Insect Strip

Insect Strip

Monday, August 31, 2015

Cool temperatures may affect sugarcane aphid control

Extension Entomologists, Drs. Angus Cachot and Jeff Gore, at Mississippi State University had an article in Mississippi Crops (http://www.mississippi-crops.com/2015/08/24/sugarcane-aphid-control-with-falling-temperatures/), which suggest Transform and Sivanto performance is effected under cooler conditions. They and also Dr. David Kerns, LSU, had noticed problems in 2014. A graduate student of Cachet and Gore conducted a study comparing efficacy of Transform @ 1 oz and Sivanto @ 4 oz in growth chambers showed reduced aphid mortality at 60℉ compared to 85℉. There is still a question of whether reduced control is directly related to chemical activity, reduced absorption of the plant, or reduced metabolism and feeding of the aphid. Keep in mind this is only preliminary data, but we may want to keep this in mind when temperatures this September begin to cool. When temperatures do cool to <60℉ the SCA reproduction will also slow down. Applications could then be delayed until temperatures do rise again.

Sugarcane Aphid Stories of Insecticide Resistance and Feeding on Corn

With any new pest, and particularly when the insect populations build to astronomical levels, there are many kinds of stories floating around. Many will be factual, some ridiculous, and some are alarming. Recently, one of the stories that was alarming said that the sugarcane aphid in Mexico has developed resistance to insecticides and was eating up corn. 
With the help of Texas A&M AgriLife Extension Service Entomologists, Dr. Robert Bowling (Corpus Christi),Dr. Raul Villanueva (Rio Grande Valley) and Pioneer sorghum breeders we were able to learn more about the situation in Mexico.
Dr. Villanueva wrote “SCA have been found in great number in many areas of Mexico including: Sinaloa (pacific coast) Veracruz (Gulf of Mexico approx. 600 miles south of the border) and even Guanajuato the central area is approx.1600 meters above sea level, this area is the second largest region where Sorghum is planted in Mexico.  In Guanajuato as well as in Sinaloa, the Mexican INIFAP (something like USDA-APHIS), the regional agricultural authorities, or the universities were not prepared in spite of the presence of this pest last year. This year there are extremely heavy populations of SCA in all those areas, just FYI you can see >1000s winged SCA on the flag leaf, during the evening you can see SCA clouds invading urban areas and clouds of aphids invading other crops. Broccoli is planted to be exported into the US and Europe; and farmers were worried about this contamination and even there was miscommunication that SCA has been feeding in these plants.
In corn, SCA was observed in the border rows in Guanajuato, where the winged arrived and laid nymphs. However, these nymphs so far have not developed to the adult stage, something that Scott Armstrong had studied and Danielle and I observed in 2014.  I hope this switch of host does not occur. Additionally in Guanajuato, where they plant wheat, growers were worried about this crop, but again Scott Armstrong showed that this change of host is not occurring, … again so far.

In most of these areas OP, carbamates , several phase out products have been used, farmers are spraying with dusts and hand held sprayers, without theadequate water volumes and pressure, because there small patches of land. I am aware that in Guanajuato there had been intoxications due to the misuse of insecticides.”
Dr. Bowling, a former Pioneer employee, contacted a Pioneer sorghum breeder that has plots all across Mexico. Robert reported the following from his conversation with the breeder and he added some of his own comments; 
  • “Sugarcane aphid populations are extremely heavy in parts of Mexico.
  • It is possible that some sorghum field will fail (Mexico) because of SCA damage even where insecticides have been sprayed because of the unusually heavy SCA pressure and NOT because of insecticide resistance.
  • Insecticide applications have been effective for about 7-days and the fields are re-infested with SCA. This is not too unusual with exceedingly heavy SCA pressure (Danielle and Raul saw this in the RGV last year)…some sorghum fields in Corpus Christi were treated two or three times through the season. Without knowing insecticide rates, application methods, final volumes, hybrids, seeding rates, etc…it is very hard to say what is going on but resistance has never been mentioned among Pioneer Sorghum Breeders (In the U.S. or Mexico).
  • SCA has been found on corn in Mexico but they are not causing damage to corn. Again, we found SCA on corn, sugarcane, and cotton growing in the Coastal Bend area. However, the aphid was not colonizing those fields nor were they causing damage.“

Can the sugarcane aphid develop resistance to the insecticides being used to provide control and could the sugarcane aphid become a pest of corn? Yes to both. Insecticide resistance is a possibility because Transform (4C) and Sivanto (4D) belong to the neonicotinoid insecticide classification. The multiple applications of the products first along the Gulf Coast and Rio Grande Valley, secondly in Central Texas, and lastly in the Texas High Plains places a great amount of pressure for selecting resistance. Also, since both of these products are neonic insecticides there could be cross-resistance. As to the question of whether we have resistance in the population now, I would say NO. The issues with poor control now  has more to do with poor chemical coverage within the canopy and making applications when populations have already become high. 
An article by Singh et al. in 2004 reviewed the literature about the sugarcane aphid host range, damage and crop losses, cultural practices, natural enemies, chemical control among other areas. In this article the list of publications from 1922 to 2001 shows the predominate hosts are Sorghum bicolor (L.) Moench, sorghum; Saccharum officinarium, sugarcane; Sorghum halepense (L.) Per, johnsongrass and related grasses; and Setaria italica (L.) Beauv., different millet varieties. In the United States (USA) the primary hosts are sugarcane, sorghum, and johnsongrass. A few grasses, such as barnyard grass and hairy crabgrass, have been reported as hosts in the USA. It was noted in the article that SCA winged and non-winged adults had a strong preference for sorghum and johnsongrass. There was on paper from Bhutan in 1985 that reported Zea mays (L.), corn, as a SCA host. I would expect the SCA biotype we have is not the one that will survive on corn. I hope the SCA we find in corn is only from winged aphids landing on corn and giving birth to nymphs (immature aphids).

Friday, August 21, 2015

New Invasive Aphid Discovered on the Texas High Plains

Sipha maydis, An Invasive Aphid

As if the sugarcane aphid is not enough for us to be concerned about, a new invasive aphid to the United States was found in Lipscomb and Hockley counties on Tuesday, August 18. What is ironic is that Jim Elzner, crop advisor - Dumas, sent me a picture of the aphid on Tuesday morning. Then when I sent the photo to the Extension agents - IPM and Dr. Pat Porter that afternoon Kerry Siders called letting me know that someone had brought in some aphids to him that looked like the aphids Jim had found. Both of the colonies found in Lipscomb and Hockley counties were on sorghum.



This aphid is the Sipha maydis, but has no official common name. The aphids are black in color with a sclerotized dorsum and white spiney hairs on the body.




The aphid was first discovered in California in 2007 on giant wild rice, Leymus condensatuse, and then in Georgia in 2012 on wheat in a greenhouse. It has been intercepted at the Florida Agricultural Interdiction Stations as winged adults on lettuce from California in 2011 and 2012. I first heard about this aphid from a news release in Entomology Today on February 3, 2015. The article stated that Tessa Grasswitz, a New Mexico State University entomologist, had found the new aphid in the Albuquerque area on oats. Colorado then conducted surveys and found the aphid on annual wheatgrass, unidentified wheatgrass, and hare barley in February and March of 2015. And some aphids were collected from wheat and barley fields in late March and early April of this year. The Colorado entomologists have proposed calling it the Hedgehog grain aphid. 

What I can find about this aphid is that there are 30 different grass hosts this invasive aphid lives on including sorghum, but the preferred hosts are wheat and barley. It prefers drier and warmer climates. The aphid is a vector of the barley yellow dwarf virus. Feeding damage, as described by Dr. Grasswitz, is yellowing, rolling, and desiccation of leaves. Reports indicate the aphid cause yellowing of the leaf near where aphids are feeding, reduces leaf area, and inhibits head growth (Corrales et al. 2007). There is a sexual stage where eggs are laid and they can overwinter, but Colorado entomologist indicate observing non-sexual overwintering in Mesa County. Another concern is how quickly it can spread. An example to this is the spread in Argentina after it was discovered in 2002. It only took four years for the aphid to spread across the grain producing areas as it took the Russian wheat aphid to spread in 10 years. However, we do not know if or when the aphid will become a pest or how quickly it will spread across the Texas high plains. 


Based on the limited information management of the aphid will be to protect the flag leaf from feeding damage. We do not have any information on insecticides that would provide control of this pest.

However, this newly discovered aphid does pose a threat to our wheat production. Please contact your County Extension Agent, Extension  Agent - IPM or Dr. Pat Porter and myself if you find these aphids.

References Cited
Corrales, C.E., A. Castro, M. Ricci and A.F.G. Dixon. Sipha maydis: Distribution of Host Rage of a New Aphid Pest of Winter Cereals in Argentina. J. Econ. Entomol. 100(6): 1781-1788.

Halbert, S. E., G. L. Miller, and L. M. Ames. 2013. The genus Sipha passerini (Hemiperta:aphididae) in North America. Inseccta Mundi. Paper 831. 

Friday, August 14, 2015

Sugarcane Aphids moving into the Texas Panhandle and a change in Threshold

Sugarcane Aphids Moving North to the Panhandle
After last weeks confirmation of Sugarcane aphids (SCA) in Ochiltree county, we have more confirmations and reports of the SCA infesting more fields in the Texas Panhandle. There is confirmation that SCAs are in Castro, Carson, Deaf Smith, Gray, Hansford, Oldham, Randall, and Wheeler counties. And, there are reports of them being found in Moore county. Fields in Donely, Carson, Deaf Smith, Oldham, and Randall counties were at treatable levels. Because of the drastic change in the infestation levels and a little more experience from infestations in the South Plains area, the Extension Entomologists (including myself) and the Extension Agents-IPM believe we should use a different treatment threshold than what is currently being used. The following is an article by Dr. Pat Porter that describes and explains why we have made the change to a different threshold. Also, included are photographs by Dr. Porter showing the severity of the sticky shiny honeydew accumulation when this aphid is not controlled.
Sugarcane Aphid Threshold Lowered for the Texas High Plains
Now that we have had at few weeks of experience with field-scale sugarcane aphid control in the southern High Plains, it appears that we need to move to a more conservative treatment threshold than the one currently in use. What we are finding in commercial fields and our insecticide trial is that our insecticides do not seem to be working quite as well as they do in more southern locations with higher humidity and less intense sunlight. Whether our environment affects the insects, plants and/or insecticides differently is unknown, and what we are seeing could be a combination of all three factors – or two or one or none, we just don’t know. Insecticide coverage issues may also be in play. We could be experiencing insecticide interception by excessive honeydew such that some of the insecticide never gets to the leaf surface.  We also do not know the importance of reduction in coverage and canopy penetration attributable to aerial application rather than ground application with higher volumes of water. Additionally, we also have reports of narrow row fields (less than 36 inches) having reduced insecticide efficacy, and this of course is a coverage issue.

The preceding paragraph is basically to say that we are not sure what is causing reduced control. We want to make it absolutely clear that there is no reason to think this is a resistance issue. However, with regard to application timing the prudent thing to do is to initiate insecticide applications sooner, before the aphids reach 50-125 aphids per leaf. For that reason we are recommending the action thresholds in use in Mississippi.

The threshold for soft dough stage sorghum is when 30% of the plants are infested and there are localized areas of heavy honeydew and established aphid colonies. This threshold would trigger significantly earlier insecticide applications than our Texas threshold of an average of 50–125 aphids per leaf. The full explanation of the Mississippi threshold can be found here: http://www.mississippi-crops.com/2015/02/24/management-guidelines-for-sugarcane-aphids-in-ms-grain-sorghum-2015/ . Note that this document estimates a 21% yield loss if fields at soft dough stage are left untreated after reaching the threshold. Missing an application at the boot stage threshold of 20% of plants infested with localized heavy honeydew and established aphid colonies would cause a 67% reduction in yield.

Of course another prudent step would be to increase the insecticide rate if possible. Bayer CropScience has some good recommendations for tank additives on the High Plains. Insecticide applications made at relatively low to normal numbers of aphids can be tank mixed with MSO/silicone blends. For heavier infestations they are recommending that Crop Oil Concentrate or High Surfactant Crop Oil be added at the recommended rates. The thought here is do drive the insecticide deeper in to the canopy.

Sugarcane aphid "honeydew" accumulation on grain sorghum leaves. Photo by Dr. P. Porter

Sugarcane aphid "honeydew" dripping on to the ground. Photo by Dr. P. Porter


Tuesday, August 11, 2015

Spider Mites in Sorghum and Moth Trapping

Spider Mites in Sorghum
Field infestations have been reported from the southern high plains to the northern panhandle. When we begin talking about spider mites it is usually about infestations on corn. The two most common species are the Banks grass mite and the twospotted spider mites. Their biology, life cycle, feeding damage is the same on sorghum as it is corn. Mites begin on the underside of the leaf in the lower portion of the sorghum canopy. As populations increase feeding damages a greater portion of the leaf area and can kill entire leaves. Control decisions should be considered when 30 percent of the leaf area of most sorghum plants in a field show some damage symptoms from mite feeding. Only two acaricides (Comite II® and Onager®) are registered for spider mite control on grain sorghum. 
For Comite II® the application rate is between 24 and 36 fl. oz. per acre. The recommended  application volume for ground application is a minimum 20 gpa and aerial application a minimum 5 gpa. Only 1 application per season is permitted. Comite II® is phytotoxic to some sorghums and the pre-harvest interval is 30 days for silage and 60 days for grain.
The use rate for Onager® is between 10 and 24 fl. oz. per acre. Ground application is recommended at 15 to 20 gpa and a minimum of 5 gpa for air application. Only 1 application per season and the total amount per season is 24 fl. oz. per acre. The pre-harvest interval is 30 days. There is no distinction on the label for grain or silage pre-harvest interval.

Just as for corn, spray coverage is extremely important to the performance of these two acaricides. So the minimum application volume should be used. Applications of pyrethroid insecticides for headworms, stinkbugs, and sorghum midge will also flare spider mite populations by removing natural predators. Applications of chlorpyrifos or dimethoate for aphid control may provide an initial knockdown of spider mites. But populations can resurge because only adult and immature spider mites are killed, leaving the eggs for immatures to hatch out. Also, these two insecticides will eliminate the natural predators.

Moth Trapping
In short, southwestern corn borer moths have sharply increased this past week, fall army worm moth activity continues to decline and western bean cutworm moths substantially dropped. County Extension agents in Dallam, Hartley, Deaf Smith, and Parmer counties reported the increase in southwestern corn borer (SWCB) moth activity.



Monday, August 3, 2015

SCA or YSCA - What's the Difference

This past week sugarcane aphids (SCA) and the yellow sugarcane aphids (YSCA) have caused a great deal of concern for us on the high plains. SCA infestations have been confirmed to be at treatable levels in Floyd, Crosby, and Lubbock counties. Also, infestations have been confirmed in Dawson, Hale, Hockley, Lamb, Swisher, and Terry Counties, but mostly at below treatable levels at this time. On July 31, Blayne Reed, Extension Agent - IPM, reported that only Floyd of my three counties, Hale, Swisher, & Floyd has had any sugarcane aphids at threshold, and that is just a very few fields with other issues too.    Most fields in our scouting program are only running 1-2 sugarcane aphids per leaf averaged across the field. This does not mean that other fields are not infested and need to be treated because depending on the infestation levels when a field is initially infested SCA may reach damaging levels in 5 to 14 days.

The other situation is that the YSCA has moved further north into the Panhandle. Infestations have been reported in Ochiltree County by J. R. Sprague, County Extension Agent - Lipscomb and Scott Strawn, County Extension Agent - Ochiltree, on Thursday, July 30th. And, on Friday, July 31st, I met Jody Bradford, County Extension Agent - Carson, to identify aphids that were being found in several of the farmers' fields. The aphids were the YSCA. The other SCA may be in fields in the Panhandle but to date populations have not been confirmed.

What has become evident is that there is confusion between these two aphids. Because of this confusion a table that compares differences between the SCA and the YSCA is below. It is important to know how to identify each of these pests because the insecticides and management options are different for the SCA and the YSCA.

Since this is the first year for us to have the SCA in damaging infestations, we are unsure of what to expect, what is the SCA, and how to manage the SCA. What has been learned in southeast Texas, where SCAs have been a pest since 2013, is to know how to identify the aphid and thoroughly scout fields. If you find aphids in your field that are unfamiliar to you, collect a sample to be taken to the County Extensions office or contact you County Extension Agent to collect a sample for species identification.


 Another concern is what to do when there are other pest infestations in the field. Our Extension Entomologists recommendations are to deal with the pest at the time that will limit yield and deal with other pests as they become an issue. Updated information about the SCA distribution, scouting procedures, treatment thresholds, insecticides, and management options with other pests are also found at http://www.txscan.blogspot.com and http://www.texasinsects.org/sorghum.html.

Comparison Table 
Yellow Sugarcane Aphid
Sugarcane Aphid
Identifying Characteristics
Identifying Characteristics
Usually lemon yellow, but may be pale green
Pale yellow, gray or tan
Body covered with small spines (hairs), cornicles are very small are not easily seen, and tips of feet and antennae are not black
Tips of cornicles (tailpipes), feet, antennae are black
Hosts - grain sorghum, forage sorghums and sorghum related plants like johnsongrass and dallisgrass and many different grasses.
Hosts - grain sorghum, forage sorghums and sorghum related plants like johnsongrass and dallisgrass.
Damage
Damage
Primarily a pest of seedling plants, but feeding damage can still be significant on older plants. Feed on the underside of leaves of seedling and older leaves. Populations do not develop to high numbers per leaf.
Feed on the underside of all leaves. Populations develop to extremely high numbers per leaf from seedling, boot, and heading growth stages.
Injects a potent toxin when feeding that can kill leaves. Very few aphids per leaf cause seedling leaves to turn purple and older leaves yellow.
Does not inject toxin when feeding, but feeding cause leaves to turn yellow, purple, and finally brown as leaf tissue dies. Large pre-boot infestations can stunt growth and uneven head emergence from boot causing significant yield loss.
Does not produce honeydew.
Produce heavy amounts of honeydew. Sticky leaves, stalks, and head clog combines along with reducing grain separation from heads at harvest.

Honeydew contaminated leaves and stems can gum up cutter bars when harvesting for silage, forage, etc.
Sampling
Sampling
Colonies infest the lower portion of the canopy. Look for discolored lowered leaves when scouting.
Inspect underside of leaves from both the upper and lower canopy. If honeydew is present, look for sugarcane aphids on the underside of the leaf above the honeydew.

If no sugarcane aphids are present, or only a few individual wingless or winged aphids are present on upper leaves, then continue once a week scouting. 


If sugarcane aphids are found on lower or mid-canopy leaves, begin twice a week scouting to determine if aphid densities exceed the economic threshold.
Yellow Sugarcane Aphid
Sugarcane Aphid
Management Decisions
Management Decisions
Grain Sorghum
Seedling plants - Economic injury levels have been established for seedling plants up to the three true-leaf stage (http://aglifesciences.tamu.edu/entomology/wp-content/uploads/sites/12/2014/07/B-1220.pdf).

Larger plants - No economic injury levels have been established for vegetative plants after the three true-leaf stage and during head development, but damaging infestations may develop and cause yield losses. Using the following action threshold that was developed for greenbugs can prevent excessive yield losses when YSCA are infesting older grain sorghum.
6 inches to boot - Treat when colonies  are causing red spotting or yellowing of leaves and before any entire normal-sized leaves on 20% of plants are killed.
Boot to heading - Treat if there is death of one functional normal-sized leaf on 20% of plants.
Head to hard dough - Treat when colonies are sufficient to cause death of two normal-sized leaves on 20% of plants.
Grain Sorghum
If the field average is 50-125 sugarcane aphids/leaf or greater,      apply an insecticide within 4 days and evaluate control after 3-4 days (refer to insecticide labels for re-entry intervals). Consider treatment at 50 aphids/leaf if limited to only once a week scouting.

If the field average is less than the threshold level, continue scouting twice a week.

Forage Sorghum
Treatment thresholds for SCA infesting forage sorghums and Johnsongrass meadows have not been determined. Until those thresholds are available, the thresholds used for grain sorghum can provide a guide to making treatment decisions.
Suggested Insecticides
Suggested Insecticides
All commercially treated seed insecticides will control seedling infestations for about 4-5 weeks.

Foliar insecticides - Field experience has shown that chlorpyrifos 4E at 12 floz/A mixed with dimethoate 4E at 12 floz/A provides good control. But do not apply dimethoate after sorghum heads emerge from the boot.
All commercially treated seed insecticides will control seedling infestations for about 4-5 weeks.

Foliar insecticides
Transform WG - 0.75 - 1.5 floz/A, 1.0 floz/A suggested, no more than 3 floz/A per season and only 2 applications per season. Minimum application volume - full plant coverage by ground or 5 gpa  by air. Pre-harvest interval - 14 days for grain or straw, 7 days for grazing or forage, fodder or hay harvesting.
Sivanto 200SL - 4 - 7 floz/A, 4 floz/A suggested, no more than 28 floz/A per season. Minimum application volume - 10 gpa by ground, 2 gpa by air. Pre-harvest interval - 21 days for grain or straw or stover, 7 days for grazing, forage, fodder, or hay harvest.

Both Transform and Sivanto will control greenbugs and yellow sugarcane aphids when there are mixed infestations with sugarcane aphids.