• Richard Molinar, UC farm advisor for Fresno County, who talked of weed control in pomegranate orchards.

Molinar cautioned that annual weeds can produce thousands of seeds and said the best way of avoiding the spread of weeds is to prevent them from going to seed, “keep weed seeds out of the soil profile.”

Two weeds, both of which are Roundup resistant, are major seed producers, he said. A single horseweed or marestail plant can produce as many as 800,000 seeds, and a fleabane plant 120,000.

Prowl, Goal and Surflan are among effective pre-emergents for controlling some weeds, Molinar said, and Prowl is most commonly used. Shark and Roundup are commonly used post-emergents, and it’s best to use them “at the youngest stage; if weeds are 6 inches tall, they’re difficult to control,” Molinar said.

He cautioned growers to beware of spreading some weeds with cultivation, citing the example of Johnson grass and nut sedge. “Be sure to kill them, not spread them,” Molinar said.

More details are available at http://ucanr.edu/sites/weed_management/.

• Themes Michailides, plant pathologist with UC Kearney, talked of research he and others have conducted on black heart disease with the help of funding from Paramount Farming Co.

Michailides said infections from the disease occur during bloom and the most vulnerable stage is when flowers are fully open. Fungicide sprays are effective in reducing the threat, but because flowers open in various stages, a single spray is not sufficient.

Michailides said holes in the fruit can be pathways for infection as well. Those can be made by insects that include the leaf footed bug, cracking of the fruit and thorns.

Tree decline, which devastated a Firebaugh orchard in 2008, is likely linked to very low temperatures, Michailides said. He said the orchard lost half its trees.

A sudden drop in temperatures in late fall and early winter in milder areas where the trees are not fully dormant is the main contributing factor to tree decline, Michailides said.