Mark Bolda
                                      Hillary Thomas


The use of pheromone based twist ties has found significant success in reducing the incidence of light brown apple moth mating in caneberries grown on the Central Coast of California.  With the recent advent of light brown apple moth infestation in area strawberries, especially those in organic production, there has been a groundswell of interest on testing the same technology there.

The following is a brief description of a trial mounted on the part of the authors in testing whether the use of pheromone based twist ties could be useful and successfully applied in strawberries.  On June 15, twist ties wound around chopsticks were distributed evenly (every other strawberry row with 16 to 18 feet between each stick) across 8 acres of organic strawberry at the rate of 300 per acre (higher end recommended label rate), with another 8 acres left alone as an untreated check.  This was replicated 4 times in various fields around Watsonville.

A matrix of twelve traps using pheromone lures was placed in each 8-acre field to test the ability of the pheromone based twist ties to prevent males from finding females emitting the same pheromone.  The idea is that if the males are unable to locate the pheromone lure in the trap, they will not be able to locate females and subsequently not be able to mate, resulting in population reduction.

Traps were checked yesterday, June 29.  Out of the 48 total traps placed over the four treated plots, only a single male moth was captured, while the traps in the untreated check contained two moth males on average.

 

Trap Captures of Light Brown Apple Moth Males, June 29, 2010
Totals are from 12 traps in each plot 

         with pheromone        without pheromone

Field 1              1                      23                   

Field 2              0                      27                   

Field 3              0                      23                   

Field 4              0                      42                   

The results suggest the twist ties may be useful as part of an integrated strategy to reduce light brown apple moth populations in fields, especially for organic growers who have limited available management tools.

by Steven Koike
UC Cooperative Extension

Starting around mid-May and extending into June, strawberry growers and pest control advisors in coastal California are observing the fruit problem known as bronzing. This problem occurs every year to some extent but can result in large economic losses in some seasons. Bronzing results in a tan or bronzed discoloration on green and ripening strawberry fruit. Bronzed fruit have dried, rough surfaces that render the fruit unmarketable (Photos 1 and 2). The skin of such fruit can later crack.

There are three types of bronzing. Type I bronzing occurs on distinct, localized parts of the fruit, often beneath the fruit calyx or around the strawberry seeds (achenes), and is caused by insect feeding, primarily thrips (physical damage due to abrasion (Photo 3) is also very localized). Type II bronzing is caused by chemical sprays that cause a one-sided bronzing to the side of the fruit exposed to the application. In contrast, Type III bronzing covers virtually the entire surface of the fruit, occurs during certain periods of time, and can result in devastating crop loss. It is notable that Type III bronzing in coastal California tends to occur when the weather is sunny and warm.

Field-based research has demonstrated that Type III bronzing is associated with fruit exposure to stressful environmental conditions that include extreme solar radiation, high temperatures, and low relative humidity. This Type III problem is not caused by sulfur applications or feeding by thrips, mites, or other pests.

The problem is difficult to manage and prevent. Strawberry cultivars differ in their susceptibility to Type III bronzing, so growers should consider this factor when selecting cultivars for planting. Growing the strawberry crop so as to reduce physiological stress to the plants is a general overall recommendation. Observant growers and PCAs noted that commercial fields that happened to receive insecticide or fungicide sprays prior to a high temperature, high-sunlight intensity bronzing period had in many cases significantly lower bronzing losses compared to adjacent untreated fields. This situation likely occurred because commercial pesticides usually contain additives that protect the products from solar and ultraviolet radiation; such sprays also provided similar protection to the strawberry fruit.

People using light brown apple moth (LBAM) pheromone traps as a monitoring tool for this pest should be aware that the traps do not exclusively trap LBAM, and currently another moth species is showing up frequently in the traps.  This moth is in the family Crambidae, while LBAM is in the family Tortricidae.  It is important that growers know what this crambid moth looks like and not be alarmed when they find it in their traps.

Crambid moth identification courtesy Dr. Hillary Thomas, UC Davis.

Below are several pictures of what is very likely is light brown apple moth (LBAM), the invasive leafroller currently under quarantine, damage in strawberry.  While leafrollers traditionally have not been a problem in strawberries on the Central Coast, a number of growers are currently dealing with them right now.  This fact along with several positive LBAM detections in strawberry by USDA inspectors leads one to believe that these infestations are in a large part LBAM.  It continues to be imperative that growers act on evidence of any leafroller infestation, since discovery of a single LBAM larva by USDA inspectors in the field still means closure until no further larvae are found.

Not all small green larvae in strawberries are leafrollers.  As can be seen on the last photo below, beet armyworm is also present in significant numbers and is damaging fruit.  Growers, PCA's and other professionals should note the distinct light stripe and spot on the side above the second leg when making this determination.

Captions refer to photos above them.