Bagrada Bug on Desert Cole Crops: Seven Years After the Outbreak
With the desert produce season finally completed, now is a good time to reflect on pest issues from last fall. I think most would agree that bagrada bug population pressure were very low last fall. In fact, the lightest infestations we’ve seen since the widespread outbreaks in 2010 when the bagrada bug first occurred on desert cole crops at damaging levels. It has since become an established pest, though one might not have thought so this year. In an attempt to document the severity of bagrada bug infestations on direct-seeded and transplanted cole crops and the intensity of chemical management, we have annually surveyed growers and PCAs from Yuma, Imperial and Maricopa counties since 2010. We recently conducted our annual survey in April. Since 2010, the cole crop industry has experienced widespread bagrada bug infestations throughout the desert from September into November, although some years have been less intense than others. Last fall (2016) was the lightest year we’ve seen to date. Based on seasonal population abundance studies of adults infesting non-treated broccoli plants at the Yuma Ag Center (see graphs below), bagrada bug infestations in the fall 2016 were lower than what we had observed since the pest first showed up in the desert. Bagrada bug population abundance on non-treated broccoli plots have also been consistently declining since 2013. Estimates of stand losses from bagrada bug infestations at stand establishment in both direct-seeded and transplanted crops have decreased significantly the past 5 years, and were particularly low in 2016. The lower losses reported in 2016 are likely due to the lighter bagrada pressure experienced last season. Plant injury, defined as plants with multiple heads, forked terminals, and/or blind terminals resulting from Bagrada feeding, was also lower in 2016 compared to previous years. These data suggest that PCAs have adopted effective management programs to protect seedling crops during stand establishment. Insecticide usage to control this pest remains high, and the percentage of acreage was treated in 2016 was consistent with previous years. Pyrethroids remain the primary product used for controlling bagrada bug adults either via chemigation or with foliar spray applications. Based on survey results, products that have contact activity appeared to provide the most effective control against bagrada adults on both direct-seeded and transplanted cole crops. Results from the survey also showed that a large percentage of direct seeded broccoli was treated with clothianidin (NipSit) in 2016, and performed well in controlling adults and protecting stands. Overall, the results of the PCA survey are consistent with results obtained in research trials conducted at the Yuma Agricultural Center over the past four years. A summary of the 2010-2016 survey results can be found in the following report: Impact of Bagrada Bug on Desert Cole Crops.
In response to the recent outbreaks of Diamondback moth (DBM) , Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur this fall.
Alfalfa is a major crop grown in Yuma area as a cover crop before vegetable season. Generally expected to be a hardy and easy crop to grow, alfalfa production still can be affected by many pests and diseases. Root and crown rot in alfalfa is a common problem. The pathogen Phytopthora megasperma thrives on standing water, overwatered, and/or in soil that lacks good drainage.
The above ground symptoms typically consists of plant wilting, usually occurring quite suddenly, often followed by plant death. The roots turn tan-to-brown, sometimes turning black. Sometimes orange-to-reddish streaks can be observed in rotted roots. Occasionally, the symptoms can be seen in crowns too. Infected plants succumb to death, or grow at reduced rate thus being susceptible to other pests and diseases.
The causal organism survives in soil as mycelia in infected plant tissue or as thick-walled oospores. It also produces thin-walled sporangia that release motile zoospores in the presence of free water. So it is important to grow alfalfa in well drained soils. Adjust irrigation water in a way that there is no standing water for too long. If possible, install tailwater ditch to remove excess water. Plant resistant cultivars like Agate, Apollo if the problem persists in the field. Till the soil deeply to reduce wet soil pockets, level the land before planting.
If diagnosis is confusing, bring the samples to the Yuma Plant Health Clinic for proper diagnosis. Make sure to bring healthy looking plants, sick plant, plants in between etc. Remember, there is no such thing as too much plant tissue when it comes to submitting samples to the clinic!
Controlling Fusarium Wilt of Lettuce Using Steam Heat – Trial Initiated
Earlier this week, we initiated a trial examining the use of band steam for controlling Fusarium wilt of lettuce. The premise behind this research is to use steam heat to raise soil temperatures to levels sufficient to kill soilborne pathogens. For Fusarium oxysporum f. sp. lactucae, the pathogen which causes Fusarium wilt of lettuce, the required temperature for control is generally taken to be > 140°F for 20 minutes. Soil solarization, where clear plastic is placed over the crop bed during the summer, exploits this concept. The technique raises soil surface temperatures to 150-155˚F, effectively killing the pathogen and reducing disease incidence by 45-98% (Matheron and Porchas, 2010).
In our trials, we are using steam heat to raise soil temperatures. Steam is delivered by a 35 BHP steam generator mounted on a custom designed elongated bed shaper (Fig. 1). Preliminary results were encouraging. The device was able to increase the temperature of the top 3” of soil to over 180°F at a travel speed of 0.5 mph as shown in this video of the machine in action (shown below). These temperatures exceed that of those known to control pathogens responsible for causing Fusarium wilt of lettuce (> 140°F for 20 minutes).
Stay tuned for final trial results and reports on the efficacy of using steam heat to control Fusarium wilt of lettuce.
If you are interested in evaluating the technique on your farm, please contact me. We are seeking additional sites with a known history of Fusarium wilt of lettuce disease incidence to test the efficacy and performance of the device.
References
Matheron, M. E., & Porchas, M. 2010. Evaluation of soil solarization and flooding as management tools for Fusarium wilt of lettuce. Plant Dis. 94:1323-1328.
Acknowledgements
This project is sponsored by USDA-NIFA, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support.
A special thank you is extended to Cory Mellon and Mellon Farms for allowing us to conduct this research on their farm.
Weeds are one of the most visible of all agricultural pests. They can’t move or hide and once established often stick up over the crop. Just one weed in a 10 acre field is annoying to look at. With insects and diseases, the damage is often more visible than the pest. That is not the case with weeds. A moderate weed infestation is approximately 10 weeds per square foot. If a herbicide produces 90% control, that leaves 1 weed per square foot or 43 weeds per acre. Without an untreated check, this can look like the herbicide failed! It is easy to leave an untreated spot in a field and it is well worth doing. Many applicators do so unintentionally because of skips, powerlines and other causes. They help determine crop injury and weed control. Here are some examples of what various levels of control looked like from one of our cole crop trials:
Corn earworm:
CEW moth activity declined a bit in the past 2 weeks and remains below average for late spring.
Beet armyworm: Moth counts increased slightly, but remain very low consistent with seasonal temperatures, and below average for this point in the season.
Cabbage looper: Slight increase in activity, but moth counts remain unusually low for this time of year, as they have all season.
Whitefly: Slight incidence of Adult movement in the Gila Valley, but overall low numbers consistent with temperatures.
Thrips: Thrips adult movement beginning to pick up considerably, particularly in Tacna and Roll. Movement is still below average for early March.
Aphids: Seasonal aphid counts down considerably compared with the past 2 months. Counts highest in Bard and Gila Valley. About average for this time of year.
Leafminers: Adult activity increasing in some locations, particularly active in Yuma and Gila Valleys.