Herbicide trials on processing tomatoes in Merced County in 2004 showed a tank-mix of the new nutsedge material Sandea with Matrix to be initially phytotoxic to certain varieties, although the effect was temporary and yields did not suffer.

Scott Stoddard, farm advisor for Merced and Madera counties, conducted the tests near Los Banos to evaluate current nightshade and nutsedge herbicides on weed control efficacy and crop performance of with five processing tomato varieties.

The varieties used were Halley 3155, H9665, PS296, SUN 6119 (not a commercial variety), and H9780. A strong variety-by-herbicide interaction, Stoddard reported, "indicated that the amount of phytotoxicity caused by the herbicide treatments was different between the varieties."

SUN 6119 and H9780, he added, "had more than 50 percent phytotoxicity one week after spraying, however, there was no significant effect on yield."

His trials in 2003 demonstrated that the combination of Sandea (halosulfuron-methyl) and Matrix (rimsulfuron) gave excellent control in fields having nutsedge and nightshade problems. The plots treated with the combination yielded as well as the untreated check in spite of the phytotoxicity observed earlier.

The 2004 plots of moderately saline, Dos Palos clay loam were transplanted May 8, and the herbicide treatments were broadcast, over-the-top, on June 16, when the crop was in full bloom.

Weed control ratings were very limited, Stoddard said, until the end of the season. A preplant application of Dual Magnum kept weeds under control. "Additionally, the field had been in Roundup Ready cotton the previous year, which eliminated much of the nightshade and nutsedge pressure."

Season-end weeds

But by the end of the season, mallow, pigweed, and johnsongrass were present in the field, and the herbicide treatments significantly reduced the amount of weed pressure as compared to the untreated check.

In other 2004 research, Michelle LeStrange, farm advisor for Tulare and Kings counties, conducted a trial with two varieties, Halley 3155 (medium-sized-vine variety) and AB2 (large-sized-vine variety), near Five Points to learn more about the effects of crop density on curly-top virus infections.

The virus is vectored by the beet leafhopper, Circulifer tenellus, which goes not only to tomatoes but beans, cucumbers, melons, peppers, squash, along with other crops and weeds.

Damage to tomatoes ranges from a twisting and yellowing of new leaves to thickening and rolling of older leaves that take on a purplish venation. Infected plants become stunted and fruit ripens prematurely before plants completely collapse.

The leafhopper overwinters on foothill rangeland vegetation, and when those native hosts dry up, it migrates to the valley floor to infect crop hosts. Historically, populations accumulate during dry and mild winter weather and their cycles are difficult to predict.

LeStrange noted that virus damage to tomatoes has appeared to be greater in transplanted fields than direct-seeded fields.

Density effects

"Growers," she said, "have been switching to transplants for a number of reasons, and in the process, the total number of plants per acre has been reduced. Fewer plants per acre may create conditions favorable for the beet leafhopper, since it is believed that dense stands of tomatoes discourage visitation by leafhoppers."

Although early pressure from the virus turned out to be light in 2004, the trial was initiated to determine the effects of planting densities. Disease incidence in the trial was too low to affect results.

Transplants with densities of one, two, and three seeds per plug were seeded and grown out in a commercial greenhouse and then hand-transplanted in 15-inch and 30-inch row spacings.

Results from the May 21 planting of transplants showed generally low yields for Fresno County, and LeStrange said this may have been due to the late planting and fruit-set problems associated with heat.

Over all the density treatments, the medium-vined Halley 3155 averaged 2.3 tons per acre more than the large-vined AB2. This proved statistically significant, she added, although the tonnage difference between varieties at the density treatments was small.

At the 15-inch plant spacing across all plug densities, Halley 3155 averaged 28.3 tons per acre and AB2 averaged 26.6 tons per acre. At the 30-inch spacing across all plug densities, Halley 3155 averaged 24.7 tons and AB2 21.7 tons.

Transplant or direct

Gene Miyao, farm advisor for Yolo, Solano, and Sacramento counties, looked into the direct-seeded versus transplant question during the 2004 tomato season in trials near Woodland.

Plots were direct-seeded or transplanted mainly with Halley, but he also used AB2 and HM830 varieties.

"It seems," he reported, "that further evaluations would likely produce results where some locations and conditions would slightly favor one planting method, but without a consistently superior method identified.

"The upshot appears to be that establishment method is comparable between the two."