Variety Selection in Pest Management Bruce Potter IPM Specialist University of Minnesota Extension Service SWROC “Remember, I’m only the messenger”

SW MN Counties Which biotic and abiotic factors influence yield? What is the prevalence of factors influencing soybean production? How can county trials be used to predict variety performance?

Yield and Biotic / Abiotic factors Yield was POSITIVELY correlated with : –P soil test –K soil test Yield was NEGATIVELY correlated with: –SCN soil samples at planting Yield was NOT correlated with: –Soil test pH –Brown stem rot incidence

Selecting a variety High yield Stable yield –Race horse vs. work horse Do you need defensive traits? –There is no free lunch

Soybean variety performance from county soybean grower association trials % yield of indicator Freeborn

What causes variability in yield? Abiotic stress –Nutrients ( P, K, Fe, etc.) –Moisture –Temperature –Light –Chemical and mechanical stress Biotic stress –Disease –Insects –Nematodes –Weed pressure

Don’t ask genetics to solve too many problems! Rps1k BSR RES. PI < WHITE MOLD ANTI YELLOW DRGHT TOL. CAN’T LODGE

Selecting defensive traits What is (are) the worst problem(s) in the field? –There can be more than one Can the problem(s) be dealt with through tillage, chemical, planting date etc.? Which varieties have the best combination of defensive character(s), yield and other agronomic traits ?

Tolerance vs. resistance Host Growth GoodPoor Parasite Growth Good:TolerantSusceptible Poor:ResistantIntolerant Dropkin and Nelson 1960 nematodes

Tolerance vs. resistance Susceptible- Insects attracted to and feed/reproduce normally on plant. Plant growth suffers Non preference – Insects not attracted to plant. Antibiosis – Insects attracted but do not feed well (Bad taste or chemical compounds) Tolerance – Insects attracted and reproduce well but plant growth little effected Painter insect resistance

Soybean Pest Management The variety selection problem Variety selection Phytophthora (rps and tolerance) Brown stem rot* SCN* White mold * Iron chlorosis * Roundup Ready No variety choices Insects* Other root rots* Other disease* * may be tolerance differences First line of defense for predictable problems

TOLERANCE is not RESISTANCE Specific (vertical) resistance –One to few genes –Easiest to find, rate and breed General (polygenic, horizontal,nonspecific) resistance –Several to many minor genes General resistance (tolerance) –Crop yields well in spite of stress –No reduction in pest population

The Problem with Vertical Resistance

Defensive characters Do not inherently increase yield Should reduce yield variability caused by the matching pest or environmental stress Are relatively inexpensive A stress-proof soybean (or corn) plant has not yet been developed

So what does this all mean and why worry? You are paid for yield –Select high yielding varieties High yield and stable yield are not the same –Look at consistency in many sites/years You may need to give up short term yield for long term benefits –Defensive characters do not pay every year Variety selection IS risk management