What is in this article?:
- Lettuce varieties fight against disease challenges
- Lettuce dieback, weeds, wilt
- Downy mildew, nitrogen
- Some lettuce plants are fighters, prepared to deliver a knockout punch to disease challenges. Others are more susceptible.
Downy mildew, nitrogen
• Steve Klosterman, with USDA/ARS in Salinas, discussed downy mildew, which he termed the most widespread and destructive spinach disease in California.
His research has included developing a DNA-based detection program and use of a trapping system to collect airborne spores. He said it appears hot dry winds over the Salinas Valley appear to move “a blanket of spores over the region.”
Spore traps were set up in sites that included Gonzales, Soledad and King City.
• Jim Farrar, director of the Western IPM Center, talked of the center’s role in research funding.
California leads the Western region in grant dollars spent between 2004 and 2012: $702,630, followed by Arizona at $461,490. Thirty four grants were provided in each state in that period.
• Richard Smith, UC farm advisor in Monterey, San Benito and Santa Cruz Counties, looked at treatment of tile drain and surface water to remove nitrates with a denitrification bed reactor, using plastic-lined pits filled with wood chips.
While the beds did lower nitrate levels, questions remain on whether use of them is economically feasible.
To develop nitrogen credits from prior crops, Smith also studied harvest residue from spinach, head and romaine lettuce and cauliflower harvesting to measure the release of mineral nitrogen, finding that most of the nitrogen from spinach residue was available in two weeks after incorporation into the soil. Lettuce and cauliflower residues mineralized more slowly, taking six to eight weeks.
Because mineralization can occur so quickly, Smith said, care must be taken with irrigation of the succeeding crop to keep nutrients in the root zone.
Looking at drip uniformity and the impact on water and fertilizer distribution, he found that leaks, plugged emitters and low pressure were especially problematical.
“Addressing water quality regulations will require improving irrigation management,” Smith said.
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