Pest Pressure on Desert Produce and Melon Crops in 2012
At a recent meeting, I made the statement that the insect pest pressure on produce and melons crops in the Yuma area this fall was as heavy as I’ve seen it in many years. That comment was based largely on my observations, both on and off the Yuma Ag Center, as well as from anecdotal reports from PCAs and growers. This claim is further supported by a quick analysis of both recent and historic data on pest abundance recorded from our research plots here in the Yuma area. First, whitefly adult numbers on fall melons and produce were extremely high. In fact, my untreated melons plots on the Ag Center wilted and died rapidly as a direct result of heavy whitefly feeding. Furthermore, captures of whiteflies on yellow sticky traps placed near cantaloupe fields in the Wellton, Tacna Texas Hill area, were twice as high as they have been in the past 5 years, and CYSDV incidence in cantaloupe fields in this area was also higher in 2012. Similarly, worm pressure - particularly beet armyworm and cabbage looper- was higher than I’ve seen it in the past 6-7 years. Populations began infesting plots in early September, and egg deposition and larval development remained steady through October. In fact, worm numbers were 3-fold higher in 2012 than we what observed last fall. Additionally, corn earworm was present in higher numbers than what I’ve observed in past years. Finally, Bagrada bug infestations were the highest I’ve seen on the Ag Center since the invasive stinkbug first showed up in Yuma in 2009. The low-moderate population appeared in early September, but reached very high levels by mid-September and peaking in early October. The numbers I observed were much higher than the populations that occurred last season, and actually slightly higher than we saw in 2010. The infestation levels in our untreated broccoli plots this year remained at damaging levels throughout October. In contrast, thrips population numbers have been low, relative to what we normally see this time of the year, and I have not picked up any winged aphids or colonies on lettuce thus far. However, I’m not sure how that translates to potential population pressure in January and February, and you should anticipate them showing up as usual. I’ve been asked why the pest pressure was so relatively heavy this year. I really don’t know. Could the heavy monsoon moisture we had in July and August have been an influence? It may have, but it may not have. Insect abundance is dictated by many abiotic and biotic factors in our cropping system, and it’s nearly impossible to consider all the factors necessary to draw a reliable conclusion. Nonetheless, graphics showing these recent trends in Whitefly, CYSDV, Lep Larvae and Bagrada abundance can be found at Pest Abundance on Desert Produce and Melon Cops in 2012.
Widely accepted definition of a living organism “A living organism has a cellular structure and is manifest by growth through metabolism, reproduction, and the power of adaptation to the environment through changes that originate internally”. Viruses are not cellular and do not metabolise, but they reproduce and adapt.
A virus is a set of one or more nucleic acid template molecules, normally incased in a protective coats of protein or lipoprotein and is able to organize its own replication but only within a suitable host cells. Record of plant viruses do not go as far as human viruses, but plant viruses have caused considerable loss in agriculture system.
One of the most common virus we see in agriculture system in todays world is Cucumber mosaic virus(CMV). CMV belongs to family Bromoviridae. The genome size of cucumber mosaic virus (see pic) is about 8000 to 9000 nucletotide bases (1 base=1 letter of AGTC). The genome size of Covid19 Coronivirus is about 30,000 bases and the genome size of human DNA is 6.4 billion bases.
CMV has a very wide host range and is transmitted by aphids in nonpersistent manner (stylet borne). This means that the aphids acquire the virus particle in their stylet within seconds of feeding in infected plants, hop on to next plant and start feeding on next plant. The virus is transmitted to the next plant immediately.
Next is incubation period. Viruses cause systemic infection. It can take anywhere from few days to few weeks from initial entry of the virus to symptom exhibition in your plants. The severity of symptoms varies depending on many factors. The age of plant (infection stage), the general plant vigor (health), varietal susceptibility, conducive environment (viruses express better in colder weather than hot weather), a plant that has already been infected with other viruses (preesisting condition) are to name a few.
Attachment – the virus attaches itself to the outside of a new plant cell
Penetration – the protein pushes the nucleic acid strand into the plant cell
Replication – the viruses’ nucleic acid uses the plant cell DNA to make many new nucleic acid strands and protein sheathes
Assembly – the nucleic acid and protein assembly into millions of new virus copies
Release – the viruses leave the cell – at this stage the cell is normally dead and bursts releasing the viruses
Transmission – the viruses move using a vector to new cells to infect.
When you see the symptoms in your plants, the first thing you have to understand is virus infection is systemic. The best you can do to manage the virus is to limit the transmission (flatten the curve). Some viruses need a vector for transmission like insects and nematodes. Some viruses are mechanically transmitted from one infected plant to another. Washing field tools between plants/field whenever possible limits the transmission of virus. Soap, bleach, and disinfectants reduce transmission by protein denaturalization of the virus.
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.
Corn earworm:
CEW moth counts decrease to very low levels in areas, about average for this time of year.
Beet armyworm:
Trap counts low; increased slightly in the Yuma Valley; lower than average compared to previous years.
Cabbage looper:
Cabbage looper counts deceased in most traps and below average for this time of season.
Diamondback moth:
DBM moths counts increased Gila and Yuma Valley. About average for this time of the year.
Whitefly:
Adult movement negligible, average for late winter.
Thrips:
Thrips adult counts remain low, likely in response to cumulative rainfall this winter. Currently, numbers are below average compared with previous years.
Aphids:
Aphid movement decreased significantly in the past two weeks; about average for mid-February
Leafminers:
Adults remain low in most locations, increased in Yuma Valley; average for mid February.