 Reasons for variable Rhizoctonia disease Rhizoctonia ISG present Population density Environment Temperature Moisture Soil type Plants Sugarbeet Wheat Corn Beans Weeds

14 Rhizoctonia control strategies Correct diagnosis of root rot problem Symptoms May require lab analysis

15 Rhizoctonia

16

17 Non-typical Rhizoctonia Aphanomyces

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19 R. solani AG ISGs effects on: Rotation crops Sugarbeet

20 Soil inoculated R. solani AG 2-2 IV, IIIB & control Planted to rotation crops followed by sugarbeet

21 R. solani AG ISGs & rotation crops Spring wheat No increase on roots No effect on yield Historically, RSA of sugarbeet following wheat (barley) very good on wide range of soil types Soybean Symptoms may/may not be observed Increase populations in both ISGs (IV and IIIB)

22 Susceptibility of corn to AG 2-2 2ISGs Corn: susceptible to 2-2IIIB 2IIIB No above-ground symptoms No effects on yield Lesions on roots Build-up up ponroots 4/5 field trials

23 Spring wheat Soybean Corn Not inoculated

24 Spring wheat Corn Soybean R. solani AG 2-2 IV

25 Soybean Corn Spring wheat R. solani AG 2-2 IIIB

26 Corn variety & R. solani AG 2-2 2ISGs Inoculated soil Grew full-season crop of several transgenic corn varieties Planted sugarbeet following year (2 sites)

27 Non inoculated control following corn

28 R. solani AG 2 2 IV following corn

29 R. solani AG 2 2 IIIB following corn

30 RCRR on sugarbeet also can affect soybean Carry-over roots/root parts of infected sugarbeet are focal points for basal stem & root rot of soybean

31 Sugarbeet 2007, Soybean 2008

32 Sugarbeet 2007, Soybean 2008

33 Sugarbeet 2007, Soybean 2008

34 Some follow-up questions Ideal rotation of crops to prevent build-up? up? Ideal rotation of crops to reduce R. solani population p in infested fields? Minimum threshold level of R. solani population for disease management? Role of soil moisture & temperature & R. solani population on time of infection, disease development & symptoms? Models to predict conditions favorable for Rhizoctonia diseases?