NAVEL ORANGEWORM FOUND IN A PECAN NUT

On January 25, I received a pecan nut, with a hole in it, which a grower had found in his orchard and suspected to be infested with pecan weevil. I opened it, found a moth pupa, put the nut and its contents in a rearing cage, and completely forgot about it. Recently, I found 4 unfamiliar moths in that rearing cage. From the close-up photographs that I sent out, Bill Ree and Mark Muegge determine it to be the navel orangeworm. I mailed all the specimens to Kira Metz, Entomologist Identifier, USDA-APHIS in College Station, for confirmation. The navel orangeworm is a pest of citrus, walnut, almond, pistachio, macadamia, and figs in California, but I have not found a publication that deals with this pest in pecan. Bill Ree suspects that El Paso pecan growers should not be worried about this insect at the moment because the navel orangeworm cannot enter a pecan nut unless there is a crack in the shell. Potentially, this insect could become a stored product pest of pecan. The University of California IPM website mentions that the navel orangeworm does not damage sound walnuts, almonds, or pistachio, but nuts become susceptible when hulls begin to split.

COTTON THRIPS AND PLANT STAND DENSITIES

All cotton fields in our area have been planted and “capped off”. A majority of them have plants at the cotyledon stage. I have not seen much thrips damage yet. In the Texas high plains, thrips are considered a key pest in pre-squaring stage cotton (David Kerns et. al., Developing an action threshold for thrips in the Texas high plains, 2010). The currently accepted action threshold for thrips is 1 thrips per true leaf, but based on recent findings, these AgriLife Researchers suggest that it may be necessary to update thrips thresholds in cotton to the following levels: cotyledon stage = 0.5 thrips per plant, 1 true leaf = 1 thrips per plant, 2 true leaves = 1-1.5 thrips per plant, and 3-4 true leaves = 2 thrips per plant. Cotton plants are most susceptible to thrips damage at the cotyledon stage and this susceptibility decreases as the cotton plant grows. Another caveat is that whole-plant samples placed into jars containing alcohol have been shown to be a more accurate sampling technique than simple visual inspections. Usually, warm weather allows cotton seedlings growth to compensate for thrips damage. The weather forecast calls for the next couple of days below average temperature and then return to warm conditions. I do not expect thrips to be a problem in El Paso and Hudspeth Counties this year, but it is wise to monitor the crop for thrips levels. There are some plants showing sandblast damage; especially in sections of fields with soils high in sand content.

            In recent years, I have observed that cotton fields in our region have an average plant stand density around 55,000 plants/acre, with fields planted as low as 30,000 plants/acre and as high as 63,000 plants/acre. Yesterday, I obtained four samples per farm from 4 cotton farms. For each sample I counted the number of plants in 11 feet of row. The first 3 farms had plant stand densities falling within expectations: 41,818; 59,459; and 63,828 plants/acre. However, the last farm sampled now holds the highest plant stand density that I have observed so far: 105,981 plants/acre. It is generally accepted that 2-4 plants/foot of row maximizes yields. This is equivalent to 26,136 - 52,272 plants/acre in fields with 40 inches between rows. Most cotton fields that I have visited this season have been planted at 40 inches between rows and a few at 38 inches. It seems to me that some growers could gain substantial savings in seed costs by planting at recommended densities.

LEAFMINER DAMAGE IN ALFALFA

A 14-acre alfalfa field south of Fabens has been affected by an undetermined leafminer, possibly the American Serpentine Leafminer (ASL), Liriomyza trifolii. This field had areas with severely damaged plants next to areas with plants that had little damage. Approximately 30% of the field was affected. I recommended an early harvest and immediate removal of the alfalfa to reduce both the pest and susceptible host. Additionally, that field could also benefit from prompt irrigation. A sample of adult leafminers was submitted for species identification. Dr. Scott Armstrong, a research entomologist with ARS-USDA in Weslaco, TX, reports that this species has been a problem in cotton and vegetables in southeast Texas this year.  ASL is one of the most widespread and economically-important leafminers in the world. It is a very polyphagous leafminer species that feeds on a wide variety of row crops, ornamentals, weeds, and native plants. Therefore it can maintain continuous populations even when crops are not in cultivation (C. E. Stegmaier Jr., The Florida Entomologist, Vol. 49, No. 2). In general, leafminers can become key pests in crops where insecticides are used excessively.  Usually, leafminers are kept in check by natural enemies, especially small wasps that parasitize eggs, larvae, and pupae stages. They are called “parasitoids”. Parasitoid is defined as an organism that, during its development, lives in or on the body of a single host individual, eventually killing that individual. Sometimes there are also “hyperparasitoids”, which are parasitoids that develop in other parasitoids. The leafminers are very tiny insects so you can imagine the size of its associated hyperparasitoids. When insecticides are applied too frequently, the populations of natural enemies may crash and this results in leafminer outbreaks. Interestingly, alfalfa fields in our region receive very little insecticide applications, if any. The good news is that we are definitely not dealing with the Alfalfa Blotch Leafminer, a major alfalfa pest in other parts of the country; especially the Midwest.

The Entomology Science Conference 2010

The Entomology Science Conference 2010 (Texas A&M - College Station) was highly informative. It included entomological research summaries and discussions on cotton, pecan, corn, soybean, potato, sorghum, rice, grape, turfgrass, insecticide resistance, insect physiology, urban pests, ornamental plants, livestock, and others. Following, I present highlights of some of the presentations on cotton and pecan at this meeting:

      Cotton Entomology Research in the High Plains: Overview and Potential Areas of Collaboration / Megha Parajulee and David L. Kerns: The Texas High Plains is the engine of the U.S. cotton industry. This is the world’s most concentrated cotton-producing region. Research areas include insect-plant interaction, molecular ecology, biology & behavior, systematics & morphometry. A multi-year area-wide survey identified alfalfa, sunflowers, mustard, pigweed, and Russian thistle as primary hosts of Lygus hesperus.  Russian thistle and alfalfa are the hosts that consistently attract more adults and nymphs. Cotton has a tremendous ability to compensate fruit loss especially if it happens during early plant stages. Up to 33% early fruit loss usually results in no significant yield differences.

      Omnivory of Western Flower Thrips (WFT) in Cotton: Implications for Management Strategies / Justin Fiene, Christian Nansen, Marvin Harris: WFT spread from western U.S. since the late 70s. Currently, they are worldwide and extremely polyphagous. WFT feeds on pollen, leaf foliage, spider mites, and mite eggs. In 2009, thrips was considered the number one pest in U.S. cotton. The cotton plant is vulnerable to thrips damage from seedling to 5-6 leaf stage, as it delays plant maturity. Female thrips feed more on plant juices than on mites. Immature thrips feed equally on plants and mites. Females live much longer than immatures and females are 35.4 times more destructive than immature thrips. Potential for host plant resistance breeding programs: in no-choice conditions, pima cotton is more susceptible than upland cotton, but in choice experiments, WFT prefer upland over pima cotton.

      Evaluation of Systemic Granular and Cotton Seed Treatment Insecticides With and Without Foliar Acephate / Roy Parker: Foliar applications of Orthene (acephate) resulted in the lowest number of thrips, but there was no effect on plant damage. Orthene applications did not result in any yield gain. Orthene had the lowest yield. Temik, Gaucho Grande, and Cruiser as seed treatmens for thrips resulted in a significant increase in cotton lint production compared to the untreated check. Temik was the highest yielding treatment.

      Effects of Neonicotinoid Insecticides on Induced Defenses to Spider Mites in Cotton and Corn / Adrianna Szczepaniec, David Kerns, Micky Eubanks: Neonicotinoids leave a good first impression: reduced environmental impact, long residual toxicity, and highly effective. However, imidacloprid has resulted in spider mite outbreaks. Why? The natural enemy elimination hypothesis has not proved conclusive, but there is increasing evidence of plant-mediated effects. Changes in plant physiology and compromised plant defense following imidacloprid applications may have a direct effect on spider mite fecundity. Imidacloprid decreased expression of defense genes in tomato plants. Thiamethoxam applications decreased expression of defense genes in cotton as well. Imidacloprid had a two-fold increment in mite abundance in tomato. However, there is no evidence of spider mite outbreaks in cotton fields following imidacloprid applications. 

      Treatment Timing Targeting Cotton Fleahoppers. When and how many treatments are needed? / Roy Parker:  This study used PHY367WRF as the cotton variety and Centric 40WG at 1.25 oz/acre to control thrips. Treatments A: 1, 2,3, 4 (weeks of squaring); B: 2, 3, 4; C: 3, 4; D: untreated check (UTC).  UTC had greater number of unopened bolls. All insecticide-treated plots had greater yields than UTC.

      Sampling Sucking Bugs and Symptoms of Boll Injury on Cotton: Are There In-season Predictors of Lint Loss, Seed Loss and Boll Rot? / Mike Brewer, Darwin Anderson, Scott Armstrong: The cotton fleahopper was the key sucking pest from squaring to bloom. Green plant bug was an important pest in late bloom. Up to 25% of bolls showed boll rot in coastal areas. Green bolls had signs of rot when infested with green plant bugs.

      Sampling Strategies for Cotton Fleahopper and the Green Plant Bug (Creontiades signatus) / Darwin Anderson, Mike Brewer, Scott Armstrong, Raul Villanueva: Treatments: visual, KISS (an air blower coupled with a sweep net), beat cloth, beat bucket, and sweep net. The beat bucket has greater advantages because it picks up less trash and it is easier to check captured insects. The sweep net has a lot of variability because insect scouts use different plant canopy depth, force, and net impact angle. KISS takes the shortest time, picks up very little trash, and is very efficient in sampling young plants. Experience plays a large role in sampling accuracy especially as plants become larger.  The beat bucket and sweep net performed better especially for experienced samplers.

      Evaluation of New Insecticides for Cotton Aphid Control / Brant Baugh, David Kerns, Rick Minzenmayer, Dustin Patman, Chris Sansone: CMT-4586 at 8 fl oz/A (spirotetramat + imidacloprid) performed well. Intruder at 0.6 oz (acetamiprid); Centric 2.5 oz (thaimethoxam); Bidrin 8 fl oz (dicrotophos); Trimax Pro 1.8 oz (imidacloprid); Carbine 1.5 oz. (flonicamid); Belay 4 oz (clothianidin)=was a poor performer. Neonicotinoids are hard on lady beetles. Carbine is easy on beneficials. Intruder, Bidrin, and carbine are good choices for aphid control.

      Controlling Mixed Populations of Bollworms, Fall Armyworms and Pink Bollworm Monitoring / Manda Cattaneo, Brant Baugh, Dustin Patman, Warren Multer, Tommy Doederlein, Charles Allen, David Kerns: Applications of Mustang Max, Karate, or Holster resulted in good bollworm control. Belt performed poorly.

            Imidacloprid Resistance Monitoring and Insecticide Efficacy Screening in Pecans / Bill Ree: Black-margined aphids: in laboratory studies, concentrations of imidacloprid at ¼ of the lowest recommended rate (according to the label) in aphid samples obtained from an organic orchard (no insecticide used in the last 12 years) resulted in 100% mortality of black-margined aphids one day after treatment. Using aphid samples obtained from a "problem orchard", 16% of black-margined aphids survived, at the highest labeled rate (7 oz/A), after 3 days of exposure. This shows a wide range of susceptibility. Stink bug tests: bifenthrin applications (Brigade WSB) at 8 and 12 oz/A provided 93 and 100% mortality at 7 days with 48 hour exposure respectively. Brigadier (bifenthrin + imidacloprid) provided good control at the lowest and highest labeled rates, resulting in 90 and 87% mortality at 7 days, with 48 hr exposure, respectively