Vegetable Report 2003
ABOUT THE COLLECTION
The Vegetable Report is one of several commodity-based agricultural research reports published by the University of Arizona.
This report was first published in 1965.
The purpose of the report is to provide an annual research update to farmers, researchers, and those in the agricultural industry. The research is conducted by University of Arizona and USDA-ARS scientists.
Both historical and current Vegetable Reports have been made available via the UA Campus Repository, as part of a collaboration between the College of Agriculture and Life Sciences and the University Libraries.
Contents for Vegetable Report 2003Insects
- Beet Armyworm and Cabbage Looper in Head Lettuce: Control with Selective and Reduced-Risk Insecticides
- Comparison of Sampling Methods for Estimating Western Flower Thrips Abundance on Lettuce
- Compatibility of Fertilizer and Neonicotinoid Soil Applications for Whitefly Control in Spring Cantaloupes
- Final Report on the Use of Parasitoids to Control Sweet Potato Whiteflies in Open Arizona Agriculture
- Foxglove Aphids in Lettuce: Control with Reduced-Risk and Conventional Insecticides
- Management of Aphids is Brassica Seed Crops with Selective Insecticides
- The Emergence of the Foxglove Aphid, Aulacorthum solani, as an Economic Pest of Lettuce in the Desert Southwest
- Whitefly Control with Foliar Insecticides in Cantaloupes
- Comparison of Fungicides for Management of Downy Mildew of Broccoli in 2003
- Evaluation of Lettuce Cultivars for Resistance to Fusarium Wilt in 2003
- Evaluation of Lettuce Cultivar Susceptibility to Powdery Mildew in 2003
- Evaluation of Products to Manage Sclerotinia Leaf Drop of Lettuce in 2003
- Examination of New Chemistries to Control Powdery Mildew of Cantaloupe in 2002
- Fungicide Performance for Control of Powdery Mildew on Lettuce in 2003
- Comparison of Efficacy and Safety of Oxyfluorfen Formulations on Broccoli
- Efficacy and Safety of Combinations of Preemergence and Postemergence Herbicides in Cantaloupes
- Evaluation of Kerb Applied by Sprinkler Irrigation to Lettuce
- Evaluation of Preemergence and Postemergence Herbicides for Sweet Corn Weed Control
- Preemergence Herbicide Combinations for Weed Control in Cantaloupes
- Sandea Herbicide Rotational Crop Replant Study
- Screening Herbicides for Lettuce, Broccoli, and Spinach
Screening Herbicides for Lettuce, Broccoli, and SpinachNicosulfuron, quinclorac, triflusulfuron, MKH-3586, pyraflufen, and tribenuron applied PREE appeared to be safe on the lettuce crops while demonstrating variable activity against weeds. Head lettuce and romaine were not as tolerant to POST herbicides compared to PREE herbicides. Sulfosulfuron, MKH-3586, rimsulfuron, ethametsulfuron and pyraflufen applied POST caused various degrees of injury on the lettuces that were less injurious than other treatments. Thifensulfuron, nicosulfuron, and quinclorac applied PREE or POST showed acceptable broccoli tolerance. Ethametsulfuron exhibited adequate safety when applied POST on broccoli. Thifensulfuron, nicosulfuron, and quinclorac applied PREE also showed spinach tolerance. Similar to head lettuce and romaine spinach was not as tolerant to POST herbicides compared to PREE herbicides.
Sandea Herbicide Rotational Crop Replant StudyBroccoli and red table beets emerged and established a stand in Sandea treated plots at 0.5 or 1.0 oz product/A. Table beets planted into the beds treated with Sandea did not exhibit significantly different rates of emergence and stand establishment relative to the untreated check. The broccoli that emerged and established a stand did not show any significant differences or numerical trends between the untreated check and the two Sandea treatments during any of the observation dates. Spinach, the third indicator crop, did not emerge adequately in the test site.
Preemergence Herbicide Combinations for Weed Control in CantaloupesSandea, Valor, and Outlook offered promising results in different combinations applied preemergence (PREE). The combination of Prefar plus Sandea gave 95% control of pigweed and continued to control lambsquarters at 90% late in the season. Prefar combined with Valor gave acceptable pigweed control and lambsquarters were controlled at acceptable levels at 88 and 86%, respectively. Outlook combined with Valor was safe and gave good early pigweed control and later control of lambsquarters. Strategy alone at either 1.0 or 2.0 pt/A did not provide acceptable levels of weed control and no significant crop injury was observed.
Evaluation of Preemergence and Postemergence Herbicides for Sweet Corn Weed ControlCallisto at 0.24 lb AI/A applied PREE gave a similar level of control of prostrate pigweed as did Dual Magnum, Outlook, and Prowl. POST applications of Callisto at 0.188 lb AI/A were equivalent to the higher rate of 0.24 lb AI/A. Callisto, Distinct, and Clarity provided excellent POST control of pigweed. Callisto applied POST was the same as PREE followed by POST sequentially. Aim provided marginally acceptable control of pigweed.
Evaluation of Kerb Applied by Sprinkler Irrigation to LettuceThree tests were conducted to compare delayed applications of Kerb applied by air with those applied through the sprinklers. Early (6-5-02) season and mid (10-20-02) applications made through the sprinklers were significantly more effective than those applied by air. The late season (11-17-02) application was made too early and the weed control was poor demonstrating the need for proper timing regardless of the application technique. It was concluded that chemigation can be an effective technique for making delayed applications of Kerb to lettuce in the low deserts.
Efficacy and Safety of Combinations of Preemergence and Postemergence Herbicides in CantaloupesSandea at 0.03 lb AI/A combined with rimsulfuron at 0.02 lb AI/A gave exceptionally good control of prostrate pigweed and lambsquarters at 98% and 96%, respectively, when applied postemergence (POST) in cantaloupes. Sandea applied POST in a tank-mix with increasing rates of rimsulfuron showed marginally acceptable to unacceptable crop injury. All POST applications of Sandea following preemergence (PREE) herbicides or applied alone provided 90% or better control of lambsquarters. Sandea and Strategy gave unacceptable control of pigweed and lambsquarters at 60-70% relative to the standard, Prefar. Sandea applied alone POST was less effective against pigweed than lambsquarters. A treatment of a PREE herbicide followed by Sandea was not as efficacious as the Sandea plus rimsulfuron tank-mix applied POST to control both pigweed and lambsquarters.
Comparison of Efficacy and Safety of Oxyfluorfen Formulations on BroccoliThe 4lb/gal (4F) formulation of oxyfluorfen was significantly safer than the 2 lb/gal (2XL) formulation on broccoli when applied at the 2 or 3-leaf stages of growth. At 6 days after treatment of the first application at the cotyledon stage of the broccoli, significant injury to the broccoli ranged from 30 to 66% for all oxyfluorfen treatments. Crop stand reduction did not occur with either formulation. The 4F formulation at 0.25 lb AI/A gave nearly the same weed control as the 2XL formulation at 0.063 lb AI/A. The 4F formulation applied at the broccoli cotyledon stage of growth provided longer effective weed control for more than 3 weeks after applications. Later applications gave effective weed control for a period of time between 1 to 2 weeks.
Fungicide Performance for Control of Powdery Mildew on Lettuce in 2003Powdery mildew on lettuce is caused by the fungus Golovinomyces cichoracearum (Erysiphe cichoracearum). This disease is favored by moderate to warm temperatures and dry weather conditions. Several potential new fungicides were evaluated for control of powdery mildew on lettuce in 2003. Powdery mildew appeared in our plots by Jan 9 and reached high levels by plant maturity on Feb 19. Compared to non-treated plants, all treatments significantly reduced the final severity of powdery mildew on lettuce statistically. However, only a limited number of compounds, such as Rally, Microthiol Disperss, Quinoxyfen, Flint, Zoxamide, Maneb, Pristine and Cabrio, provided the degree of disease control that would be of value to growers. The trial was intended to be a downy and powdery mildew trial; therefore, some of the treatments within this study were specifically included for downy mildew. No downy mildew developed; however, the downy mildew test products did offer some protection against powdery mildew.
Examination of New Chemistries to Control Powdery Mildew of Cantaloupe in 2002Powdery mildew can occur on melons annually in Arizona. Podosphaera xanthii (Sphaerotheca fuliginea) is the plant pathogenic fungus that causes powdery mildew of cucurbits, such as cantaloupe, honeydew, watermelon, cucumber and squash. When environmental conditions are favorable, disease incidence and severity can reach economically significant levels. Development of powdery mildew on melons is favored by moderate temperatures and relative humidity, succulent plant growth and reduced light intensity brought about by a dense plant canopy. Potential new fungicides were evaluated and compared to existing chemicals for control of powdery mildew of cantaloupe in a field trial conducted during the spring of 2002 at the Yuma Agricultural Center. Among treatments, the degree of powdery mildew control ranged from minimal to essentially complete. One notable observation was the relative decrease in performance of Flint compared to earlier field trials. An isolate of the fungus from this trial was tested at Cornell University and found to be less sensitive to Flint compared to other isolates of the pathogen not previously exposed to this fungicide. This potential development of resistance by the pathogen to Flint will be examined in further studies. A moderately high level of disease had developed by crop maturity (Jun 25) on non-treated plants. The better performing treatments included Cabrio, Flint+pHortress, Foliar Supreme, Microthiol Disperss, Pristine, Procure, Quadris+Latron B-1956, Quadris+LatronB- 1956+Actigard, Quinoxyfen, Rally, Topsin M+Trilogy, and UCC-A1639. The potential availability of chemistries with new modes of action could help improve overall control of powdery mildew as well as facilitate the implementation of effective fungicide resistance management strategies.
Evaluation of Products to Manage Sclerotinia Leaf Drop of Lettuce in 2003Sclerotinia leaf drop in Arizona is caused by two soil-borne fungi, Sclerotinia minor and S. sclerotiorum. Moist soil and moderate temperature favor this disease. Some registered products as well as new chemistries in development were evaluated for control of leaf drop on lettuce during the winter vegetable growing season in 2002-2003. Sclerotia of each pathogen were applied to plots after lettuce thinning and just before the first application of test compounds. In plots infested with Sclerotinia minor, all materials tested at an appropriate rate significantly reduced disease. The best treatments included an application of Contans followed by an application of Endura (BAS 510), as well as two applications of an experimental compound or the standard materials Ronilan and Rovral. Other useful products included Endura, Serenade, Pristine (BAS 516), Botran, Switch and Contans. In plots infested with S. sclerotiorum, two applications of Contans provided the best level of disease reduction among tested materials. Three applications of Endura or Pristine also were very efficacious. Other compounds that provided some reduction in disease caused by S. sclerotiorum included Botran, Serenade and Switch. Two of the products tested, Contans and Serenade, are biological control materials. For a valid comparison of products for control of Sclerotinia drop of lettuce, it is important to compare the results obtained from more than one field study. The reader is urged to review previous studies in addition to this report to get a true picture of the relative efficacy of tested compounds for control of Sclerotinia drop.
Evaluation of Lettuce Cultivar Susceptibility to Powdery Mildew in 2003Powdery mildew, caused by the fungus Golovinomyces cichoracearum (formerly known as Erysiphe cichoracearum), can cause economic losses in lettuce fields harvested in March and April, the last months of the production season in western Arizona. A field study was conducted to evaluate 14 different cultivars of lettuce for potential resistance to this disease. Cultivars Two Star and Big Green COS were very resistant to powdery mildew. All other tested cultivars would have required application of fungicides to reduce the amount of powdery mildew to acceptable levels. On the other hand, planting lettuce cultivars with some disease tolerance may require less fungicide inputs to achieve acceptable disease control compared to planting very susceptible cultivars. Among tested cultivars, Slugger was most susceptible to powdery mildew.
Evaluation of Lettuce Cultivars for Resistance to Fusarium Wilt in 2003In the 2001-2002 production season, Fusarium wilt was observed for the first time in six different lettuce fields in the Gila and Dome Valley production areas of Yuma County, Arizona. The disease was found in 11 additional sites during 2002-2003. Fusarium wilt presents a serious threat to the health of the lettuce industry in Arizona. The only effective means of controlling Fusarium wilt of lettuce at this time is to avoid infested fields. On the other hand, Fusarium wilt in other crops, such as tomatoes and melons, is controlled effectively by planting cultivars resistant to the pathogen. The relative resistance of lettuce cultivars grown in the Arizona desert production region is unknown; therefore, a cultivar evaluation trial was established in a field known to contain the wilt pathogen, Fusarium oxysporum f.sp. lactucae. Tested cultivars were grouped into three different planting dates: Sep 7, Oct 17 and Dec 6, 2002. A majority of the cultivars within each planting date were those that would be planted in the desert at that time. Fusarium wilt was severe in the early planting of lettuce (Sep 7), moderate in the second planting (Oct 17) and very mild in the third planting (Dec 6). Disease severity was low in some lettuce cultivars in the second planting and most cultivars in the third planting. Among the types of lettuce tested, head lettuce was usually least resistant whereas romaine was most resistant. The data presented in this report are preliminary findings, subject to confirmation in another study planned for the next lettuce production season.
Comparison of Fungicides for Management of Downy Mildew of Broccoli in 2003Downy mildew of broccoli, cauliflower and cabbage is caused by the oomycete pathogen Peronospora parasitica. Cool moist environmental conditions favor the development of downy mildew on these crops. Several potential new fungicides were evaluated for control of this disease on broccoli in 2003. A moderate level of disease had developed by crop maturity. Actigard, Actigard alternated with Quadris, Acrobat+Maneb and DPX-KP481 were among the best treatments in this trial. Actigard is not a fungicide, but is classified as a plant activator. When applied to plants, this compound stimulates a defense response in plants to some diseases. Actigard also has performed well in previous trials. Several other new products and some chemistries that are currently available provided significant levels of disease control as well.
Whitefly Control with Foliar Insecticides in CantaloupesCourier, Knack, Assail, Calypso, and Oberon treatments on cantaloupe were effective in maintaining reduced numbers of WF eggs, immatures, and adults for 30 DAT. After 30 DAT, all treatments showed that WF adult counts began to increase. Courier, Knack, Assail, Calypso, and Oberon treated cantaloupe leaves had adult WF counts of one-half or less that of the untreated check and remaining treatments. The pyrethroid plus endosulfan treatments were effective for 7 to 13 DAT in reducing immature WF. After 21DAT, the pyrethroid plus endosulfan treatments and Actara showed a greater increase in the numbers of eggs, immatures, and adults compared to Courier, Knack, Assail, Calypso, and Oberon treatments. The seasonal average number of eggs, immatures, and adults was the least on Assail treated cantaloupes. Knack, Courier, Calypso, and Oberon treated cantaloupes consistently had less eggs, immatures, and adults compared to the untreated check.
The Emergence of the Foxglove Aphid, Aulacorthum solani, as an Economic Pest of Lettuce in the Desert SouthwestSeveral studies were conducted during the past two growing season to examine the population growth, distribution and damage potential of the foxglove aphid on head lettuce in the Yuma Valley. Light populations of foxglove aphids were first found colonizing untreated head lettuce in small experimental plots at the Yuma Agricultural Center in the spring of 2001. In the spring of 2002 foxglove aphids reached high population levels at YAC on spring plantings, but were not reported in commercial fields. This past spring foxglove aphid populations were wide-spread throughout the Yuma Valley, particularly in fields near the Colorado river, adjacent to citrus orchards and residential areas, and not treated with Admire. Experimental studies suggested that foxglove aphids can reach economic levels on desert head lettuce, particularly crops planted during late November and December.
Management of Aphids is Brassica Seed Crops with Selective InsecticidesReplicated studies were conducted to examine aphid distribution and insecticidal control in a commercial cauliflower seed crop in 2001, and in large plots at the Yuma Agricultural Center in 2003. Results were generally consistent in both studies. The primary aphid species found colonizing pre-blooming crops were cabbage aphids, turnip aphids, and green peach aphids. During the bloom period (March-April), the population was almost exclusively cabbage aphid feeding on seed pods and extensions. During the pre-bloom growth period, green peach aphids tended to colonize plants slightly earlier and were found primarily on the older frame leaves low on the plant. In most cases, male and female plants were colonized to the same extent. Cabbage and turnip aphids did not appear to have a clear preference between older and younger leaves, and appeared to colonize males and females equally. Once the plant began to bloom and set seed, cabbage aphid was the primary species (>90%) found feeding on developing seed pods in both tests. These aphid populations were very susceptible to contact insecticides and quickly knocked down by both Capture and MSR. Of the selective, bee safe products, Pirimor provided the most consistent residual aphid control. Assail and Fulfill worked well against aphids on foliage, but did not provide comparable control on seed pods. Aphid densities were extremely high in the untreated check and resulted in almost complete loss of the crop in these plots. Seed yields were not taken due to heavy losses to Sclerotinia and bird damage.
Foxglove Aphids in Lettuce: Control with Reduced-Risk and Conventional InsecticidesSeveral small-plot studies were conducted in the spring of 2003 to compare the residual efficacy of several new reduced risk insecticides with a number of conventional aphicide compounds on head lettuce and romaine. Our efforts were primarily directed at determining efficacy against the foxglove aphid, a newly discovered pest in Yuma. In general, several new neonicotinoid foliar compounds provided good residual control of all aphid species including foxglove aphid. Other new compounds were less consistent. Admire, the standard soil systemic used in lettuce, was inconsistent against Foxglove aphid providing 85-90% control relative to >95% control against other aphid species present in the plots. Conventional aphid compound such as Capture, dimethoate, endosulfan, Orthene and MSR consistently provided good, economic control of Foxglove aphids in both head and romaine lettuce. Based on the results of these and previous studies, a sampling procedure and action threshold are recommended for foxglove aphid control in desert lettuce.
Final Report on the Use of Parasitoids to Control Sweet Potato Whiteflies in Open Arizona AgricultureThe effect of three different release rates (1x [label rate], 10x, and 20x the recommended rate of 10,120/acre) of the parasitoid Eretmocerus eremicus on sweet potato whitefly populations found in open fields of cantaloupe was evaluated against populations in untreated control plots. Parasitoids were released from a point source in the center of each of nine treatment plots. Whitefly population growth, encompassing all developmental stages, and rates of parasitism were monitored within a 33 ft radius surrounding the center point in all 12 plots over a 52-d period. The rates of sweet potato whitefly population increase during this time were equivalent regardless of the parasitoid release rate. Whitefly densities were not limited in any of our treatment plots when compared to those found in the control plots. Moreover, mean rates of parasitism did not increase with time nor did they differ among the three treatments or control plots (7.9 ± 6.5%). Finally, estimated rates of parasitism were density dependent responding positively to increasing host numbers. The ineffectiveness of this parasitoid in controlling whitefly populations in the field may be due to its high propensity to disperse at low host densities or to influxes of immigrating whiteflies. Hence, the use of E. eremicus alone is not an efficient means to reduce whitefly populations in melon crops in the southwestern United States.
Compatibility of Fertilizer and Neonicotinoid Soil Applications for Whitefly Control in Spring CantaloupesStudies were conducted in the spring of 2001 and 2002 to evaluate the interaction between starter and side dress fertilizer mixes with neonicotinoid insecticides and their performance against whiteflies in spring cantaloupes in Yuma, AZ. No incompatibility was observed between the fertilizers and the Admire and Platinum mixtures applied at planting and side dress, and both insecticides provided comparable control of whitefly populations regardless of fertilizer used. However, based on our experience in 2001, we suggest that growers use a dilute mixture with the final applied volume to avoid any potential "clumping" problems in the mix tank. In some cases the addition of the DuneUp® starter fertilizer appeared to improve plant growth, but was probably more due to the unique mixture of NPK rather than the combination with the insecticides. Based on the results of these studies growers should not hesitate to apply either Admire or Platinum with starter and side dress fertilizers in melon crops.
Comparison of Sampling Methods for Estimating Western Flower Thrips Abundance on LettuceSeveral relative sampling techniques (direct visual counts, beat pans and sticky traps) were compared to absolute counts (plant wash) to determine sampling reliability for estimating western flower thrips population levels in lettuce. In numerous plantings of experimental plots of head lettuce, the relative sampling methods indicated similar thrips population trends throughout the season and all relative estimates of abundance were significantly correlated with absolute densities. However, both relative methods could only account for a proportion of the adult thrips infesting head lettuce plants, where they estimated about 30% of the actual absolute population. For larvae, beat pan sample estimated about 18-20% of the actual population density, whereas direct visual counts accounted for less than 10% of the thrips present. Comparison of sampling methods in insecticide efficacy trials indicated that beat pan and direct visual counts did not always accurately estimate treatment differences for adult. For densities of thrips larvae however, beat pan and visual counts methods did consistently provide accurate estimates of treatment differences in efficacy trials. Overall, both beat pan and direct visual count procedures are reliable thrips sampling methods that will generally provide precise estimates of thrips abundance necessary in lettuce pest management programs. Furthermore, these methods, and the beat pan in particular, also may serve as effective research tools that provide reliable estimates of treatment differences.