Reproductive phase crops call for yield-preserving management

By Bob Streit, Crop Consultant, Boone, IA 515-709-0143

Specific observations as of July 16:

Now is when we are saving or adding yield. There are still lots of decisions and actions to make on the 2015 crop. Hopefully the weather will cooperate. Here’s an update around Iowa.

1. So far only about four hot days have happened. Corn has grown rapidly, since it does not stop growth for three days following a night below 50 degrees, as beans do. Tasselling and silking is generally on schedule or ahead.

2. The best time for a corn health fungicide application is usually at early brown silk, since those products are meant to protect leaf area for maximum grain fill. No grain fill occurs until about 10 days after tasseling, which is blister stage on corn. Fields that streaked dramatically are at the greatest risk of serious disease issues. Overall, the best control plan is to have each plant so nutritionally sound that diseases don’t attack it.

3. For my money the cheapest and most cost effective fungicide to use would be branded or generic Folicur. Bayer makes both. For soybeans and control of Septoria, a strobe is required. The best products are the mixes, especially the ones that include one of the new carboximides as do the BASF products such as Priaxor. Remember that each gallon of Headline Amp means more money in the pocket of Diane Feinstein’s husband. Look it up.

Another big threat in beans will be from white mold. It loves thick canopies, cool soil temps as in <74 F, and high humidities and wet conditions. The best fungicidal products to control it would be Stratego YLD or Priaxor.

4. I found my first soybean aphids about a week ago near Marshalltown, Iowa which is along highway 30. Near Morris, MN they are finding up to 100 per plant. Any NW winds will blow them in or spread them between fields.

5. Corn rootworm populations and damage have been very light so far. About 30% of any larvae along Hwy 20 are in the pupal stage already.

6. The biggest corn yield robber which crop scouts are seeing if they have been educated (or missing if they have not been educated) are those caramel colored lesions on the leaves down at ground level at V3 or V4 — leaves that have been already sloughed off.

Based on lab work, electron microscopic work and past experience, this is the “new” Goss’s Wilt. Growers who sprayed the correct preventive products for this bacterial disease last year saw tremendous yield benefits, as in 20 to 40 Bu/A.

The plant stayed green longer and filled for more days. This year, be sure to scout for this symptom. Having a strip test kit from Agdia is helpful if you are a rookie in looking for this.

The two products we are recommending would be a copper based product called 42 PHI and a new experimental one we are testing called Bio Impruv.

The experimental one is a biological extract that has looked very good in other crops. I got it into some early treated fields and it looked great. The main potential with it is to add it to any early ground applied application and avoid late season passes or needing a high clearance rig. We hope to get it tested at several universities and on private research farms. I have a small supply for that purpose. We’re working with a few growers to do strips or a few half fields. We may end up finding out that these last 40 bushels are almost guaranteed if and when we see the plants ghost out in Mid August across a multi-state area, as they have the last six years.

7. Expect to be applying fungicide, insecticide, seed set mixes just in front of 30-in. row closure near July 20-25th — and earlier if you are using narrower rows. A closed canopy means higher humidities and more leaf disease.

A broader view of recent field observations (As of July 12)

The most noticeable happening in corn fields now is that many of the fields have been shooting tassels in the past few days. Having another three inches of rain and a few warm days spurred the last foot of growth and tassel emergence. It happened first on the fields planted before Easter and then a few of the earlier maturing hybrids planted the few good days right after that holiday. This was a few days earlier than expected. During my scouting what can be detected is that many varieties are putting on 17 leaves instead of the normal 19 or 20. That hastened the event by 4 to 5 days.

A trait that is becoming evident again is that corn breeders continue to advance varieties that force out silks even before the tassels have fully extended and before any pollen is shed. Two decades ago, one of the worst or perhaps most talked about fears was concern that in a dry year, all pollen would be shed before any silks came out, leaving many kernel sites and perhaps entire ears blank. When those two crucial events coincide, it removes that fear of having poor pollination in a stress year.

Now that the corn is tasseling, or soon will be, the plants enter the reproductive phase — where they become more disease susceptible. Any lack of several micronutrients will increase disease susceptibility. Energy that until now has been used to repel fungal attack has to be dedicated to the formation of pollen and silks.

Scouting for the small disease lesions becomes an important part of managing the corn crop.

There are still many fields in different sections of Iowa where saturated soil existed too long, and a significant amount of nitrogen was lost to leaching or denitrification. The yellow leafed plants show up as a surrender flag that growers have to recognize and respond to correctly if they are going to meet yield goals. Sidedressing nitrogen at this point requires high-clearance sprayers and either drops or dead-on-dribbler attachments.

In soybeans, the issues growers faced this spring were either bean plants that were competing fiercely with taller weeds or remained yellowish and stunted.

With the weeds, there were fields where a variety of broadleaf weeds kept growing through residual herbicides for a number of reasons and had to be knocked back with some of the burner mixes.

And there were fields that had been clean until the 15 inches of rain over several weeks diluted the residual products.

While scouting both 30” and 15” row beans, it was possible to think of two or three reasons why either row width was best. Having an earlier full canopy does help keep weed growth down, but makes it tougher to get herbicide spray to penetrate the canopy. It was easy in the narrow rows to find waterhemp plants just below the weed canopy, waiting to burst above the bean plants just after the sprayer had passed.

Herbicide Issues?

It can be a ticklish situation when any issue with herbicide by soil type or variety appears. Those products will act differently out in a field than in a growth chamber, where unfavorable weather does not occur.

What farmers and agronomists are seeing is that the HPPD and PPO herbicides applied this spring are acting differently than they did in 2014 or 2013. It’s partly due to this year being very wet and last year being very hot and dry after application. Both of those modes of action, as with SUs and ALS, offer residual activity that can vary in timing and effectiveness depending on soil types and soil properties, amount and timing of rainfall, sunshine and GDU amounts, and varietal characteristics.

The products used last year, the timing of their application and rainfall between their use and fall freeze up, and degree of degradation can and do influence the percentage and amount of product that can be carried over from the 2013 to 2014 season. A number of companies have had reps out walking fields and trying to determine what actually transpired. They actually want to determine and analyze what series of events led to any problem.

What is worth knowing is that the product sold as Authority is not at fault and is giving good performance. Back when it was an experimental product about 15 years ago, it was found to burn a few late Group 4 varieties from a major seed company.

This year we might be able to safely say everyone learned how to manage it best. With some of the more recent releases, those products may have encountered the wettest conditions since they began being tested.

After learning more from several excellent fertility texts such as Marschner and Huber/Datnoff and recognizing that most herbicides work by chelating minerals such as copper, manganese, or zinc, we recognize that dry conditions (or those unfavorable to nutrient release via biological activity) have a bearing on herbicide activity and phytoxicity.

If those minerals are only present in the oxidized form rather than the reduced state, an element may not be available for the plant to use to detoxify a herbicide or allowing a safener to function.

In a conversation with a herbicide product manager, we were discussing what products could be used for broadleaf control in beans or corn if the PPOs and HPPDs fell by the wayside with the previous #1 not being effective anymore or considered unsafe by growers.

Thus the physiological herbicide degradation pathways known as GST, Cytochrome P450 pathways, and glucose conjugation are terms that growers intent on learning about the older herbicides and their characteristics are things they will have to understand and master.

A good battle plan on stunted, yellowed beans might be to apply a micronutrient mix and a biology stimulator like Foliar Blend to spur growth.

Be ready for Corn Rootworm beetles that should be emerging over the next two weeks. If and when they appear, have your battle plan in place if you have seen lodging problems in your fields. Does controlling the egg laying beetles sound like a good plan to you?

It seems early due to our shorter bean plants, but aphids are already floating in and having babies. They are not the cuddly kind. Good luck in your fields.