Posted: 08 Sep 2016 04:33 PM PDT
If you are growing soybeans or alfalfa on the Texas High Plains it would be a good idea to scout for green cloverworms. I was in a soybean field near Ralls earlier in the week that had approximately 8 larvae per plant, and I just got a call about soybeans near Clarendon that were heavily infested.
In both cases the people making the reports thought the worms were soybean loopers. It is easy to tell the two caterpillars apart because loopers have two pairs of prolegs on the abdomen while the green cloverworm has three pairs. Loopers are fairly lethargic, but green cloverworms hop around quickly when disturbed.
Green cloverworm larvae near Ralls
Typical defoliation in soybean caused by green cloverworm
Fortunately the green cloverworm is only a leaf feeder in soybean and it does not damage pods. For alfalfa here is a quote the Oklahoma guide, "These defoliators are rarely a significant problem in established alfalfa, although seedling stands can be heavily damaged by their feeding." However, if there are enough of them present they can cause defoliation, which in turn will reduce the amount of nutrients the plants can store for overwintering.
For soybeans, University of Tennessee has good list of insecticides in their publication here. Oklahoma State University has control suggestions for alfalfa here.
Friday, September 9, 2016
Dr. Pat Porter reported yesterday about heavy infestations of the green cloverworm in alfalfa and soybeans (http://focusonagriculture.blogspot.com), The following is the article that he published in "Focus on Entomology". One of the fields he got a call about was near Clarendon. Blayne Reed, Extension Agent - IPM, also, reported finding heavy infestations in soybean fields in Floyd county. I have not heard of any other fields in the Panhandle but there is high probability that the fields are infested.
Friday, July 22, 2016
Spider Mites on the Increase
After the heavy infestations of western flower thrips about 6 weeks ago, spider mite infestations in corn have been hard to find. But, spider mites seem to be recovering. In my field trials near Hart, Tx spider mites were beginning to build in some of my plots. The infestations were increasing in some plots, but not in all plots, next to the field edges. And spider mites were also increasing in other plots that were further out into the field. The mite predator densities per leaf were very low, < 0.5 predator / leaf. The primary predator found was the six spotted thrips adults and larvae.
John Quillin sent me this photograph yesterday of spider mites. So, be on the look out for hot spots of spider mites. They could be found throughout the fields.
|Photo: Mr. John Quillin|
Moth Trapping Activity
Southwestern Corn Borer (SWCB)
Deaf Smith county had a very noticeable increase in SWCB moth activity in two out of 4 location across the county (See SWCB graph). Last week there was an average of 10.5 SWCB moths per trap compared to this week’s collection of 54, 80, 206, and 347 moths per trap. None of the other counties saw this type of increase of SWCB moths. The other counties had less than 10 SWCB moths per trap. These moth trap collections in Deaf Smith county are still low compared to previous years when peak collections have been in the hundreds or thousands. These increases are an indication we are beginning the second generation SWCB moth flight.
Fall Armyworm (FAW)
Again Deaf Smith county, along with Dallam and Randall counties, had fall armyworm moths trap catches ranging from a low of 31 at a location to a high of 160 at another location. All other FAW trap numbers for the other reported locations were < 20.
Western Bean Cutworm (WBC)
The western bean cutworm moth numbers ranged between 6 to 53 moths per trap, with the mean at 33 WBC moths per trap. The counties reporting these numbers were from Dallam, Hartley, Moore to Hutchinson and down to Deaf Smith and Randall counties. These numbers are 1/8th to 1/4 the numbers we have trapped in other years. Although the numbers are low, we still need to be diligently looking for egg masses and larvae.
Friday, July 15, 2016
Late Wednesday evening, Blayne Reed (IPM Extension Agent - Floyd, Hale, Swisher Counties) reported sugarcane aphids were found on the eastern side of Floyd county by independent crop consultants (http://halecountyipm.blogspot.com/2016/07/sugarcane-aphid-in-floyd-county-sca-ipm.html). And, Katelyn Kowles (IPM Extension Agent - Crosby, Lubbock Counties) reported finding the aphids in the eastern part of Crosby County. The SCA infestations were very low in both counties. Infestations were from <1% of plants infested in Floyd to <5% of plants infested in Crosby. Colony sizes were also very small. Still they are here now.
Dr. Pat Porter has written the following summary or highlights from what we learned last year about SCA management.
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.
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.
Western Bean Cutworm
Last week I wrote about WBC moth activity beginning to increase and the possible concerns about reduced activity of Cry1F Bt toxin in Bt corn. After writing the article I began to wonder how our extreme hot temperatures would affect WBC egg and larval survival. I contacted an entomologist colleague from the University of Nebraska to get his input about these temperatures and WBC. His comments were “Hot temps will have greater impact on leaf temp if the plants are under any stress and this could dry egg masses and increase their falling off the plants. We have seen this happen some in fields that have been stressed. Perhaps the greatest impact from the heat will be to shorten adult life spans and decrease egg laying. In very hot weather the moth flight period is constricted and females tend to lay fewer eggs (fewer egg clutches). The larvae will seek protection, and if plant is not too stressed they will find it (e.g. developing tassels in whorl), should do well. They are very good at finding hospitable microclimates on the corn plant.” Also, he is an author on a journal paper that looked at WBC survival at different field location. I have copied a graph (below) from the paper that illustrates the number of days for eggs to hatch decreases from 12 days to 6 days as temperatures increase from 60o F (16o C) to 86o F (30o C). But, also at the higher temperature the percentage of eggs that hatch declined to 51%. So, when temperatures reach 105o F (40o C) or more the percentage of eggs hatching should be even less. Unfortuantely, having fewer egg clutches will mean take more time to find them when scouting and harder to make decisions for when to treat.
|J. Econ. Entoml. 106 (3): 1274 - 1285 (2013)|
Last week I reported heavy grasshopper activity in the northwestern part of the Panhandle. I noticed this week at the research facilities at Bushland the grasshoppers activity was increasing. But, nothing like the activity up north. Here are a few photographs sent to me that shows how heavy the grasshopper populations are and how much damage they are causing.
|Photo courtesy: John Quillin|
Moth Trapping Activity
Southwestern Corn Borer (SWCB)
There has been a dramatic drop in southwestern corn borer across the high plains region, which probably represents an end of the 1st moth flight. But, we could begin to see emergence of the 2nd generation SWCB moths from the egg lay of SWCB in early June in a couple of weeks. Non-Bt corn will need to be closely inspected for eggs. Generally the 2nd SWCB moth flights last 4 to 6 weeks with the peak flight occurring during the 3rd to 4th week.
Fall Armyworm (FAW)
We have had a couple of peaks already of fall armyworm moth activity. But, Deaf Smith county, particularly, had an increase this past week. Have had calls about whorl infestations in grain sorghum. infestations often do not result in economic losses even when leaves are really ragged by larval feeding. Control of infestation in the whorl can be difficult because few spray droplets are deposited in the whorl.
Western Bean Cutworm (WBC)
Dallam, Hartley, Moore counties, where traps are located, continue to have active moth flights of WBC. It should be noted that we have WBC moth activity moving out into Hansford and Deaf Smith counties.
Friday, July 8, 2016
In the last few days there has been a lot more chatter about sugarcane aphid (SCA) distribution. On July 2, we received a report from Joel Webb, EA-IPM Runnels and Tom Green counties, that he had identified SCA in the San Angelo area. Other than earlier reports of SCA overwintering on johnsongrass in cages in Dawson, Hale, and Swisher counties, this was closest report of SCA activity to the High Plains area. Then there was more chatter on July 7 with a report from Tom Guthrie, County Extension Agent in Mills County of SCA population building on sorghum and some fields at treatable levels in Mills, Comanche, and Hamilton counties. Also, we had word a private consultant were reporting SCAs at treatable levels in Nolan, Fisher, and Jones counties. And finally on July 7, I received a call from a J. R. Sprague, County Extension Agent from Lipscomb County. He had seen on Facebook that sugarcane aphids were found near Clinton, OK. As a crow flies this about 175 miles east of Amarillo, TX on interstate 40. I contacted Dr. Tom Royer, Oklahoma State University entomologist, to see if this could be confirmed. He stated that low numbers of sugarcane aphids were beginning to be found in several Oklahoma counties. Fortunately, there are no known reports of SCAs in sorghum fields on the Texas High Plains. But, as Dr. Pat Porter wrote “SCA are on our doorstep”. This link provides information on how to recognize the SCA (http://txscan.blogspot.com/2015/02/recognizing-sugarcane-aphid.html).
|Closeup of Sugarcane Aphids, Photo: Pat Porter|
It is July and I was hoping grasshoppers weren’t going to an issue this year. But, reports are coming from the Northwestern Panhandle counties that grasshopper populations are a concern. So, just a heads up for something to be watching for. The following link provides information about grasshopper biology and control (http://txppipm.blogspot.com/2015/06/grasshoppers-spider-mites-and-fall.html)
|Grasshopper on Corn, Photo: Ed Bynum|
Western bean cutworm (WBC) moth activity and egg lay is beginning to increase in the northwestern counties of the Texas Panhandle. Our moth traps have had an increase in western bean cutworm moths, particularly this past week. I have received reports of consultants finding sporadic egg lays in fields. Some fields with as many as 15% to 20% plants with egg cluster and some clusters already hatching. Based on past moth trapping numbers we should expect WBC moth activity to continue to increase for another couple of weeks before peak activity and then relatively high numbers another two to three weeks after peak activity.
We have 5 Bt toxic proteins for lepidopteran pest control that are used in different combinations in our Bt corn. However, western bean cutworm caterpillars have never been highly susceptible to many of the different toxins. But, in the past few years decreasing efficacy of one fairly effective toxin, Cry1F, against western bean cutworm caterpillars has been noted in particular. Environmentally hot dry conditions may also adversely impact the expression of the Cry1F toxin in the pollen during kernel fertilization. The pollen may not be as toxic when the small caterpillars feed on pollen before moving into the ear. Also, a seed company that sells Cry1F corn makes these three comments in a fact sheet on WBC and Cry1F Bt toxin. “When egg hatch occurs at brown silk stage or later, the larva can move quickly to the ears since fresh pollen and pollen sacs are not available to feed on. A supplemental insecticide application may improve the control of this later flush of the pest, even on hybrids with the X trait (referring to Cry1F). Since some control will be provided by the X trait, an infestation of about 20% of the plants with at least one WBC egg mass may justify treatment of this later flush”. This is another suggestion that control from the Cry1F toxin may not be as good as in the past. This Bt toxin could provide good control of WBC under certain conditions, but producers and consultants should be aware of these concerns for WBC control in Bt corn with the Cry1F toxin. The newest toxin that has good activity against WBC is the Vip3A toxin. The toxin is a new and different class of protein with insecticidal properties for many different lepidopteran pests of corn and cotton. But, the toxin is sold in very few Bt corn hybrids. This may not be an exhaustive list, but these hybrids are Agrisure Viptera 3110, Agrisure Viptera 3111, Agrisure Viptera 3220 E-Z Refuge, Agrisure Duracade 5222 E-Z Refuge, Optimum Leptra, and Optimum AcreMax Leptra.
When scouting look for eggs and larvae on the upper leaf surfaces in the upper third of the plant. Prior to pollen shed larvae may be found feeding in the tassel. After pollen shed larvae may be found in the leaf axil. Because of the sporadic distribution of the egg lay, entomologists from across different states have recommended checking 10 to 20 consecutive plants in at least 5 locations per field. And, the treatment threshold is from a low of 5% to as high as 14% of plants with egg masses or larvae. Most of the recommendations state that insecticides should be applied when the crop is at 90% to 95% tasseled and before larvae begin feeding on the silks. When we have an extended period of egg laying with different corn growth stages across the Panhandle a second application could be needed. The following table provides a listing of insecticides from our current guide for “Managing Insect and Mite Pests of Texas Corn”. As noted in the remarks section all products except Prevathon® and Belt® may flare mites. Either Prevathon® 14 oz/acre or Belt® at 2 oz/acre should provide up to 14 days of control. A recent comment from a consultant was that grasshoppers were becoming a problem and Prevathon would be his choice for WBC if the grasshoppers were moving into the corn field.