June 11, 2020
If you have experienced hail or wind damage, the following site provides guidance via information and videos for early-season hail damage: https://go.unl.edu/u5ns. Be patient and wait four to seven days to
determine recovery. Warm temps can help. For home owners, there has been a great deal of tree and plant damage. Make clean pruning cuts and donāt treat or paint over cuts, donāt add fertilizer, and leave as much leaf area as possible.
This weekās questions centered around soybeans. The majority of my soybean questions have been around emergence problems.
Two common things Iām finding: many were planted around May 18and they have a great deal of PPO-inhibitor injury to hypocotyls. In touching base regarding what we were seeing, John Mick with Pioneer shared some soybean varieties are more sensitive to PPO-inhibitor injury. āSensitive varietiesā means later on plants appear stunted and chlorotic in appearance. These plants also tend to have wavy leaves with some leaf cupping, which may have been mis-diagnosed as off-target growth regulator injury in the past.
Iāve seen those symptoms for several years but just told people the plant was working to metabolize the pre-emergence herbicide and it was most likely taking longer because of the environmental conditions at the time. So, in a way, it was correct, but now we can all be more aware there are sensitive varieties to PPO-inhibitors. Thus, itās important to talk with your seed dealer or agronomist about their variety ratings (if they exist).
If planting a sensitive variety, itās better to apply your pre-emergence application a week or so before planting to reduce the herbicide load on that germinating seedling. Iāve put a lot more explanation and pictures in a CropWatch article and the pictures are on my blog.
The pre-emergence products did a great job for the most part. Thus, a common question-discussion this week was around spraying essentially ācontactā herbicides in the absence of weeds. Could appreciate those thoughts. Regardless if the farmer wanted to apply glyphosate, liberty or dicamba, we did talk about the importance of spraying earlier than one thinks is necessary and the need for residual products. I was going to share more about that here, but Amit Jhala wrote a good article in this weekās CropWatch at: https://go.unl.edu/y3r8. He explains which products are options to consider at this point depending on if you have emerged weeds or not, what growth stage they can be applied, and some label restrictions. Thereās a picture on my blog soybean development stages. The cotyledons are not counted. The unifoliolates are counted as V1 only when the trifoliolate leaf edges above them are no longer touching. This continues up the plant. New nodes with leaves will be produced every 3.75 days. Note that early planted soybean may flower soon; they donāt have to wait till June 21 (longest day of year) to do so.
Because of that, for those near the 45 day window for post-dicamba application to soybean, be sure to check fields as the label states 45 days after planting or R1 (at least 1 flower on any node), whichever occurs first. Follow label instructions and Iām also recommending documenting development stage via pictures or video on all post- applications to crops this year. Regarding use of soybean dicamba, Nebraska Department of Agriculture Director Steve Wellman stated, āThe Nebraska Department of Agriculture has not issued a stop sale order and will enforce the sales and applications of these products as they are currently registered in Nebraska.ā
Thistle caterpillars are being observed in some early planted soybean fields. Threshold for pre-flowering is 30 percent defoliation.
Recommendations for any applications this year: Go into the field (beyond the endrows) and document growth stage of the plant via pictures and video using the leaf collar method or split stalks (once reach V6 due to leaves sloughing off). Do this before any applications are made to the field. If the growth stage isnāt correct for the application, donāt spray. I explain the split-stalk method of development staging: The growing point emerges above ground around V6. Dig a plant without breaking the stalk.
Carefully split the stalk down the middle through the root ball. At the base of the stalk is an inverted triangle that contains Nodes 1-4 (but they canāt be differentiated). Next look for the white area above that (about 1ā2-3/4ā) followed by the next visible band. The white area is the internode with the band being the 5th node (V5). Thereās about an inch of internode between V5 and V6. After that, internode length is more dependent upon air temperature instead of soil temperature. Every leaf is attached to a node. Pull off the fully collared leaves and follow them back to where they break off at a specific node. Count the nodes on the stalk to the highest collared leaf that breaks off at a node to determine the growth stage.