This year's Annual Strawberry Production Research Meeting is will be held February 4 at the Elk's Lodge in Watsonville and features a slate of strawberry science favorites and some newcomers.  Please note that because of the large amount of information being generated in strawberry research as of late, we are extending the meeting into a bonus afternoon session.

Given the prospect of a strong El Niño this winter, a number of strawberry growers planted cover crops on the furrow bottoms to maximize infiltration into the soil and reduce erosion. Cover crops planted in late October or early November have now grown up even with the bed top and now is the time to control them to minimize shading of the strawberries which might affect yields. The control method depend on (1) the production system (conventional vs organic), (2) the type of cover crop (cereal vs mustard), (3) tractor access in the field, and (4) labor availability.

In one experiment, well managed furrow-bottom cover crops that were controlled before they shaded the strawberry plants, did not affect the yields of strawberries (Table 1). We have no data on what would happen is furrow bottom cover crops shaded strawberry plants, but seems likely that cover crops shading strawberry plants might slow their development and ultimately reduce the yield.

Table 1. Strawberry yield evaluations

(18 harvests from May 1 to June 29, 2007 Yields followed by the same lower case letter are not significantly different based on the least significant difference (LSD) at P=0.05.

Mechanical control options: Obtaining access to the fields when they are wet is a key concern and controlling the cover crop without damaging the plastic mulch is also important. Often the edges of the mulch extend down below the soil and may flair a bit towards the furrow which necessitates shallow or no tillage along the edge of the furrow. Planting the cover crop in a narrow band on the furrow bottom center may facilitate mechanical control by tillage because the implement can be adjusted tofocus just on the middle of the furrow; however, if the cover crop is rooted next to the edge of the plastic it will be more problematic to control with tillage. Cereal cover crops are hard to kill with tillage when the soil stays wet, as is often the case with strawberry furrows in the winter. Mustard cover crops are easier to kill with tillage because the stems are more brittle and uprooted plants have less tendency to reroot on wet soil.

Weed wacking is a great way to control and or kill mustard cover crops and has the advantage of not disturbing the soil. However, carefully managing the weed wacker to avoid damaging the plastic can be tricky. Some growers have found that in furrow bottoms, plastic or metal bladed weed wacker heads are easier to control than string weed wacker heads. Cutting the tops off of cereals will not kill them because the growing point are below the soil surface and it will be necessary to repeat the operation to control regrowth.

Pushing the mustard cover crops down into the furrow bottoms by walking on them or by driving a tractor on them may also be a way to prevent them from shading the bed tops but may require repeated management to be effective.

Chemical control options: Cereal cover crops can be controlled with grass selective herbicides that are registered on strawberries: clethodim (Select Max) and sethoxdim (Poast). These materials can be sprayed over the top of strawberries or as a directed spray towards the furrow. They are slow acting, but over a period of 10-14 days the plants will begin to yellow and eventually die (See photo below). Organic herbicides will not be an effective way to control cover crops in furrow bottoms.

The latest summary of UC short day and day neutral strawberry varieties is provided on the graphics below by Doug Shaw.

Note the new UC short day varieties Petaluma, Grenada and Fronteras in comparison to their predecessors, and the new UC day neutral variety Cabrillo in comparison its predecessors Albion, San Andreas and Monterey.  

JUSTIFICATION AND OBJECTIVES:

IR4, the branch of the USDA focused on speciality crops, identified research on SWD as a priority need.  The purpose of this efficacy and crop safety trial was to determine the level of SWD control by organically registered biopesticides in caneberries to determine the impact on plant and yield variables.

TEST SYSTEM DESIGN and STATISTICAL METHOD:

The test site consisted of three replicates of each treatment in Table 1 below.  Plots in the active organic raspberry ranch were arranged in a randomized complete block design.  Since SWD is a mobile pest, the 3 replicate plots of each treatment (see Table 1 below) were large, consisting of three raspberry hedgerows across, being 54 ft long and 14 feet wide (756 ft²).   Statistical analysis was done on ARM, version 9.

TEST SUBSTANCE APPLICATION:

All test substances were applied with a motorized Maruyama 058 backpack sprayer with a hand gun at a pressure of approximately 120 psi. Each material was mixed in a water carrier rate of 75 gpa. Three total applications were done; beginning 9/17/2015, 9/25/2015 and 9/30/2015. Because of excessive residues for the Cimexa Gel material and request of the collaborating grower that this material no longer be applied, no applications of any treatment of Cimexa Gel were made on the last date.

INSECT AND YIELD EVALUATION:

One day prior to the first application of September 17, samples of 10 marketable fruit were collected from each replicate plot and further a section of 18 ft long from the center hedgerow was vacuumed with a Bug-vac for adults. Fruit were held for several days and then each evaluated under the dissecting scope for SWD larvae and eggs. The vacuum sample was evaluated for female and male SWD, along with other insects taken in the sample.

Subsequent sampling and evaluation dates were Sept 22 (pre-sampling), Sept 28, Oct 5 and Oct 16.  The sampling date for October 5, taking place after full application of all treatments and thereby likely to give the most meaningful results, is given below.  Note that no evaluations were done of treatments containing Cimexa Gel on the last sampling date.

SUPPLEMENTAL CROP TREATMENTS:

No supplemental treatments of any kind were made to the crop during the course of this study.

DISCUSSION:

While there was a tendency for treatments containing Entrust to have lower numbers of larvae found in fruit as other treatments after completion of all three applications on the Oct 5 sampling date, none of these differences are statistically significant and as such regarded with caution.

Furthermore, the residue of CimeXa Silica Gel Dust on leaves, canes and fruit of plants subjected to its application was unacceptable and as such this material is not recommended for further study.

Hat tip to research assistants Don Yoshimura and Monise Sheehan, without whom I could not have possibly done this trial.