4 pp. / This bulletin will provide a comprehensive update of the statewide guidelines for whitefly management in cotton (Last version, 4/96), including guidelines for crop and host management, scouting and decision-making, areawide impact, and effective chemical use. A new set of resistance management guidelines will be highlighted.

Genetically modified cotton expressing the Cry1Ac toxin has been used in Arizona since 1996 with exceptionally positive results in terms of economic returns to growers and reductions in insecticide use in cotton. Since 1995, average insecticide use in Arizona cotton has declined from greater than six applications per acre to less than two in 2000. Bt cotton has contributed greatly to these savings to growers, as have insect growth regulators used for whitefly control. Collections of pink bollworm, Pectinophora gossypiella, made in 1997 and subsequently exposed to Cry1Ac in the laboratory from 1998 to 2000, yielded a laboratory strain with susceptibility to Cry1Ac reduced 1,000 to 3,000- fold, relative to highly susceptible field populations. Unparalleled measures have been taken to detect and manage this resistance. In this report we summarize results of statewide monitoring of pink bollworm susceptibility to Cry1Ac conducted from 1997 to 2000, and results of field evaluations of the effectiveness of Bt cotton from 1995 to 2001. Susceptibility of Arizona pink bollworm to Cry1Ac, increased from 1997 to 2000. Mean corrected mortality in 1μg/ml Cry1Ac assays was 57.4% in 1997, 90.6% in 1998, 97.9% in 1999 and 97.4% in 2000. Mean corrected mortality in bioassays of 10 μg/ml also increased: it was 94.1% in 1997, 99.9% in 1998, 100% in 1999 and 100 % in 2000. Field performance of Bt cotton in 2000 continued to be excellent at 39 locations throughout Arizona cotton at which paired Bt and non-Bt fields were evaluated. Whereas non-Bt cotton fields had mean infestations of over 15% infested bolls, Bt cotton fields averaged less than 0.15% infested bolls. Thus, after six years of intensive use of Bt cotton in Arizona, pink bollworm populations show no signs of being resistant to Bollgard cotton. Indeed, for reasons that are not understood at this time, they have been found to be significantly more susceptible to the Bt toxin in Bollgard cotton at the end of the 2000 season than they were in 1997.

Arizona cotton experienced a severe crisis in 1995 stemming from resistance of whiteflies to synergized pyrethroid insecticides. The insect growth regulators (IGRs) Knack® (pyriproxyfen) and Applaud® (buprofezin) served a pivotal role in resolving this problem. Statewide monitoring of whitefly resistance is conducted annually in Arizona to assess the status of resistance in this important pest. In this paper we provide an update on results from whitefly collections made from 19 cotton fields located throughout Arizona. Overall, whitefly control in Arizona cotton remained excellent in the 2001 season and there were no reported field failures. However, we detected major decreases in susceptibility to Knack of whiteflies collected from cotton. Whereas it was extremely rare to have any whiteflies surviving bioassays of 0.1 μg/ml from 1996 to 1998, this changed in 1999, and by the 2001 season over 60% of Arizona sites evaluated had •2% pyriproxyfen-resistant whiteflies. One collection from Eloy, Arizona, in 2000 had >50% of whiteflies surviving Knack bioassays of 0.1 μg/ml. Whiteflies throughout Arizona continued to be moderately less susceptible to Applaud, relative to susceptibility levels in 1996, when the IGRs were first introduced. In contrast to our findings with Knack, changes in susceptibility to Applaud have been only moderate and quantitative. Arizona whiteflies continued a six year trend of reduced resistance to synergized pyrethroid insecticides, as indicated by bioassays with mixtures of Danitol and Orthene. Problematic frequencies of whiteflies resistance to synergized pyrethroids were found at only two of 19 locations sampled. Steps should be taken now to prepare for the onset of more severe resistance to IGRs in Arizona cotton. Factors that could undermine the current success of whitefly resistance management in Arizona are discussed. Education efforts should reinforce the importance of limiting IGR use in cotton to a maximum of one treatment each per season and rotating conventional insecticides as recommended in the three-stage resistance management strategy implemented in 1996. Because Knack and Applaud have received registrations for use in Arizona vegetable and melon crops grown in proximity to cotton, it is now especially critical that Extension education efforts focus on cross-commodity coordination of IGR use recommendations to preserve the activity of these important insecticides.

Monitoring of Arizona pink bollworm (PBW), Pectinophora gossypiella, susceptibility to the Bt toxin Cry1Ac has been conducted annually since 1997. PBW were collected from cotton fields located throughout the Southwest in 2002, cultured in the laboratory, and tested for susceptibility to Cry1Ac using diet-incorporation bioassays. A total of 13 Arizona collections were successfully reared and bioassayed. Collections from California (6), New Mexico (1), and Texas (1) were also tested. Laboratory selection of pink bollworms collected from Arizona in 1997 and exposed to Cry1Ac in diet produced a strain capable of surviving on Bollgard® cotton. Subsequent studies showed that 10 g Cry1Ac/ml of insect diet was a reliable diagnostic concentration for detection of pink bollworm that were homozygous for resistance to Cry1Ac. On this basis, resistant PBW were detected in 2002 in only 2 out of 13 Arizona strains. The overall frequency of resistant PBW in 2002 for Arizona was 0.17% and ranged from 0.0 to 1.7%. One of six California collections evaluated had a single resistant survivor. No resistant pink bollworms were detected in the single New Mexico and Texas collections evaluated. Resistant PBW were significantly more abundant in Arizona in 2001 and 2002 than they were in 1998, 1999 or 2000. However, the frequency of resistant survivors in bioassays was low for 2001 and 2002, and markedly lower than in 1997. The Arizona Cotton Research and Protection Council evaluated the efficacy of Bt cotton in 2002 using adjacent pairs of Bt and non-Bt fields at 43 locations across Arizona. Pink bollworms were found in an average of 23.3% of these non-Bt boll fields. Bolls from Bt cotton fields yielded an average of 0.144% (range 0 to 1.300%) infested bolls. Of these, all but three of the pink bollworm recovered from Bt cotton plantings came from bolls that tested negative for Cry1Ac. We conclude from these findings that there is no indication that pink bollworm resistance to Cry1Ac was a problem at the locations sampled in 2002. Bt cotton continued to exhibit exceptional field performance in Arizona.

Cotton, Gossypium spp., varying in leaf color (green vs. red), leaf shape (normal vs. okra) and leaf hairs per cm2 of leaf area were evaluated for sweetpotato whitefly (SPW), Bemisia tabaci (Gennadius) Biotype B preference. Regression analysis showed SPW adults, eggs and nymphs were significantly related to leaf hairiness. Seasonal mean numbers of SPW adults, eggs, and nymphs were high variable within and between leaf color, shape, and hairiness types. Further studies are justified since some of the cottons may be potential sources of SPW resistant germplasm.

Bt cotton is an extremely important tool for integrated pest management in the Southwest. It has been a major factor in the current historic low levels of conventional insecticide use in cotton of this region. This is due to Bt cotton’s unprecedented efficacy against the pink bollworm, Pectinophora gossypiella, and its selectivity in favor of key natural enemies of arthropod pests. Due to the pivotal importance of Bt cotton and widespread concerns about the development of pest resistance to transgenic crops, a multi-agency resistance management program was established to monitor and pro-actively manage resistance development in the pink bollworm. This report constitutes results from the ninth year of this monitoring program. Larvae were obtained from bolls collected in cotton fields located throughout the Southwest, cultured in the laboratory, and offspring tested using diet-incorporation bioassays that discriminate between susceptible and resistant pink bollworm. A total of 11 Arizona and four California collections were successfully reared and tested for susceptibility to Cry1Ac using a discriminating concentration of 10 μg Cry1Ac/ml of diet. Susceptibility to Cry2Ab2 was estimated similarly for 12 strains from Arizona and four from California using diagnostic concentrations of 1.0 and 10 μg Cry2Ab2/ml of diet. Success of pink bollworm eradication in suppressing pink bollworm populations in New Mexico and Texas precluded successful collection of samples in those states. No survivors of 10 μg Cry1Ac/ml were detected in any bioassays of 2005 strains (n=5358). The grand mean frequency of PBW survival of 10 μg Cry1Ac/ml in 2005 was 0.000%. A susceptible culture, APHIS-S, used each year as an internal control, yielded 99.3% corrected mortality in tests of 10μg/ml Cry1Ac (n=490). All twelve pink bollworm strains collected in 2005 were highly susceptible to Cry2Ab2, based on contrasts with baseline data collected from 2001-2003. There were no survivors of bioassays of either 1.0 μg Cry2Ab2/ml (n=1,000) or 10 μg Cry2Ab2/ml (n=3425). The susceptible APHIS-S culture had 82.5% corrected mortality in tests of 10 μg/ml Cry2Ab2 (n=200) and 100% mortality in tests of 10 μg/ml Cry2Ab2 (n=120). Field evaluations of efficacy of Bt cotton were conducted by the Arizona Cotton Research and Protection Council in adjacent pairs of Bt and non-Bt fields at 44 Arizona locations. Statewide, large pink bollworm larvae were found in an average of 15% of non-Bt bolls sampled from borders of refuge fields. This was on the low end of the range of infestation levels observed in refuges during the past decade. Bolls from adjacent Bt cotton (Bollgard™) fields yielded an average of 0.28% infested bolls. This value was down slightly from the previous year. Over 70% of the pink bollworm recovered from collections in Bt fields were from bolls that did not express Bt toxin. We conclude that there was no indication of problems with pink bollworm resistance to Cry1Ac or Cry2Ab2 at the locations sampled in 2005. Moreover, Bt cotton continued to exhibit exceptional field performance in Arizona.

We report biotype identifications and susceptibility to insecticides of whiteflies (Bemisia tabaci) collected from cotton, vegetables, melons and ornamental plans during the 2005 season. No major problems with field performance of insecticides against whiteflies were confirmed in 2005 in Arizona. Whitefly resistance to pyriproxyfen did not increase, relative to levels recorded in 2004. However, we detected pyriproxyfen resistance in all Arizona whitefly samples tested. A single sample collected from cotton in Holtville, CA, had no detectable resistance to pyriproxyfen. Samples from cotton in Buckeye, Coolidge, Scottsdale, and stanfield, Arizon,a had the highest levels of resistance, with > 31-45% of eggs surviving diagnostic concentration bioassays of 0.1 ug/ml pyriproxyfen. Whitefly susceptibility to buprofezin (Applaud®/Courier®) has not changed significantly since 1997. Resistance to synergized pyrethroids (e.g., Danitol® + Orthene®) has decreased strikingly on a statewide basis since 1995, though unacceptably high frequencies of resistant whiteflies were detected in some 2005 collections from all commodities sampled. Whiteflies collected from Arizona cotton, melons, and vegetables continued to be highly susceptible to imidacloprid (Admire®/Provado®). One whitefly collection from poinsettias in Phoenix (05-39) was substantially less susceptibile to imidacloprid, and the related neonicotinoid insecticides, acetamiprid, and thiamethoxam. Regression analysis yielded a significant correlation between acetamiprid and thiamethoxam. Whiteflies from cotton that were least susceptibile to acetamiprid were also significantly less susceptible to thiamethoxam (Actara®/Centric®/Platinum®). The most worrisome of our 2005 findings was that 6 out of 13 samples of whitefly-infested poinsettias collected from retail stores in metropolitan Tucson and Phoenix consisted of only the Q biotype of Bemisia tabaci. The plants were infested with very low whitefly numbers and thus we were unable to establish them in laboratory cultures and evaluate their resistance status. The Q biotype is native to Spain and was first detected in the US by our group in 2004 on a sample taken from poinsettias. Our concern is that the Q biotype strain we detected in 2004 was highly resistant to a broad range of insecticides used to manage whiteflies in Arizona. None of the 26 field collections evaluated in 2005 was the Q biotype.

Weed control and desiccation are routinely executed with herbicides. Potato vine desiccation facilitates harvest, improves skin set, and regulates tuber size. Saflufenacil, glufosinate, saflufenacil plus glufosinate, and carfentrazone plus glufosinate were compared to diquat applied at 43, 31, and 17% B potatoes; similar vine desiccation (14 days after treatment), skin set, and yield were noted amongst treatments. Residual herbicides are routinely used for weed control in pumpkin. Fluridone and acetochlor formulations applied preemergence were evaluated in direct-seeded pumpkin compared to other labeled herbicides. Fluridone resulted in total crop loss following heavy rainfall immediately after planting; less rainfall resulted in transient injury. Acetochlor formulations resulted in significant pumpkin injury (34 to 39%) 14 days after planting. S-metolachlor controlled weeds similar to acetochlor without significant injury. Palmer amaranth has developed resistance to six different herbicide modes of action. The weed grows rapidly and is best controlled <10 cm in height. To control glyphosate and ALS- resistant biotypes, fomesafen plus dicamba were applied at first postemergence (POST) to small Palmer amaranth (<5 cm, 0 d) and at simulated delays of 7, 14, 21, and 28 d. All plots received lactofen plus dicamba 14 days after first POST. Palmer amaranth control 14 days after first POST was 100% when delayed 0 or 7 d and 62% at the 28 day delay; control increased to 88% following lactofen plus dicamba applied second POST. Yield was significantly reduced when first POST was delayed 28 days at one location. / Master of Science in Life Sciences / Herbicides effectively control weeds by either applying them to the soil prior to emergence or applying them to foliage. Herbicides are used for desiccation of potato vines to facilitate harvest, improve skin set, and regulate tuber size. Potatoes with tougher skin have a longer shelf life and are more resistant to disease. Potato grade classifications include size chef, A, and B potatoes. Size B potatoes hold the greatest value for redskinned potatoes. Experiments were conducted in Virginia to evaluate saflufenacil, glufosinate, saflufenacil plus glufosinate, and carfentrazone plus glufosinate as desiccants compared to diquat applied at 43, 31, and 17% B potatoes. All desiccants resulted in similar vine desiccation 14 days after treatment, skin set, and yield. This research demonstrates that glufosinate and saflufenacil are effective alternatives to diquat for potato vine desiccation; however, further research is needed to evaluate the safety of saflufenacil applied to potatoes prior to harvest. Soil applied herbicides are commonly used in pumpkin production. Fluridone and two acetochlor formulations, herbicides that effectively control troublesome weeds in other crops, were evaluated for pumpkin production in addition to fomesafen, ethalfluralin, clomazone, halosulfuron, and S-metolachlor. Fluridone and acetochlor formulations resulted in significant pumpkin injury early in the growing season and total crop loss was observed by fluridone in 2018. Fomesafen significantly reduced pumpkin iv stand and yield. S-metolachlor, a member of the same chemical family as acetochlor, provided similar weed control without significant pumpkin injury. This research demonstrates that fluridone and acetochlor formulations are poor candidates for pumpkin production. Palmer amaranth is a troublesome weed in soybean that grows rapidly and is resistant to many herbicides. Palmer amaranth is best controlled at a height of 10 cm or less, but timely applications are not always feasible. Fomesafen plus dicamba were applied to small Palmer amaranth (<5 cm, 0 day) and at simulated delays of 7, 14, 21, and 28 days. All treatments received lactofen plus dicamba 14 days after the initial postemergence. Palmer amaranth control 14 days after first postemergence was 100% when application was delayed 0 or 7 day whereas Palmer amaranth control was 62% when first postemergence was delayed 28 days. Lactofen plus dicamba applied second postemergence increased control to 88% when the first postemergence was delayed 28 days. Compared to nontreated plots, Palmer amaranth biomass was reduced 99% by all treatments. This research demonstrates that fomesafen plus dicamba followed by lacofen plus dicamba can be effective for rescue control of Palmer amaranth.

Recently, cotton production throughout the southern U.S. have declined substantially. Additionally, the pest status of bollworm, Helicoverpa zea (Boddie), has increased in soybean. As a result, there is growing interest to have commercial access to transgenic soybean varieties that express the Bt toxins to help manage against lepidopteran pests. However, soybeans are assumed to be a key host in the natural refuge concept used for Bt cotton. Research was conducted to determine if the introduction of Bt soybeans into the U.S. would present an unacceptable risk to the sustainability of other crops. This project examines the contribution of soybean to the susceptible heliothine populations in the natural refuge system, the potential of delayed in-season emergence of H. zea from field corn, effects of soil moisture on emergence and pupal duration, fitness of adult H. zea from Bt and non-Bt corn, and provide more accurate parameters for future resistance development models.

A survey was conducted by phone to nearly 1,200 growers in six states (Illinois, Indiana, Iowa, Mississippi, Nebraska, and North Carolina) in 2005. The survey measured producers’ cropping history, perception of glyphosate-resistant (GR) weeds, past and present weed pressure, tillage practices, and herbicide use as affected by the adoption of GR crops. The objectives of this study were to determine the effect of GR crop use on producers’ tillage practices; changes in herbicide use patterns after adoption of a GR crop; effect of grower awareness of GR weeds on sources of information growers’ use; and growers’ perceptions on resistance management based on knowledge of GR weeds in their farming operation. The adoption of GR cropping systems contributed to large increases in the percentage of growers using no-till and reduced-till systems. Tillage intensity declined more in continuous GR cotton and GR soybean (45 and 23%, respectively) than in rotations that included GR corn or non-GR crops. Tillage intensity declined more in the states of Mississippi and North Carolina than in the other states, with 33% of the growers in these states shifting to more conservative tillage practices after the adoption of a GR crop. This was in part due to the lower amount of conservation tillage adoption in these states prior to GR crop availability. With respect to herbicide use patterns, frequently used herbicides for fall applications were 2,4-D and glyphosate; these herbicides were often used for preplant, burndown weed control in the spring. As expected, crop rotations using GR crops had a high percentage of respondents that made one to three POST applications of glyphosate per year. Overall, glyphosate use has continued to increase, with concomitant decreases in utilization of other herbicides. Concerning grower awareness of GR weeds and perceptions of resistance management in 2005, the majority of the growers (88%) were aware of a weed’s potential to develop resistance to glyphosate, while 44% were aware of state-specific, documented cases of glyphosate weed resistance. Growers that have had experience with GR weeds were more knowledgeable about resistance management practices that could be used to mitigate them.