Help Us Document the Heavy Insect Pressure in Desert Lettuce This Season
With the produce season winding down rapidly, now is a good time to reflect on pest activity and insecticide usage you experienced this season in desert lettuce. The 2023 Lettuce Crop Losses Workshop will be held live, in-person Tuesday, May 9th at the Yuma Agricultural Center from 11:30 until 3:00 pm (see agenda below). Get there early as lunch will be provided. The meeting has been approved for 2.5 CA/AZ CEUs. Participants will be asked to complete two short surveys to document pest pressure and control tactics used on lettuce this season. This workshop has been invaluable to our Vegetable IPM Team over the past 18 years because it allows us to develop accurate “real world” data on crop losses and pesticide usage which is important to the assessment of IPM programs in Arizona. It’s also valuable to PCAs, as it can translate their efforts into economic terms for their growers and confirms their value to the lettuce industry by showing the importance of key insect pests and their cost-effective management in desert lettuce production.
It's no secret, the insect activity this spring was exceptional. Lettuce aphids and green peach aphids were abundant most of the spring, and thrips numbers were down until late in the season. As I’ve reported previously, I think this may be one of the heaviest aphid years I’ve experienced in the desert in a long time. Earlier Lettuce Insect Losses surveys from theses workshops estimated that over a 18-year period, PCA made on average 1.5 sprays on lettuce for aphids (ranging from 1.0 to 2.5 sprays). For the complete report see: Insect Losses and Management on Desert Lettuce: An 18-year Summary. Based on reports from PCAs this spring, it is likely that considerably more sprays were applied this spring for green peach aphid, and perhaps fewer for thrips. Also, a wide variety of insecticides products were reportedly used by PCA’s, some with mixed results. You can review the historical database of insecticides used for aphids and other insects here: Insecticide Usage on Desert Lettuce, 2021-2022The bottom line: from a historical perspective, it would be quite useful to document insect pressure and sprays applied this year compared to previous years. In addition to the reporting, Marco Pena will be presenting the latest results of his herbicide trials and areawide weed survey. Finally, I will be providing the latest efficacy trial results on aphids, thrips, worms, and whiteflies. So, we hope you can make it to the workshop and participate in this important process.
Lettuce Crops Losses Workshop
May 9, 2023 11:30-3:00 pm
Yuma Agricultural Center Conference Room
Agenda
11:30-12:00 pm Lunch (It will be yummy)
12:00- 12:30 pm Impact of IPM on Lettuce Insect Losses John Palumbo
12:30-1:00 pm Individual Completion of LIL Questionnaires Attendees
1:00-1:30 pm Historical Results of Insect Losses /Insecticide Usage John Palumbo
1:30-2:00 pm Weed Management Research Update Marco Pena
2:00-3:00 pm Insect Management Research Update John Palumbo
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!
Band-Steam Applicator for Controlling Soilborne Pathogens and Weeds in Lettuce
Steam sterilization of soils is commonly used in plant nurseries and greenhouses for effective control of soilborne pathogens and weed seeds. The technique, however, is highly energy intensive as the entire soil profile is heated. This is too costly and slow to be practical for field scale vegetable production. To reduce energy consumption and cost, use of band-steaming, where steam is applied only in the area where it is needed – in the plant root zone, is proposed. In this method, narrow strips of soil centered on the seed line are treated with steam rather than the whole bed.
Over the course of the last year, we developed a prototype band-steam and co-product applicator that is designed to raise soil temperatures in a band 2” deep by 4” wide to levels sufficient to control soilborne pathogens (140 °F for > 20 minutes) and weed seed (150 °F for > 20 minutes). The device is principally comprised of a 35 BHP steam generator and a co-product applicator mounted on top of a bed shaper (Fig.1). The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper. An exothermic compound can be co-applied via shank injection and/or a banding spray nozzle. The rationale behind co-applying an exothermic compound with steam is that exothermic compounds react and release heat when combined with water, thereby reducing energy requirements and increasing travel speed.
Preliminary testing of the device this spring in Yuma, AZ were very promising. Trial results showed that application of steam alone effectively raised soil temperature in the center of the seed line to levels required for effective pest control (140 °F for more than 20 minutes). Use of the exothermic compound increased soil temperature by about 10 °F. A video of the device in action can be found at the link provided below.
We are currently evaluating the device in field trials with lettuce in Salinas, CA. Target pests in these experiments conducted in collaboration with Steve Fennimore, UC Davis, are soil pathogens which cause Sclerotinia lettuce drop and in-row weeds. Future articles will report the findings of this research.
This fall, we will be replicating these tests in Yuma, AZ and also investigating the effectiveness of band-steam for controlling Fusarium oxysporum f. sp. lactucae which causes Fusarium wilt of lettuce. Heat has been shown to effectively kill Fusarium oxysporum spores and control Fusarium wilt disease. As an example, soil solarization, where clear plastic is placed over crop beds during the summer, raises soil temperatures to 150-155˚F at the soil surface, effectively killing the pathogen and reducing disease incidence by 45-98% (Matheron and Porchas, 2010).
These projects are sponsored by USDA-NIFA, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support.
If you are interested in seeing the machine operate or would like more information, please feel free to contact me.
See the band-steam and co-product applicator in action!
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.
Sprangletop has become increasingly widespread in Arizona mostly because of its growth habits and tolerance to many commonly used herbicides. It is in the Leptochloa genus which is derived from the Greek words leptos (thin) and chloa (grass). There are more than 150 species of sprangletop worldwide but only three in Arizona and two in Yuma County. The two that are the most common in the low desert are Mexican Sprangletop, which is Leptochloa uninervia and Red Sprangletop, Leptochloa filiformis. A third species, Bearded Sprangletop, Leptochloa fascicularis, is more common at higher elevations of 1500 feet or higher. It is not uncommon to find both Red and Mexican Sprangletop in the same field and it is not hard to distinguish them when they are side by side. Red Sprangletop has a light green leaf blade which is similar in width to watergrass and barnyardgrass. It has very fine hairs and very small and fine branches and spiklets. It also has a long membranous ligule. The name Red refers to the leaf sheath, which is characteristically red, rather than the seed head. Mexican Sprangletop has a thinner leaf blade which is darker green or grayish in color and similar in appearance to common bermudagrass. The seed head is distinctly coarser than that of Red Sprangletop. Side by side, leaf color and size of the seed make it easy to distinguish these two. Both of these grasses are classified as summer annuals, but they grow more like perennials in the low desert. Sprangletop does very well in the hottest part of the summer and typically germinates from seed during the hottest period between July and September. Once established, however, it often survives through the cold winter months. It grows into clumps that often appear to be dead during the winter. New shoots commonly grow from these established crowns the next season. When this occurs, preemergent herbicides such as Trifluralin or Prowl are ineffective. Some Sprangletop plants stay green and grow through the winter. Many of the postemergence, grass specific herbicides that control many grasses are ineffective on Sprangletop. This also has contributed to the spread of these weeds. Sethoxydim (Poast) and Fluazifop (Fusilade) do not control either Red or Mexican sprangletop. Only Clethodim (Select Max, Select, Arrow and others) is the only one of these grass herbicides that is effective and only at the highest labeled rates. Two applications are often necessary to achieve season long control.