Richard Smith, Larry Bettiga and Daniel Hasegawa
Farm Advisors with UCCE Monterey and Research Entomologist, USDA ARS, Salinas
Impatiens necrotic spot virus (INSV) is a serious disease of lettuce in Monterey County. It is a tospovirus that is spread by an insect vector, the western flower thrips (Frankliniella occidentalis). INSV also infects a wide range of other host plants and is spread when thrips acquire the virus from infected host plants and migrate into uninfected lettuce fields. Lettuce is a key host for INSV during the lettuce production season, but during the winter when there are no lettuce fields, the virus survives in weedy host plants in a variety of habitats: roadsides, ditches, waste areas around equipment yards, and natural areas. Vineyards can also be habitat for INSV due to the presence of infected weed hosts. This article will discuss the specific role of vineyards in providing habitat for INSV host plants.
The vineyard floor in grape production in Monterey County, consists of the area under the vines (vine row) that is irrigated with drip irrigation. Weeds are managed here using herbicides or cultivation or a combination herbicides and cultivation. As a result, the area under the vine row generally has low weed populations and is not the area of concern for INSV host weeds.
Vegetation in the area between rows (row middles) is managed by mowing or discing, but it is most often vegetated with a cover crop or resident vegetation. The vegetation in this area is generally managed by mowing.
Grass cover crops or resident grass weeds are not a concern for INSV because grasses are not hosts. However, broadleaf weeds in row middles that are INSV hosts can serve as a source of INSV. Key weeds in Monterey County vineyards that are of concern include:
|
Species |
Host rating* |
|
Hairy fleabane |
Good |
|
Annual sow thistle |
Good |
|
Common lambsquarter |
Good |
|
Purslane |
Good |
|
Field bindweed |
Good |
|
Little mallow (malva) |
Good |
|
Mare's tail |
Good |
|
Nettleleaf goosefoot |
Good |
|
Shortpod mustard |
Fair |
|
Bull Mallow |
Poor |
* Based on percent of plants infected in INSV in a recent survey
Of the weeds listed above, little mallow, annual sow thistle, and nettleleaf goosefoot have the combination of being common in vineyards, having relatively high levels of infection, and being good hosts for thrips, particularly when flowering.
The row middles can have substantial populations of broadleaf host weeds if the grasses do not dominate. Increasing the density of grasses in the row middles can be accomplished by supplemental seeding of grass cover crops (various cereals) or resident grasses (e.g. Blando brome). The herbicide Shark (carfentrazone) can be sprayed on the row middles when broadleaf weeds are small to selectively remove them and allow grasses to grow. 2,4-D is registered for use on grapes during the dormant winter period and will also remove broadleaf weeds, but extreme care would need to be taken to safeguard the grapes as well as surrounding crops to consider use of this option.
The most common weed option used in vineyards to control weeds in the row middles is mowing. In 2021 we observed a vineyard where the row middles were not mowed and which was infested with nettleleaf goosefoot, sow thistle, little mallow, and shortpod mustard. The nettleleaf goosefoot, little mallow, and sow thistle all had levels of infection >35% and the adjacent lettuce crops were highly infected with INSV, particularly on the edges adjacent to the vineyard. The shortpod mustard had a much lower level of infection with INSV, but it was flowering, supporting thrips populations. In this situation, it is not clear if mowing would have reduced levels of infection in the adjacent lettuce, but mowing would have managed the weeds by weakening them and thinning out their population.
Weed control is particularly important in the spring when thrips populations begin to increase. It is unclear how far thrips can move, but they rely heavily on the Salinas Valley winds for long distance dispersal. Monitoring efforts showed that thrips are equally distributed in the wind column up to 10 feet high and have even been detected in moderate numbers at heights above 20 feet.
Losses from INSV in 2020 exceeded $50 million. The INSV Task Force, composed of growers, PCA's, the Grower-Shipper Association, the County Agricultural Commissioner and researchers, meets weekly to discuss ways of reducing the spread of INSV. The Agricultural Commissioner in 2021 included a notification with each pesticide permit discussing the need for growers to control weeds on their properties and outlined their authority to address nuisance weed issues.
In 2021 growers undertook a coordinated efforts to aggressively control winter weeds to reduce the level of infected host plants in the county. These efforts included outreach to all vegetable growers in the valley, Cal Trans (along the 101 corridor), railroad, and the city of Salinas (municipal roadways). While it is hard to say for sure, these efforts appear to have reduced the levels of INSV infected fields in some areas.
In 2022 we hope to increase efforts to reduce over-wintering habitat for INSV host plants by continuing outreach and promoting best management efforts to all for the benefit of lettuce growers in the Salinas Valley. For more information: Contact Richard Smith, 831-759-7357 or Larry Bettiga, 831-759-7361.
2021 Pest Management Meeting
Sponsors: UCCE, Monterey; CSUMB; USDA-ARS, Salinas; Monterey County Agricultural Commissioner
Thursday, November 18
Spreckels Veteran's Memorial Building
7:50 a.m. to 12:30 p.m.
No Advanced Registration Required- Free Attendance
7:50 Introductions
8:00 Vegetable weed control studies: Injection of Kerb through drip systems and herbicide testing in Brassica vegetables
Steve Fennimore, Extension Vegetable Weed Scientist, UC, Davis
8:30 Update on the use of steam and automated weeders for control of weeds and soilborne diseases in lettuce
Steve Fennimore, Extension Vegetable Weed Scientist, UC, Davis
9:00 Epidemiology and management of Fusarium wilt of lettuce
Alex Putnam, Plant Pathology Specialist, UC, Riverside
9:30 Epidemiology and management of Pythium diseases on spinach
Jim Correll, Professor of Plant Pathology, U of Arkansas
10:00 Management of Pythium wilt of lettuce
JP Dundore-Arias, Plant Pathology Professor, CSU, Monterey Bay & Richard Smith, Vegetable Crop and Weed Science Farm Advisor UCCE Monterey
10:30 Break
11:00 Biology and Management of Diamondback Moth
John Palumbo, Professor and Extension Specialist, U of Arizona
11:30 Approaches to managing aphids and thrips in lettuce
Ian Grettenberger, Extension Entomology Specialist, UC, Davis
12:00 Research update on thrips and INSV
Daniel Hasegawa, Research Entomologist, USDA ARS, Salinas
12:30 Conclusion
4.0 DPR continuing education credits have been approved (other category)
For more information, contact Richard Smith @ 831-759-7357, email: rifsmith@ucdavis.edu
The University of California prohibits discrimination or harassment of any person in any of its programs or activities. (Complete nondiscrimination policy statement can be found at http://ucanr.org/sites/anrstaff/files/107734.doc). Inquiries regarding the University's equal employment opportunity policies may be directed to Affirmative Action Contact and Title IX Officer, University of California, Agriculture and Natural Resources, 2801 2nd Street, Davis, CA 956:18, (530) 750-1397; titleixdiscrimination@ucanr.edu.
21Pest Management Meeting November 18 (003)
- Author: Larry J Bettiga
New online course on diagnosing herbicide injury now available
—Petr Kosina, UC Statewide IPM Program
A brand-new online course on Diagnosing Herbicide Injury focusing on how an herbicide injury situation can arise, what information can help diagnose symptoms during field investigations, and what tools are available to you, is now available from the UC Statewide Integrated Pest Management program (UC IPM).
When unexplained damage is noticed on a crop or other non-weed plant, herbicides are often a primary suspect. That is no surprise because herbicides are very powerful and effective tools used to control weedy plants in a wide variety of locations. However, symptoms of many other plant stresses, such as diseases and nutrient deficiencies or toxicities, can closely resemble the injury symptoms caused by herbicides. Economic implications of herbicide damage can vary–in some cases visible injury may have very little direct economic effect while in others, even slight herbicide symptoms can affect the marketability of affected plants. In addition, the presence of an unregistered herbicide on non-target crops can result in illegal residues which could have both safety and legal consequences.
The new online course was developed by Dr. Brad Hanson and Dr. Kassim Al-Khatib from the Department of Plant Sciences at UC Davis, and UC IPM instructional designers. If you are a grower, pest control adviser, or pesticide applicator, then this course is a great opportunity to learn about how to approach crop injury investigation when herbicide is suspected cause. You will learn how herbicides injure plants, how long herbicide symptoms may last and factors that may influence the time that herbicide injury symptoms are visible, possible scenarios of herbicide exposure based on uniform and variable injury patterns observed in the field, how to prepare samples for the laboratory analysis and more.
The course content is free to anyone who wishes to view it. For those requiring a certificate of completion and continuing education units (CEUs), the regular cost is $30, but we are offering a reduced price of $15 through October 31, 2021. Diagnosing Herbicide Injury course has been approved by the California Department of Pesticide Regulation (DPR) for 1.5 continuing education units (CEU) of Other, Certified Crop Advisor (CCA) for 1.5 units (IPM), and the Arizona Department of Agriculture for 1.0 Credit.
If you are a DPR license or certificate holder with a last name beginning with letters M through Z, then this will be your year to renew. Now is a good time to check out the other UC IPM online training courses offered. All are 50% off the regular price through October 31st. DPR strongly suggests returning renewal packets back to them by October so that your license or certificate can be renewed before it expires. Many of our courses are accredited by DPR for continuing education hours and also by the California Structural Pest Control Board (SPCB), Certified Crop Advisor (CCA), the Western Chapter of the International Society of Arboriculture (WCISA), and the Arizona Department of Agriculture.
Oakleaf goosefoot a new weed concern in the Salinas Valley
Richard Smith, Farm Advisor, UCCE Monterey County
Oakleaf goosefoot (Chenopodium glaucum) is a new weed to the Salinas Valley that has become more prevalent. Its population has been on the rise for several years and it has become a significant weed in some parts of the valley. It ranges in vegetable production fields from Castroville to King City. High populations are still spotty in the valley, but in some fields it is one of the principal weeds.
Oakleaf goosefoot is closely related to lambsquarters (C. album) and nettleleaf goosefoot (C. murale). A variety of oakleaf goosefoot is native to eastern California (C. glaucum var. salina). The variety that we have here in the Salinas Valley is not the native, but rather the non-native variety C. glaucum var. glauca which is widely reported as a weed in many parts of the United States.
Oakleaf goosefoot can be distinguished from the other Chenopodium species by the shape and texture of the leaves. The undersides of the leaves are white-mealy (Photo 1), while the rest of the plant is glabrous or nearly so (Photo 2). The leaves tend to be thickened and the margins of the leaves can be coarsely serrated. The plant is more prostrate than lambsquarters or nettleleaf goosefoot and that is a good way to distinguish it in the field (Photos 3-5). The stems of oakleaf goosefoot tend to be reddish.
Oakleaf goosefoot can inhabit vegetable production fields as well as the margins of fields and ditches (Photos 6-7). At this point, it appears to be susceptible to the same herbicides as the other Chenopodium species. In one trial, it was shown to be highly susceptible to the combination of Kerb and Prefar. That is the good news. The bad news is that it is spreading and is taking full advantage of opportunities along field edges to set great quantities of seed. At this point, the populations of this weed have increased to the point that several growers and PCA's have commented about it and have expressed concern for its growing populations. It is good to recognize this weed and address it as you would the other Chenopodium species.
Photo 1. Oakleaf goosefoot: above and lower leaf surfaces shown
Photo 2. Oakleaf goosefoot seedling
Photo 3. Oakleaf goosefoot showing prostrate growth form and coarsely serrated leaves.
Photo 4. Oakleaf goosefoot in comparison with lambsquarter seedling (on right).
Photo 5. Oakleaf goosefoot just below nettleleaf goosefoot seedling
Photo 6. Flush of oakleaf goosefoot seedlings and more mature plants in a ditch
Photo 7. Flush of oakleaf goosefoot growing along the edge of a ditch
Compost for a climate resilient Salinas Valley
Compost para un Valle de Salinas resiliente al clima
