Moving from the High Plains of Texas, I thought I was leaving the windiest place in Texas only to discover that I had moved to the windiest place in the nation! And the wind does blow in Corpus Christi. Very warm conditions along with strong southerly winds AND mobile sugarcane aphid in the Rio Grande Valley have created a little buzz around what to expect with the aphid in 2017. It is still too early to say but recent observations of sugarcane aphid colonies and winged aphids in a few LRGV sorghum (~5 weeks earlier than first observations in 2016) has many folks speculating that this could be an aphid year in sorghum. Time will tell. If you missed the update about finding the sugarcane aphids in the valley click here to learn more.
Needless to say, this year has been more unique than most. Danielle was talking about hearing cicadas back in February and I heard a few cicadas in Corpus Christi earlier this month. There is an old wives tale that winter is six weeks away when the first cicada sings. Looks like winter will be way early for south Texas!
Farmers in south Texas were able to get an early jump on seeding crops. Favorable growing conditions have resulted in great stands and rapid early growth of corn and sorghum…cotton also looks very good. There has been very little in the way of insect issues in winter/spring seed crops so far. There was a little downtime from some much welcome rain events earlier in the month resulting in about a two to three week gap in finishing up some sorghum and corn acres. These later seeded fields will be attractive to worms…most noteably sorghum midge and fall armyworm. I often have this discussion around whorlworms and the value of spraying them in whorl stage corn and sorghum. There is very little to no value in spraying worms in vegetative corn or sorghum unless the worms are starting to feed on tassels or panicles. Leaf feeding always appears much worse than the impact it will have on yield.
What to look for in this edition of Rolling with Bowling:
- Graduate student corner: Isaac Esquivel summarizes his Ph.D. work on cotton fleahopper and verde plant bug
- Sesame…the crop with no insect issues…or is it?
Research Overview by Isaac Esquivel: With this year’s cotton season approaching, what are some trends we have seen in the past couple years in pest populations of Cotton Fleahopper and Verde Plant Bug?
The cotton fleahopper and the verde plant bug (Hemiptera: Miridae) have become more problematic in recent years in the cotton growing regions of South Texas. They feed on reproductive tissue: squares (cotton fleahopper) and young bolls (verde plant bug). Feeding during these stages can cause severe damage to the final cotton yield as well as introduce cotton boll rot. A pest management issue is that outbreaks vary from year to year and their densities vary from field to field. For example, one field may have a large population of plant bugs and another field adjacent to it may have none. The reasoning behind this phenomenon is not relatively understood and a graduate student working with Dr. Mike Brewer is currently investigating this phenomena on a spatial/landscape scale.
In landscape ecology, edge is defined as the distinct border between two different land cover types. These edges can be soft or hard and natural or anthropogenic. In our case, since this is an agricultural setting, our edges are hard anthropogenic edges between one crop type and another or one crop type and natural un-cultivated habitat. An edge effect refers to the high population density and diversity of a species or species in the outer portion or edge of a patch of habitat. In our case, fields. Ecotones are defined as the area occurring at the interface of two or more distinct landscape elements. In this study ecotones, would be the transition between different crops (i.e interface between cotton and sorghum) and natural habitat. We aim to investigate the role edges and ecotones has on the populations of these pests with two approaches, transect and random point sampling.
Field studies over the past couple seasons have yielded results that can be useful in the management of these insects. Sampling regimens have shown significant relationships between pest density and distance from the edge of a field (Edge Effect) for both pest species. This means that there are higher numbers of pests at the edge of the field and drops off as you enter the field to up to 300m approaching. Pest populations approach .025 bugs/plant at the farthest sampled points. For the cotton fleahopper a significant interaction was seen between edge and ecotone—neighbor—which suggests that field arrangement has effects on fleahopper populations. This means that depending on what is neighboring the edge of a particular cotton field has an effect on the edge effect we see in the field. For example, in edges adjacent to natural habitat, a stronger edge effect was seen compared to edge adjacent to sorghum or another cotton field.
This ecotone or neighbor effect is not as apparent for the verde plant bug as it is with the fleahopper. We did not see a consistent interaction between ecotone/neighbor and edge effect. This suggests that at least for verde plant bug, the edge effect is equal among the ecotones. We did see a significant interaction however in 2015 in one of our transect sampling data. This is probably a result of the highly mobile nature of the verde plant bugs and we may not be obtaining true pest estimates using our sampling method. However, upon our analysis of green boll inspections, there is a significant edge and ecotone effect. In other words, there is more boll damage at the edge of the field and dissipates as you enter it and that this edge effect is higher in certain areas of the field (cotton adjacent to natural habitat) than others.
What do these findings mean when it comes to monitoring and management of these pests? Since there is a significant edge and ecotone effect, growers should consider field position when monitoring for these pests i.e. focus monitoring efforts in areas that may be of higher risk for infestation. These areas would be neat natural habitat and at the edges of the field for both species. When it comes to verde plant lab managers should also look at green boll damage data as it may be more reflective of the presence of verde plant bugs. Also for future consideration a zone management scheme could possibly be implemented for controlling these pests. If you look at the figure below, you can see for cotton fleahopper we are only above threshold at sites less than 100 meters from the field and mainly in areas of the field that are adjacent to natural habitat.
Antigastra catalaunalis – Sesame Leaf Tier: Last year I received several reports of sesame being damage by a leafroller (or leaf tier). Several sesame fields near Charlotte, Texas were effected by the leafroller. The culprit, the sesame leaf tier (or sesame leafroller), Antigastra catalaunalis.
This moth is common in tropical and subtropical regions of the world. In the United States it has been reported in Southern Arizona to the eastern Mojave Desert and north to the northern areas of Utah. And now in Texas.
The larvae feed on a variety of plants such as snapdragons, toadflax, sesame, and figwort. Conditions favoring sesame leaf tier outbreaks include warm temperatures during dry periods and low humidity.
Eggs are laid singly on the underside of of leaves, on pods, and on branches. Sesame leaf tier eggs are small and conical in shape. Freshly laid eggs are white and turn dark white to tan prior to hatching. Once an egg is laid it takes approximately three days to hatch.
This leaf tier has 5 larval stages. Newly emerged larvae are creamy white and it is this first instar that begins tieing leaves together with silken threads. First instar sesame leafroller lasts about 4 to 6 days before molting to the second instar. It is in the second instar that dark spots (tubercles) develop on the abdomen. The secon instar feeds witin the webbing on leaf tissue, soft parts of the branches, and bore into pods. The second instar lasts approximately one to two days.
During the third instar, brown hairs (setae) and black dots become more apparent. The larva remains a light color but it prolegs become green. At this stage the larvae bore into flowers and pods. The third instar lasts about one day.
The fourth instar sesame leaf tier changes color from a creamy white to green and each abdominal segement will have two groups of three black spots. Fourth instar larvae feed on leaves, branches, and bore into flowers and pods. Once in the pod, they will feed on developing seed. This instar lasts about one day.
Fifth instar larvae become darker green with one thin longitudinal line on its back from the thorax to the last abdominal segment. This instar feeds on flowers and pods. Duration of this instar is 2 to 3 days. The average larval period is from 9 to 15 days.
The adult is a medium sized moth with a wing span of ~one inch. Forewings are dark reddish brown having dark reddish veins on the upper side and a series of black dots towards the margins. White dots are present on the ventral side of the wings beneath the black dots. Hind wings are transparent. Females are slightly larger than males. Mating occurs at night. A female will produce from 30 to 90 eggs and eggs are laid early in the oring.
Webbing and infested pods are typically filled with excrement. There is likely multiple generations of sesame leaf tier in Texas. There is not an economic threshold for the sesame leaf tier in sorghum. There are a number of biological insecicides that may be used against the sesame leaf roller on sesame but these products tend to have a short residual and may not be effective against larger worms. Rynaxypyr is labeled for sesame (product name is Coragen, DuPont). There are a few pyrethroids labeled for sesame but applications made against this insect last year were ineffective against this worm.
Nesidiocoris tenuis (Reuter) – Tomato bug. Another unexpected and unwelcomed insect pest of sesame is the tomato bug. This plant bug is somewhat of a Dr. Jeckyl/Mr. Hyde in agriculture. It is a predaceous insect of several crop pests but has a special affinity for white flies and aphids. Although it has value as a predator of some crop pests, it also feeds on and damages crops, such as sesame.
Adults are bright green and ~0.2 inch long with several black specs on on their hind wings. Immature tomato bugs start off yellow green but become bright emarald green as they develop. Eggs are laid into plant tissue and cannot be seen without the aid of a hand lens. Eggs hatch in about seven days and nymphs take about 14 days to develop into adults. The tomato bug has a piercing/sucking mothpart and damages sesame by removing sap from leave and stems with indirect damage to pods.
They are typically found on the underside of leaves and the growing points of plants. They blend in well with their surrounding and may be difficult to see.
Symptoms of feeding injury include spotting and holes in the leaves and feeding rings on the plant stem and petioles. Feeding injury causes stunted growth, deformations in the growing point, uneven pod set, feeding spots on the fruit, and abortion of the flowers.
There is not an economic threshold for tomato bug on sesame but large populations can cause significant yield reduction of the crop. Imidacloprid and some pyrethroids have been effective at managing the tomato plant bug. Please read and follow label directions before applying any insecticide.
For more information on the sugarcane aphid and other field crops topics check out our new website at: (http://betteryield.agrilife.org/).
Robert Bowling, Ph.D.
Assistant Professor and Agrilife Extension Entomology Specialist
Texas A&M Agrilife Research and Extension Center at Corpus Christi
10345 Hwy 44
Corpus Christi, TX 78406