Is there any advantage in late-season planting of processing tomato varieties bred for extended field storage (EFS) to avoid fruit set problems during high temperatures on the San Joaquin Valley's West Side?

There may be, suggests Michelle LeStrange, farm advisor for Tulare and Kings counties, on the basis of her 2005 trials with three sequential plantings of 10 EFS varieties. Levels of pH, however, may be an issue.

“None of the varieties was exceptional in setting fruit under hot conditions, but a few performed better than the majority of others,” LeStrange reported.

The purpose of her research was to evaluate comparative performance of EFS varieties to learn if they might both store well in the field and set fruit well in the heat.

The EFS varieties in the trial were H 8504, H 9780, H 9997, Hypeel 849, PS 345, Sun 6368, Sun 6374, U 37, U 567, and U 886. The standards, Halley 3155 and AB 2, were used as check varieties.

Adjust strategy

The outcome, she said, might lead to a management strategy to select better varieties to hold in the field during backlogs in harvesting.

She scheduled the series of planting dates so the second harvest coincided with the first harvest of the successive planting. Seeding dates were April 12, April 27, and May 17, with three harvest dates for each.

In describing the trials at a recent growers meeting at the West Side Research and Education Center at Five Points, where the trials were planted, LeStrange said the first two plantings set fruit under “normal” conditions, and the third flowered and set during challenging “hotter than normal” conditions, which had a detrimental effect on yield.

She said overall average yield decreased by more than 5 tons per acre with each successive planting date. “Average yields decreased with each successive harvest of the first two plantings, but not all varieties had a similar response.

“The third planting experienced a yield gain when harvested a week later, which was attributed to delayed ripening of green fruit. It was observed that the second harvest of the second planting outyielded the first harvest of the third planting by 6.9 tons,” she said.

Timing benefit

“This result suggests a benefit of planting earlier to maximize fruit set during favorable temperatures and holding the fruit in the field rather than planting later, especially with some varieties.”

Samples from the machine-harvested plots were sent for laboratory analysis by the Processing Tomato Advisory Board (PTAB) and the University of California, Davis Food Science Department.

LeStrange said the “grower's main interest” in harvest results is tonnage, rotten fruit, and soluble solids, while the “processor's interest” is solid red fruit with low pH and high soluble solids.

“Under the growing conditions of 2005, a later harvest of an earlier planting yielded more tonnage than an earlier harvest of a later planting,” she said.

While tonnage and rotten fruit changed significantly over time, soluble solids, although they decreased slightly, were “fairly stable.”

PTAB analyses showed pH to be generally very similar for each planting date, and pH increased by one-tenth with each successive harvest. Although the UC, Davis lab showed similar trends, pH values were higher and some varieties reached undesirable levels greater than 4.6 with extended field storage.

LeStrange noted that pH could be the limiting factor in the combination of variety and planting dates. The processing industry prefers pH in the range of 4.3 to 4.6 to prevent growth of Clostridium botulinum bacteria.

Her results, she said, may provide some guidance within the requirements of growers and their processors. The better performing varieties and other data for each planting date can be found in the complete report on the trials available at http://cetulare.ucdavis.edu/Vegetable_Crops.

She said she would be willing to continue the research if grower, processor, and seed industry interest is sufficient.

LeStrange reported on another of her 2005 projects, pre-emergence herbicides in transplanted bell peppers.

The trials showed, she said, possibilities for developing a weed control system for early and late season weed control in peppers without the use of plastic mulching.

The project included LeStrange's trials in Fresno County for San Joaquin Valley conditions and those of Richard Smith, Monterey County farm advisor, in Monterey and Santa Clara counties to evaluate materials and methods on the Central Coast.

Weed control in the crop is particularly difficult since it must compete with weeds during the 40 to 60 days following transplanting.

The long growing cycle means bell peppers face flushes of both winter and summer weed species.

The research concluded that Goal Tender applied to shaped beds 30 days prior to transplanting (but not worked prior to transplanting) gave good weed control and acceptable safety to peppers on the Central Coast.

This use pattern, LeStrange said, could provide an alternative “at planting” treatment for weed control during the first 30 days following transplanting.

Outlook herbicide was applied over-the-top in both trials. Although it was found to be damaging to the crop in the Fresno County trial, it did not reduce yields in the Central Coast plots and LeStrange and Smith believe it should be studied further as a pre-transplant treatment there.

Trials in both regions showed that Chateau impregnated on fertilizer has promise as a post-transplant application.

Dual Magnum, Outlook, and Dacthal all gave good layby weed control. Although Dacthal is registered for this use, the Dual Magnum label would need to be adjusted to allow for its use in this way.

Pre-emergence herbicides presently registered for bell peppers have gaps in the spectrum of weeds they control.

Growers may spend from $200 to $350 per acre on weed management. Field selection, field sanitation, cultivation and plastic mulching are common practices. Combinations of fumigation and plastic mulches are more effective than either method used alone.