It starts with lots of rain. Or drought. Or cold weather. Or hot. No matter what the environment, it seems there's pressure for something that could destroy your flourishing soybean field.
It is those, and other, unpredictable conditions that make it difficult for Extension entomologists and pathologists to predict what you should be looking for in your soybean fields this summer. But, they've given it their best guess.
“If we get dry conditions early in the summer, we'll see more spider mites,” says Ron Hammond, Ohio State University Extension entomologist. “And if it continues on a two-year cycle, 2009 will be an aphid year.”
Those “ifs” continue with diseases.
“I would also expect a return to prominence of charcoal rot,” says Doug Jardine, pathologist at Kansas State University. “This is traditionally Kansas's number one disease problem, but because of timely rains across the state, it was present only at trace levels in 2008. I don't think we can expect to be so fortunate on rainfall patterns two years in a row.”
WEATHER ALSO PLAYS a part in the predictions from Minnesota.
“Weather, varieties and location will be major factors that drive how much pressure will occur from each disease throughout Minnesota,” says Dean Malvick, University of Minnesota pathologist. “Depending on the disease, wet or dry weather can be favorable, but especially wet weather from May to early July.”
So, no matter what the weather or what pressures you had last year, it doesn't hurt to have an idea of what to watch your fields for in 2009. Following are some insects and diseases that Extension professionals think will impact the 2009 soybean crop.
Also, please note that soybean rust is always something to have on the radar. Dependent on the weather that spreads the disease, it's nearly impossible to predict its severity. While it's generally not a problem for northern growers, southern growers tend to experience it frequently. For more information, see Ramping Up For Rust on page 22.
SOYBEAN APHID
SYMPTOMS: Plant sap is removed via sucking from the small, yellowish, glob-shaped aphid, causing leaves to wilt and curl. If numbers are high, leaves may become yellow and distorted; the plant may be stunted, covered in dark, sooty mold. From seedling to blooming, aphids will colonize tender leaves/branches, later moving down to colonize near the middle/lower underside of leaves and stem.
TIME OF ATTACK: V1-V2 on upper leaves, petioles, stem (scout twice/week); R1-R4: on undersides of mid-canopy leaves, stems.
CONDITIONS FAVORING: Northern states with cooler summer temps; fields with previous aphid populations; late plantings; crops stressed by hot, dry weather; high overwintering populations.
MANAGEMENT: Foliar-applied insecticide when populations reach 250/plant and continue to increase and 80% of field is infested; time treatment to maximize effectiveness. Beneficial lady beetles could help in control.
BEAN LEAF BEETLE
SYMPTOMS: Feeding is identified by small, round holes between veins. Entire pods may be clipped and the outside layer of pod tissue entirely consumed. Beetles feed on plants at all stages of development. Overwintering populations feed on cotyledons and leaves. The next generation feeds on leaves and the final generation feeds on leaves and pods.
TIME OF ATTACK: All season; first generation: late V, early R; second generation: pod-fill stage.
CONDITIONS FAVORING: Early planting and above-normal summer temperatures. Late-planted fields and below-normaltemps cancause better conditions for second-generation beetle pod feeding.
MANAGEMENT: Timely application of rescue treatment if sampling/defoliation threshold is reached.
STINK BUGS
SPECIES: Redbanded, Southern green, Brown, Green
SYMPTOMS: Flat pod syndrome and delayed maturity; brown and green species attack pods and seeds. Feeding punctures cause small brown/black spots. Young seeds can be deformed or undersized; older seeds become shriveled and discolored.
TIME OF ATTACK: R1-R7 reproductive stages.
CONDITIONS FAVORING: High populations of bugs and vulnerable growth stages; common along Louisiana and Texas Gulf coast.
MANAGEMENT: Cultivar selection and planting date. Rescue insecticide treatments when threshold reached while scouting. Populations also partially suppressed by predators and parasitic wasps.
SPIDER MITES
SYMPTOMS: Leaves appear sandblasted. Heavily infested leaves turn red-brown and die. Webbing may be present on undersides of leaves. Heavy infestation causes leaves to wilt and die.
TIME OF ATTACK: V2-R7
CONDITIONS FAVORING: Drought conditions
MANAGEMENT: Treatment by air or ground application if infested areas increase in size (no established threshold). Cool, wet weather conditions may reduce infestation.
DISEASES
SOYBEAN CYST NEMATODE (SCN)
SYMPTOMS: Difficult to spot in high-yielding fields or when soil moisture is optimal. Yellowing and stunting of plants; white to yellow lemon-shaped cysts on roots.
TIME OF ATTACK: As soil warms and root systems develop.
CONDITIONS FAVORING: Those that favor soybean growth. May first appear near field entrances, flooded areas, weedy areas, high-pH spots, lower-yielding areas. Moisture and fertility stress can enhance disease.
MANAGEMENT: Crop rotation, resistant varieties (rotate resistant varieties as well), introduction prevention. Test soil samples.
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SUDDEN DEATH SYNDROME (SDS)
SYMPTOMS: Leaves become brown, with veins remaining green; leaf blades drop off but petioles remain attached. Brown to gray discoloration of internal taproot.
TIME OF ATTACK: During pod set and fill.
CONDITIONS FAVORING: Cool, wet conditions throughout summer; well-fertilized fields; early planting/maturity; soil compaction; fields with history of SDS; co-infection with SCN.
MANAGEMENT: Resistant cultivars; avoid early planting — wait until soils are warmer and drier; eliminate soil compaction.
CHARCOAL ROT
SYMPTOMS: Small, black sclerotia form on lower stem and roots, both internally and externally. Early season infection produces red-brown lesions. Premature plant death; plants wilt and eventually die.
TIME OF ATTACK: R3-R6
CONDITIONS FAVORING: Extended periods of hot, dry weather.
MANAGEMENT: Reduced plant populations; rotation; planting fullest maturity group; irrigation, if available. No way to stave off damage in drought year.
ROOT ROTS
TYPES: Phytophthora, Rhizoctonia, Fusarium
SYMPTOMS: Rhizoctonia: reddish-brown lesions, damping off at seedling stage; Fusarium: dark discoloration, reddish-brown or stunted roots; Phytophthora: pre/postemergence damping off, wilting, plant death.
TIME OF ATTACK: Phytophthora: shortly after planting in saturated soils; Rhizoctonia: dry to very wet soils; Fusarium: after warm, humid weather.
CONDITIONS FAVORING: Cool, wet spring weather; saturated soils for most root rots; warm, humid weather for Fusarium.
Editor's Note:Please keep in mind this is just a general, short list of pests and diseases to keep an eye out for. Others mentioned included seedling blight, anthracnose, white mold soybean loopers and Japanese beetles. For specific information for your location, contact Extension specialist.
