It appears that there might be some confusion about a maggot that is showing up in new strawberry plantings up and down the coast of California. This maggot is the larva of the fungus gnat, a fly which commonly is found in very moist environments such as greenhouses and around potted plants indoors. The continually moist weather accompanied with the cool temperatures of late is quite likely encouraging the growth in numbers of these flies in our strawberries.
According to the UC IPM guidelines, fungus gnats are not harmful to plants and feed on organic mulch, leaf mold, compost, root hairs and fungi. They are not known to major pests of crops cultivated outdoors.
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.