IPM STUFF NOTES - 6/20/2024
How wet is it?
Many of us have received significantly more rainfall than we ordered. Low, and not-so-low, areas are filled with standing water in the hardest hit areas. Hopefully, we can return to a more moderate weather pattern next week.
Aside from the obvious risk of drowning, crops may see additional, chronic issues from saturated and flooded soils. Rain-saturated soils can experience loss of nitrogen or sulfur and yellowing. However, poor root function from reduced oxygen or root disease can also lead to stunting and yellowing.
This consistently wet soil and foliage this spring leads me to expect we have been set up to see root and foliar diseases show up down the road.
White mold ascospores may take advantage of cool, rainy weather. Nearby risk is moderated in most fields by the open soybean canopies. Weather conditions have been favorable for Physoderma infection if any highly susceptible hybrids are still being planted. Crazy top disease can show up where corn has been flooded.
Weather continues to make weed control difficult. Watch crop heights on herbicide labels. Mid-April planted Mid-Group II soybeans at the SWROC were flowering last week.
The yellowing from SCN is present on V3 and larger soybeans and the females are visible on some roots now.
Those darn rootworms
Corn rootworm hatch is well underway. Yesterday, I received a report of rootworm larvae from northern Minnesota.
Flooded fields are prompting some optimists to question the possibility of drowning rootworm larvae. In addition to areas where the corn has died, there will be some mortality of larvae. The diapausing eggs of western and northern corn rootworms are likely tolerant to submersion. Until established inside a root, the newly hatched rootworm larvae are vulnerable. Molting larvae and pupa are also outside the root and exposed. At 77o F, 50% of 3rd instar larvae died after more than 20 hours of immersion. The younger 2nd instar larvae tested survived twice as long. Similar to corn and soybeans; rootworm larval mortality slows with cooler temperatures.
[Hoback, W.W., Clark, T.L., Meinke, L.J., Higley, L.G. and Scalzitti, J.M. (2002), Immersion survival differs among three Diabrotica species. Entomologia Experimentalis et Applicata, 105: 29-34. https://doi.org/10.1046/j.1570-7458.2002.01029.x ].
Later this summer, replanted corn, and corn replanted to a non-host crop, will concentrate beetles and egg laying in portions of fields.
Happy Trails!
Bruce