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Crop watch

By Staff | Jul 26, 2019

Another week in July passed and there’s only one more in the month of July. It is typically the time when corn goes through its critical stage of pollination and soybeans continue their rapid early growth forming branches and pods while closing their thirty inch rows.

It was very warm and humid over much of the Midwest, where mid-July temps are typically in the mid 80s with tolerable humidities. However someone turned up the cookers and we had one of the hotter weeks in recent years.

Many farmers and commodity analysts were searching for documentation on what the mid and high 90 degree temps were going to be doing to the corn plants and what if any projected yield losses could be expected. It is tough for climatologists to place an absolute figure on bushels that may have been lost. Most estimates suggest that each 24 hours where the temps and humidity levels added up to 150 or more constituted a stress day. Each day can cause a 1 Bu/A yield loss. Four or more in a row multiplied that figure. Factors such as lack of moisture in the root zone, soil compaction, or lack of oxygen to the roots would also create a greater yield loss. Fields in Southern Iowa where rain was has been scarce since mid-June will be more affected. With the combination of heat and dryness in southern Iowa the fields that were first to tassel last week could be the ears that will be tipped back or have kernels missing.

Working outside without a cab or scouting fields was warm and keeping a cold thermos with plenty of ice available was a good idea. In the grand scheme of things being a four legged animal, being black in color, carrying around a thick fat layer and wearing a fur coat without shade would have been a lot worse. There did not seem to be any problem with fat cattle deaths as we have in past heat spells. Luckily the heat wave broke on Saturday for the state and conditions are projected to be more tolerable this week.

In hindsight, the product called StressTech, which is a fungal endophyte that gives corn plants heat tolerance up to 160 degrees-plus enhance drought tolerance, should have been applied to more acres. The results from 2017 yield checks showed a tremendous benefit to its application. At a cost of $4 or $5 per acre for seed application the returns may be sizable this fall.

The topic of a ‘flash drought’ has been mentioned in the press and over the radio. It is sometimes described as a recent phenomenon, but in reality conditions are supposed to be warmer and drier between July 15th and August 15th. That is when moisture from rainfall is supposed to infiltrate into the soil and be stored by the organic matter for use during that time window. If the rains run off because of lack of residue cover and the organic matter level has declined substantially shouldn’t it be termed a man made drought situation? Any prevent planted field if and when tillable should be planted to a multi-species cover crops to improve the soil tilth.

There are still tasks to be taken care of the fields. From now until fall, is when the photo-synthates accumulate as yield. Any nutrient deficiencies not corrected via preseason or planter applied nutrition should have been corrected with a V5 to V8 foliar application. A number of the plant essential minerals work to improve drought tolerance.

Smaller plants with their smaller root systems are less able to tolerate drought situations. Later planted corn doesn’t tolerate hot and dry conditions as well as earlier planted fields where the root system can reach twice as deep. For good info on how stress weather affects pollination read an article by UNL’s Tom Hoegemeyer posted at www.centralIowaAg.com

Field days

Neighborhood and regional field days will often be held the last part of July through mid August. There was a smaller Dow/Dupont demo near Mason City last Friday. We were able to view the results on a no-till corn and bean plot at a site south of the NIACC campus. We could view the success or failures of a number of different mixtures. The take home message was that the era of overlapping residual is here while total post is a thing of the past for soybeans. Waterhemp now emerges through mid-August and those late emerging plants may only reach 4 to 6-inches in height but will still form a seed head. Reducing rates and leaving control or product gaps can be costly and can lead to the quicker development of or selection for weed resistance.

One larger retailer is having their technology plot show near Sioux Falls this week. In recent years they have invited high yield achievers to formulate their management programs and then follow through in managing their plots. After harvest the yields, gross revenue, and then net returns are factored in so they can announce a winner of the income portion of the contest. That makes it very similar to the Webster County corn and bean contests from a decade or two ago to where realism to budgets are limited and products have to produce.

As to which products have looked best overall, it gets murkier. The Zidua Pro containing Zidua, Pursuit and Sharpen has looked excellent when applied early on no-till fields. Getting the prees on before receiving a 3/4-inch of rain seems to help adhere the PPOs to the soil colloids and reduce splash burn. The Authority mixes looked good where the soils were worked and still belong in many mixes. Until we see the waterhemp develop resistance to the Group 15 herbs we have to use them as the product of choice to provide post emerge residual activity.

Slow developing soybean plants

See major size differences between the plants in soybean fields is very common this season. Several factors can be suggested as the cause of the differences. After a two week period of warmer temps some of the fields have begun to add height and appear ready to close 30-inch rows in the next ten days while others seem like they will not cover the ground even if they are in 15-inch or 20-inch rows.

One early factor was the cool nights dropping down to 50 degrees that halted growth for 3 days. Cold or compacted soils which restricted root growth, nutrient uptake and oxygen availability likely played a part. When that happens the solution is to get busy with a foliar program where you apply vital minerals to the plant and products to stimulate microbial activity that will stimulate the formation of growth promoting compounds.

After viewing lots of fields that seemed have stalled the common theme seemed to be that the PPO herbicides caused major leaf burn. The loss of green tissue resulted in energy deficient plants unable to find the power to form flowers. This is where the products, such as those by SprayTech, that allow the AMS and a portion of the MSO to be reduced/eliminated, left plants able to harness more sunlight so they didn’t slow down after the weed control application.

More trips and diseases control

After the V8 stage any additional trips through the fields via high clearance sprayers or plane will generally be to apply late season nitrogen, minerals, or fungicides for fungal control. Proper micronutrient levels are vital to plants in spurring their drought tolerance and facilitating the disease immune response. Allowing them to enter the pollinations phase lacking those minerals will always lead to increased disease incidence and severity.

The first part of the season has been very wet with lots of dew. As the two major crops reach their reproductive phase disease pressure will ramp up. If you have not learned to identify the symptoms, buy a pictured guide and purchase a folding 12 -24 power hand lens to do your own scouting, or hire a crop scout who has pathology and mycology training.

Most farmers have become acquainted with Gray Leaf Spot (GLS), Northern Corn Leaf Blight (NCLB), and Common Rust. But pressure in the future could come from Southern Rust, Tar Spot, and Bacterial Leaf Streak. Fungicide use can be a tool now, but we need to prepare for the day when fungicide resistance is more common.

I have to visit a field near Ft. Dodge tomorrow, where Bacterial Leaf Streak/Stripe has been diagnosed, to gather samples for the ISU plant diagnostic clinic. If it is confirmed the consequence is that no major company has a product to control it.

At that point only one private chemist has a finished product to be used against it. It is Gram negative, which differs from the Gram + Goss’s Wilt. We have a copper based product in place, as a combination of phosphite, minerals and AAs can be effective. Wish this grower luck as crop scouts believe the bacteria is already widespread. The prediction a few years ago by seasoned pathologists was that bacterial diseases would become increasingly problematic. It appears they are correct.

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

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