Sugarcane Aphid at Treatment Threshold in Southern High Plains Counties

At a minimum, Floyd, Crosby and Lubbock counties now have sorghum fields at the economic threshold of 50 to 125 sugarcane aphids per leaf and insecticide applications started over the weekend. Blayne Reed, Extension Agent - IPM in Hale, Swisher and Floyd counties said that private consultants called in the first Floyd County applications today. Monti Vandiver, Syngenta Crop Protection and former Extension Agent - IPM, said that the aphids in Crosby and Lubbock counties are now at treatable levels. 

This is in no way meant to imply that the other infested counties don't have fields at threshold level, so it is imperative that all sorghum fields on the Southern High Plains be scouted. This aphid can go from barely noticeable to exceeding the economic threshold in as little as 5 days. All of the scouting procedures, treatment threshold and insecticide information is presented here: http://www.texasinsects.org/sorghum.html . 

This is a reprint of a news article I just posted on the Sugarcane Aphid News Site at http://txscan.blogspot.com . The SCA news website is the best place to stay current on Texas sugarcane information news and view the latest distribution maps. 

Fall Armyworms in Corn and Sorghum, Early Midge Warning

Fall armyworm in corn and sorghum

Fall armyworm trap captures at Lubbock are up this week and we are on course to approximate the high numbers experienced in 2014.

FAW trap capture as of 7/8/15. Click for a larger view. 

Larvae feed on corn ears and ear shanks and behind leaf collars. Our recent research at Lubbock has shown that one fall armyworm larva, when boring through the side of an ear, causes an average of 0.20 lbs. of yield loss per ear through direct kernel injury and damage by associated fungi. In our experiments the mycotoxin (fumonisin) levels in grain greatly increased in ears damaged by fall armyworm side entry damage. Heavy infestations may result in substantial yield losses because larvae feed directly on the ear. Additional losses can occur when shank feeding causes ears to drop and when stalks lodge as a result of feeding damage to the nodes. 

Non-Bt corn and single toxin Bt corn (Cry1F Herculex) should be scouted carefully as it approaches silking and for at least two weeks thereafter. Scouting for fall armyworms can be difficult. Check corn leaves and grasses in the furrow for egg masses. There may be 50 to 100 eggs per mass. Also check for small larvae behind leaf collars and at the bases of primary and secondary ears. Small larvae differ from late instar larvae in that they are pale tan in color and have a small black spot on each side toward the head. Larger fall armyworm larvae tend to be brown in color while corn earworm is more brightly colored in yellow, red, pink or beige. 

Unfortunately, we do not have a treatment threshold for fall armyworms on reproductive stage corn. Our research trials at Lubbock have shown that if an insecticide is needed applications should optimally occur in a five day window starting at or just prior to silking. Applications made 7 days after silking were less effective at control because many of the larvae were protected inside ears. 

Larvae hatching from a fall armyworm egg mass.

On larger fall armyworm larvae the "inverted Y" on the head capsule is thicker and more pronounced than on the corn earworm.

Posterior ends of fall armyworm (top) and corn earworm (bottom) larvae. Fall armyworm has 4 relatively equally spaced dots on the second to last segment. Corn earworm has more and longer "hairs". 

Fall armyworm (top) and corn earworm (bottom).

All photos by Pat Porter.

Suggested insecticides for fall armyworm in corn. Click for a larger view. 

Sorghum

Fall armyworm infests whorl stage, boot stage and headed sorghum. Whorl stage sorghum can withstand significant damage. Sorghum in the boot stage through grain fill should be scouted for headworms (fall armyworm + corn earworm). Prior to the arrival of sugarcane aphid in sorghum we would have said to determine which caterpillar species was predominate in a field and then choose either a pyrethroid (if corn earworm) or a non-pyrethroid (if fall armyworm). This distinction is because pyrethroids are not very effective on larger fall armyworm but are good at controlling corn earworm.  However, things change when sugarcane aphid is present in a field; pyrethroids and organophosphates should be avoided because they destroy the beneficial insects that suppress sugarcane aphid populations. Insecticide considerations for "other" pests when sugarcane aphid is present are covered in our special publication here. 

Treatment thresholds for headworms are based on the size of the larvae, the value of the crop per acre and the cost of control. The following table refers to corn earworms, but action levels are really caterpillar numbers whether they are corn earworms or fall armyworms. Note that there are two separate thresholds, one for large larvae and one for medium-sized larvae. Full details are presented in Managing Insect and Mite Pests of Texas Sorghum.

Sorghum midge

A future article will cover sorghum midge in more detail, but it is possible that midge problems may be worse than normal this year because of the abundance of Johnsongrass, an early season host of sorghum midge. It is generally true that fields that bloom before August 4th in the Plainview area will not have economic midge damage. However, Greg Cronholm, Independent Crop Consultant and Extension Agent - IPM (retired) has found midge on sorghum as early as July 25th. If we start out with abundant midge numbers coming from Johnsongrass then the August 4th assumption may not hold up this year. 

Sugarcane aphid and whorl stage sorghum on the Southern High Plains

By Tommy Doederlein, Pat Porter, Blayne Reed and Kerry Siders

Sugarcane aphid arrived early in south Texas this year but its northward expansion was apparently slowed by the record rainfall. However, in the last two weeks it has made a rapid advance and was found in Lubbock County on June 29^th.  This is two months earlier than the August 27^th, 2014 first detection by Blayne Reed in Floyd County. Last year’s late arrival allowed us to avoid making insecticide applications. While it is still too early to guess how severe the problem might be this year, we would like to provide some information on management practices prior to boot stage.

When on whorl stage sorghum, economic populations of sugarcane aphids can result in near total yield loss because it destroys leaf cells that provide nutrition to keep the plant growing, exert the panicle and fill the grain. The worst case is a heavy sugarcane aphid infestation on whorl stage plants. Later infestations on headed sorghum are somewhat less of a problem and may only result in minor yield losses and harvest difficulties due to honeydew accumulation.

Early detection is the key to successful sugarcane aphid management. All fields should be scouted weekly from shortly after emergence until one week before harvest. If sugarcane aphids are not found in a field then the weekly scouting should continue. If light populations of sugarcane aphids are found then the scouting should occur twice per week. The doubling of the scouting interval is because of the rapid reproduction of the aphid. As Angus Catchot, Entomologist at Mississippi State University, put it, “This is the first pest I have seen that can go from ‘barely there’ to ‘Oh my God’ in five days.

Sugarcane aphids are easy to differentiate from the other aphid pests of sorghum and there is a recognition guide posted here: http://txscan.blogspot.com/2015/02/recognizing-sugarcane-aphid.html .

The treatment threshold is an average of 50 – 125 aphids per leaf on whorl stage plants. Research in Texas has shown that an average of 250 aphids per leaf is around the break point where yield declines equal the cost of control, but this many aphids can cause a honeydew and sooty mold problem. The goal is to apply the insecticide soon enough to keep the aphid numbers below 250 per leaf. Quick action is needed when fields reach the economic threshold, so don’t delay in pulling the trigger. The treatment threshold is the same for susceptible sorghum and the “resistant” or “tolerant” sorghum hybrids; once threshold is reached then insecticides should be applied as soon as possible. Blayne Reed, Extension Agent in Hale, Swisher and Floyd counties, with support from all our regional IPM specialists, is leading our 2015 research on how the “resistant” hybrids withstand sugarcane aphid. It is far too early to say anything other than, from a management perspective in 2015, expect resistant hybrids to perform in line with susceptible hybrids. The so-called resistant hybrids should be scouted like susceptible hybrids and sprayed like susceptible hybrids with the yet field-unproven hope there will be fewer aphids or better performance from the “resistant” lines.

There are two good insecticides available; Sivanto and Transform. Expect each product to provide around 10 days of control. Be sure to visit the field 3 – 4 days after the application to make sure the insecticide is working. If a follow-up application is needed after 10 days then rotate to the other insecticide. Insecticide rotation is critical for resistance management; aphids are extremely dangerous as far as resistance because they are genetic clones (no sexual reproduction and mixing of resistance and susceptibility alleles). If the mother has resistance alleles then the offspring will have the same resistance alleles; if the mother survives the dose then the progeny will survive the dose, and so will all of their progeny and their progeny across generations and growing seasons. The only way to kill these resistant insects is with the other insecticide. Insecticide rotation is the key to preventing resistance, and aphids are exceptionally adept at becoming resistant.

It is important to preserve beneficial insects – they won’t prevent sugarcane aphid from reaching threshold on the High Plains (yet), but they will slow the aphid down. There is evidence from the Gulf Coast that, after three seasons of the aphid and the beneficial insects coexisting, the beneficial insects are starting the season in high enough numbers to exert a significant amount of control on the aphids. This is not the case in the High Plains; our beneficial insects have not had the chance to arm up against the aphids and we don’t have enough of them to keep aphid populations under control. But we do have enough of them to slow the aphids down and perhaps avoid an additional insecticide spray later in the season. The best way to help the beneficials is to avoid pyrethroid and organophosphate insecticide applications; use Sivanto or Transform and let the beneficials live.  We have a new publication called InsecticideSelection for Sorghum at Risk to Sugarcane Aphid Infestations, 2015. This publication discusses insecticide choice for sugarcane aphid control and insecticides to use on other pests in fields that have sugarcane aphids in them. Other sugarcane aphid resources available at http://www.texasinsects.org/sorghum.html. We have established a statewide sugarcane aphid news website at http://txscan.blogspot.com.

We don’t know what to expect in 2015 as far as sugarcane aphid. All we know for sure is that it has arrived two months earlier than last year and is now threatening whorl stage plants. We encourage weekly field scouting until the aphids are found and then twice-weekly scouting thereafter. Apply insecticides when there are 50 – 125 aphids per leaf and use either Transform or Sivanto. Check to make sure the insecticide worked and, if an additional application is needed later, be sure to rotate insecticides in order to prevent resistance.

Update on Fall Armyworm

Things have been quiet on the fall armyworm front since the large trap captures earlier in the season. However, Greg Cronholm, Independent Crop Consultant and Extension Agent - IPM (retired), called earlier in the week to report finding very heavy egg deposition on small corn in Hale County. Greg said that the eggs were from a species in the armyworm group but he did not think they were fall armyworm. Yellowstriped and beet armyworms are a possibility as is a different armyworm species. We will try to rear out some larvae to determine the species.