Renewable Farming

Consultant Bob Streit advises how to help late, stressed crops

Each week during the growing season, crop consultant Bob Streit alerts clients to ways they can make the best of current growing conditions. We’ve excerpted key guidance and inserted the highlights below. For the extended report, you can visit the Central Iowa Agronomy site at:

June 16, 2016 — We’ll add a couple of recommendations alongside those Bob offers below. Central Iowa Agronomy is a distributor of WakeUP, which is a highly cost-effective companion for the nutritional remedies that Bob discusses in this excerpted report. We’ve found that if a needed trace element nudges corn yields up 5 bu. when used alone, adding WakeUP in the tank mix adds another 80% to that yield gain, or about another 4 bushels. 

Bob encourages tissue testing as a guide to which nutrients your crop may need.

We’ll go one advance further and encourage you to use this season as an opportunity to learn about sap testing. This technology gives you 10 days to two weeks earlier “warning time” of emerging deficiencies, compared with tissue tests. Tissue tests are, however, better than simply watching for symptoms. By the time you see yellowing or other visible deficiency signs, it’s too late to recover lost grow time. Visit the Crop Health Labs website at for an overview of sap testing. Sap testing protocol takes a bit more planning, such as getting sample bags in advance and learning the routine. But it can pay off.  

Here’s the core of Bob Streit’s report this week:

By Bob Streit

Yellowing of corn plants still continues in most fields with some improvement in the appearance and color. We can conclude that cold and saturated soils lacked much biological activity plus many roots had not explored much of the soil profile for nutrients. Last week and this will be the optimum time to pull plant samples and have them analyzed for micronutrients.

Based on the results from a small batch of samples I sent in last week, the exact minerals we suspected to be the cause of some of the yellowing did show up as being deficient. Realize that taking corrective action will have a cost of $6 to $10 per acre, depending on what minerals are short. Not taking corrective action will also have a cost from lower yields, possibly more stalk problems and a greater need for fungicide applications. And even if a fungicide knocks out the causal fungus or fungi, you still have not cured the underlying nutrient deficiency.

Bob Streit

If results from any tissue samples you submitted are classified as being deficient, you can either get on the ball and make an application as called for using a shotgun approach, or wait another week or two and see if the plants return to a green color. If you have been using a Spad meter, which rates each plant as to its degree of greenness, getting a reading below 60 indicates the plants need help.

Make note about whether the yellow plants are just a lighter shade of green or if they are more of a bronze green. If they are the latter the problem could be caused by low N efficiency caused by a lack of Mg, Zn and Cu. Be sure to request that Moly be tested, since is it crucial to good plant usage of N. It is typically deficient about 90% of the time.

Another trick to speed plant growth is to start a foliar fertilizer program that utilizes different forms of liquid solutions low in salt and containing P. Charged P carries energy around in the plant as well as building chromosomal material and different forms of liquid zinc.

If the plants are just in the V3 growth stage now, they will have to hurry to get much grain fill completed before the early plant death syndrome occurs in the Aug 15th to 25th time frame. Try to have the greenest corn in your neighborhood as it is an indicator of healthy corn.

Remember that higher levels of Ca in the soil are beneficial. Calcium helps to build strong cell walls and structural rigidity.

Also be scouting on a regular basis for early signs of leaf diseases. Before religiously applying fungicides, get a plant mineral analysis to see if a nutrient shortage went unnoticed and kept the plants from optimal health.

Do your own math now. Count the number of leaf collars on plants in your different fields. Assume an average of 2.25 leaves forming per week to grow the 18 to 19, which is a normal count. Recognize that no dry matter gets deposited until late blister stage, which is about ten days after pollination. From late blister, the grain fill period should last about another 50 days for hybrids in central Iowa. Based on your calculations, when should your grain fill period get over with? If your date is after August 20th or 25th, what do you plan to do to keep your plants healthy enough to survive as long as they need to? Wishing that it happens rather than being proactive and making it happen using the correct plant health products could be doubly important.

Soybean management

In a high percent of the bean fields, plants look like they will be severely challenged to meet pre-seasonal expectations. The stands are generally lighter and much later than in 2016. Again there are aggressive growers who will be helping their bean plants by applying the fertilizers and nutrients known to improve plant health while also working to add additional branches. There are several products that have been used successfully. These often center on sugar, liquid forms of high grade P, and hormonal products.

What I have seen is that guys who formerly planted beans late (mid June) after taking off an alfalfa cutting or a cover crop and normally saw yields in the mid 20s, changed course and learned how to maximize their plants’ physiology and architecture. They learned that yields in the mid 50 bu. range planted after June 10th were possible.

In the meantime keep a sharp eye out for plants that are not as green as they should be. There is still time to take corrective action as soon as problems are identified.

Bob Streit is an independent crop consultant and columnist for Farm News. He can be reached at (515) 709-0143 or