A Pain In The *****

The one weed we get asked about the most, often in the winter after the season is finished, is perennial sowthistle.  It has always been around, but seems to be increasing in number. 

It is seen this time of year in patches.  Later in the summer you will see groups of pretty yellow flowers above the soybean crops.  It is a perennial weed that grows from root reserves, which makes it a tough critter to deal with.  Glyphosate in the spring is not effective against sowthistle, which partly explains why this weed is increasing, because the root reserves allow it to regrow.  Glyphosate will burn the top, but will not go to the roots, so the sowthistle grows back.  

There are three strategies for controlling perennial sowthistle.

1. In glyphosate resistant corn, apply glyphosate as late as possible.  Sowthistle will start to replenish it's root reserves when it starts to flower.  A late spray can get to some of the roots and weaken the weed.

2. Apply Classic as late as possible in soybeans.  Classic rates a 7 for sowthistle control in Pub 75, which means it is good, but not perfect.  In glyphosate resistant soybeans, Guardian (glyphosate plus Classic) improves the score to an 8.  The Classic needs to be applied before soybeans start to flower in late June.

3. Apply glyphosate in the fall, early September after wheat is best.  This works because after sowthistle flowers, it will be replenishing root reserves and glyphosate will then translocate to the roots.  We need good moisture for this to work.  If the sowthistle is under drought stress we get lousy uptake of the glyphosate and the weed survives to come back in the spring.

Walk your fields now to locate patches of perennial sowthistle and plan accordingly.

Corn in Recovery Mode (cont'd)

The frost on Monday morning has given us an opportunity to illustrate the effect of heat on recovering corn plants. This is the shot of the corn plant from Thursday's post, 72 hours after the frost event.  It spent the first 24 hours outside, then brought inside.  At a constant 20 degrees inside temperature, there is an accumulated 30 heat units every 24 hours.  When we include Monday this plant has accumulated 65 heat units over the 72 hour time frame.

The shot above is from a plant on Friday morning, 96 hours after the frost and kept inside for 72 hours.  You can see the rapid emergence of new leaf tissue that resulted from an addtional 30 heat units accumulated from Thursday to Friday, for a total accumulation of 95 heat units.  In the picture below, the plant to the right was selected on Friday morning from the same corn field as the plants above.

The plant on the right suffered for 96 hours outside from Monday to Friday where it accumulated less than 50 heat units and had to deal with one inch of cold rain.  Not only can you see a big difference in leaf development, but notice the abundance of root growth on the indoor plant.  The good news is the corn stand is recovering and as of this morning (Saturday) you can start to see rows of plants in the field.

These plants will have a sick and yellow look for a while, but they will live to fight another day.

Corn in Recovery Mode

The morning of Monday May 10 saw widespread frost across the area with temperatures dipping to -5 in the early morning hours.  Later in the day, corn was looking similar to this picture and by the end of the day all leaf tissue had totally blackened and disappeared.  The extent of damage depends on many factors, including soil type and topography, to name just two. 

The picture below, taken on Wednesday May 12, illustrates the fine line between no damage and apparent death.

Beside this mature windbreak of 20' tall evergreens, the corn plants survived.  This effect extended out 20 rows or 50' from the edge of the windbreak.  The rest of the field is barren, no corn and no weeds.  This actually is backed up by research that predicts the positive effect of a windbreak to be 2.5 times the height of the windbreak.  But on a frosty night there is little to no wind and we may wonder why we still get the benefit of the windbreak.  This is because the living trees give off enough trapped heat to warm the surface temperaure of the soil and this slight temperature difference was enough to protect the crop from frost damage.  The weeds between the rows are also doing fine, but that will be easy to fix.

I believe the corn crop will survive and regrow.  The next picture is a plant taken from our own field, which had emerged and was at the two leaf stage before the frost.  On Tuesday I brought a few plants inside to warm up.  This picure was taken Thursday morning, 72 hours after the frost and 48 hours after being brought inside and kept at 20 degrees.

 

You can see the new leaf growth emerging from the whorl, which indicates the growing point is still alive and well.  I will post a picture tomorrow to show what another 24 hours of warmth will do.  It has been too cold and wet this week to see much growth recovery in the field, but I remain confident corn will show some life this weekend when it warms up. 

I have been asked what effect this frost has on yield and this is a difficult question to answer.  The balance of the growing season will have more impact on yield than this frost.  One thing we do know, it will impact maturity somewhat.  The plant was shocked and it takes some heat, maybe 30-50 heat units, to put the plant on the road to recovery.  This heat would have been put to use in advancing growth under normal circumstances, but now has been used for recovery.   

Be Careful What You Wish For

There were too many of us a week ago wishing for some rain. We sure got it. At time of writing here on Saturday afternoon the area received between 1-4" of rain depending on which thunderstorm happened to pass by. Heavy rains are very destructive to soil structure. Big rain drops are like small atomic bombs, which completely shatter soil particles. The result is a tight film of smashed particles across the surface of bare soil and the weight of the standing water adds to the problem. The finer the seed bed, the worse this condition is and many of our fields worked down like powder in April. If your crop was close to emerging, it will still make a stand without too much trouble. If it had just been planted, we will need to keep an eye on crusting problems and be ready to react with some type of crust fighting device.



The other issue for those of you that have corn emerged, with no herbicide down, will be to get that crop sprayed as soon as possible.

I have attched a photo from Aaron's Agronomy Blog showing a 3 leaf corn plant. Research has proven a corn field needs to be weed free by the 3 leaf stage or yield losses can start to accumulate. This is because the weeds, particularly small grasses, compete for the same light as the corn plant. Too many grassy weeds reduce the photosynthetic capability of the young corn plant. The saturated soil conditions will prevent sprayers from moving for several days and more rain is in the forecast. It is another reason why I like some residual herbicide down at planting time. It keeps the crop clean through its early growth stages.

Fasten Your Seat Belts

The Pioneer corn research team from Tavistock showed up in our yard last Thursday. They needed a parking spot to inload their Kinze planter so they could plant a hybrid test location on a neighbour's farm. You guys with your 16 row planters have nothing when compared to an 8 row research corn planter.

They were able to plant 10 acres of plots including hundreds of hybrids, each plot being 2 rows wide by 13 ft long, in just 3 hours. In the research game that is moving at the speed of light. They were able to finish before the first thunder storms arrived that afternoon.

They also have a 4 row planter that was working at a different location that same day. All of this activity is done in the name of bringing us new and better corn hybrids as efficiently as possible.

Beans Beans

This picture was taken this morning from a field that was planted on April 20. Most farmers would say "keep the drill out because these beans don't stand a chance", they will be frozen to death in a matter of days. We will see.

All I know is soybeans are tougher than we give them credit for. The book says because the growing point is always exposed a soybean plant cannot take a frost when compared to a corn plant, which has the growing point below ground up to the 5-6 leaf stage. I guess nature doesn't read the same book because I have seen small corn plants hurt by frost and soybeans in the same field without any damage. Time will tell.

Heat Unit Tips

It is easy to know how many heat units have accumulated if you watch corn emergence closely.
From the day you plant to the day the crop emerges, you automatically know you heave accumulated about 150 heat units.

After that you need a chart like this which gives you an idea of how many heat units accumulate on any given day. All you need to know are the maximum and mimum temperatures received on that day.

For example, on a spring day where the night time low is 5 degrees and the daytime high is 13 we accumulate 5 heat units.

On a summer day where the low is 15 degrees and the high is 30 degrees we accumulate 26 heat units.

Also take note that as daytime highs exceed 30 degrees the accumulated heat units start to decline. This is because the corn plant starts to suffer heat stress, just like we do, and tries to shut down.

I will return to this chart later in the year.

I Love It When A Plan Comes Together

Corn is emerging. This corn was planted April 14. It takes about 150-160 heat units to get corn out of the ground from 1.5' deep. Ideal conditions this past week has corn emerging that was planted two weeks ago. Early stands will be excellent due to mellow seedbeds and gentle, warm rains.

For a great summary of early corn physiology and growth, check out the attached link.

http://www.aaron'sagronomyblog.com

My Pet Peeve - Dandelions

Those of you who read the financial press know when an author writes about a company they should disclose whether they own shares of that company.

Here is my disclosure for the day. It is dandelion season and I hate dandelions. Cathy, who loves flowers more than most people, hates dandelions. Dandelions are relatively easy to control when they are young, but much tougher when they are 3-4 years old like the rascals in this picture.

On our farm we have a three step formula for keeping dandelions out of our crops.
1.It starts with a fall application of glyphosate in wheat stubble. Dandelions seed in the summer and early fall. Glyphosate is deadly on seedling dandelions in the fall. Dandelions also do not like being disturbed. We use a light tillage pass with a disc, or other vertical tillage tools or sometimes heavy tillage with a disc ripper. This eliminates dandelions from our corn crop.
2.In the corn crop we use soil residual herbicides like Primextra or this year we have tried some Integrity, a new product from BASF. If we need a post emerge application we use glyphosate to tidy up the field. Nor sure what impact this has on dandelions, but we have a clean field and very few dandelions in our corn stubble.
3.In soybeans we always include Classic as part of our herbicide mix. Classic gives practically 100% control of young dandelions through the growing season. We rarely have to spray our wheat in the spring for dandelions and I credit this to our use of Classic. Our goal is to get a wheat crop that looks like this.

In our opinion, farmers get into trouble with dandelions by waiting too long to go after them and putting too much faith in glyphosate alone in the spring.

This is an example of the effect alfalfa cutting dates have on dandelions the following spring. The left hand side of the photo was cut in the fall, the right hand side was left uncut last fall. The healthier regrowth on the right has kept the dandelion population in check.