Tuesday, July 23, 2013

Go For A Walk

If you are standing around getting frustrated waiting for the wheat to dry and need a diversion, take a walk in your soybean field.  Brian came in this morning and alerted me to increasing soybean aphid numbers. He is right, we need to watch this situation.
Look at the newest developing trifoliate. This is where they start because the youngest leaves are the juiciest.
Soybean aphids are born pregnant and can multiply rapidly.  Brian has already sprayed a couple of fields this year that got out of hand.  This is what the plants looked like before he sprayed.
The reason aphid numbers were so high was due to this grower not using any Cruiser seed treatment. Cruiser is extremely effective at controlling early infestations of aphids. The insecticide effect of Cruiser has now worn off.  Reports of aphids infecting treated soybeans are starting to come in.  Check different areas in the field.  Aphids will accumulate in "hot spots".  If you locate aphids come back to the same spot in 2-3 days.  If the numbers are increasing, pay close attention.  The threshold for spraying is 250 aphids per plant AND increasing numbers.  A terrific tool for helping determine whether you need to spray or not is a smartphone app that can be downloaded free from http://www.aphidapp.com/

Monday, July 15, 2013

Emotional Rescue

Last Thursday Brian and I spent the day walking on top of, instead of through, corn fields like this one. Strong winds from Wednesday's storm blew down corn from just west of Rannoch through St Marys and followed a path across Embro, Hickson and Innerkip.  Hail was mostly confined to the town of St Marys causing more damage to vehicles sitting outside than to field crops, so we were spared that particular problem. The wind however left many magnificent fields laying in ruins.  By the end of the day we were both in need of some emotional rescue.  It had been a depressing day.
By Monday morning the same spot in the field pictured at the top looked like this.  Recovery was dramatic. There is still some goose necking and a few plants snapped off, but compared to last Thursday you would not believe it was the same field.
One clue that the plant had been on the ground is the mud caked on the top leaves.  The impact on yield will not be as large as it first appeared.  A summary of a two year trial looking at the effect of wind lodging vs stage of development can be found at this link.


The fact that the corn plants are in the vegetative growth stage of development is the reason for the quick recovery.  Last Wednesday a lot of corn was in the V8-V10 stage of growth.
A V10 corn plant looks like the plants above.  V10 just means there are 10 visual leaf collars.  A leaf collar is formed when the leaf is fully developed.  You have to remember to account for the bottom leaves that are no longer there because they were lost in the May 25-26 frost.
A V10 corn plant will have 12-13 leaves visible and 9-10 leaf collars.  A mature corn plant has 15-16 leaves.  If you carefully pull the plant apart you will find the rest of the leaves and tassel rolled up inside the whorl.
This V10 plant still has to push out three more leaves plus the tassel.  At his time of year you can expect a new leaf to emerge every three days.  3 leaves x 3 days is 9 days plus two more days for the tassel to fully emerge equals a total of 11 days of vegetative growth.  These 11 days give the plant time to recover from the wind damage, grow more roots, stretch upward to the sun and prepare for pollination.  This is why the actual yield loss from the wind damage will probably be less than 5%.  After tassel and pollination is complete the corn plant diverts all of its energy to grain development and yield losses due to storm damage increase dramatically.

Since we are talking plant physiology we should point out one more thing.  Ear shoots are visible in a V10 corn plant.  Carefully removing the leaves reveals ear shoot formation occurring at each node.  There is one dominant shoot that takes priority over the rest, but the plant prepares for the future by generating 4-5 ear shoots and if the environment allows it then has the ability to produce multiple ears.

This is a close up of the largest and most dominant ear shoot.  You can make out the beginnings of the new ear in the centre of the shoot.  Silks from the ear shoot will begin to emerge slightly ahead of the tassel emerging.  Every year the question is asked about why silks emerge ahead of the tassel.  It is normal and healthy for silks to emerge first because a corn silk will remain receptive to pollen much longer than a pollen grain can live.  A corn plant generates pollen for about 5-7 days and the plant starts extending the silks slightly ahead of the tassel to match the timing of maximum silk availability with maximum pollen shed.
So steadfast and true, the corn plant comes to our emotional rescue.

Sunday, July 7, 2013

The No Win Scenario

The "no win scenario" is a famous line among Star Trek fans.  James T. Kirk did not believe that a no win scenario ever existed.  However, the good captain of the Enterprise never faced harvesting a wheat field badly infected with fusarium head blight.  Fusarium has infected most wheat fields in our area and the wheat harvest is not going to be any fun. Recent rains and humidity are adding to the problem by promoting growth of this disease with the associated higher DON levels that make elevator owners and farmers trade punches over the counter. Why is it such a problem?
Fusarium is a disease that flourishes under damp weather and moderate temperatures. It also is a disease that needs a very specific timing for infection.
Infection occurs at flowering time.  Wheat heads neither emerge nor flower all at the same time.  Main heads always emerge sooner than tiller heads.  Each head itself starts flowering at the base of the head and progresses to the top.  Without going into detail, fusarium spores explode in bursts and if the wheat flower is receptive to the spore, the spore will infect the flower and prevent the kernel from forming.  This timing of spores vs flower receptivity is very precise and is why only part of the head is infected. Temperature and humidity fluctuation from one day to the next can greatly change infection levels.  Sometimes the infection is at the bottom of the head, sometimes the middle, sometimes the top.  It is frustrating to know that it can't be totally prevented.
There is a temptation to believe the money spent on fusarium protection is wasted, but not so.  Fungicides contribute to reduced infection levels by protecting the flowers from infection.  However, the labels of both Prosaro and Caramba claim suppression, not complete control of fusarium head blight.  With heavy disease pressure there will be some infection.  Where no fungicide is used infection levels skyrocket and can result in a product that is practically unmarketable.  It literally can be classified as toxic waste. Fungicides definitely give us a fighting chance.
Economic losses from fusarium come from two directions.  Infected flowers do not produce a kernel or at best a light kernel.  The direct result is lower yield.  The bigger problem is with the right weather the infection moves within the stem of the head and spreads onto the skin of healthy kernels.  These stick out like a sore thumb in a grain sample and we can't keep them out of the sample.  The weather has been perfect from the fungus point of view.  That is where the no win scenario comes into play.
The standard recommendation from the agronomy crowd is to harvest early and pay the drying charges for one very good reason.  Grade discounts are higher than drying charges.  DON levels will rise every day the crop stands in the field.
Grizzled combine veterans have little patience for agronomists telling them when to go to the field.  Few agronomists have had to write the cheque for the extra fuel burnt while harvesting high moisture wheat.  Few agronomists have spent much time sitting on the edge of the seat in a combine cab hoping that the next wad of green straw going into the cylinder is not followed by complete silence.  Few agronomists have struggled with cylinder, concave and sieve adjustments necessary to separate wet kernels from tough straw and at the same time keeping lighter infected kernels from contaminating the sample. Some combines are just not capable thrashing tough wheat no matter how good the operator.  The ultimate no win scenario.  Regardless, harvesting as early as possible is still the best tactic against the no win scenario.
Can a pre-harvest glyphosate help dry the plant enough to make a difference in harvestability and reduction in DON levels? The short answer is yes, it will help.  If there is no clover under seeded or if you know your combine struggles badly in tough wheat, it will tip the odds of a clean  sample more in your favour.  Get some advice before you spray.  A good agronomist may not know a rasp bar from a top sieve, but he or she will know how to properly time the spray.  The wheat plant must be physiologically mature.
The 2013 wheat harvest will be a test of will.