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Thursday, May 26, 2011

Lettuce Tipburn

From Rutgers Plant & Pest Advisory <Subscribe>

Weather conditions over the past couple of weeks support CA research conclusions linking lettuce tipburn to environmental conditions

Severe cases of lettuce tipburn have occurred this past week in southern NJ resulting in 75+ percent incidence in some fields rendering it physically and economically impossible to salvage those plantings. This comes at a time when those fields are just ready to harvest.

--Rick VanVranken
--Andy Wyenandt
Deceptively beautiful field of Romaine
lettuce... unmarketable due to
tipburn on the inner leaves.
Like blossom end rot in tomato, tipburn in lettuce is a physiological disorder related to calcium availability in the rapidly growing tissues of the plant. Correcting soil pH and calcium levels, and foliar applications of calcium are common practices that are often used to try to avoid tipburn. However, research done by University of California Cooperative Extension reported in 2007 suggests that the disorder may have more to do with environmental factors than the amount of calcium in the soil or applied to the leaves.

After evaluating common methods used to test for soil calcium to determine which best predicts plant calcium uptake, and studying the impact of applied calcium on tipburn, the UC researchers found three forms of calcium applied through drip irrigation water during the final two weeks of growth, compared to an untreated check, had minimal effects on tissue calcium concentration and tipburn severity.

At that point, they looked at evapotranspiration data and discovered an interesting correlation. By comparing evapotranspiration trends during the worst incidences of tipburn to a 10-year average, severe tipburn occurred only under conditions of low reference evapotranspiration (ET) and moderate temperature.

As reported in Western Farm Press, Tim Hartz, UC vegetable crops specialist indicated, “About July 17, 2005, ET dropped precipitously for about four days, then rebounded rapidly, [resulting in] the worst cases of tipburn ... later recorded. Under these conditions, a transient calcium deficiency was apparently induced in rapidly growing leaves by the restricted volume of transpirational flow. It’s not the amount of calcium in the soil — it’s the amount of calcium in the transpirational flow, or the transpiration per unit of growth potential. It’s not a soil issue — it’s an environmental issue."

Hartz also commented that he believes calcium applications are not necessarily wasted and may be more important on coarse-textured soils with low soil solution calcium, in soils with low calcium in saturated paste extract tests, and in low pH soils (like most of our Jersey sands).

But that only clouds the issue about what, if anything, to do about tipburn. Hartz recommends that growers need to be aware of the conditions that are conducive to the problem. “If you get fog rolling in [or several cool, cloudy days in a row], the temperatures don’t necessarily change that much, but ET falls off the cliff,” he said in the article. “Then if ET rebounds quickly [on a bright sunny day], the plant starts growing faster, and it’s difficult for the plant to supply those developing leaves with enough calcium. If you see that type of weather pattern, you might want to consider harvesting earlier than you normally would in order to avoid problems. Even if you’re sacrificing poundage, you’re saving marketability.”
These are the conditions we saw in southern NJ over the past couple of weeks, and the tipburn is showing up now.

Rick VanVranken, Atlantic County Agricultural Agent 
Andy Wyenandt, Ph.D., Specialist in Vegetable Pathology