Ground Application vs. Aerial Application at Harvest Time

The following is an excerpt from the West Plains IPM Update and was written by Kerry Siders, Texas A&M AgriLife, EA-IPM, Hockley & Cochran County.

 

Ground Application vs. Aerial Application at Harvest Time:

Received a call from Larry Smith yesterday about something we have contemplated before, but never really put a pencil to. That is if the damage caused by a ground rig to good irrigated cotton, which is lapping the middles when applying a harvest aid, exceeds the cost of putting a plane in the field. So this can be a perennial question for many.  Let us try to break it down and put a pencil to it.

 

In this example we will use a ground rig which covers twenty-four rows per through. The wheels will make contact with four rows, which is 1/6 or 0.167 of the area. For sake of a conservative calculation we will say that the ground rig will damage (remove from plant or render non-harvestable) 0.5 bolls per plant the rig comes into contact with. For calculation purpose we will use a plant population of 42,000 plants per acre.  So if we damage 0.5 bolls per 42,000 plants that is 21,000 bolls per acre, and we only effect 16.7% of the area (21,000 X 0.167) which is 3507 bolls damaged per acre. Does not seem that bad so far. This is pretty good irrigated cotton so it will take 300 or less bolls to make a pound of lint. So 3507 bolls divided by 300 = 11.69 pounds of cotton lint.  At $0.70 per pound lint, 11.69 lbs cotton has a value of $8.18 per acre. So the ground rig could possibly cost $8.18 in lost/damaged cotton, not to mention the cost of the operating the rig.

 

Last I checked the cost per acre on a plane was less than that.  So thank you Larry for prompting me to put a pencil to this.  Each of you may need to consider the damage you may be causing with a ground rig to cotton ready for harvest aid.  Each field situation is different, but this may give you a method of considering if it would be advantageous to put a plane on the field vs. a ground rig. Call if questions.

Thanks Kerry,

Please call or come by if you have any questions,

Blayne

 

Cotton Harvest Aid Season Starts

          Both by the calendar and what I am seeing in the field, cotton harvest aid considerations are coming to the forefront in another year.  Harvest aid decisions truly do seem more art than science with so many variables affecting product performance and application timing.  This time of year everyone in the industry pays extra attention to the weather forecasts and keeps an eye toward the cotton stage as we strive to take as much of the guess work out of harvest aids as we possibly can.  Producers certainly do not want to miscarry a crop this late in the game.  Consultants and advisors must be on their toes. Applying harvest aids too early can cause yield reduction, be harmful to fiber quality, and will damage seed weight and quality while applying too late exposes the precious fiber to the elements which can cause fiber degradation, and lint string and outright drop. 

With that in mind, the 2013 High Plains and Northern Rolling Plains Cotton Harvest-Aid Guide is now available through http://lubbock.tamu.edu/.  The Harvest-Aid Guide is stuffed with useful information updated annually for the purpose of helping producers and specialists make educated harvest aid decisions.  Of particular interest to me are the latest Cotton Harvest-Aid Decision Tables.  These tables contain the current list of locally tested and labeled harvest aid products complete with recommended rate ranges and surfactants.  For a full overview of all cotton harvest- aid considerations, please reference the 2013 guide.  There can seem to be endless factors effecting harvest aid decisions.  Here, I would like to review the three main FIELD MEASURABLE factors influencing the basic ‘field ready’, or ‘field not yet’ question in cotton harvest-aid decisions. 

If there is one factor that can be (or for some odd reason must be) used alone I would suggest evaluating the uppermost harvestable boll’s maturity.  I prefer to utilize the old standard boll maturity rating system of 1 through 3.  To evaluate the maturity of a cotton boll, use a sharp knife to cut into the boll somewhere between the upper half and upper third.  If the boll is watery or jelly-like on the inside, then it is immature and needs more heat units.  This boll can be rated as a maturity 1.  If limited or no additional heat units are available from the environment, that boll can likely be considered as not harvestable, and another boll farther down the plant needs to be evaluated.  If boll development is such that the knife cannot slice through the lint easily, then the boll is nearly mature.  Close inspection of the seed will give further indication of boll maturity.  If the seed coat is turning tan and the seed leaves (or cotyledons) are fully developed, the boll is nearing maturity.  This boll could be rated as a maturity 3.  In between these two ratings is a maturity 2.  Fields that have an average boll maturity rating of 2.4 can be considered ready for harvest aids.  We need only evaluate enough bolls to be confident in the average rating for that field that day.

A second factor is the NACB (nodes above cracked boll) stage of the field.  For those who are accustomed to making in season NAWF (nodes above white flower) evaluations, this evaluation is very similar with one difference.  In place of counting nodes from white flower to uppermost unfurled leaf, we count from uppermost cracked open boll to uppermost harvestable boll.  When the cotton field averages 4 NACB, the field is likely ready for harvest aids. 

The third factor is percent open boll.  This is likely the easiest factor to understand, but requires the most effort to obtain.  I prefer to measure 10 row feet from several locations within the field, counting the number of open bolls over the total number of bolls within all 10 foot areas to obtain an accurate percent open boll count for the field (percent open  boll = # open bolls / # total bolls).  Once a field reaches 60% open boll, then it can be considered ready for all harvest aids, except for pure desiccants which requires a 90% open boll count and is only really utilized in dry-land situations.  Taking the percent open boll counts does take more effort but once we have taken the 10 row feet counts, other useful knowledge can be gleamed from the information such as yield estimates and field variability.  

  Ideally we should utilize and combine all three of these field measurable factors to help put as much science into our harvest aid art as possible.  This data, gathered correctly, should then be considered along with many, many other factors, such as expected two week temperature, available sunshine, night time temperature, leaf drop, plant moisture content, expected freeze date,… just to name a few .

Please call or come by with any questions,

Blayne

 

Moth and Worm Invasion

               Local insect populations have built, or possibly rebounded, over the summer months.  The season’s rains, while not drought busting, have provided lush habitats for several species.  As a result, we are feeling inundated with multiple, sometimes overlooked, species of insects.  The most notable belong to the Lepidoptera order.  In Hale and Swisher Counties we are already dealing with economic populations of FAW (fall army worms) and bollworms in sorghum and some cotton, but these are far from our only species of interest, or the only ones that could pose problems. 

                Over the past few weeks, other area and regional entomologist and I have noted and fielded several questions about high numbers of ‘odd’ caterpillar larva and moths of various species causing a stir.  The White-lined sphinx moth was the focus of Dr. Ed Bynum’s (Texas A & M AgriLife Extension Entomologist - district 1) August 30^th edition of the Panhandle Pest Update.  In July, Manda Anderson (EA – IPM, Gaines County) mentioned garden webworms in her weekly newsletter.  This week Dr. Pat Porter (Texas A & M AgriLife Extension Entomologist – District 2) sent out alerts regarding the yellow stripped armyworm (true armyworm).  All district IPM agents responded to Dr. Porter’s alert stating that they too were finding the yellow stripped armyworms at varying levels alongside several other foliage feeding larvae. 

                After noting intense feeding upon pigweed by an unknown Lepidopteron species in the area, I enlisted the aid of Dr. Bynum and subsequently Dr. Porter in identification.  This species turned out to likely be the garden webworms that Manda had mentioned back in July spreading, in very high numbers, across the region.  These garden webworms can currently be found locally by the thousands feasting upon Palmer, kochia, and even some Johnson grass, doing what our best efforts in weed control could not (unfortunately they are doing it after the weeds have seeded out).  However, the garden webworms are not working alone.  There is a healthy mix of yellow stripped armyworms, beet armyworms, various cutworms, multiple looper species alongside the webworms, and likely several others such as the smartweed borer. 

                So far, this conglomeration of foliage feeding caterpillars has focused on weed species and just a few field margins.  Several of these species are known crop pests.  It is possible, maybe even likely, that once the weeds have been laid to waste, these hungry caterpillars could move to our area crops, gardens, and yards.  As veracious as these caterpillars are, they could devour and ruin a small garden, hedge, or certain trees in a matter of hours and a crop field in days.  On the crop side; any BGII cotton should be safe as should any Bt corn.  All sorghum and other non-Bt crops are at risk. 

I suggest keeping an eye on these caterpillars.  In the meantime, we are getting to see much of our weeds turn brown.  Hopefully, that is all they will attack.

 

Please call or come by if I can help,

Blayne

               

Fall Army Worm Concerns in Sorghum (& corn)

           We have been expecting some pest troubles to develop in our later crops in Hale & Swisher counties for some time.  Last week we found several sorghum fields (most just entering soft dough stage) with economic bollworms, one of the species that commonly make up the sorghum headworm complex.  Unfortunately, we are finding that the bollworms are not alone. 

            This week we are finding several FAW (fall army worms) following the bollworms into the sorghum fields, just a touch behind.  The ET (economic threshold) for any sorghum headworm is roughly the same without much regard to larva species.  Literature regarding headworm control, etc. can be found in Managing Insect and Mite Pests of Texas Sorghum.  However, species identification is crucial if your field does have an economic headworm problem.  Most of the labeled products for bollworm (i.e. corn earworm) will not control FAW larva.  In this case, we must change our recommended treatment to a product that has a chance to control both.  Changing products does come with a higher sticker price, so we really need to make certain of your species present before applying any labeled product for headworms.  Good photos to aid with larva identification between bollworm and FAW can be found in the July 5 edition of FOCUS.

            Of course sorghum is not the only area crop the FAW will attack.  Corn, cotton, early planted wheat, and even several hay crops are at risk.  I am finding several FAW in late planted corn, and a small number in cotton, but at this time they seem to prefer the later planted sorghum that is just moving toward soft dough stage. 

 

Please call with any questions,

Blayne

Bollworm, Earworm, or Headworm?

                For the past several weeks, we have been expecting a large moth flight this month, based upon regional trap catches and what we, and other area entomologist, have been seeing in the field.  Now that we have had some moonlit nights, we are starting to pick up fresh bollworm egg-lay in our program fields this week.  There has also been some debate about which area crop the bollworm would choose.   With a large amount of late planted corn and sorghum, it was suspected that the bollworms would prefer to lay eggs in late corn first, late sorghum second, and cotton as a last resort.  Early indications from the field show that this is probably correct. 

                Yesterday, August 19^th, a field scout reported finding 15 bollworm eggs per plant in a late corn field with a mix of brown and green silks, a prime bollworm habitat.  This morning, August 20^th, I scouted a field just starting green silk stage, a field where we would expect to only see the beginnings of moth attractiveness, and found 2 bollworm eggs per plant.  I feel it is likely that this trend of corn preference will continue as long as green corn remains prevalent in the area this fall.   Typically we are not economically concerned about bollworms that choose to be earworms.  Even heavy egg lay of bollworms in corn should not be a major economic concern for Hale & Swisher Counties.  Eventually, the larval caterpillars will cannibalize each other until there will only one worm per ear remains ensuring that the strongest survive.  While we do not like to see even one worm feeding in our corn, it is not economically feasible to attack those few earworms who are protected inside the corn shucks with multiple, predator damaging sprays, especially with spider mites already in the mix. 

                The bollworms that choose to be headworms in sorghum (and millet) are much more of an economic threat.  Mostly because we can make effective sprays to the exposed head of grain, but also headworms do more damage to our sorghum yields proportionally.  Yesterday, August 19^th, I scouted a field in milk stage and found 0.5 small headworms per head.  This is sub-economic but something to watch nonetheless.  Roughly half these headworms were FAW (fall army worms), another important species that make up the sorghum headworm complex.

                Any non-BGII cotton is now at a heightened risk, but doubly so if that field is not near any late corn.  This morning, August 20^th, I scouted a late and growthy cotton field not near any grass crops and found 7,199 bollworm eggs per acre.  With no corn or sorghum in the vicinity, I would expect bollworms to settle on cotton, the lusher the better for the worms.  So far, we are not finding bollworm eggs in cotton if late corn is in the area. 

 

                We already know that FAW is an economic concern in cotton and sorghum.  Recent research, much of which is still ongoing by Dr. Pat Porter, indicates that FAW should be a concern in corn, especially late corn.  Gary Cross, CEA – Hale, and David Graf, CEA – Swisher, are assisting Dr. Ed Bynum in some area wide moth trapping studies.  Their FAW trap catches remain low, and we are still finding large FAW larva in whorl stage sorghum.  We are also not finding FAW egg masses at any significant level yet.  All of these indicate that FAW are late but may join the mix in the moth flights soon, at least locally.  

 

Please call with any questions, or leave a comment about what you are seeing.  Thanks,

Blayne

Bollworm or Headworm

 

        Corn earworm, sorghum headworm, and cotton bollworm, no matter what you call it, this insect is a nuisance.  We have found a few bollworms in cotton fields this summer, but none at threshold yet.  As the area’s corn begins to harden, we should see the next generation of moths moving into the cotton and / or sorghum to lay eggs.

            The adult bollworm will lay its eggs just about anywhere on the plant these days, but the old textbook states that they prefer the upper 1/3 of the cotton plant on the upper side of the leaf surface.  The eggs are small, oval shaped and pearly white in color, with a slight dent in the tip.  If you have eggs in a field, even huge numbers of eggs, you don’t have to treat yet.  The eggs can be parasitized or eaten by a variety of things and some may even be unviable, so several won’t get to hatch.  Once the caterpillars hatch they begin to feed on whatever is nearby, but move to the fruit as soon as possible.  These worms do live in a world where it is survival of the fittest.  The caterpillars will often cannibalize each other, if their eggs have been laid too close together or they attack the same fruit, ensuring that the strongest larva will survive.  These factors combined are why we usually wait until we find a threshold number of caterpillars (the smaller you catch them the better) before treating a field.  The size of the caterpillar changes the threshold as well, since during the last two instars, the caterpillars consume up to 90% of the total amount they consume before pupating.

            ¹We really start looking for bollworms in cotton when our blooms have started becoming bolls, but they can infest cotton earlier if their preferred host (corn) is unavailable.  The threshold for this insect in non-Bt cotton with bolls forming is about 10,000 worms ¼ of an inch or smaller per acre and 5,000 worms larger than ¼ of an inch per acre.  In Bt cotton, we look for 5,000 worms larger than ¼ of an inch per acre with 5 t o15% damaged fruit on the plant.  Once the insects reach this threshold, treatment should be considered.

            The threshold for sorghum also varies with the size of the insect and the crop value.  The worry starts when the caterpillars found are ¼ of an inch or larger.  While they are ¼ to ½ of an inch long, the way to determine the threshold by considering the economic injury:

Number of larvae per head =

 

Cost of control in dollars per acre x 9754 Grain value in dollars per cwt x number of heads per acre x 0.19

                                                   

     When they are larger than ½ of an inch, the formula to calculate the threshold by considering economic injury is:

Number of larvae per head =      

Cost of control in dollars per acre x 9754

Grain value in dollars per cwt x number

of heads per acre

 

 

            A sorghum headworm ET threshold calculator is available for Droid phones from

the Google Play Store at http://goo.gl/8mXvv, or for other systems on the internet at http://goo.gl/5k7ZtU.

 

Good Luck!                                                                            Please call or come by the office if

   you have any questions.  Thanks!

        Kate                                                                                                        Blayne

 

References

1          http://amarillo.tamu.edu/files/2010/11/Panhandle-Pest-Update-v4i11-8-24-2012.pdf. Panhandle Pest Update on August 12, 2013

       

 

 

Spider Mites

           The past couple years spider mites have put pressure on our area’s corn and the mites are at it again in 2013.  There are two species we run into commonly, most often we find the Banks grass mite, and occasionally the two spotted spider mite.  The two spotted spider mite has dark spots on either side of the body and can be more damaging than the more solidly colored around the its body edges Banks grass mite.  Hot and dry conditions favor spider mites, and their populations can boom in these conditions.

            Spider mites can be difficult to control, and often beneficials can provide control if enough are present in your field.  Fields that have been treated to control Lepidopteron pests, such as southwestern corn borer and western bean cutworm, are often more likely to develop mite problems.  Insecticide applications to control caterpillars in a field can actually knock back predator populations and cause mite populations to flare.  This summer we have been working on a miticide trial in Hale County, and we actually had to flare the mites by spraying a pyrethroid before the mites started becoming problematic.  We are comparing all possible products labeled for mite control: Portal, Oberon, Onager, and Zeal for best mite control, some at variable rates.  We will be sharing the data from the trial as soon as it becomes available.  We are as eager as you are to see the miticides compared to one another, hopefully before they cause any economic damage for you.  At 3 DAT we had no statistically significant differences between any treatments and the untreated check, but noted several dead mites in all treatments.  This is not uncommon due to the nature of our usable miticides. 

A corn plant can tolerate reasonable mite damage to the lower leaves before mites become economic.  Mites begin to be an economic threat when they near the ear leaf.  When this leaf, the zero leaf, is nearing 50% coverage by mite colonies and the leaves below have heavy colonies and you note some mite movement above, it’s time to seriously consider a miticide treatment.  This is a lower threshold then many of us utilized in years past, but remember all of our newer miticides do not have a very quick knockdown but rather take time to work and rely upon support from beneficials for absolute control.  Many of the older chemistries might still be labeled for mites, but the mites have proven to be resistant to them.  Meanwhile, these newer miticides are much more predator friendly, but if mites do reach ET, treatment needs to be swift.  Only if your corn has reached a solid dent stage, and has near threshold mite populations, you may be able to consider holding off a treatment.  When the corn is starting to dry down, mites do not cause as much economic damage.  However, if the mite populations remain too high, they can cause lodging in the drying crop.  Be sure to consider your options and take a good look at mite populations, plant stage, and predators before treating, but treat quickly if needed.