This is Nathan Mueller, UNL Extension Educator for Cropping Systems and Agricultural Technologies, in Fremont, NE. Diseases and insects growers may be seeing with week include bacterial blight in soybeans, leaf spot in alfalfa, and southern corn rootworm beetles. Should we be concerned and if so, what can we do?
Bacterial blight in soybeans are very common across the area due to both a source of inoculum and favorable environmental conditions. Initially, the leaves will have a yellow-green halo around the brown lesion. The older lesions will fall out making the leaf look torn and ragged. This can be mistaken as insect defoliation or hail damage. This bacteria overwinters in crop residues and is favored by wet and cool temperatures in the 70-80s early in the growing season. It is moved by wind and rain onto soybean plants into natural openings and wounds caused by hail and wind. Warmer and dryer weather will be a natural control mechanism. Fungicide applications will not be effective option for this bacterial disease.
Second cutting of alfalfa started this week so did some fungal leaf spots in alfalfa fields. Stemphylium leaf spot, a fungal plant pathogen, is favored by cool and moist conditions. Management options include early cutting if severity is high enough to result in leaf loss. Fungicide applications are generally not economical unless alfalfa is being raised for seed.
You may see some south corn rootworm beetles around area. These beetles have a different life cycle from western and northern corn rootworms. They overwinter as adults in the southern US and may be found much earlier than northern and western corn rootworm adults. They do not cause economic damage to corn, and feed on a broader range of plants than the other corn rootworms.
This coming Wednesday, July 9th, come join me at the UNL Extension Herbicide-Resistant Weed Management Field Day in Fremont, NE. To register for this event, visit my blog at croptechcafe.com or cropwatch.unl.edu. Feel free to contact me, Nathan Mueller, at 402-727-2775.
Have a great 4th of July weekend!