Review of Pest Pressure on Fall Produce and Melon Crops – 2018
Seems like every year around this time I make the comment that insect pressure this season was more unusual than normal. Well, this year it’s true. A quick look at both recent and historic data on pest abundance recorded from our University of Arizona research plots and areawide and pheromone/sticky traps suggests that insect pressure this fall was historically low for most key pests. For the supporting data see Pest Abundance on Desert Produce and Melon Cops in Fall 2018.
Whitefly/CYSDV: Areawide, whiteflies in fall melons were again historically light and were very similar to last season. Accordingly, CYSDV incidence at harvest in cantaloupe fields was as low as we’ve seen it since the virus first showed up in 2007. The virus incidence at harvest in over 30 commercial plantings was very low in most fields, with just a couple of hot spots were observed in Texas Hill and Tacna. For the most part, whiteflies were similarly light in produce crops with an occasional flare-up in some isolated areas. Data from our untreated broccoli/cauliflower plots at the Yuma Ag Center (YAC) show that colonization by whitefly nymphs was the lightest we’ve seen in 10 years.
Beet armyworm, cabbage looper, and corn earworm: Very light worm year in Yuma. Population abundance on untreated lettuce at the YAC this fall was the lightest we’ve seen since 1996. Similarly, numerous reports from PCAs suggest that fewer sprays were applied this fall, and in some recent fields spray intervals have been stretched to almost 30 days. This lower activity is likely due to the cool nighttime temps in Oct and Nov., and activity appeared to slow down dramatically in October, following the back-back tropical storms we experienced. Although corn earworm trap catches in October were the highest, we’ve seen recently, larval abundance in head lettuce at YAC and in commercial fields was light.
Diamondback moth (DBM): DBM was not a problem again for local desert growers in 2018; about what we normally expect for the fall. We received no calls from PCAs reporting difficulty in controlling populations. Areawide pheromone trapping showed that DBM trap captures began in early September and trended very similarly to 2017 numbers. At YAC, the larval populations were the lightest we’ve seen since 2001, even though moth numbers were similar to 2017. Caution: DBM is usually a spring pest in the desert, so keep your eyes open for larvae and damage on those Feb-Apr cole crops and late seed crops.
Thrips: Similarly, the western flower thrips pressure was light this fall; significantly lighter than the previous two falls. These lower population levels were likely a result of rains from tropical storm in early October. Bean thrips abundance was also lighter in 2018 relative to the previous two seasons. Scarring damage was negligible in untreated lettuce plots. Flea beetles: Beetle activity at YAC was considerably lower than what we “normally” experience in the fall. However, we’ve had reports of sustained flea beetle movement onto commercial lettuce (with significant feeding damage) from alfalfa and other sources within the last several weeks.
Bagrada bug: Adults and their feeding was again almost non-existent. For a fourth consecutive year, bagrada adults were so light in my research plots that we were not able to conduct any efficacy trials. A few sightings in late-September and early October from PCAs of adult presence in transplanted crops, but the populations disappeared following a single pyrethroid chemigation. So, it was truly an unusually low insect year. Can’t wait to see what next year brings us. Have a Merry Christmas!
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.