Since digging for strawberry plants destined for Salinas and Watsonville started at Macdoel just a few days ago, I thought it would be judicious to have a look at how many chill hours we've accumulated so far and what it means for additions to supplemental chill, especially for our day neutral varieties.

I checked with the Lassen Canyon nursery chill accumulator here: http://lassencanyonnursery.com/cumulative-chilling-hours-and-weather-conditions/ .

Looking at the data for Oct 18 of this year and running my calculations via the Utah model (which subtracts chill hours for temperatures realized above 60^oF, see previous posts), we have currently accumulated 325 units of chill. Given that last year's chill accumulation was 164 units and by most commentator's opinion a decent accumulation, 325 accumulated chill units this year is very satisfactory.

So what does this mean for adjustments on supplemental chill? Personally, I think growers may want to take the strong field chill in stride, and now look forward to what sort of winter we are going to have. Looking at the NOAA data, we are probably in for a weak “La Niña” system this year, which according to the “Color Outlook Maps” for temperature, we have something like a 40% chance of having slightly warmer than normal temperatures in November, December and January.

http://www.cpc.ncep.noaa.gov/products/predictions/multi_season/13_seasonal_outlooks/color/churchill.php

The question then is what sort of adjustment should or needs to be made to supplemental chill. It's actually not an easy question to answer, given the strong field chill.  Then again the odds of a slightly warmer than normal winter would give me some reason to err on the side of caution and go a tad longer than customary on the supplemental chill .

Article out of this morning's Wall Street Journal.  Apparently American consumers are going wild over knobbled carrots, weird apples and mis-shapen potatoes.

Consumers, we have a deal for you!  Catfaced strawberry fruit and poorly pollinated blackberries we can deliver by the pallet. Step right up!

Seriously, this is something pretty intriguing.

http://www.wsj.com/articles/in-supermarkets-now-weird-apples-knobbled-carrots-and-spuglies-1474561531

The question has come up more than a few times from industry participants on how to adjust nitrogen (N) inputs for strawberry varieties more productive and of larger plant size than Albion for which the original DRIS study was done.

Simple math says one could just increase simply N uptake estimate to cover the added fruit and bigger plant, so if Monterey produces 20% more fruit, and is that much larger a plant, one just adds 20% more nitrogen to the standard annual fertility program to make up the difference. However, as simple as this math may seem, it could quite possibly be incorrect, since it is not at all unknown that different strawberry varieties have variations in N content in the fruit and leaves.

The work to determine N content of Monterey compared to that of Albion was done over two samplings (one in early May, the other mid-July) of five fields of Albion and five fields of Monterey. We found that Monterey had marginally higher N concentrations in both the leaves (Table 1) and the fruit (Table 2) on both sample dates. An evaluation of plant size, without fruit, found that Monterey also ran about 20% larger than Albion from the five fields sampled.

From this information, we can say that N uptake is at least as high in Monterey as in Albion per unit of plant growth. That is to say, if a grower expects and has experienced 20-25% increases in fruit yield with Monterey over that of Albion, then the amount of N uptake to support that level of productivity will also be 20-25% higher than for Albion.

We need to be careful here however. This is not a call for growers of Monterey to automatically increase their N fertilizer additions by 25%. If a grower is finding his or her seasonal practices in the lower half of typical grower practice, then an increase in nitrogen application could be tested, but if a grower is already using a lot of N, say above 250 lbs per acre, then that might be enough to absorb the higher N requirement of Monterey.

Table 1: Nitrogen (N) concentrations in dry leaves

Table 2: Nitrogen (N) concentrations in dried fruit

Many thanks to the growers who participated in this study, and generously allowed me to tear plants out of their fields for the plant size sampling.

Lygus bug (Lygus hesperus) (Fig. 1) is a major pest of strawberry in the Central Coast. Lygus bug populations develop on weed hosts surrounding the strawberry fields such as wild radish, common groundsel, lupines, and mustards (Zalom et al. 2012). Time to time, adults migrate into the strawberry fields and lay eggs. Eggs hatch, and molt through five nymphal stages before molting into adults. Lygus bug feeding on the developing embryos affects the normal development of tissues surrounding the embryo (Handley and Pollard 1993) and affected fruits are misshapen often referred as “catfaced fruit” (Fig. 2) which are deemed unmarketable. Although both nymphs and adults can cause catface injury, nymphs are considered more destructive than adults. The young fruits up to ~10 days after petal fall are considered vulnerable to economic injury from lygus bug feeding (Zalom et al. 2012).

Chemical control continues to be an effective tool for lygus bug control and growers are always seeking effective and softer insecticides for its control. A replicated trial comparing the efficacy of insecticide treatments against lygus bug was conducted in first-year strawberry ‘San Andreas' in Watsonville, CA in 2016. The details on insecticide products and rates used in the trial are shown in Table 1. The insecticides were applied twice at 10 day interval using commercial tractor mounted sprayer. The water volume used for both the applications was 150 gal per acre and was applied at 140 psi. Dyne-Amic (surfactant) was added at 0.25% v/v to all the treatments. Insect samples were collected using regular sized Rubbermaid container by hitting 20 flowering strawberry plants with lid. In addition, 60 fruits were sampled from each plot to determine catface injury.

Pre-count sample did not show any difference in number of adult and nymphal lygus bugs among treatments (Figs. 3 and 4). Overall, all the insecticide treatments reduced the number of lygus bug adults and nymphs compared with untreated plants. The combination treatments using pyrethroid insecticides such as Danitol and Brigade suppressed lygus bugs and general predators such as bigeyed bug, minute pirate bug, and damsel bug as well as spiders (Figs. 5-8). Data show that reduced-risk insecticides, Rimon and Beleaf suppressed lygus bug nymphs as well. Sequoia, not yet registered on strawberry, provided a decent lygus bug control. Sivanto initially provided a good suppression of adults and nymphs but could not adequately sustain the control for more than a week. Two rates of Avaunt (unregistered insecticide on strawberry) was included in this experiment and were comparable to other effective insecticides in this experiment. 

Insecticide use certainly reduced catface injury on strawberry fruit. Number of fruits with catface injury was lower in all the insecticide treated plants than untreated except the lower rate of Avaunt (Fig. 9). Catface injury on fruits treated with Sequoia was lower than untreated but not different from other insecticides (except lower rate of Avaunt).

References

Handley, D. T., and J. E. Pollard. 1993. Microscopic examination of tarnished plant bug (Heteroptera: Miridae) feeding damage to strawberry. J. Econ. Entomol. 86: 505-510.

Zalom, F. G., M. P. Bolda, S. K. Dara, and S. Joseph. 2012. Strawberry: Lygus bug. UC Pest Management Guidelines, UC ANR Publication 3468.http://www.ipm.ucdavis.edu/PMG/r734300111.html