Caneberry growers in Santa Cruz and Monterey Counties are to be reminded that the threat of light brown apple moth (LBAM) has not gone away and that they should maintain or replace the pheromone based twist ties in their fields. Please bear in mind that the ties generally are effective for four months in most conditions. While the weather has become colder and there is little foliage on many blackberry and raspberry varieties, there is still LBAM moth activity on the Central Coast and fields will benefit from having mating disruption deployed.
Likewise for strawberry growers, especially organic growers, it is a very good idea to maintain or replace the twist ties in their fields going into a second year of production.
See photos below for tips on twist tie placement in the field.
One of the first posts to this blog regarded the importance of chill, both field and supplemental, to the day neutral (ie Albion, San Andreas, Portola, Monterey among others) strawberry varieties. Right now, field chill in MacDoel is in the area of 600 hours, which is plenty, even in the light of the very warm stretch of weather that took place in September. Still, be reminded that this abundance of field chill should not be considered to be a replacement for supplemental chill taking place in the cooler after the transplant has been harvested.
However, this year because of the delay in transplant harvest growers really should be striving to strike a balance between getting adequate supplemental chill to obtain good vigor and planting sufficiently early to get sufficient plant growth here in the fall. To accommodate this idea, every one of the day neutral varieties listed above can be well established with supplemental chill of 7 to 10 days, but no less. More days of chill, up to 18 days, are of course in the printed recommendations, but this year a large delay in planting may not result in acceptable plant growth and establishment.
If one follows the suggestion given above, supplemental chill will end up being on the low side, and subsequently growers must be more vigilant than usual in planting practices. Transplants must not be allowed to dry out in the field during planting, transplants should be properly placed the planting hole (no “J” rooting, and only portion of the crown above the soil line) and irrigation for establishment should keep the beds at field capacity for a few weeks.
Steven Koike and Mark Bolda
The agenda has been set for the upcoming Plant Disease Seminar with UC Cooperative Extension in Salinas. On November 16, updates on plant diseases of vegetable and strawberry/cane crops will be shared at this annual update on coastal crop problems (contact: Steven Koike). There are no fees for this meeting and continuing education units have been requested.
For more information check the calendar section at the UC Cooperative Extension—Monterey County website.
Over the past three weeks, a trial investigating the efficacy of imidacloprid (Admire- registered in caneberries but not to be used within 7 days of fruit harvest) and thiamethoxam (Platinum- not registered) was done in raspberries. The description below gives the details and results of the study.
Admire was applied at the equivalent rate of 14 fluid ounces per acre and Platinum was applied at the equivalent rate of 4.01 ounces per acre. Both insecticides were applied through drip tape attached to an ordinary hand pump sprayer (see photos of application below) at the equivalent water carrier rate of 25 gallons per acre and followed by a full irrigation through the regular system. The advantage of this system was to make application of the trial pesticides isolated to the treatment replicate without contaminating the rest of the row. Four replicate plots were also left untreated in order to compare the effect of the two pesticides to doing nothing at all.
Application was made on August 24 and a fruit sample of 25 mature raspberry fruit taken on August 24 (immediately preceding the application), and samples of 15 fruit taken on August 30, September 6 and September 14. Fruit was allowed to stand for four days at room temperature before evaluation. SWD larvae at this stage develop quickly and are larger and easier to count within this period of time.
Results were quite conclusive in that neither imidacloprid nor thiamethoxam were successful in reducing to any extent the amount of infestation of raspberry in the three weeks of the trial.
There are several insecticides mentioned for control of spotted wing drosophila flies in this article. Before using any insecticides, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.
I am grateful for the assistance of Ed Show, who designed and built the injection system for this study.
Post Doctoral Scholar, UC Davis
UC Cooperative Extension
Light brown apple moth (LBAM) is an introduced species of leafroller (Lepidoptera: Tortricidae) that was first detected in California in 2007, and is currently present in high population densities throughout the Central Coast. It is a class A pest with a broad host range that is subject to state and federal quarantines. This has resulted in strict regulation of its many host crops, mandating zero tolerance for larvae in fields or on harvested fruit, and occasioned the financially devastating closure of several fields of caneberries in 2009, and again in strawberries during the 2010 season.
Central Coast strawberry growers have a variety of management methods available to them, which they can deploy in their efforts to prevent LBAM from being detected in their fields. Foremost, monitoring for the presence of LBAM is key. Leafrollers may be identified using timed visual inspections or pheromone traps. Where any levels of LBAM are detected, available management tactics include (1) pheromone mating disruption, (2) insecticide use, and (3) cultural management techniques such as vacuuming and manual removal of leafrollers. Natural biological control by wasps has also been observed and may play a more central role in its control with time. The following is summary for growers of how best to integrate available control methods to achieve the greatest result.
Mating Disruption: Field trials currently being conducted by UC Davis began in early summer, 2010, and have confirmed that pheromone based mating disruption can be useful for managing light brown apple in strawberries.
Mating disruption with pheromone based twist ties is an attractive tool to growers, because of low toxicity, compatibility with biological control, high specificity to the target pest, reduced risk of resistance, and ease of application. However, the use of twist ties should be supplemented with well-timed insecticide sprays and cultural controls whenever possible, because it is not certain whether twist ties used alone will result in zero detection of light brown apple moth larvae in fields, as currently mandated by state and Federal regulatory agencies. The presence of any suspicious looking leafrollers (even if later confirmed to be native leafrollers such as garden or orange tortrix) can delay the shipment of berries from coolers after inspection, and could result in economic loss.
Pheromone mating disruption is a tactic that, when effective, interrupts male moths from detecting potential female moths to mate with. It is a target (species)-specific tactic that will not affect other lepidopteran (moth) pests. It is also not an insecticide or growth regulator, and its mode of action will not kill moths outright. Larvae or pupae that are already present in a field just prior to the application of twist ties will not be controlled by this tactic and should be managed by available chemical or cultural controls. Therefore it is important to think of mating disruption as one strategy within an integrated pest management program to target multiple generations of LBAM. Because its effects will reduce the number of viable eggs in the following generation, it may have increased utility for LBAM in strawberry fields maintained for two years of production, or when well timed to target peaks of emerging LBAM adults throughout the year.
The following summarizes our knowledge of LBAM’s life cycle and population phenology (generational timing) in California. Pheromone trapping by UC Davis and as reported by USDA surveys suggest that annual flights of light brown apple moth generally occur at peaks 3 times a year, although lower levels of moth activity continue year-round. They are anticipated in higher numbers in the spring between March-April, summer between June-July, and a fall population peak between October and November. The exact timing of the peaks is temperature and weather related, may vary by year, and may be site-specific, so it is important to monitor fields to ensure that mating disruption techniques are deployed PRIOR to an observed peak in adult LBAM presence.
Twist ties are expected to be effective for 4-6 months after their application. Environmental conditions such as temperature or UV exposure can affect their longevity so currently it is recommended that growers be conservative and replace them after 3 ½ to 4 months, depending on the remaining length of harvest or intentions to carry over to a second year of production. Mating disruption works best when applied over large continuous areas and over longer periods of generational time.
In strawberries, the first recommended timing is a winter application in late February or early March. This application will likely have continued efficacy through a June or July LBAM flight peak, but if there is heavy population pressure in the area or if it is desired to act conservatively, a second placement of twist ties may be made in June to carry the field to completion of strawberry harvest in the fall. For strawberries continuing to a second year of production, another placement of twist ties should be made in November and then again in March of the following year.
Twist ties should be placed all across the production field and distributed at an even rate. At a minimum, twist ties should be placed down every other row of the strawberry field at an even spacing between each tie to arrive at the recommended per acre rate. If possible, it is suggested to place twist ties as far out as the edges of the field or slightly farther where possible, to reduce the probability of a mated female moth flying in from external sources. The recommended label rate is between 200-300 twist ties per acre. In strawberries, mating disruption has been effective when deployed evenly at a rate of 300 twist ties per acre at a height of less than 18" above the strawberry canopy. This reduced male LBAM pheromone trap captures to zero for the first several months of a 2010 trial. Since in strawberries, there is no pre-existing support system such as a trellis, growers should mount twist ties on supports such as chopsticks (see picture below), pin flags or sharpened wooden dowels of at least 9 inches in length. Ties simply deposited on the bed surface may shift, become buried in the soil, or may be difficult to later collect for the purposes of field-sanitation, particularly if multiple twist tie applications are made each year. However, the presence of loose twist ties in the field does not pose any health or regulatory risk. If in-field monitoring is being conducted and there is a rise in adult moth finds 3-6 months after initial twist tie application, this could be an indication of reduced pheromone release by the dispensers.
While other leafroller species in Central Coast strawberries are not common, it may also be useful to manage similar looking leafroller species, to reduce the probability of economic loss due to delays for leafroller identification during cooler and field inspections. Many insecticides that target LBAM will also be effective for management of native leafrollers.
Insecticides: The use of twist ties should be supplemented with the use of insecticides where possible, to reduce the probability of an in-field light brown apple moth find. This also has the added benefit of targeting similar looking leafroller species, such as orange tortrix or garden tortrix.
Since leafroller populations are lower in February and March, it is recommended to take initiative at this point in time by commencing a program of pesticide application. This is especially true for producers of organic strawberry, since the selection and efficacy of materials available is quite limited. As there is a wide variety of good conventional leafroller pesticides available, growers should seek materials that have a lower impact on beneficials and the surrounding environment. Materials should also be rotated to mitigate the potential for resistance to a single pesticide.
Following the initial early season spray, it is important that growers continue to monitor the field for leafrollers. Growers should look for leaf surfaces that are webbed or rolled together, and underneath the calyces of the fruit (see photos below and see the May 26, 2010 post of this blog ). Concentrate monitoring activities in suspected or previously infested areas.
Any sign of leafroller activity should be a signal to protect the crop. It should be emphasized here that the economic threshold for leafrollers during this period of regulation is zero, and subsequently the threshold for spraying is much lower than one would deploy in an integrated pest management program.
Cultural Controls: Because of the zero tolerance mandated for light brown apple moth infestation in fields, it is recommended that growers impress upon crews involved in weeding, runner removal and harvest the importance of manually removing suspect rolled leaves, larvae and webbed fruit. Considering that crews are passing over every foot of strawberry row at least three times a week during the harvest season, they can be very effective in reducing LBAM and other leafroller numbers. It is worth noting that LBAM larval infestations tend to be clustered, so the presence of leaf webbing on one plant means that it is near certain that there could more webbed leaves nearby. An incentive program which rewards leafroller finds in the field can be implemented to encourage participation with such a campaign of larval removal.
In annual strawberry culture, sanitation of the field after completion of the harvest is not an issue. However, in strawberries which will be carried over to a second year, proper sanitation practices during the dormant season will be an essential part of light brown apple moth management since larvae and pupae will overwinter in leaf trash and surrounding weeds. Leaves from plants should be deposited in the furrow and later incorporated into the soil. Growers should be aware too of the potential of certain species of plants on the Central Coast to be major sources of infestation and the need to control LBAM there when possible.
There are pesticides mentioned for management of leafrollers in this article. Before using any of these products, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.