Impact of Bagrada Bug on Desert Cole Crops from 2010-2014
The bagrada bug, Bagrada hilaris, first occurred on desert cole crops at damaging levels in the fall of 2010, and has since become an established pest. 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 survey in early 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 (2014) was one of the lighter years. Based on seasonal population abundance studies of adults infesting non-treated broccoli plants at the Yuma Ag Center (see graph below), bagrada bug infestations in the fall 2014 were much lower than we had observed the previous two seasons. However, with the warmer temperatures this winter, spring populations occurred very early and at higher numbers than in the previous 4 years. Estimates of stand losses from bagrada bug infestations at stand establishment in both direct-seeded and transplanted crops has decreased by almost 50% over the past 5 years. Lower losses in 2014 are likely due to the lower 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 2014 compared with 2010. 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, but a lower percentage of acreage was treated in 2014 than in 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. However, more neonicotinoid products (Venom, Endigo) are beginning to be implemented into PCAs IPM programs. 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 2010-2014 survey results can be found in the following report: Impact of Bagrada Bug on Fall Cole Crops, 2010-2014.
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 Disease and Weeds with Band-Steam – Yuma Trials Show Good Promise
In previous articles (Vol. 11 (13), Vol. 11 (20), Vol. 11(24)), I’ve discussed using band-steam to control plant diseases and weeds. Band-steaming is where steam is used to heat narrow strips of soil to temperature levels sufficient to kill soilborne pathogens and weed seed (>140 °F for > 20 minutes). The concept is showing good promise. This past season, three trials were conducted examining the efficacy of using steam for disease and weed control in Yuma, AZ. In the studies, steam was applied in a 4-inch-wide by 2-inch-deep band of soil centered on the seedline using a prototype band-steam applicator (Fig.1). The band-steam applicator is principally comprised of a 35 BHP steam generator mounted on top of an elongated bed shaper. The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper.
Trial results were very encouraging as the prototype applicator was able to raise soil temperatures to target levels (140°F for >20 minutes) at viable travels speeds of 0.75 mph. Steam provided better than 80% weed control and significantly lowered hand weeding time by more than 2 hours per acre (Table 1). Results also showed that Fusarium colony forming units (CFU) were reduced from 2,600 in the control to 155 in the 0.75 mph and 53 in the 0.5 mph treatments, respectively (a more than 15-fold reduction). A significant difference in Fusarium wilt of lettuce disease incidence was not found, however disease infection at the field site was low (< 2%) and differences were not expected. At 0.5 mph, fuel costs were calculated to be $238/acre which was considered reasonable and consistent with the values reported by Fennimore et al. (2014).
An unexpected finding was that plants in steam treated plots appeared to be healthier and more vigorous than untreated plots (Fig. 2). This trial is still in progress and it will be interesting to see if this improved early growth translates into increases in crop yield.
In summary, early trial results are showing good promise for use of band-steam as a non-herbicidal method of pest control. We plan on conducting further trials in this multi-year study. If you are interested in evaluating the device on your farm and being part of the study please contact me. We are particularly interested in fields with a known history of Fusarium wilt of lettuce and/or Sclerotinia lettuce drop that will be planted to iceberg or romaine lettuce.
As always, if you are interested in seeing the machine operate or would like more information, please feel free to contact me.
Acknowledgements
This work is supported by Crop Protection and Pest Management grant no. 2017-70006-27273/project accession no. 1014065 from the USDA National Institute of Food and Agriculture, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
A special thank you is extended to Mellon Farms for allowing us to conduct this research on their farm.
References
Fennimore, S.A., Martin, F.N., Miller, T.C., Broome, J.C., Dorn, N. and Greene, I. 2014. Evaluation of a mobile steam applicator for soil disinfestation in California strawberry. HortScience 49(12):1542-1549.
Click link below or picture to see the band-steam and co-product applicator in action!
Carryover of Vegetable Herbicides to Wheat Grown in Rotation
Almost all the herbicides used on lettuce, cole crops and melons have restrictions on how soon wheat can be planted in rotation after they have been used. Experience has demonstrated, however, that safe intervals can vary considerably based upon many factors and are almost always much longer than they need to be. The most important factors are rate applied, irrigation practices and tillage. For example, when Kerb used to be banded at 2 to 4 lbs. per acre after planting and incorporated with furrow irrigation, it was common to see treated strips across wheat fields which followed. This is uncommon now that lower rates are Chemigated. We still see some Balan injury at ends of fields or in overlaps especially when sudan is planted. Wheat it not very sensitive to Prefar and carryover injury is uncommon.
Results of pheromone and sticky trap catches can be viewed here
Corn earworm: Moth activity remains seasonably low, but noticeably increased again in
the North Yuma Valley. Below average compared with previous seasons.
Beet armyworm: Moth activity increasing comparable to fall numbers, particularly in Tacna, Dome Valley and Gila Valley; consistent with reports of larvae in fields. Slightly about average compared with previous seasons.
Cabbage looper: Similarly, cabbage looper moth activity increasing Tacna, Dome Valley
and Gila Valley and remains above average for this time of the year. Above average compared with previous seasons.
Whitefly: Adult movement is relatively absent; typical for this time of the season.
Thrips:Thrips activity remains seasonably low; but is increasing in the Yuma
Valley. Well below average compared with previous seasons
Aphids: Area-wide aphid flights decreased in the last 2 weeks. Most aphids found on traps were green peach aphid. Below average movement compared with previous seasons.
Leafminers: Adult activity remains seasonably low in all locations, and below average for this time of year.
Diamondback moth:
Diamondback moth (DBM) counts in pheromone traps trended downward over the past 2 weeks, and remained low in many locations with the exception of the N. Yuma Valley. Across all locations, trap counts remain higher now than trap counts recorded this time last year, but significantly lower than 2017 following the fall 2016 outbreak.