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 1998-2000. % 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! CAN’T LODGE DRGHT TOL. ANTI < WHITE MOLD YELLOW Rps1k PI 88788 BSR RES.
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 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 1951 - insect resistance
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 Soybean Pest ManagementThe variety selection problem 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
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