Trochanter Mealybug: Perhaps a Reason for Yellowing of Soybeans - (Christian Krupke and John Obermeyer)
It has been a couple of years since last mention, but the trochanter mealybug is still on the radar. This was first found in Indiana in 2009, though we have not had any reports since.
These are insects in the same group as aphids – plant-sucking, relatively sedentary creatures. Similar to other mealybugs in appearance, these small, whitish insects live beneath the soil surface and feed on plant juices. The above-ground symptoms are similar to K-deficiency – yellowing of foliage and stunting. If you have soybeans that exhibit these symptoms, we would recommend digging them up and inspecting for the whitish crawlers seen attached to the roots. Shaking the roots over dark-colored paper will make them more visible and the grayish-white insects will soon begin crawling around the paper. A hand lens may be required to confirm diagnosis.
Potassium deficiency symptoms could be a sign of mealybugs below (Photo credit: Ohio State University
Mealybugs, white fluffy mass on the soybean root
Close-up of mealybugs on soybean root
Soybean development in Indiana ranges from just planted to flowering. As of the 3rd of July, 94% of the soybeans had emerged and 3% were blooming. The rate of bloom is about 10% less than the 5-year average and 20% less than last year's fast pace. Management decisions are based on the growth stage, the time of the year, and pest (weeds, insects, disease) occurrence. We will overview the early reproductive stages of soybean for proper scouting.
Reproductive Growth Stages:
R1 – Beginning Bloom is defined as any open flower(s) on any of the main stem nodes. Flowering normally begins at the third to sixth main stem node (including the cotyledon and unifoliate nodes). A node is the point where the lateral leaf branch attaches to the main stem. It will form a bump, which is helpful in determining the nodes of the cotyledons and the unifoliates. Cotyledons and unifoliates eventually abscise as vegetative growth progresses up the plant. These nodes will have a bump on opposite sides of the stem followed by alternating nodes of the trifoliates (see R1 picture). Flowering begins around six to eight weeks after emergence and it is both temperature and photoperiod responsive. Vertical root growth rate increases rapidly. Approximately 65 days away from the beginning of physiological maturity (R7).
R2 – Full Bloom is where any open flower is located at one of the two upper most nodes of the main stem. Plant has accumulated~25% of the total dry weight and ~50% of the total node number. Rapid dry weight and nutrient accumulation begins and continues until physiological maturity. Nitrogen fixation rate increases as does the plant's nitrogen demand. Approximately 60 days away from the beginning of physiological maturity (R7).
R2: Full Bloom
|Growth Stage||Duration Median||Duration Range|
|# of Days|
|R1: Beginning Bloom||4||1 to 7|
|R2: Full Bloom||10||5 to 15|
|R3: Beginning Pod||10||5 to 15|
|R4: Full Pod||10||4 to 26|
|R5: Beginning Seed||15||11 to 20|
|R6: Full Seed||20||9 to 30|
R3: Beginning Pod
R3: Full Pod