Sugarcane Aphid Management on the High Plains

Now that sugarcane aphid has been found in Floyd County it is safe to assume that we will shortly find it in surrounding High Plains counties. We all went through the aphid invasion last year and there is no need to go in to great depth on scouting and management, so I will just hit the highlights from lessons learned last year. If you want to read our complete 2016 sugarcane aphid management publication it is here.

Early planting is going to pay off

The earlier the aphid arrives during crop development, the more damage it can do. Infestations prior to boot can cause sterile panicles and decrease yields to essentially zero. Infestations at or after flowering, while still very serious, are somewhat less potentially damaging. This is why our treatment thresholds vary by crop stage.

Treatment threshold:
Pre-boot: 20% of plants with aphids.
Boot: 20% of plants infested with 50 aphids per leaf.
Flowering to Milk: 30% of plants infested with 50 aphids per leaf.
Soft dough through dough: 30% of plants infested, localized areas with heavy honeydew, and established aphid colonies.
Black layer: Heavy honeydew and established aphid colonies with treatment only for preventing harvest problems.

Our earlier planted sorghum has either finished flowering or is now flowering and has moved to the place it can withstand more aphids. In part this might matter because we have a relatively high number of beneficial insects in the system, and they have a better chance of keeping populations below treatment thresholds when those thresholds are higher. And even if one insecticide application is necessary, the need for a second application is far less likely in a much more mature crop.

Weekly scouting is a must

Under hot, dry conditions, the reproductive capacity of this aphid (which is born pregnant) is something approaching Shock And Awe, and everyone who went through the 2015 season will agree.  Missing a weekly scouting might mean missing populations low enough to be brought under control with insecticides. In 2015 we had many fields that were sprayed too late and adequate control was not achieved without a second application. Once the aphid has been found in a field, then twice-weekly scouting is important. Last year I would have linked to our guide to recognizing the sugarcane aphid, but this year I think we all know what the enemy looks like.

"Tolerant" hybrids are susceptible hybrids

There are a few hybrids with resistance to sugarcane aphids, although the seed industry chooses to call these "tolerant" hybrids because they rightly don't want to give the impression they are bulletproof. Our best resistant hybrids are what could be called moderately resistant, and this won't stop the aphids from reaching treatment thresholds. It may slow them down, and it may let the beneficial insects have more time to exert control, but all other things being equal it is merely a delaying action. Fields of "tolerant" hybrids should be scouted and sprayed based on the treatment threshold just like fields of completely susceptible hybrids.

Insecticide choice matters - a lot

Last year saw everything in the book, and some things not in the book, being thrown at sugarcane aphids. Many of these insecticide products were our old aphid standards, and what we found was that they were not very good at killing aphids, but they were very good at killing beneficial insects (the big guns in aphid control after an application). Our insecticide trials confirmed this; we had massive aphid resurgence where we killed the beneficial insects. There are only two good insecticide choices for sugarcane aphid: Sivanto and Transform. Both of these provide high efficacy with minimal impact on beneficial insects.

Make the first application count

Last year we observed insecticide applications of Sivanto and Transform made with high rates and plenty of carrier volume most often did such a good job of control that the few surviving aphids were cleaned up by beneficial insects. Conversely, we observed that fields sprayed with lower rates and/or insufficient carrier volumes frequently did not get control and required a second application.

Experience is a good teacher

This pest is manageable. Last year was a bit of trial and error, but after one growing season of intense aphid pressure we are much better equipped in 2016.

Southern Plains of Texas: Time to Look for Fleahoppers

Suhas Vyavhare and Blayne Reed, Texas A&M AgriLife Extension Service

The high temperatures, high humidity, and the passing of light cotton showers over the last couple of weeks have been very conducive for rapid crop growth and development. Most cotton fields on the Southern High Plains are past the 5^th true leaf stage and are sporting pinhead through ¼ grown squares.  This should mean they are no longer vulnerable to economic damage by thrips. There are some late fields and re-planted fields which can still be injured by thrips, however, and we should continue to scout these fields for thrips. With the high temperatures potential for rapid plant growth, and a lessening thrips pressure in general these field might be able to escape from any serious thrips damage.

As the crop is approaching reproductive phase, we should be looking for fleahoppers—many of us scouting regularly in the field are already seeing a few on squaring cotton.  There are already a small handful of regional fields reaching an economic level for this pest.  If you see the smaller and freshly adorned squares turning brown and dropping to the ground, and / or missing from the plant, the problem could be physiological or weather related but most likely the damage was caused by fleahoppers. Fleahoppers can be found in abundance on their preferred weedy hosts like silver leaf nightshade, woolly croton and horsemint. Although cotton is not the primary preferred host, it is a choice secondary host that fleahoppers will move to once weeds are killed by herbicide application, mechanical cultivation, or physical hoeing .

The adult fleahopper is about 1/8 inch long, pale green, and have piercing and sucking mouthparts which they use to suck proteins and other nutrients from the developing squares. Their bodies are flat with an elongated, oval outline and prominent antennae. As their name suggests, they do slightly resemble a whitish or yellowish-green flea, mostly due to the appearance of their hind legs looking much like the hind legs of a common cat flea.  Nymphs resemble adults but lack wings and are initially almost white in color or sometimes pinkish until they feed. After feeding, the immature stage is pale green with prominent, often reddish eyes.

Both adults and nymphs suck sap from the tender portion of the plant, often targeting the smaller squares (immature flower buds).  Matchhead, pinhead, and even smaller size squares are the preferred cotton feeding sites even after the plant develops larger squares.  Unfortunately the all-important first squares put on the plant are at the most risk.  While cotton has the ability to replace some level of early fruit loss, losing too much early fruit set will affect cotton’s growth patterns causing rankness and could impact fiber quality by the end of the season via fruit maturity. When fleahoppers are abundant, heavy early fruit loss may occur. Cotton is particularly susceptible to cotton fleahopper damage during the first three weeks of squaring but remains at risk until the second week of blooming when blooms become widely abundant throughout the field.  At that time, fleahoppers will feed upon readily and easier accessible pollen and be of no economic importance.  Later in the season, fleahoppers are known to even feed upon a few bollworm eggs and small larva as a predator, but early season economic populations should not be ‘saved’ for any beneficial potential. 

The 1^st week of squaring economic threshold for fleahoppers in match head stage cotton is 35% infested plants with 90% square set or worse.  This percent fleahopper infested plant calculation can be made via whole plant inspection or beat bucket methods.  As plants get older, many entomologists prefer to scout for fleahoppers with drop cloths or sweep nets.  This allows the field scout to check dozens and hundreds more plants over the same period of time scouting in the field.  The 35% infested economic threshold and treatment level translates into roughly 1 fleahopper / 1.5 – 2.5 row feet for the drop cloth or sweep net method with the same percent square set calculation. 

As cotton plants develop, higher levels of fruit loss to fleahoppers becomes acceptable.  Given sufficient time and if early losses were not heavy enough to impact plant development, cotton is often able to compensate for lost squares during the pre-bloom period with little impact on yield, up to a point.  Thankfully, quite a bit of research has gone into finding those levels.

Cotton fleahopper action threshold is 25-30 cotton fleahoppers/ 100 terminals with:
Week of squaring	Square set
1st week	<90 percent
2nd week	<85 percent
3rd week to 1st bloom	<75 percent
After 1st bloom	Treatment is rarely justified

Please Report Unexpected Insect Damage to Cotton, Corn and Sorghum

It has been 20 years since Bt corn and cotton were put on the market, and we are now seeing signs that some of the Cry toxins in Bt crops are less effective than they once were. It is certain that fall armyworm is resistant to Cry1F in parts of the country (but not known to be resistant on the High Plains), and corn earworm/cotton bollworm is showing elevated levels of tolerance to several of the toxins in Bt cotton and corn. I want to make it perfectly clear that I am not suggesting we have resistance on the High Plains, but, given what is happening elsewhere in the country, I am saying that it would be prudent to begin watching our fields for elevated levels of damage from fall armyworm, corn earworm/cotton bollworm, southwestern corn borer and western bean cutworm. (This also goes for corn rootworm that is known to be resistant to at least one toxin in Bt corn.)

On top of this we have the old world bollworm, Helicoverpa armigera, knocking on the southern door of the U.S.A., and it may bring with it resistance to some Bt toxins. This species is indistinguishable from our domestic corn earworm/cotton bollworm, except by dissection of the adults. The Texas A&M University Department of Entomology and the AgriLife Extension Service have rapid sampling teams ready to collect from fields that might have H. armigera. 

This post is a request for growers and consultants to report any signs of higher than normal damage to  corn and cotton regardless of whether they have Bt or not, but especially if they have Bt. We can visit a field and determine whether the damage is within the bounds of "normal" and, if not, we can collect insects for resistance and/or H. armigera screening. My office phone number is (806) 746-6101. Pat Porter. 

Start of Summer Update

As we begin the summer season there are not any significant pest problems to report in corn and sorghum. Blayne Reed has reported treatable thrips levels on cotton in some fields in Hale and Swisher counties, and Katelyn Kowles is reporting lower levels in fields in Lubbock and Crosby counties. Regardless of the reports, all cotton should be scouted for thrips through the 5th true leaf stage.

Foremost in our thoughts is when sugarcane aphid will colonize sorghum. We know the insect overwintered in Hale County and near Lamesa, and we found it on Johnsongrass in Lubbock County on May 3rd, but as yet it has not appeared on sorghum. The beneficial insect activity in wheat was higher than average this year (due to higher aphid numbers in wheat), and it is possible these beneficials found some or most of the early aphid colonies on Johnsongrass and provided suppression. However, the Hill Country and areas south of the High Plains do have aphids in significant numbers, and it is reasonable to expect winged aphids to arrive soon. Last year the first find of sugarcane aphids on the High Plains was in Lubbock County on June 27th. So for sugarcane aphids we are in a period of watching and waiting. When it does arrive we will begin the several control and economic threshold trials that we have pending.

Things are quiet in corn and the only real insect of note has been fall armyworm on non-Bt corn. The most recent trap counts are pictured below. I have not heard of any non-Bt fields with an economically important fall armyworm infestation. Hopefully all late planted corn is with a good Bt trait to blunt the high numbers of fall armyworms we traditionally have later in the season.

Because most of our corn is rotated, the risk of corn rootworm is nonexistent in these fields. The few non-rotated fields may be getting root injury at this time. 

Southern Plains of Texas: Scout for Thrips

Suhas Vyavhare and Blayne Reed, Texas A&M AgriLife Extension

It has been a very stop and go spring planting season for cotton in the Southern High Plains of Texas.  Here we are again, waiting for rain to end so we can resume cotton planting. From Plainview north, an area consisting of our usually more calendar date conscientious producers, about 70% of the cotton has been planted while only about 50% South of Plainview. Rainfall this week has added much needed topsoil moisture helping dryland fields greatly and planting conditions in general.  Cotton planting should continue through early June as fields dry out on many dryland acres from Lubbock south.

For these “late” planted cotton fields we can generally state that early planted cotton can receive higher thrips pressure than later planted cotton. This is usually due to timing, or should we say the timing of area wheat drying down and becoming an unfavorable host for thrips as compared to the availability of favorable host plants to choose from.  Many early and mid-May planted fields often find themselves as an only acceptable host plant for these hungry thrips moving from the drying wheat.  Meanwhile, later planted fields generally have more acceptable host plants for the thrips to choose from, if they are still moving from wheat by the time the young plants would be at risk to thrips damage.  This year, having quite a bit of later planted cotton could affect thrips field pressure and so the strategies to control thrips.

Insect pressure can vary by year and by the field, so insecticide application should be based on scouting observations made in each field, and not by a pre-determined schedule or even spray convenience. Cotton that has emerged is now at risk for thrips damage. We should now be checking fields regularly, prepared to apply foliar insecticide at first leaf as needed. Adult thrips take flight on breezes and winds from drying wheat and move onto young plants as soon as they spot the tender and vigorously growing young plants. They feed on the lower surface of cotyledons first or any exposed true leaves before moving to the very tender terminal bud or growing point of developing seedlings. When feeding, thrips unleash their unique piercing-sucking (once referred to as rasping-sucking) mount parts stab and rasp away at plant surfaces causing sever scaring while they suck up the sweet plant juices as the plant “bleeds.”

Controlling thrips at an early stage is very important as we try to protect these young and rapidly developing plants from damage.   Excessive amounts of damage to these first leaves or growing point can have a huge impact on how the plant develops later and ultimately performs. Preventive insecticidal seed treatments or some of the still available seed box treatments provide control up to 3 weeks after planting. However, this can vary.  Cooler temperature can also slow down plant growth and expose plants to severe thrips injury for longer periods of time. Environmental conditions can also affect the uptake of systemic insecticide applied on seed. Fields should be scouted on a regular basis even during any suspected residual period from preventive insecticidal thrips treatment.  One sure sign that seed treatments are losing residual and performance is the presence of immature thrips on young cotton plants.

Once the plant reaches the 3 to 4 true leaf stage, with a healthy growing point and true leaves, growth accelerates rapidly and the risk of thrips damage can start to decrease. However, the plants will need to reach pinhead-square stage before they are truly past economic thrips damage.  During the plant’s early growth stages, growers should apply foliar insecticide at a threshold level of 1thrips per true leaf stage. When scouting for thrips, there is truly no substitute for whole plant inspections from a representative sample from across the whole field.  For these inspections, we recommend looking both the upper and lower surfaces of the leaves over and then opening the tender folds of the growing and developing tissue of the terminal with a small knife of pen and looking for thrips adults and larvae there.  While scouting we will need to keep a careful count of number of thrips total, plants counted, and average true leaf stage of the field to calculate the actual thrips pressure and population in that field in terms of thrips per true leaf stage.

Mixing insecticidal treatments for thrips control with herbicide applications has proven highly effective however; we should not wait to tank mix if the field is experiencing economic loss due to thrips damage. The importance of field scouting for thrips cannot be overstated.  We strongly feel that the best thing growers can put on their crop is their shadow. We recommend scouting thoroughly across the field at least weekly with representative samples and more often if the emerged field is adjacent to wheat in the process of drying down and to make prompt thrips applications as economically needed.

Corn Planting Decisions and Two New Publications That Can Help

There is still a lot of uncertainty about which crops to plant in parts of the southern High Plains of Texas. Cotton prices are down, sorghum faces a significant threat from sugarcane aphid, and corn requires more water than these other two crops. Many factors are involved in making planting decisions this year, and this article is strictly focused on the insect part of the equation, and the insect part is admittedly relatively minor as compared to available water, aphids and market prices.

Given that our pest pressure from caterpillars like the fall armyworm and corn earworm goes up as the season progresses, and that we have a range of Bt corn technologies with respect to their price and ability to kill these pests, there is room to save money on the front end of the season. Ed Bynum, Extension Entomologist in Amarillo, and I are suggesting that early planted corn can be non-Bt or one of the older and less expensive Bt technologies that has fewer toxins. On the southern High Plains, fall armyworm, not corn earworm, is the major threat to corn (see last year's post), and fall armyworm populations generally remain low until mid-season and then increase through the remainder of the season. Corn planted early in the planting window, and that planted in the first half of the normal planting window, stands a good chance of escaping significant fall armyworm damage. (Corn earworm is far less of a threat to corn in general because it is a tip feeder and does not puncture the sides of ears like fall armyworm.) If corn does need to be treated for fall armyworm, then we have two excellent insecticides available but they need to be applied in a window of six days centered around first pollen shed.

This being said about planting in the first half of the window, it also follows that corn planted in the second half of the normal planting window, and corn planted late, should have a very capable suite of Bt toxins if significant fall armyworm damage is to be avoided.

I should note that none of our Bt corn has any affect on spider mites, so the mite threat is the same on Bt corn as it is in non-Bt corn. Later planted corn is at less risk for significant spider mite infestations than is early and standard planted corn.

One final general statement is that there will be a lot of corn grown on the southern High Plains with reduced irrigation, and some with no irrigation. It has been demonstrated in many studies, including ours at Lubbock, that corn grown under moderate to severe drought stress is more prone to have high aflatoxin levels than corn grown with adequate water. Some people are saying that our very best Bt corn, because it has essentially no caterpillar damage, will not have aflatoxin. This is incorrect. Insects cause wounds where aflatoxin fungi can enter an ear, but even without such wounds there are many corn hybrids that can still get a lot of aflatoxin. This is a function of the genetics (susceptibility) of the hybrid as related to the amount of aflatoxin available in the system to colonize the plants at their susceptible stages. Yes, insect damage can make things worse, but no, there are no hybrids that won't get aflatoxin if the insects are controlled.

Now that I have presented the big picture I will get specific. Our newly revised "Managing Insect and Mite Pests of Texas Corn" has, for the first time, a list of recommended Bt technologies for the major caterpillar pests. These are all of the types of Bt corn that we know to be effective against a specific pest. Note that for fall armyworm the list is not as long as it would have been a few years ago; fall armyworm seems to be adapting to at least one of the older Bt toxins. To dive even deeper, the newly revised "Handy Bt Trait Table" lists the number and types of toxins in each technology. So when I say that more toxins are better, look in the Handy Bt Trait Table at the list of Bt toxins for each seed company's products. The newer and "better" (which is a relative term) Bt hybrids appear toward the end of the list of products within a seed company. Right now the very best protection against caterpillars comes from corn that contains Vip3a in combination with other toxins.

The Handy Bt Trait Table and Managing Insect and Mite Pests of Texas Corn are meant to be used together. We are indebted to Dr. Chris DiFonzo at Michigan State University for allowing us to create a southern version of her very popular Handy Bt Trait Table for the corn belt. Our version is for the cotton growing regions that have larger mandated refuge requirements than in the corn belt. All we did was take Dr. DiFonzo's publication and change the refuge requirement column. Her original version for the corn belt and counties at the top of the Texas Panhandle is here: http://msuent.com/assets/pdf/28BtTraitTable2016.pdf .

Time to prepare for Zika virus mosquitoes

You can't listen to the national news without hearing stories of Zika virus, and it is proper that people exercise caution this summer. Last year's hordes of mosquitoes are still fresh in the minds of those of us who work in the field, and if the rains come again this year we will be in a similar situation. But even a few mosquitoes can be a bad thing when they have the potential to carry a serious virus.

Mosquitoes on the front of a truck that left Plainview clean and arrived in Lubbock like this, spring, 2015.

The Wall Street Journal recently ran a story about US-based insect repellent manufacturers adding shifts and running factories around the clock in expectation of exceedingly high demand in the southern USA this summer. This was a week before the news broke in an article in the New England Journal of Medicine that said the geographical ranges of two known mosquito vectors of Zika, Aedes albopictus and Aedes aegypti, may be much broader than originally thought. A. aegypti may range as far north as Illinois and eastward as far as New York City. The article also said that A. albopictus ranges across the Southwest through parts of the Midwest as far north at Minneapolis, Minnesota and through most of the eastern United States including New England. The potential distribution maps from CDC are here: http://www.cdc.gov/zika/vector/index.html .

So what should we due this summer in addition to buying our mosquito repellent early? Drs. Sonja Swiger and Mike Merchant, Texas A&M University AgriLife Extension Entomologists, have just published a two page guide called Zika Virus: What Texans Need to Know. The publication came out today and is available in English and Spanish.  All of our Zika virus and mosquito control information is at a centralized location here. 

The New England Journal of Medicine just published a review article on Zika (March 30th).