Growers have numerous challenges that affect production and ultimately their bottom line: crop diseases, insect infestations, weather issues, as well as high input costs, low market prices, labor shortages, and food safety issues. This article will discuss issues that don’t necessarily immediately come to mind when growers talk about crop production problems, but that can greatly affect crop yield and quality: abiotic issues.
In the Monterey County Extension office, we receive a large number of plant samples each year from growers and crop consultants that have production issues. Most issues are due to biotic factors such as disease or insects. However, a sizeable number of issues are caused by abiotic issues that range from nutrient deficiency or toxicity, problems from excess salt or herbicides, as well as problems from fertilizer burn, temperature extremes, water stress, and physiological issues. We work as a team to diagnose these issues. Once it is determined that biotic factors are not the cause of the issue, we then turn our attention to abiotic factors.
Gather The Facts
The first step in identifying abiotic issues in vegetable crops is to have as much information as possible on the background of the crop such as the variety, fertility and irrigation programs, weather conditions, and spray history. There often is not a laboratory test to confirm abiotic issues if they are not caused by chemical or nutrient issues. Oftentimes with some of the issues, it is not clear for problems that are less well defined or that perhaps are new. However, given enough background information and tenacity, it often is possible to formulate a list of likely suspects and formulate a plan to avoid the problem in the future.
An example of one common abiotic issue that we get many samples of each year is caused by a combination of a nutrient disorder and environmental factors. It is called blossom end rot on tomatoes and peppers, and tipburn on lettuce and cabbage, and is caused by a localized calcium deficiency in affected tissue.
Blossom end rot and tipburn causes the death of young, actively growing tissue. On tomatoes and peppers, it is seen as necrotic tissue toward the tip of the fruit and, in the case of lettuce, it is seen at the edges of young developing tissue.
Although the necrosis caused by blossom end rot and tipburn is caused by calcium deficiency, in California, most soils have adequate levels of calcium. We have measured adequate soil calcium levels in the Salinas Valley on all soil types except occasionally on very sandy soils.
Understand Calcium Movement
The main reason calcium deficiency develops on these crops is due to the way calcium moves in the plants. This chemical element moves in the xylem of the plant with the transpirational stream, and localized calcium deficiency occurs because of the inability of the plant to effectively translocate calcium to fast-growing, susceptible tissue. For instance, foggy weather in the Salinas Valley creates conditions for tipburn on lettuce because of the reduced level of transpiration and growers often refer to this as “fog burn.”
An example of severe calcium deficiency was seen in 2014 and 2015 when higher than normal nighttime temperatures in the Salinas Valley induced tipburn on a number of crops besides lettuce, such as celery (aka, blackheart), cabbage, napa cabbage, radicchio, and fennel. Given higher-than-normal nighttime temperatures, the plants continue to expand their cells and grow, but there is no transpiration at night, which resulted in higher-than-normal levels of localized calcium deficiency on these crops.
Crop breeders have provided a partial solution to this malady by selecting for blossom-end-rot-resistant tomatoes and tip-burn-resistant head lettuce varieties. Romaine lettuce is more susceptible to tipburn than head lettuce, primarily because currently there has been less effort put toward developing tipburn-resistant varieties.
Tipburn is just one example of a number of abiotic problems that cause quality issues on crops and reduce yield. Abiotic issues can be induced by weather conditions, fertilizer issues, soil, and nutrient issues or varieties reacting to unfavorable growing conditions.
Keeping good records and keenly observing trends in the fields can help you better understand why some abiotic issues occur and how to reduce the incidence of these issues in the future.