Diamondback Moth Control and Resistance Management 2016
What started off as a moderate insect season this fall has turned into one of the heaviest worm seasons on produce crops we’ve experienced in many years. Since mid-September, cabbage looper (CL), beet armyworm (BAW) and diamondback moth (DBM) populations have been consistently abundant in various areas throughout Yuma county. For the most part, CL and BAW have been relatively easy to manage with our standard insecticide products. In some cases, however, spray intervals have been shorter than normal due to overlapping egg lays and warm nighttime temperatures driving development of multiple overlapping generations in fields. Given the warm weather this fall and the abundance of alternate hosts for them to develop on all summer, the presence of these heavy infestations is not unusual. However, what is unusual is the emergence of DBM as a fall pest of cole crops. It’s been my experience, that DBM has become a fall pest within the past 7-8 years. Prior to then, I considered DBM a spring pest, occurring in fields once the weather warmed up. Because DBM attacks only cole crops (Cruciferae), they do not survive in any great abundance during the summer due to the lack of host crops. However, it is not unusual for fall transplanted cole crops to arrive in fields with DBM, regardless of the origin of the transplants. This certainly would explain how DBM populations can become so quickly established in September and October. Under ideal temperatures (~85 °F), DBM can complete a generation in a little over two weeks, as opposed to about 3 weeks necessary for CL and BAW. Thus once established, DBM populations can rapidly build up multiple generations in the field. Management of DBM in cole crops often requires intensive insecticidal management, more so than what is generally required to control BAW and CL. In some growing locations (e.g., Florida or Hawaii), protection of cole crops often requires multiple spray applications, sometimes as often as twice per week to break the DBM cycle. Unfortunately, intensive management can lead to insecticide resistance which DBM has a long history of. I’ve become concerned this fall because I’ve had numerous reports from PCAs who have had difficulty in controlling DBM in transplanted cole crops; transplanted cabbage and cauliflower in particular. In some cases, there have been reports of our standard insecticide products not providing adequate efficacy against DBM. It impossible to explain for sure why this poor field performance has occurred as many operational and biological factors (i.e., application timing and frequency, rates, choice of product, weather and resistance) ultimately determine the level of efficacy. Although resistance is unlikely, we will be collecting and bioassaying a few of these populations just to make sure this is not one of these factors. For the short term though, PCAs should remain diligent in their worm control using the standard products (Radiant, Proclaim, Coragen, Exirel, Intepid) at labeled rates and by ground whenever possible. Also it is important that PCAs practice sound insecticide resistance management (IRM) by rotating modes of action following each application. This is particularly important with the Diamide group of insecticides (IRAC group 28) because these products can be applied as both foliar sprays and soil injections and multiple generations of Lep larvae can potentially be exposed to variable doses of this chemistry. The most effective way to delay the onset of resistance by worms in leafy vegetables is to consider the recommendations provided in the guidelines recently updated entitled Insecticide Resistance Management Guidelines for Lepidopterous Larvae in Lettuce.
We are on the final section of virus transmission. Virus transmission by insects is one of the most efficient and economically important transmission in agriculture. When you have insects in your crops, not only you are losing your crops because of feeding/chewing by insects, a lot of insects also act as a vector of plant viruses.
Seven out of 29 orders of insect feeding on living green land plants are vectors of plant viruses.
Insect transmit viruses in 4 distinct modes:
Non persistent transmission: The insects can acquire the virus in a matter if seconds/minutes and they are immediately viruliferous. The virus in retained in the stylet of the insect and are transmitted to the next plant the insect feeds on. The virus is retained in the vector only for few minutes and is lost after insect molting. Most viruses transmitted by aphids are non persistent. So when you see few aphids in your melon field and see cucumber mosaic virus symptoms 1-2 weeks later in your field, don’t be surprised. Aphids are efficient vectors, and since viruses are systemic it takes anywhere from few days to 2-3 weeks for the plants to show symptoms. Thus it is very important to manage insects in the field even if you don’t think the ‘pressure’ is not as high.
Semi-persistent transmission: The insects can acquire the virus in minutes/hours and there is no latent (incubation) period in the insect. The virus can stay in the insects foregut for hours and is lost after insect molting. Some species of aphids and whiteflies fall in this category. Example: Cucurbit yellow stunting disorder virus in melons transmitted by whiteflies.
Persistent circulative: Insects have to feed on virus infected plants for hours/days to acquire the virus and the virus has to incubate for hours/days in the insect. After insect can transmit the virus for weeks. Virus can be present in the vectors hemolymph but there is no multiplication of virus in the insect body. Vectors in this transmission includes: Aphids, leafhopper, whiteflies, treehopper.
Example: Beet curly top virus transmission by beet leafhopper
Persistent propagative: Insects have to feed on virus infected plants for hours/days to acquire the virus and the virus has to incubate for hours/days in the insect. After insect can transmit the virus throughout its lifespan. The virus can multiply in the vector system and often times the virus particles are also passed on to the insect offspring. Tomato spotted wilt virus is transmitted on persistent propagative manner by 9 different species on thrips.
Save the Date : 2024 Plant Pathology Workshop
When: August 29th 8AM-12 PM ( breakfast and Lunch provided by Gowan Company and BASF)
Where: Yuma Ag Center, 6425 W 8th Street
What will covered: Plant Pathology program Updates, past season field trial results (we
have some exciting results to share), Q&A to help better Plant pathology program,
Industry panel discussion for all your industry related questions! See you in few weeks!
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.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
