Pre-Harvest Thoughts – Soybeans
Harvest is quickly approaching and while we can see the light at the end of the tunnel, there is still a lot going on in soybeans to think about before combines get rolling.
For those growers who irrigate, don’t shut your water off too soon. From beginning maturity to harvest soybean plants can require 0.05-0.2 inches a day of water. Pulling irrigation too soon can lead to the soybeans not reaching their maximum weight and yield. Fields that had frequent water early in the season and around flowering will be more sensitive to water stress at pod fill. Irrigation, or increased rain, at flowering generally leads to increased yield potential (seeds per plant), and therefore requires additional water to fill the additional pods.
Diseases such as Soybean Sudden Death Syndrome (SDS) and Soybean White Mold (SWM) have shown up in many new fields this season. These diseases are soil borne and will likely be present in the field from here on out. Both SDS and SWM can be partially managed with genetics that reduce susceptibility and SDS can be significantly reduced with the seed treatment iLeVo. Document hot spots (new and old) to help choose the correct varieties and seed treatments next time the field is in soybeans. Additional diseases such as Anthracnose, Soybean Pod and Stem Blight and Charcoal Rot have been documented this year. It is important to document and scout these as well to choose the correct management decisions for each disease. It is easy to forget without writing it down! Contact your local Jacobsen Seed Representative for help scouting and identifying any problem areas in your fields.
Two other issues have come up often this summer Soybean Gall Midge and Soybean Cyst Nematode. Soybean Gall Midge is a relatively new pest that we know very little about. It has been documented in NE Nebraska, SE South Dakota, and NW Iowa. The main issue with this pest is that it causes early plant death and significant plant lodging as they infect the lower stem. Field borders along heavy grass or groves seem to be hit the worst. UNL has a majority of the current resources on this pest. If you have a field you suspect may be infect please call your Jacobsen Seed Representative and/or your local extension office to help the Universities track this new pest.
Soybean Cyst Nematode is an old pest that is coming back into focus as recent studies have shown building resistance to our most common resistance gene, PI 88788. Fields with low levels of SCN may show no visible symptoms but yields may be reduced. High levels of SCN may cause stunting or yellowing in plants. SCN can be diagnosed with a soil sample or by visually seeing adult females (cysts) on the soybean roots. Female Cysts start a milky white and slowing turn brown as they mature. They are much, much smaller than soybean nodules but can be seen with the naked eye or a small hand lens. You can manage SCN with some simple steps –
1) Rotate to a non host crop such a corn for one season.
2) Use some sort of nematode management seed treatment such as VotiVo.
3) Always use different soybean genetics of a field even in a corn rotation. Different soybeans express resistance genes slightly differently and can help manage resistance development within SCN populations.
Begin making your fertilizer plans as soon as possible so that you can move forward with soil sampling or spreading as soon as soybean fields begin to empty. Keep soil samples up to date to insure fertilizer dollars are going to exactly what is needed and where.
Accurate soil samples are very important when applying ag lime. Correct soil pH is important for nutrient availability and natural chemical reactions. Grid samples are very valuable with lime because adding ag lime to an area of high pH can actually be detrimental to yields as well as a waste of fertilizer dollars. Next focus on soil samples in the Very Low to Low category as they are the first to return their investment dollars. For areas testing Optimal or above manage crop nutrient removal rates to keep from ‘mining’ your hardest working soils. You can get nutrient removal rates from Iowa State University’s PM1688 publication that is easily accessible online.