Insect Strip

Insect Strip

Thursday, September 11, 2014

The Sugarcane Aphid Arrives on the Southern High Plains


Blayne Reed, Patrick Porter and Ed Bynum 

We have been watching for the possible arrival of the sugarcane aphid, Melanaphis sacchari, on the High Plains, and we must now report that it has been found. Clay Golden, an independent crop consultant serving the area, discovered a small pocket of the aphids on soft dough stage sorghum in an extreme northwestern portion of Floyd County on September 9, 2014. Upon his find Clay enlisted the aid of Blayne Reed, EA-IPM Hale & Swisher counties, who supported Clay’s identification of the aphid. Dr. Pat Porter and Dr. Ed Bynum were then presented with aphid samples and confirm the identification.
Photo: Pat Porter
Given the proximity of this aphid population to neighboring counties; 1⁄2 mile from Briscoe, 2 miles from Swisher, and 7 1⁄2 miles from Hale, combined with some possible smaller and un- confirmable sugarcane aphid hits in nearby sorghum in Swisher and Hale and that this aphid is often dispersed by prevailing winds, it is logical to assume that it is present over a wider area encompassing small portions of all four counties or in other counties across the High Plains. Many of the aphids in Clay’s sample were at the developmental stage just prior to becoming winged adults, so we expect that further dispersal is happening now.
After Clay’s discovery, we asked for some help and perspective from our downstate colleagues who have been dealing with this pest since last year. Here is a summary of information from Raul Villanueva, Robert Bowling, Stephen Biles and Mike Brewer.

  • It takes ten days to two weeks for isolated aphids to establish significant colonies on sorghum. So scouting should be concentrated on finding the first few infesting aphids in the field on lower leaves.
  • Stephen Biles, Extension Agent IPM in Victoria, has done some very recent work on an action threshold in sorghum in the reproductive stage. Stephen’s work suggests that a good action threshold for treating is an average of 100 aphids per leaf. He suggests sampling 10 plants per location within a field (several locations) and picking the leaf below the flag leaf and an additional leaf from the middle of the plant. If there are an average of 100 aphids per leaf (2,000 total on all 20 leaves), then come back in two days and re-sample to see if the population is increasing. If the numbers are going up then consider treating. If the numbers are not going up then don’t treat but continue to monitor. Observations of this aphid from downstate have shown that some populations can crash very quickly. We don’t know how to predict which populations will crash and which will increase.
  • Transform (available under a Section 18 exemption) is the most effective insecticide. It can be used at a rate of 0.75 to 1.5 ounces per acre. Our downstate colleagues have had good results at the 0.75 ounce rate, but good coverage is essential at this rate. They strongly recommend 10 gallons of carrier volume per acre by ground and, if this can’t be achieved with aerial application, they recommend a bare minimum of 5 gallons per acre and a minimum rate of Transform of 1.0 ounces per acre. (Which is to say the 0.75 oz rate of Transform may not work by air at 5 gallons per acre.) We do not know if a 1.0 oz rate can be put out at less than 5 gallons per acre. Our colleagues have also said that Dimethoate is not a good option because it is not a consistent performer.

Photo: Pat Porter
This aphid is not going to be Atilla the Hun on the High Plains. Invasive species often do the most damage in their first year or two of invasion before natural enemies can respond to the new pest. For this year at least, the aphid is arriving late in the season and will not be infesting whorl stage plants which will be limiting the aphid in time to build into an economic problem. We also have products that have proven to control this aphid. This, combined with the implementation of good scouting techniques, give us confidence that this aphid can be effectively controlled if necessary. The Section 18 allows for two applications of Transform (1.5 oz maximum per application), with the total application for the season not exceeding 3.0 ounces. There is also a mandatory 14-day waiting period between the first and second application. So this gives us six weeks of good control, assuming 14 days of activity from each application. This should be sufficient to carry us through harvest.
It is not known whether the sugarcane aphid can overwinter on the southern High Plains; it is a subtropical species and overwintering survival is very much in doubt. We also do not know how fast the sugarcane aphid can reproduce given the predicted cooler temperatures in this week’s weather forecast. We will have to watch for it next year when our sorghum is in the whorl stage, but for this year we can handle the problem if it arises.

Photo: Pat Porter
The sugarcane aphid is fairly easy to recognize and distinguish from our other common aphids. Look for black-tipped antennae and legs. Dr. Ed Bynum recently posted an article on identifying the sugarcane aphid: http://amarillo.tamu.edu/files/ 2010/11/PPU-V6i6-5-23-2014.pdf . Our publication Sugarcane Aphid: A New Pest of Sorghum is available here: http://www.agrilifebookstore.org/ product-p/ento-035.htm . We will of course keep you informed of new developments. 

Thursday, September 4, 2014

Potential Pest Problems in Late Planted Crops

Fall armyworms (FAW) are a concern in late planted grain sorghum, and possibly in cotton and corn. Last week while checking  sorghum fields with county extension agents in the Southeastern part of the Texas Panhandle and corn fields near Morton, TX with Pat Porter, we found all stages of FAW and corn earworm (CEW) larvae in these crops. The sorghum fields were at growth stages from just starting to flower up to dough. The corn fields near Morton were at the milk stage and non-Bt corn plants had from 2 to 8 FAW and 2 to 4 CEW larvae per ear. The Bt plants had 0 to 3 FAW and 1 to 4 CEW larvae per ear. Also, FAW moth activity is increasing again which will contribute to continued egg laying for a few more weeks. 



Feeding by FAW and CEW larvae to sorghum in pre -flower and during flowering will result in a loss of panicles. Later during seed development larvae consume or partially consume seeds. Studies on how much a larva is able to consume when it is either small (< 1/4 inch long), medium (1/4 inch to 1/2 inch long), or large (> 1/2 inch long) lead to the development of an economic threshold for headworms. Since both CEW and FAW cause similar amount of damage the threshold works for each species or a mixture of both larvae. 

A calculator determining the economic threshold is located at https://insects.tamu.edu/extension/apps/sorghumheadwormcalculator/index.php. The basic components are Control Cost ($/acre), Grain value ($/cwt), and number of sorghum heads/acre. The calculator will then determine the threshold for when to treat medium and large sized larvae. This calculator has be made into a free app for android devices. Once the threshold is calculated fields can be sampled to determine if larval infestations meet or exceed the threshold level. 


The FAW can also damage cotton bolls. The photos below of FAW damage were taken in 2005 from a Bollgard field. Generally, small  bolls between 1 to 10 days old will be aborted when feed on by larvae. Bolls 12 days old and older will remain on the plant but the damaged locks will result in reduced yield (see photo of bolls at different days of age). In grain sorghum treatments are based on medium to large size larvae, but in cotton treatments should be based on larvae < 1/4 inch or > 1/4 inch.



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The following tables are the cotton thresholds for FAW and CEW/tobacco budworms. 



The reason for treating smaller sized larvae in cotton compared to larger sized larvae in grain sorghum is that insecticide efficacy is less in cotton because of poorer spray coverage in the cotton canopy compared to the grain sorghum head. The poor coverage reduces the exposure to insecticides that are needed to control larger size worms. This also becomes important for controlling FAW compared to CEW (aka boll worm). In grain sorghum heads, pyrethroid applications usually provide good control of both CEW and FAW larvae. But, in cotton, pyrethroids are more effective against CEW than FAW.  This is illustrated in the data by Dr. David Kerns, previous Texas A&M AgriLife Extension Entomologist at Lubbock. Also, note that Belt at 2 floz / acre was not that effective against CEW, but when mixed with Mustang Max it improved the FAW control.

Graph A, right, shows control of bollworms and graph B, shows control of fall armyworms

This graph show control of the mixed population of bollworms and fall armyworms

Southwestern corn borer and Western bean cutworm moth activity is finally coming to an end. The graphs show the general flight activity of the moths and the tables show the moth activity for individual counties across the Texas High Plains. County Extension agents have been collecting and reporting the moth numbers this summer. This project has been made possible by a grant from the Texas Corn Producers Board. We greatly appreciate this support because we have been able to provide this service for the past 4 years.